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X-WR-CALNAME:Theory of Condensed Matter: Hard Condensed Matter (iAnnounce)
X-WR-CALDESC:Contact: Alexander Braun
X-WR-TIMEZONE:Europe/Berlin
BEGIN:VTIMEZONE
TZID:Europe/Berlin
X-LIC-LOCATION:Europe/Berlin
BEGIN:STANDARD
DTSTART:20181028T030000
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
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BEGIN:DAYLIGHT
DTSTART:20180325T020000
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
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END:VTIMEZONE
BEGIN:VEVENT
UID:20180226T023506CET-4163GCMkpM@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:We study persistent currents for interacting one-dimensional (1
D) bosons on a tight ring trap\, subjected to a rotating barrier potential
\, which induces an artificial $U(1)$ gauge field. We show that\, at inter
mediate interactions\, the persistent current response is maximal\, due to
a subtle interplay of effects due to the barrier\, the interaction and qu
antum fluctuations. These results are relevant for ongoing experiments wit
h ultracold atomic gases on mesoscopic rings.
DTSTART;TZID=Europe/Berlin:20140527T100000
DTEND;TZID=Europe/Berlin:20140527T110000
LOCATION:Seminar Room K\, Building 2/413
SUMMARY:Optimal persistent currents for interacting bosons on a 1D ring wit
h a gauge field (J.-Prof Dr. Matteo Rizzi\, Mainz)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4175vDaSNc@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:I will provide a general and accessible introduction to the nit
rogen-vacancy color centers in diamond\, explain why these have been a foc
us of intense research in recent years\, and will also describe several ap
plications and the direction our group and various collaborators have been
pursuing at Berkeley\, Mainz\, in the desert of Negev\, and elsewhere.
DTSTART;TZID=Europe/Berlin:20140528T150000
DTEND;TZID=Europe/Berlin:20140528T160000
LOCATION:Lorentz-Room\, 05-127\, Staudingerweg 7
SUMMARY:THE PERFECT (NV) DEFECT: MAKING SENS(OR) OF DIAMOND (Prof Dmitry Bu
dker\, Mainz /Berkeley)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4185dWLrKB@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:I will present some theoretical results on spin-dependent carri
er dynamics/magnetizatin dynamics in ferromagnets after excitation by ultr
ashort optical pulses. Ultrafast demagnetization has been well established
experimentally for more than 10 years\, but there is still no agreement o
n the microscopic mechanism behind it. I will give a brief review of the e
xperimental facts and the different theoretical approaches\, and then focu
s on the contribution of Elliott-Yafet spin-flip scattering. Although this
concept from semiconductor physics has long been the most promising candi
date to explain ultrafast demagnetization\, there have always been problem
s with it and its importance has recently been challenged.[1] We have done
the first dynamical calculations of Elliott-Yafet scatterin in ferromagne
ts based on an ab-initio description of the optical exciation and electron
-phonon scattering. [2] Recently\, we have also included a time-dependent
exchange splitting in the dynamics [3]. Our results indicate that Elliott-
Yafet type spin-flip scattering does play an important role in the demagne
tization dynamics of ferromagnets\, but only if it is 'amplified' by a tim
e-dependent exchange splitting. I will also briefly present our recent ab-
initio based calculation of spin-dependent lifetimes in ferromagnets inclu
ding spin-orbit coupling [4]\, which agrees\, for the first time\, with 2-
photon photoemission data. These results cast some doubt on the importance
of superdiffusive spin transport\, which has\, so far\, been based on com
puted spin-dependent lifetimes that are in contradiction with experiments.
[1] See\, e.g.\, Eschenlohr et al.\, Nature Materials 12\, 332 (2013)\, B
attiato et al.\, Phys. Rev. B 86\, 024404 (2012) [2] Essert & Schneider\,
Phys. Rev. B 84\, 224405 (2011)\, J. Appl. Phys. 111\, 07C514 (2012). [3]
Mueller et al.\, Phys. Rev. Lett. 111\, 167204 (2013). [4] Kaltenborn & Sc
hneider\, arXiv:1403.4728 (2014).
DTSTART;TZID=Europe/Berlin:20140617T100000
DTEND;TZID=Europe/Berlin:20140617T110000
LOCATION:Seminar Room K\, Building 2/413
SUMMARY:Demagnetization dynamics and spin-dependent lifetimes in ferromagne
ts (Prof. Dr. H. C. Schneider\, TU Kaiserslautern)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-42076aVchC@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:We give a complete definition of the entanglement gap separatin
g low-energy\, topological levels\, from high-energy\, generic ones\, in t
he 'entanglement spectrum' of Fractional Quantum Hall (FQH) states and qua
ntum spin chains. By removing the magnetic length inherent in the FQH prob
lem - a procedure which we call taking the 'conformal limit'\, we find tha
t the entanglement spectrum of an incompressible ground state of a generic
(i.e. Coulomb) lowest Landau Level Hamiltonian re-arranges into a low-(en
tanglement) energy part separated by a full gap from the high energy entan
glement levels. As previously observed\, the counting of these levels star
ts off as the counting of modes of the edge theory of the FQH state\, but
quickly develops finite-size effects which we show can also serve as a fin
gerprint of the FQH state. As the sphere manifold where the FQH resides gr
ows\, the level spacing of the states at the same angular momentum goes to
zero\, suggestive of the presence of relativistic gapless edge-states. By
using the adiabatic continuity of the low entanglement energy levels\, we
investigate whether two states are topologically connected. For the spin
chains\, the entanglement spectrum from a cut in momentum space allows to
study the dimerization transition\, bulk excitation state counting\, and t
he manifestation of logarithmic CFT correction purely from the ground stat
e wave function. It provides a new formulation of non-local order in quant
um spin chains.
DTSTART;TZID=Europe/Berlin:20140701T101500
DTEND;TZID=Europe/Berlin:20140701T111500
LOCATION:Seminarraum k\, Bau 2/413
SUMMARY:Entanglement spectrum of Fractional Quantum Hall states and Quantum
spin chains (Prof. Dr. Ronny Thomale\, Würzburg)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4227jGV5LW@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The fate of the Dirac-like surface states of 3D topological ins
ulators (TIs) under the influence of electron-electron interactions and/or
a strong magnetic field is investigated. First\, a theory of combined int
erference and interaction effects on the diffusive transport properties of
3D topological insulator surface states is presented. We focus on a slab
geometry (characteristic for most experiments) and show that intersurface
interaction between the two major surfaces is relevant in the renormalizat
ion group (RG) sense and the case of decoupled surfaces is therefore unsta
ble. We predict a characteristic non-monotonic temperature dependence of t
he conductivity. In the infrared (low-temperature) limit\, the system flow
s into a metallic fixed point. At this point\, even initially different su
rfaces have the same transport properties. Second\, the unconventional (ha
lf-integer) quantum Hall effect for a single Dirac fermion is analyzed. Th
e following important questions\, which were not or only partially answere
d to present date\, are discussed: (i) How can half-integer Hall conductan
ce g_{xy} be measured experimentally? (ii) Doesn¹t Laughlin¹s flux inserti
on argument forbid half-integer g_{xy}? (iii) What is the field theory des
cribing the localization physics of the single Dirac fermion quantum Hall
effect? The RG flow and the resulting phase diagram are examined. Starting
values of the RG flow are given by the semiclassical conductivity tensor
which is obtained from the Boltzmann transport theory of the anomalous Hal
l effect. References: E. J. König\, P. M. Ostrovsky\, I. V. Protopopov\, I
. V. Gornyi\, I. S. Burmistrov\, A. D. Mirlin\, PRB 88\, 3\, pp. 035106 (2
013). E. J. König\, P. M. Ostrovsky\, I. V. Protopopov\, I. V. Gornyi\, I.
S. Burmistrov\, A. D. Mirlin\, arXiv:1406.5008 (2014).
DTSTART;TZID=Europe/Berlin:20140702T100000
DTEND;TZID=Europe/Berlin:20140702T110000
LOCATION:Medienraum (03-431)\, Staudinger Weg 7
SUMMARY:Disordered surfaces of 3D topological insulators: interactions and/
or strong magnetic field (Elio König\, Karlsruhe KIT)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4249SaU71u@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The reports on observing the quantum anomalous Hall effect (AHE
) in Cr-doped (Bi\,Sb)2Te3 has focused significant interest onto this mate
rial system for its potential as a magnetic topological insulator. In this
talk I will report on our on-going efforts in growing and characterizing
of this material system. In particular\, I will discuss several experiment
al issues which make this material challenging to work with in transport s
tudies\, and show how these must be treated with extreme care in order to
get reliable transport results. While we do not observe any quantization o
f the effect in our samples\, a strong AHE is nevertheless seen\, which co
mbined with SQUID investigations can be used to extract information about
the nature of the magnetic states in our layers. Our observations are cons
istent with that of a magnetically viscous magnetic state\, which tends to
stabilize into a true ferromagnetic state in thick layers\, but take on m
ore of a superparamagnetic character in the thin films we use in the trans
port studies. Whether such a state is representative of a homogenous layer
\, or results from inhomogeneity in the distribution and/or phase of the i
ncluded Cr atoms is a topic of on-going investigations.
DTSTART;TZID=Europe/Berlin:20140709T101500
DTEND;TZID=Europe/Berlin:20140709T111500
LOCATION:Seminar Room K\, Staudinger Weg 9
SUMMARY:Transport investigations on a magnetic topological insulator A wo
rk in progress (Charles Gould\, Würzburg)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4267D0e7Ng@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Weyl semimetals are paradigmatic topological gapless phases in
three dimensions. After a general introduction\, we discuss the effect of
disorder on charge transport in Weyl semimetals. For a single Weyl node wi
th energy at the degeneracy point and without interactions\, theory predic
ts the existence of a critical disorder strength beyond which the density
of states takes on a nonzero value. Predictions for the conductivity are d
ivergent\, however. We present a numerical study of transport properties f
or a disordered Weyl cone at zero energy. For weak disorder our results ar
e consistent with a renormalization group flow towards an attractive pseud
oballistic fixed point with zero conductivity and a scale-independent cond
uctance\; for stronger disorder diffusive behavior is reached. We identify
the Fano factor as a signature that discriminates between these two regim
es.
DTSTART;TZID=Europe/Berlin:20140725T140000
DTEND;TZID=Europe/Berlin:20140725T150000
LOCATION:Seminar room K
SUMMARY:Disordered Weyl Semimetals (Björn Sbierski\, FU Berlin)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-42800f30c4@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:We will discuss violation of spin-charge separation in generic
nonlinear Luttinger liquids and investigate its effect on the relaxation\,
thermal and electrical transport of genuine spin-1/2 electron liquids in
ballistic quantum wires. We identify basic scattering processes compatible
with the symmetry of the problem and conservation laws that lead to the d
ecay of plasmons into the spin modes and also describe their backscatterin
g. We derive a closed set of coupled kinetic equations for the spin-charge
excitations and solve the problem of electrical and thermal conductance o
f interacting electrons for an arbitrary relation between the quantum wire
length and spin-charge equilibration length.
DTSTART;TZID=Europe/Berlin:20140729T100000
DTEND;TZID=Europe/Berlin:20140729T110000
LOCATION:Seminar room K
SUMMARY:Kinetics of 1d electrons beyond the Luttinger liquid paradigm (Alex
Levchenko\, Michigan State University)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4293lxkAJZ@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The contribution of edge scattering to the conductance of graph
ene nanoribbons and nanoflakes is discussed. We used the Boltzmann equatio
n approach with the specific boundary conditions for the distribution func
tion at the edges\, which take into account different character of the ele
ctron scattering from edge imperfections\, depending on the incoming angle
of electron. Using the solution of kinetic equation and various possible
types of the boundary conditions for the electron wave function at the edg
e of graphene\, we found the dependence of the momentum relaxation time an
d conductance on the geometric sizes and on the carrier density. We also c
onsider the case of ballistic nanoribbon and nanodisk\, for which the edge
scattering is the main mechanism of momentum relaxation.
DTSTART;TZID=Europe/Berlin:20141111T141500
DTEND;TZID=Europe/Berlin:20141111T151500
LOCATION:Galilei room
SUMMARY:Edge scattering of electrons in graphene (Prof. Dr. Vitalii Dugaev\
, Rzeszow University)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4306LhSiu1@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:(Ansprechpartner: R. Orús und M. Rizzi) Recent theoretical prog
ress has indicated how to emulate tuneable models of quantum magnetism wit
h ultracold polar molecules. In this talk\, I am going to discuss the unde
rlying ideas and the effective model obtained from this ansatz\, which is
a generalised t-J model with long-range interactions. The simplest realiza
tion in 1D is a t-J_perp model\, in which only interactions of the XY-type
survive. Using the DMRG\, I discuss the effect of the absence of the orig
inal SU(2) symmetry of the t-J-model on the phase diagram\, in particular
in superconducting phases. In the second part of my talk\, I will discuss
features of these quantum simulators when going out-of-equilibrium.
DTSTART;TZID=Europe/Berlin:20141118T141500
DTEND;TZID=Europe/Berlin:20141118T151500
LOCATION:Galilei-Room\, Bau 2/413\, 01-128
SUMMARY:Far from equilibrium quantum magnetism with ultracold polar molecul
es (Dr. Salvatore Manmana\, Universität Göttingen)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-43192tk2ZK@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:In ferromagnetic metals\, the strong exchange coupling of the c
onduction electron with the local magnetization allows us to adopt an adia
batic approximation\, in which the subspaces for the majority and minority
electrons become independent but with a gauge field coming into a play. T
he gauge field is spin-dependent and known to cause nontrivial electromoti
ve force and anomalous Hall effect. In this talk\, by taking into account
the non-adiabatic spin dynamics and the spin-orbit coupling\, we will see
that there can appear an additional electromotive force and domain wall re
sistances. JGU Mainz
DTSTART;TZID=Europe/Berlin:20141125T141500
DTEND;TZID=Europe/Berlin:20141125T151500
LOCATION:Galilei room\, Staudinger Weg 9\, 01-128\, 1st floor
SUMMARY:Effective forces in ferromagnets -spinmotive force\, anomalous Hall
effect\, and domain wall resistance (Yuta Yamane\, JGU Mainz)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4331KXgkFb@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Following a general introduction into thermoelectricity in cohe
rent electronic junctions\, the efficiencies/coefficients of performance o
f three-terminal devices\, comprising two electronic terminals and a therm
al one (e.g.\, a boson bath) will be discussed. In particular\, two proced
ures are analyzed. (a) One of the electronic terminals is cooled by invest
ing thermal power (from the thermal bath) and electric power (from voltage
applied across the electronic junction)\; (b) The invested thermal power
from the boson bath is exploited to cool one electronic terminal and to pr
oduce electric power. Rather surprisingly\, the coefficient of performance
of (b) can be enhanced as compared to that of (a).
DTSTART;TZID=Europe/Berlin:20150205T110000
DTEND;TZID=Europe/Berlin:20150205T120000
LOCATION:Medienraum 03-431
SUMMARY:Thermoelectricity in nano-junctions (Ora Entin-Wohlmann\, Ben Gur
ion and Tel Aviv Universities)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4344c8McuS@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:'In this talk I will discuss the effect of the spin memory loss
on interfaces of ferromagnetic (F) and non-magnetic (N) materials in the
stackings N|F and N|F|N. In particular\, results on the size of spin flip
and spin accumulation gaps at the interfaces will be presented. The theore
tical description is based on a limit of the theory of perpendicular magne
to-resistance in magnetic multilayers by Valet and Fert.
DTSTART;TZID=Europe/Berlin:20150206T090000
DTEND;TZID=Europe/Berlin:20150206T100000
LOCATION:Galileiraum\, 01-128\, Staudinger Weg 9
SUMMARY:'Spin accumulation and diffusion in magnetic Multilayers' (Sebastia
n Müller\, Uni Mainz)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4355O7pDoJ@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Quantum computing requires the ability to write and read quantu
m information on the spinors of electrons. This work considers mobile elec
trons\, which move through mesoscopic (or molecular) quantum networks (mad
e of quantum wires or of arrays of quantum dots). Combining spin-orbit int
eractions\, whose strength can be tuned by external gate voltages\, and th
e Aharonov-Bohm flux\, which can be tuned by an external magnetic field\,
one can manipulate the properties of such networks\, so that the outgoing
electrons are polarized along a desired direction. This amounts to 'writin
g' the desired information on the spinor of the electrons. Given a beam of
polarized electrons\, the charge conductance of the same network depends
on their polarization\, allowing 'reading' the qubit information. Specific
results will be presented for a simple closed interferometer. [1] The tal
k will also report on more recent work: (a) The above filtering is robust
against leaking of electrons\, in an open interferometer. [2] (b) Filterin
g can also be achieved for a single one dimensional chain which has spin-o
rbit interactions\, when the chain vibrates in the transverse direction. [
3] (c) Real time evolution of the polarizations in the filter. [4] [1] A.
Aharony\, Y. Tokura\, G. Z. Cohen\, O. Entin-Wohlman\, and S. Katsumoto\,
Filtering and analyzing mobile qubit information via Rashba-Dresselhaus- A
haronov-Bohm interferometers Phys. Rev. B 84\, 035323 (2011)\;(arXiv:1103.
2232) [2] S. Matityahu\, A. Aharony\, O. Entin-Wohlman and S. Katsumoto\,
Robustness of spin filtering against current leakage in a Rashba-Dresselha
us-Aharonov-Bohm interferometer Phys. Rev. B 87\, 205438 (2013)\; (arXiv:1
302.6772) [3] R. I. Shekhter\, O. Entin-Wohlman\, and A. Aharony Mechanica
lly-controlled Rashba spin-splitters Phys. Rev. Lett. 111\, 176602 (2013)\
; (arXiv:1306.5125) [4] M. Wei-Yuan Tu\, A. Aharony\,W-M Zhang and O. Enti
n-Wohlman Real-time dynamics of spin-dependent transport through a double-
quantum-dot Aharonov-Bohm interferometer with spin-orbit interaction. Phys
. Rev. B 90\, 165422 (2014)\; (arXiv:1406.6258)
DTSTART;TZID=Europe/Berlin:20150206T103000
DTEND;TZID=Europe/Berlin:20150206T113000
LOCATION:Galileiraum\, 01-128\, Staudinger Weg 9
SUMMARY:Spin Filtering: how to write and read quantum Information on mobile
qubits (Prof. Amnon Aharoni\, Tel Aviv University/Ben Gurion University)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4380zLPMkL@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Recently\, the long-sough quantum anomalous Hall effect was rea
lized in a magnetic topological insulator. However\, the requirement of an
extremely low temperature (approximately 30 mK) hinders realistic applica
tions. Based on ab initio band structure calculations\, we propose a quant
um anomalous Hall platform with a large energy gap of 0.34 eV on honeycomb
lattices comprised of Sn\, called stanene. The ferromagnetic (FM) order f
orms in one sublattice of the honeycomb structure by controlling the surfa
ce functionalization rather than dilute magnetic doping\, which is expecte
d to be visualized by spin polarized STM in experiment. Strong coupling be
tween the inherent quantum spin Hall state and ferromagnetism results in c
onsiderable exchange splitting and\, consequently\, an FM insulator with a
large energy gap. The estimated mean-field Curie temperature is 243 K. Th
e large energy gap and high Curie temperature indicate the feasibility of
the quantum anomalous Hall effect in the near-room-temperature regions. Re
fs. PRL 113\, 256401 (2014)\; PRL 111\, 136804 (2013).
DTSTART;TZID=Europe/Berlin:20150211T100000
DTEND;TZID=Europe/Berlin:20150211T110000
LOCATION:Gernot Graeff-Raum\, Staudinger Weg 7\, room 05-431
SUMMARY:Quantum Anomalous Hall Effects on the Novel Honeycomb Material Stan
ene (Binghai Yan\, Max Planck Institute for Chemical Physics of Solids\, D
resden)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-43964VKUaz@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Thierry Valet will provide an overview of his current research
interests in spintronics\, both in the area of spin transport theory (out
of equilibrium quantum field theory of transverse spin transport in 'metal
s') and micro-magnetic theory (spectral formulation of linear and weakly n
on linear spin transfer induced dynamics).
DTSTART;TZID=Europe/Berlin:20150212T140000
DTEND;TZID=Europe/Berlin:20150212T150000
LOCATION:MITP\, Raum 02-439\, Staudinger Weg 9
SUMMARY:Selected topics in spintronics (Thierry Valet\, In Silicio SAS\, Ai
x en Provence)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4405N9uRSu@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:
DTSTART;TZID=Europe/Berlin:20150331T141500
DTEND;TZID=Europe/Berlin:20150331T151500
LOCATION:Lorentz Room ( Staudingerweg 9\, 01-127)
SUMMARY:Topologocial Spintronics: an ab-initio perspective (Yuriy Mokrousov
\, Jülich)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4412NCPaOu@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Landau's Fermi liquid theory has been the main tool for investi
gating interactions in condensed matter systems at low energies for severa
l decades. It describes the excitations of the interacting system through
long-lived quasi-particles which have the same\, albeit renormalized\, pro
perties as the excitations of the non-interacting system. As such it would
be natural to expect that various quantities such as the susceptibility a
nd heat capacity follow analytic series in temperature or external magneti
c field. Recently\, however\, situations where this does not remain true h
ave attracted much attention. In this talk I will discuss these non-analyt
icities\, which appear due to effective long-range interactions between th
e quasi-particles\, and show that they also appear in quasi-particle prope
rties such as the Lande g-factor\, and in experimentally accessible quanti
ties such as the conductivity and tunnelling density of states. I will als
o show that they are determined fully by low-energy scattering processes a
nd discuss how to classify these. Finally I will discuss a new approach\,
based on the functional renormalization group\, to deal with systems where
scattering is dominated by processes in multiple scattering channels. As
an illustration of the method I will consider the so-called X-ray problem.
[1] C. Drukier\, P. Lange\, and P. Kopietz\, Eur. Phys. J. B 88\, 41 (201
5) [2] P. Lange\, C. Drukier\, A. Sharma\, and P. Kopietz\, ArXiv:1502.066
25
DTSTART;TZID=Europe/Berlin:20150602T140000
DTEND;TZID=Europe/Berlin:20150602T150000
LOCATION:Galilei Room
SUMMARY:'Non-analytic corrections in Fermi liquids and multi-channel scatte
ring' (Casper Drukier\, Goethe-Universität Frankfurt)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4433IrSrfc@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Chiral symmetry can be broken in magnetic thin films and multil
ayers\, leading to the appearance of an anisotropic exchange interaction o
f the Dzyaloshinskii-Moriya (DM) form. We have studied theoretically how t
he DM interaction can strongly modify measurable features of spin wave exc
itations in ultrathin films with perpendicular magnetic anisotropy. We wil
l show how nonreciprocal channelling can appear in systems with domain wal
ls\, which has consequences for spin wave modes in confined geometries\, s
uch as strips and dots. We will also describe the breathing dynamics and c
urrent-driven oscillations of isolated skyrmions in ultrathin film dots.
DTSTART;TZID=Europe/Berlin:20150721T141500
DTEND;TZID=Europe/Berlin:20150721T151500
LOCATION:Galilei Room
SUMMARY:Magnetization dynamics in chiral spin textures: Spin wave channelli
ng and skyrmion oscillations (Joo-Von Kim\, Institut d'Electronique Fondam
entale\, CNRS and Univ. Paris-Sud)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4445zUu4DJ@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:In this talk I will present some of the results obtained over t
he last year about spin-orbit induced effects in a two-dimensional electro
n gas. At first I will discuss the spin current swapping effect according
to which a spin current flowing in the i direction with spin polarization
along the j axis is converted into a spin current flowing in the j directi
on with spin polarization along the i axis. I will analyze the circumstanc
es under which to observe the effect and its connection with the spin Hall
effect. As a second topic I will focus on the spin Hall effect due to the
skew-scattering mechanism induced by phonon scattering. A comparison will
be made with the standard skew-scattering due to impurities and the conse
quences for the temperature dependence of the spin Hall angle will be anal
yzed. Finally\, I will present a model with a striped Rashba spin-orbit co
upling\, which could possibly be realized in LAO/STO interfaces. Such a no
n homogeneous spin-orbit coupling may give rise to a spin Hall effect robu
st with respect to impurity scattering.
DTSTART;TZID=Europe/Berlin:20160126T141500
DTEND;TZID=Europe/Berlin:20160126T151500
LOCATION:Galileiraum
SUMMARY:Spin current swapping and spin Hall effect in a 2DEG (Roberto Raimo
ndi\, UNIVERSITA' DEGLI STUDI ROMA)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4461WGUovt@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:
DTSTART;TZID=Europe/Berlin:20160126T150500
DTEND;TZID=Europe/Berlin:20160126T160500
LOCATION:Galileiraum
SUMMARY:CANCELLED (Kyoung-Whan Kim\, CANCELLED)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4467lH63C9@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Semiconductors have been employed for decades as the thermoelec
tric materials of choice. More recently\, gated semiconductor nanowires ha
ve shown remarkable thermoelectric properties\, well beyond those of stand
ard bulk devices\, and are under intense experimental investigation. Indee
d\, nanostructuration allows -- at least in principle -- to engineer syste
ms capable of meeting the somewhat contradictory requirements of an ideal
thermoelectric device: (i) to be a good charge and a poor thermal conducto
r (ii) exhibiting strong particle-hole asymmetry\, (iii) which works up to
room temperature and (iv) is based on non-polluting and abundant material
s. I will show that strongly disordered nanowires\, where conduction takes
place via phonon-assisted (Mott) hopping between localised states\, act i
ndeed as very promising thermoelectrics. In particular\, I will discuss im
purity band-edge transport and an asymmetric 3-terminal setup as two compl
ementary approaches to realising flexible and performant (non-local) therm
oelectric devices.
DTSTART;TZID=Europe/Berlin:20160128T140000
DTEND;TZID=Europe/Berlin:20160128T150000
LOCATION:Medienraum
SUMMARY:Thermoelectric conversion in disordered nanowires (Cosimo Gorini\,
Institut für theoretische Physik - Universität Regensburg)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4483PxUcIl@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Magnetism is a promising candidate as the basis of next generat
ion electronic devices. Electrical manipulation of magnetization would all
ow it to be controlled rapidly in spite of its non-volatile nature. As peo
ple pursue smaller and smaller sized devices\, the effects of broken symme
tries become more and more important. In particular\, strong interface spi
n-orbit coupling as a consequence of inversion symmetry breaking shows a n
umber of interesting features. In this talk\, I present two topics related
to spin-orbit coupling. First\, despite its importance\, our understandin
g of spinorbit coupling is still incomplete. In this work\, we generalize
an existing model for electron spin transport near interfaces to construct
an analytic theory for interface spin-orbit coupling that can be applied
to various systems\, such as magnetic bilayers\, topological insulators\,
and ferromagnetic insulators. The theory gives not only corrections to the
existing theory\, but also qualitatively different physics. Second\, we d
emonstrate that the understanding of spin-orbit coupling effects in magnet
ic systems is also helpful for other systems. By utilizing a one-toone cor
respondence between textured magnetic systems and a spin-orbit coupling sy
stems\, we demonstrate the existence of an overlooked contribution to text
ured magnetic systems\, which one can infer from knowledge of spin-orbit c
oupling effects. These two topics indicate that theoretical study of spin-
orbit coupling in magnetic systems not only advances applications of spint
ronics in devices but also deepens our understanding of magnetic systems.
DTSTART;TZID=Europe/Berlin:20160128T150500
DTEND;TZID=Europe/Berlin:20160128T160500
LOCATION:Medienraum
SUMMARY:Spin transport related to spin-orbit coupling (Kyoung-Whan Kim\, NI
ST CNST/UMD USA)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4502c5KXzw@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Artificial antiferromagnets (Ferromagnetic-Normal-Ferromagnetic
spin valves (antiferromagnetically coupled by the interlayer exchange int
eraction) can be viewed as the spintronics version of the Fabry-Perot inte
rferometer. In this talk\, I will introduce the concept of dynamical contr
ol of interference pattern with ultra-fast voltage pulses. I will show tha
t this idea can be used on artificial antiferromagnets to control the magn
etic exchange interaction leading to a new sort of (dynamical) spin torque
. In a second part\, I will discuss the magnetic response of these artific
ial antiferromagnets to spin torque\, that naturally leads to spin torque
oscillator (STO) behavior even in the absence of external fields. I will a
lso take this opportunity to advertise our open source quantum transport c
ode Kwant (http://kwant-project.org)\, that was used to obtain a large fra
ction of the results shown in this talk.
DTSTART;TZID=Europe/Berlin:20160204T140000
DTEND;TZID=Europe/Berlin:20160204T150000
LOCATION:Medienraum\, 03-431\, Staudingerweg 7\, 55128 Mainz
SUMMARY:Ultrafast pulses\, spin torque and artificial antiferromagnets (Xav
ier Waintal\, INAC CEA\, Grenoble\, France)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4517UuuNvV@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:We show that the formation of a magnon condensate in thin ferro
magnetic films can be explained within the framework of a classical stocha
stic nonMarkovian Landau-Lifshitz-Gilbert equation where the properties of
the random magnetic field and the dissipation are determined by the under
lying phonon dynamics. We have numerically solved this equation for a tang
entially magnetized yttrium-iron garnet film in the presence of a parallel
parametric pumping field. We obtain a complete description of all stages
the nonequilibrium time evolution of the magnon gas which is in excellent
agreement with experiments. Our calculation proves that the experimentally
observed condensation of magnons in yttrium-iron garnet at room temperatu
re is a purely classical phenomenon which should be called Rayleigh-Jeans
rather than Bose-Einstein condensation.
DTSTART;TZID=Europe/Berlin:20160216T140000
DTEND;TZID=Europe/Berlin:20160216T150000
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
SUMMARY:Rayleigh-Jeans condensation of pumped magnons in thin film ferromag
nets (Peter Kopietz\, Institut für Theoretische Physik\, Goethe Universitä
t Frankfurt)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4531pzkRtJ@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Most of the material science problems can be reduced to a rathe
r generic formulation: how to increase an intensity of the useful properti
es or how to get rid of the unwanted ones. Diversity of the degrees of fre
edom in complex systems makes such signal-to-noise control rather sophis
ticated and expensive. Within the state-of-the-art nano-scale applications
the quality requirements for the basic technological elements are often s
tringent: high crystalline order\, precision of target compositions\, chem
ical or mechanical compatibility between different materials\, precise num
ber of atomic layers\, etc. Once these requirements appear to be too resou
rce-demanding\, one might think about the alternatives provided by disorde
r. In this context\, certain improvement can be achieved by introducing a
specific type of disorder\, suppressing the noise intensity\, but retain
ing the signal. On the nano-scale\, such engineering requires the establ
ished relationships between the properties\, electronic structure\, and a
particular type of disorder. Here I would like to discuss the modelling of
certain constructive aspects\, based on the ab-initio techniques dealing
with disorder explicitly (Coherent Potential Approximation and its recent
extensions). In particular\, I will focus on the example of the alternativ
e half-metallicity induced by the spin-selective electron localization tun
ed by the chemical disorder within the class of Heusler materials.
DTSTART;TZID=Europe/Berlin:20160407T110000
DTEND;TZID=Europe/Berlin:20160407T120000
LOCATION:Medienraum
SUMMARY:Constructive Aspects of Disorder in Solids (Stanislav Chadov\, MPI-
CPFS Dresden)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4550SrVMF8@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Graphene has proven to be a perfect platform for electronic app
lications (long mean free paths and electrons moving as massless Dirac fer
mions). However\, its potential use in the field of spintronics has been u
nder debate during the last five years. The spin-orbit coupling induced by
substrates and specific adatoms can reduce the spin relaxation time to th
e order of picoseconds making it useless for most spintronic applications.
In this talk\, I will give a brief overview of spin dynamics in two diffe
rent cases\, gold-decorated and magnetic hydrogenated graphene. In the las
t part\, the possibility to induce a spin Hall type effect by Thallium/Ind
ium adatom segregation in graphene ribbons will be also discussed. Pseudos
pin-driven spin relaxation mechanism in graphene. D. Van Tuan\, F. Ortmann
\, D. Soriano\, S. O. Valenzuela and S. Roche. Nature Physics 10\, 857-863
(2014) Multiple quantum phases in graphene with enhance spin-orbit coupli
ng: from quantum spin Hall regime to spin Hall effect and robust metallic
state. A. Cresti\, D. Van Tuan\, D. Soriano\, A. W. Cummings and S. Roche.
Phys. Rev. Lett. 113\, 246603 (2014) Spin transport in hydrogenated graph
ene. D. Soriano\, D. Van Tuan\, S. M.-M. Dubois\, M. Gmitra\, A. W. Cummin
gs\, D. Kochan\, F. Ortmann\, J.-Ch. Charlier\, J. Fabian and S. Roche. 2D
Materials 2\, 022002 (2015) Spin dynamics and relaxation in graphene dict
ated by electron-hole puddles. D. Van Tuan\, F. Ortmann\, A. W. Cummings\,
D. Soriano and S. Roche. Scientific Reports 6\, 21046 (2016)
DTSTART;TZID=Europe/Berlin:20160411T101500
DTEND;TZID=Europe/Berlin:20160411T111500
LOCATION:Medienraum\, 03-431\, Staudingerweg 7\, 55128 Mainz
SUMMARY:Spin Transport Phenomena in Graphene with Adatoms (David Soriano\,
Catalan Institute of Nanoscience and Nanotechnology (ICN2) Barcelona S
pain)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4570wlSAI2@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:A characteristic of ferroic materials is the emergence of a tem
porally static finite expectation value of an order parameter. Here\, we i
ntroduce a new mechanism [1] for ferroic order\, in which a non-zero quasi
-static magnetoelectric quadrupolar order appears due the coupling of fluc
tuating spin magnetic dipole moments and optical phonons. We show that our
proposed mechanism is consistent\, to our knowledge\, with many experimen
tal observations for the onset of the pseudo-gap phase in cuprate supercon
ductors and therefore propose the quasi-static magnetoelectric quadrupole
as a possible pseudo-gap order parameter. By using first-principles calcul
ations in combination with our recent developed formalism [2]\, to calcula
te multipole moments within a Berry phase approach\, we calculate the magn
itude of the effect for the the prototypical cuprate superconductor\, HgBa
2CuO4+δ. Using these results we finally show that our mechanism embraces s
everal key findings of experimental reports and in addition also aspects o
f previous theoretical models. [1] M. Fechner\, M. J. A. Fierz\, F. Thöle\
, U. Staub\, and N. A. Spaldin\, arXiv cond-mat.supr-con\, (2015). [2] F.
Thöle\, M. Fechner\, and N. A. Spaldin\, arXiv cond-mat.mtrl-sci\, (2016).
DTSTART;TZID=Europe/Berlin:20160413T103000
DTEND;TZID=Europe/Berlin:20160413T113000
LOCATION:Staudingerweg 7\, room 01-327\, 55128 Mainz
SUMMARY:Parity odd magnetism in transition metal oxides and the pseudo-gap
phase in cuprate superconductors (Michael Fechner\, ETH Zürich)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4588bbfEeh@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Photoemission is a well established phenomenon and an instrumen
t for physical studies with more than a hundred years history (photoelectr
ic effect). Thanks to recent advances in ultrafast lasers and streaking te
chniques it became possible [1\, 2] to trace the electron dynamics accompa
nying this process on the attosecond time-scale. In my talk I will address
from theoretical point of view the following facets of such dynamics: i)
time delay of electrons experiencing extrinsic and intrinsic energy losses
[3] as observed in recent experiment on bulk Mg [4]\; ii) transient build
up of plasmonic excitations in C60 and emission of the secondary electron
[5\,6]\; iii) long-lived quantum beatings resolved in time by two-photon
photoemission from antiferromagnetic NiO [7]. I will also briefly present
a methodological aspect of such studies\, namely propagation of the couple
d electron-boson Kadanoff-Baym equations describing the non-equilibrium el
ectrons dynamics. References: [1] R. Huber et al. How many-particle intera
ctions develop after ultrafast excitation of an electronhole plasma\, Nat
ure 414\, 6861 (2001) [2] R. Pazourek\, S. Nagele\, and J. Burgdörfer\, At
tosecond chronoscopy of photoemission\, Rev. Mod. Phys. 87\, 765 (2015) [3
] M. Schüler\, J. Berakdar and Y. Pavlyukh\, Time-dependent many-body trea
tment of electron-boson dynamics: Application to plasmon-accompanied photo
emission\, Phys. Rev. B 93\, 054303 (2016) [4] C. Lemell et al. Real-time
observation of collective excitations in photoemission\, Phys. Rev. B 91\,
241101(R) (2015) [5] M. Schüler\,Y. Pavlyukh\, P. Bolognesi\, L. Avaldi\,
and J. Berakdar\, Electron pair escape from fullerene cage via collective
modes\, Scientific Reports 6\, 24396 (2016) [6] Y. Pavlyukh\, M. Schüler
and J. Berakdar\, Single- or double-electron emission within the Keldysh n
onequilibrium Green's function and Feshbach projection operator techniques
\, Phys. Rev. B. 91\, 155116 (2015) [7] K. Satitkovitchai\, Y. Pavlyukh\,
and W. Hübner\, Ab initio study of spin-orbit coupling effects on the low-
lying excited states of NiO\, Phys. Rev. B. 72\, 045116 (2005)
DTSTART;TZID=Europe/Berlin:20160414T140000
DTEND;TZID=Europe/Berlin:20160414T150000
LOCATION:Medienraum\, 03-431\, Staudingerweg 7\, 55128 Mainz
SUMMARY:Non-equilibrium Electrons Dynamics as Observed in Time-Resolved Pho
toemission (Yaroslav Pavlyukh\, Martin-Luther-Universität Halle-Wittenberg
)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4613ag3exj@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Due to their unique topological and dynamic properties skyrmion
s in magnetic materials offer attractive perspectives for future spintroni
c applications [1]. Recently\, it has been discovered that magnetic skyrmi
ons of Néel-type symmetry cannot only occur in ultra-thin transition metal
films at surfaces [2\,3] but also in asymmetric multilayers due to strong
Dzyaloshinskii-Moriya (DMI) interactions [4]. We carry out first-principl
es calculations in order to study the stabilization mechanism of skyrmions
from ultrathin films to multilayers and we predict the emergence of skyrm
ions in a new class of multilayers based on [4d/Fe2/5d]n\, i.e. structures
composed of Fe biatomic layers sandwiched between 4d- and 5d-transition-m
etal layers [5]. In these composite structures\, the exchange and the Dzya
loshinskii-Moriya interactions\, which control skyrmion formation\, can be
tuned separately by the two interfaces. This allows engineering skyrmions
as shown by density functional theory\, Monte Carlo and spin dynamics sim
ulations. [1] A. Fert\, et al.\, Nature Nano. 8\, 152 (2013). [2] N. Rommi
ng\, et al.\, Science 341\, 636 (2013). [3] B. Dupé\, et al.\, Nature Comm
. 5\, 4030 (2014). [4] C. Moreau-Luchaire\, et al.\, Nature Nano. (2016) d
oi: 10.1038/nnano.2015. [5] B. Dupé\, et al.\, accepted in Nature Comm. (a
rXiv :1503.08098).
DTSTART;TZID=Europe/Berlin:20160420T143000
DTEND;TZID=Europe/Berlin:20160420T153000
LOCATION:Medienraum\, 03-431\, Staudingerweg 7\, 55128 Mainz
SUMMARY:Engineering magnetic skyrmions at transition-metal multilayers (Ber
trand Dupé\, Institute of Theoretical Physics and Astrophysics\, Universit
y of Kiel)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4632rwK4TV@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Spin-orbit and spin-transfer torques are competing forces that
drive magnetic domains in the heavy-metal/ferromagnet bi-layers. In this t
alk I present a microscopic theory of both effects that is naturally obtai
ned from generalised Kubo formalism. In this formalism the torques are nat
urally related to the spin-susceptibility tensors that can be evaluated mi
croscopically for a given model. Interestingly the formulation completely
avoids the notion of the spin current. I discuss the torques arising in th
e effective 2D Bychkov-Rashba model and speculate on various generalisatio
ns of the results obtained.
DTSTART;TZID=Europe/Berlin:20160602T140000
DTEND;TZID=Europe/Berlin:20160602T150000
LOCATION:Medienraum
SUMMARY:Spin-orbit and spin-tranfer torques in two dimensions (Mikhail Ti
tov\, Radboud University\, Nijmegen)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4643VrlD0L@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:We study how skyrmions in insulating chiral magnets can be mani
pulated by thermal currents. Thermal magnons couple efficiently to skyrmio
ns via an emerging magnetic field arising both from Berry phase effects an
d spin-orbit coupling. This coupling gives rise to an intrinsic damping me
chanism for the skyrmion and to forces both parallel and perpendicular to
thermal gradients. In two dimensions we study the crossover from the balli
stic limit to the diffusive limit\, where magnons interact with defects\,
other magnons or phonons within the timescale needed to transverse the sky
rmion. This crossover is described by a Boltzmann equation in relaxation t
ime approximation. We also investigate the magnon Hall effects arising fro
m the scattering from a finite density of skyrmions. Furthermore\, we disc
uss the validity of semiclassical approximations and why stochastic Landau
Lifshitz Gilbert equations are in general not suitable for caloritronics
applications.
DTSTART;TZID=Europe/Berlin:20160608T130000
DTEND;TZID=Europe/Berlin:20160608T140000
LOCATION:Media Room
SUMMARY:Skyrmion Caloritronics (Sarah Schroeter\, Universität zu Köln)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4658A12hNL@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:
DTSTART;TZID=Europe/Berlin:20160608T130000
DTEND;TZID=Europe/Berlin:20160608T140000
LOCATION:Media Room
SUMMARY:Graphene Research Overview (Nils Richter\, Mainz)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4665wvWlxE@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The focus of the talk is the dynamics of spin-dependent recombi
nation in electron-hole pairs subject to external magnetic field\, B. This
recombination is at the core of the phenomenon of organic magnetoresistan
ce (OMAR) in bipolar devices\, where recombination rate governs the passa
ge of current via the spin-blocking process. Without recombination\, the s
pins of electron and holeprecess independently in effective fields b_e + B
and b_h + B\, where b_e and b_h are the random hyperfine fields acting on
electron and hole\, respectively. In the presence of recombination\, the
precession acquires a correlated character due to the fact that the carri
ers recombine only when their spins are in a singlet state. This correlat
ion\, in turn\, exerts a feedback on the recombination rate\, and conseque
ntly\, on the current. Within the simplest transport model\, when the curr
ent flows through the system of parallel chains\, the sensitivity of curre
nt\,I\, to external field\, B\, is dominated by configurations of b_e \,
b_h for which the recombination is anomalously slow. We evaluate the st
atistical weights of these configurations and relate them to the shape\, I
(B)\, of the OMAR response.
DTSTART;TZID=Europe/Berlin:20160706T124500
DTEND;TZID=Europe/Berlin:20160706T134500
LOCATION:Gernott-Gräff-Raum
SUMMARY:Slow dynamics of spin pairs in random hyperfine field and organic m
agneto-resistance (Mikhail Raikh\, University of Utah)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4681jvivA3@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Magnetic Skyrmions are considered to be topologically stable ob
jects. However\, in discrete lattices this topological protection is not i
nfinite but can actually be overcome. This means that Skyrmions can be cre
ated or destroyed. We show how this can be done theoretically by electrica
l currents which may be either in in-plane or out-of-plane direction.
DTSTART;TZID=Europe/Berlin:20160706T134500
DTEND;TZID=Europe/Berlin:20160706T144500
LOCATION:Gernott-Gräff-Raum
SUMMARY:Current-induced Skyrmion creation and Skyrmion fission (Martin Stie
r\, Universität Hamburg)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4691z31UwC@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Angular momentum (AM) currents in spintronics are carried by co
nduction electrons\, quasiparticle magnons\, as well as macroscopic order-
parameters. Depending on materials\, one or all of these carries contribut
e to the AM current. I will discuss these AMs in several structure and mat
erials. As an example\, we show how the AM propagates in antiferromagnetic
insulators and how the different types of AMs convert at interfaces. The
results will be compared with recent experiments.
DTSTART;TZID=Europe/Berlin:20160726T140000
DTEND;TZID=Europe/Berlin:20160726T150000
LOCATION:Media Room
SUMMARY:Angular momentum transport in magnetic structures (Shufeng Zhang\,
University of Arizona)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4702tLHfI3@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:An ensemble of spin wave quanta\, also known as magnons\, can b
e treated as a Bose gas of weakly interacting quasi-particles. The excessi
ve excitation of magnons in the system causes an increase in the chemical
potential of a thermalized magnon gas. When it becomes equal to the minima
l magnon energy a magnon Bose-Einstein condensate (BEC) may form at this s
pectral point. However\, magnon-phonon interaction processes can significa
ntly modify condensation scenario. Our observations of the magnon BEC in a
single-crystal film of yttrium iron garnet (Y3Fe5O12) by means of wavevec
tor-resolved BLS spectroscopy resulted in the discovery of a novel condens
ation phenomenon mediated by magneto-elastic interaction: A spontaneous ac
cumulation of hybrid magnon-phonon bosonic quasi-particles at the intersec
tion of the lowest spin-wave mode and a transversal acoustic wave.
DTSTART;TZID=Europe/Berlin:20160802T140000
DTEND;TZID=Europe/Berlin:20160802T150000
LOCATION:Medienraum\, 03-431
SUMMARY:Bottleneck accumulation of hybrid bosons in a ferrimagnet (Dmytro B
ozhko\, TU Kaiserslautern)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4716a31cBl@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Technology where a solitary dopant acts as the active component
of an opto-electronic device is an emerging field known as solotronics\,
and bears the promise to revolutionize the way in which information is sto
red\, processed and transmitted. The goal of the talk is in part to elucid
ate the properties of Mn impurities near the surface of GaAs semiconductor
s with focus on their response to local magnetic and electric fields\, as
well as to investigate the real-time dynamics of their localized spins. Th
e second part of the talk deals with the theoretical investigation of a si
ngle substitutional Mn impurity and its associated acceptor state on the (
111) surface of Bi2Se3 topological insulator\, using combined Density func
tional theory and tight-binding calculations. The quest to understand and
control\, at the atomic level\, how a few magnetic atoms precisely positio
ned in a complex environment respond to external stimuli\, is the red thre
ad that connects these two quantum materials in this talk. Depending on th
e time\, I could talk about the energy and magnetization transport in non-
equilibrium spin systems under both thermal gradient and external field.
DTSTART;TZID=Europe/Berlin:20170131T143000
DTEND;TZID=Europe/Berlin:20170131T153000
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
SUMMARY:Magnetic solotronics near the surface of a semiconductor and a topo
logical insulator (Dr. Reza Mahani\, Kungliga Tekniska Högskolan (KTH)\, S
tockholm\, Sweden)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-47333VEUiX@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Geometrical curvature results in new physical effects in low-di
mensional ferromagnetic systems.For1Dsystemswepredictthat: (i)atorsionindu
cedsymmetrybreakingappears in dispersion relation for magnons in a helix s
haped wire\; (ii) a local wire bend creates a pinning potential for a doma
in wall\; (iii) the spin-current driven domain wall motion experiences the
curvature induced shift of the Walker limit and the torsion induced shift
of the nonadiabatic constant\, the latter can result in negative domain w
all mobility. For 2D systems we predict that: (i) magnetic skyrmion can be
stabilized on a surface of revolution by curvature effects only\, even wh
en the intrinsic DMI is absent\; (ii) topological charge of a skyrmion exp
eriences a shift\, which is determined by genus of the surface\, the latte
r results in topological triviality of magnetic skyrmion on a closed spher
ical shell\; (iii) chirality symmetry breaking takes place in the vortex p
olarity switching process for the case of a hemispherical shell. Most of t
hese effects can be treated as a result of the action of curvature induced
DMI and anisotropy\, which effectively appear in exchange energy of a cur
vilinear system.
DTSTART;TZID=Europe/Berlin:20170207T140000
DTEND;TZID=Europe/Berlin:20170207T150000
LOCATION:Galilei room\, 01-128\, (Staudinger Weg 9)
SUMMARY:Effects of curvature in low-dimensional ferromagnetic nanosystems (
Volodymyr Kravchuk\, Bogolyubov Institute for Theoretical Physics\, Kyiv\,
Ukraine\; IFW\, Dresden)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4750cvonVR@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Magnetic skyrmions are nontrivial spin configurations that are
stabilised by chiral interactions. They are nanoscale objects with particl
e-like properties and are potentially useful for information storage and p
rocessing. In this talk\, I will give an overview of our recent theoretica
l and numerical work on skyrmion dynamics in magnetic nanostructures. In p
articular\, I will discuss breathing modes in dots\, self-sustained oscill
ations due to spin- transfer torques\, and the role of disorder for curren
t-driven motion. I will discuss how these results could be useful for expe
rimental detection of skyrmions and their consequences for potential appli
cations.
DTSTART;TZID=Europe/Berlin:20170214T140000
DTEND;TZID=Europe/Berlin:20170214T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Skyrmion dynamics in nanostructures: Breathing modes\, oscillators\
, and the role of disorder (Joo-Von Kim\, Centre for Nanoscience and Nanot
echnology\, CNRS\, Univ. Paris-Sud)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-47630H1vAX@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:We theoretically investigate the ground state structure of bila
yer graphene in the quantum Hall regime. In graphene bilayers\, a double l
ayer material formed of two atomic layers of graphene on top of each other
\, the states of the zero-energy Landau level carry\, besides the real spi
n\, two pseudospin degrees of freedom: a valley isospin and a Landau level
(n = 0\, n = 1) isospin. This peculiar property leads to an octet of stat
es that is eightfold degenerate in the absence of any symmetry breaking an
d can be treated in the frame of quantum Hall ferromagnetism. If this SU(8
) symmetry is indeed broken\, an extraordinary rich phase structure emerge
s\, each phase characterized by a different spin and isospin configuration
. Recent experiments [1] have revealed a plethora of transitions upon vari
ation of the strength of an applied magnetic or electric field. We start f
rom a four-band model Hamiltonian for Bernal stacked bilayer graphene and
take into account both intrinsic symmetry breaking effects as well as the
influence of externally applied electric and magnetic fields. Using a Hart
ree-Fock treatment [2]\, we study the ground state spin and isospin phases
as a function of external magnetic and electric field strengths. For the
different filling factors of the zero-energy multiplet we predict the numb
er of phases\, as well as the nature and the properties of the phases and
the respective phase transitions [3]. [1] J. Velasco Jr\, Y. Lee\, F. Zhan
g\, K. Myhro\, D. Tran\, M. Deo\, D. Smirnov\, A. H. MacDonald\, and C. N.
Lau\, Nature Communications 5\, 4550 (2014)\; K. Lee\, B. Fallahazad\, J.
Xue\, D. C. Dillen\, K. Kim\, T. Taniguchi\, K. Watanabe\, and E. Tutuc\,
Science 345\, Issue 6192\, pp. 58-61 (2014)\; Y. Shi\, Y. Lee\, S. Che\,
Z. Pi\, T. Espiritu\, P. Stepanov\, D. Smirnov\, C. N. Lau\, and F. Zhang\
, Phys. Rev. Lett. 116\, 056601 (2016)\; B. M. Hunt\, J. I. A. Li\, A. A.
Zibrov\, L. Wang\, T. Taniguchi\, K. Watanabe\, J. Hone\, C. R. Dean\, M.
Zaletel\, R. C. Ashoori\, and A. F. Young\, arXiv:1607.06461\, [2] J. Lamb
ert and R. Côté\, Phys. Rev. B 87\, 115415 (2013)\; K. Shizuya\, Phys. Rev
. B 86\, 045431 (2012) [3] A. Knothe and T. Jolicur\, Phys. Rev. B 94\, 2
35149 (2016)
DTSTART;TZID=Europe/Berlin:20170221T140000
DTEND;TZID=Europe/Berlin:20170221T150000
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
SUMMARY:Phase diagram of a graphene bilayer in the zero-energy Landau level
(Angelika Knothe\, Albert-Ludwigs-Universität Freiburg & CNRS/University
of Paris)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4791pmmm68@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:In magnetic thin films the Heisenberg exchange interaction ofte
n leads to a parallel or antiparallel alignment of neighboring spins in th
e crystal. When inversion symmetry is broken e.g. by a surface or an inter
face\, the non-collinear Dzyaloshinskii-Moriya interaction competes with t
he Heisenberg exchange interaction. This competition can lead\, in some ca
se\, to the stabilization of complex spin textures such as spin spirals or
skyrmions. Investigation of the local dynamic properties of magnetic stru
ctures - such as skyrmion or nano-skyrmionic lattice - require the impleme
ntation of experimental technique with a high spatio-temporal resolution (
nm and sub-ns resolution). In this talk\, I will first show that spin-pola
rized STM (SP-STM) is an ideal tool to probe such non-collinear magnetic s
tructure. In a second part I will present our current progress in the deve
lopment of a new experimental technique combining ferromagnetic resonance
(FMR) with SP-STM.
DTSTART;TZID=Europe/Berlin:20170328T140000
DTEND;TZID=Europe/Berlin:20170328T150000
LOCATION:Galilei room 01-128 (Staudinger Weg 9)
SUMMARY:Spin resolved scanning tunneling microscopy: Non-collinear magnetis
m and high frequency dynamic properties (Marie Hervé\, Karlsruher Institut
für Technologie (KIT))
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4806eRr780@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The topologically protected magnetic spin congurations known as
skyrmions offer promising applications due to their stability\, mobility
and localization. In this work\, we emphasize how to leverage the thermall
y driven dynamics of an ensemble of such particles to perform computing ta
sks. We propose a device employing a skyrmion gas to reshuffle a random si
gnal into an uncorrelated copy of itself. This is demonstrated by modellin
g the ensemble dynamics in a collective coordinate approach where skyrmion
-skyrmion and skyrmion-boundary interactions are accounted for phenomenolo
gically. Our numerical results are used to develop a proof-of-concept for
an energy efficient device with a low area imprint. Whereas its immediate
application to stochastic computing circuit designs will be made apparent\
, we argue that its basic functionality\, reminiscent of an integrate-and-
fire neuron\, qualies it as a novel bio- inspired building block.
DTSTART;TZID=Europe/Berlin:20170404T140000
DTEND;TZID=Europe/Berlin:20170404T150000
LOCATION:Galileo room\, 01-128 (Staudinger Weg 9)
SUMMARY:Skyrmion Gas Manipulation for Probabilistic Computing (Daniele Pinn
a\, Unité Mixte de Physique CNRS\, Thales\, Univ. Paris-Sud)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-48211EPxR3@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Skyrmions are topologically stabilized spin structures on the n
anometer scale. They can be manipulated with electric current densities th
at are orders of magnitude lower than those required for moving domain wal
ls. Especially\, isolated magnetic skyrmions can also occur in ultra-thin
transition metal films at surfaces and interfaces. We have shown previousl
y that skyrmions exist in these systems due to a competition between magne
tic interactions beyond the first nearest neighbour approximation. We have
found that this competition can stabilize higher order skyrmions in Pd(fc
c)/Fe/Ir(111) such as antiskyrmions (S=-1) and higher order antiskyrmions
(S=-2). Here\, we present a study on the motion of these skyrmions via spi
n transfer torques. The displacement of skyrmions can be described in a ri
gid-body approximation\, whereas the motions of antiskyrmions require to t
ake internal degrees of freedom into account.
DTSTART;TZID=Europe/Berlin:20170509T140000
DTEND;TZID=Europe/Berlin:20170509T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Motion of skyrmions and antiskyrmions driven by spin-orbit torques
(Ulrike Ritzmann\, Johannes Gutenberg-Universität)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4836m92cK9@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Ultrafast magnetism has become an area of intensive investigati
ons\, following the seminal discovery of ultrafast laser-induced demagneti
zation 20 years ago in Strasbourg. The fundamental mechanisms of ultrafast
demagnetization have not unambiguously been uncovered and continue to be
debated. In this seminar I shall present recent theoretical work that aims
to quantify how much spin-dissipation mechanisms such as Elliott-Yafet el
ectron-phonon spin-flip scattering\, ultrafast magnon generation and super
diffusive spin transport could contribute. In addition\, I shall discuss o
ther recent theoretical contributions to the field\, to mention\, ab initi
o theory for all-optical switching\, derivation of the Landau-Lifshitz-Gil
bert equation from the fundamental Dirac equation\, relativistic theory of
spin-photon interaction\, and recent theory to go beyond the two-temperat
ure model for describing femtosecond laser- excitation of solids.
DTSTART;TZID=Europe/Berlin:20170516T140000
DTEND;TZID=Europe/Berlin:20170516T150000
LOCATION:Galilei room 01-128 (Staudinger Weg 9)
SUMMARY:Ultrafast magnetism: Recent theory developments (Peter Oppeneer\, U
ppsala University)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4850T1i8uJ@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Magnetic skyrmions are whirls in the magnetization with an inte
ger topological winding number. They are stabilized by exchange and Dzyalo
shinskii-Moriya interaction at scales down to the nanometer regime and tur
n out to be highly stable and mobile. Due to these properties\, they are o
ften discussed as possible candidates for future memory devices. From a ph
ysics perspective they are particularly interesting since new properties e
merge from the interplay of both energetic and topological contributions.
In my talk I will mainly focus on topological defects in the helix\, which
is another important phase that occurs in skyrmionic matter. It turns out
that a special kind of domain wall structure can occur between helical ph
ases with different orientations. The domain wall which connects the diffe
rently orientated helical phases\, can appear as a sequence of topological
ly non-trivial disclinations and can be described within our phenomenologi
cal theory. Furthermore\, skyrmions also occur as the most natural defects
in the helical phase but they have different properties as their often-st
udied counterparts in the polarized phase.
DTSTART;TZID=Europe/Berlin:20170523T140000
DTEND;TZID=Europe/Berlin:20170523T150000
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
SUMMARY:Skyrmions and topological charges in the helix (Jan Müller\, Instit
ut für Theoretische Physik\, Universität zu Köln)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-48676tFMBX@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The Landau-Lifshitz-Gilbert (LLG) equation in combination with
first-principles methods\, has been used with great success to describe th
e magnetization dynamics in a wide range of cases and materials. Such as t
he motion of magnetic textures\, e.g. domain walls and skyrmions\, and the
description of magnetic excitations such as spin waves. Recent developmen
ts have allowed for a more complete description of spin dynamics from firs
t principles thanks to the capacity to calculate the Gilbert damping from
ab-initio methods. In the following talk a small overview of the most comm
on methods used to determine the Gilbert damping from first principles wil
l be presented. The role of different considerations to the damping\, such
as the density of states at the Fermi level\, temperature\, chemical allo
ying and the spin orbit coupling [1-3] will be presented making use of fir
st principles studies of materials of great technological importance such
as half-metallic Heusler alloys and permalloy. [1] J. Chico\, et al. Phys.
Rev. B 93\, 214439 (2016). [2] F. Pan\, J. Chico\, et al. Phys. Rev. B 94
\, 214410 (2016). [3] P. Dürrenfeld\, F. Gerhard\, J. Chico\, et al. Phys.
Rev. B 92\, 214424 (2015).
DTSTART;TZID=Europe/Berlin:20170613T140000
DTEND;TZID=Europe/Berlin:20170613T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Gilbert damping from first-principles methods (Jonathan Chico\, Pet
er Grünberg Institut and Institute of Advanced Simulation\, Forschungszent
rum Jülich & JARA)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4884HGi27J@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Spin currents in magnetic insulators are currently intensely in
vestigated because of their potential to be the future information carrier
s replacing part of the conventional charge current based electronics [1].
Since there is no charge transport at all in magnetic insulators\, only m
agnons\, the quanta of spin waves\, carry the spin information. Thus\, hea
t dissipation is strongly reduced compared to the overall Joule heating of
conventional charge transport. In order to connect the magnon spin system
with conventional charge current based electronics\, new techniques have
been developed to inject and detect magnon spins in magnetic insulators\,
e.g. Y3Fe5O12 (YIG) or NiFe2O4 (NFO). The spin Hall effect in heavy metals
\, such as Pt\, next to a magnetic insulator is used to generate a magnon
spin current electrically\, while the thermal generation of magnon spin cu
rrents is induced by the spin Seebeck effect [2\,3]. In my talk\, I will s
how how the spin Hall effect and the spin Seebeck effect can be used to ge
nerate and detect the spin transport in magnetic insulators in a local and
nonlocal experiment [4-7]. Thus\, we can observe quite long magnon spin d
iffusion lengths of several microns in both YIG [4] and NFO [5]. Furthermo
re\, I will explain that the transport of magnon spins through an insulato
r provides similar transport phenomena as electrons in a metal depending o
n the direction of an external magnetic field. Here\, we found a magnon an
isotropic magnetoresistance in YIG that can be revealed in the nonlocal ex
periment [6]. In addition\, I will show signatures of magnon-polarons in t
he nonlocal magnon spin transport in YIG. These magnoelastic coupled magno
n-photon quasi particles have been recently detected via the local spin Se
ebeck effect [8]\, but show even more surprising features in the nonlocal
experiment [7]. Finally\, going from ferrimagnetic to antiferromagnetic in
sulators following the antiferromagnetic spintronics route [9]\, we could
find a sign change in the local spin Hall magnetoresistance for Pt on the
easy-plane bulk antiferromagnet NiO [10]. Thus\, we are able to use the sp
in Hall magnetoresistance as a probe to identify and study easy-plane anti
ferromagnetic materials.
DTSTART;TZID=Europe/Berlin:20170620T140000
DTEND;TZID=Europe/Berlin:20170620T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Electrically and thermally induced spin currents in magnetic insula
tors (Timo Kuschel\, Bielefeld University\; University of Groningen)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-49116uou8r@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Recent developments in surface and interfacial magnetism have r
aised the question if it is possible to realize a memory derived from sing
le atoms or nanometer sized skyrmions. Therefore\, it is important to unde
rstand how the local magnetic anisotropy driven by the crystal field symme
try\, magnetic exchange\, and hybridization influences the magnetization a
t the atomic length scale. Nevertheless\, a vast majority of atomic-scale
studies have utilized spin-polarized scanning tunneling microscopy (SP-STM
)\, limiting the scope of materials which can be probed. In order to gain
new insight into magnetism at the atomic scale\, we combine SP-STM with ma
gnetic exchange force microscopy (together called SPEX)\, based on a qPlus
tuning fork design. We use SPEX to characterize the magnetic non-collinea
r nano-skyrmion structure of a single monolayer of Fe on Ir(111). We show
that SPEX is capable of disentangling structural from electronic or magnet
ic effects\, which spin-polarized STM alone cannot achieve\, as well as pr
obing direct and indirect magnetic exchange. Furthermore\, we use SPEX to
study the structure of the complex spin spiral dislocation network in the
second Fe layer on Ir(111).
DTSTART;TZID=Europe/Berlin:20170627T140000
DTEND;TZID=Europe/Berlin:20170627T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Sensing skyrmions at the atomic scale combining magnetic exchange a
nd spin- polarized imaging (Nadine Hauptmann\, Radboud University\, Instit
ute for Molecules and Materials (IMM))
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4929ABr0hf@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The quest for device miniaturization\, decreased energy consump
tion\, and improved speeds of processing and storage units naturally led t
o exploiting the connection between electric currents and magnetization dy
namics. In this presentation\, I demonstrate that ferromagnetic and antife
rromagnetic excitations can be triggered by the dynamical spin accumulatio
ns induced by the bulk and surface contributions of the spin Hall effect [
1]. I also analyze the general concepts of magnetoresistance and Hall effe
cts together with spin-orbit- related mechanisms to demonstrate how dynami
cal currents can be dramatically enhanced and precisely controlled by appl
ying ac electric fields and static magnetic fields\, in a materials- speci
fic approach [2]. Furthermore\, I uncover how pure spin currents generated
by the spin Hall effect can be dynamically manipulated\, with effective c
onversion rates increasing up to 500% and reaching values larger than the
giant ones obtained for static currents. The combination of in-silico mate
rial design and ultrafast dynamical effects is only achievable by a micros
copic quantum mechanical theory\, utilizing an approach based on the elect
ronic structure. This work may also impact experimental techniques that us
e currents to probe and quantify magnetization precession and the torques
that induce it. [1] F. S. M. Guimarães et al.\, Phys. Rev. B 92\, 220410(R
) (2015). [2] F. S. M. Guimarães et al.\, arXiv:1703.04493
DTSTART;TZID=Europe/Berlin:20170704T140000
DTEND;TZID=Europe/Berlin:20170704T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Dynamical amplification of magnetoresistances and Hall currents up
to the THz regime (Filipe Guimarães\, Peter Grünberg Institut and Institut
e of Advanced Simulation\, Forschungszentrum Jülich & JARA)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4949h1WhNu@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Berry curvature is related to gauge field and studied in many s
ystems such as electron\, photon\, and quasi particles. One of interesting
point to study Berry curvature of spin wave in ferromagnets is change of
effective interactions by sample geometry and thickness. In general\, Berr
y curvature of spin wave is zero with only exchange interaction. Dipolar i
nteraction and Dyaloshinskii-Moriya interaction are well known to give ris
e to non-zero Berry curvature. Effective range and mechanism are different
between two interactions. We recently calculated Berry curvature of spin
waves in ferromagnetic films with dipolar and exchange interactions. In th
is regime\, the exchange interaction makes the dispersion change dependent
on the thickness. The resulting Berry curvature reproduces that in previo
us works in the magnetostatic limit. In addition\, we found that the Berry
curvature of magnons in the dipole-exchange range has a peak at the cross
ings of the eigen modes\, where hybridizations between the modes are signi
ficant. In this presentation\, I introduce example of Berry curvature and
novel phenomena in some systems at first. After that\, I discuss Berry cur
vature of spin wave in ferromagnets\, its application\, and possibility at
the last of presentation.
DTSTART;TZID=Europe/Berlin:20170718T140000
DTEND;TZID=Europe/Berlin:20170718T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Dispersion and Berry curvature of spin wave in ferromagnets (Akihir
o Okamoto\, Tokyo Institute of Technology)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4966vZe8KA@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Owing to their topology\, magnetic skyrmions are considered as
potential particles for future information technology. However\, incorpora
tion of magnetic skyrmions as information carriers or memory storage units
in future information technology nodes requires a detailed understanding
of the impact of device imperfections on their speed\, motion\, creation a
nd stability. Following our previous studies [1\, 2]\, I will discuss firs
t-time fully ab-initio based simulations of single magnetic skyrmions in P
d/Fe/Ir(111) surface interacting with 3d and 4d impurities and investigate
the impact on the energetics\, electronic and magnetic properties. With a
careful analysis of the hybridization of the electronic states\, the impo
rtant mechanisms behind the expulsion or pinning of single magnetic skyrmi
ons as function of the chemical nature of the impurities are identified. I
will highlight the universality of the skyrmions energy landscape when in
teracting with transition metal defects and the possible impact on skyrmio
ns motion. [1] D. Crum\, et al. Nature Commun. 6\, 8541 (2015). [2] M. Dos
Santos Dias\, et al. Nature Commun. 7\, 13613 (2016). Funding provided by
the European Research Council (ERC) under the European Union's Horizon 20
20 research and innovation programme (ERC-consolidator grant 681405 DYNA
SORE).
DTSTART;TZID=Europe/Berlin:20170808T140000
DTEND;TZID=Europe/Berlin:20170808T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Impact of the chemical nature of defects on the pinning of magnetic
skyrmions (Imara L. Fernandes\, Peter Grünberg Institut and Institute of
Advanced Simulation\, Forschungszentrum Jülich & JARA)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-4985U5kS3l@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The main subject of this presentation will be the study of meta
llocenes deposited on copper surfaces. Their adsorptions and electronic pr
operties are experimentally studied by scanning tunnelling microscopy (STM
) and scanning tunnelling spectroscopy (STS). Our results were confirmed b
y density functional theory (DFT) computations. More precisely\, we studie
d how ferrocene FeC10H10 and nickelocene NiC10H10 are adsorbed on copper.
We found that these metallocenes spontaneously create networks alternating
horizontal and vertical molecules. We added a cobalt atom to the ferrocen
e in order to modify its structure and we characterized the magnetic prope
rties of the new molecule we created\, in particular the appearance of a K
ondo effect showing that magnetic properties appeared in the molecule. The
spectroscopic study of nickelocene revealed an excitation of the molecule
at low bias. This excitation consist in a change in the spin orientation
of the molecule\, going from an orientation perpendicular to the main mole
cule axis to an orientation parallel to this axis. We finally transferred
a nickelocene to the STM tip and used this molecular tip to probe the stat
es of a second molecule. We consequently obtained a double spin excitation
in our tunnel junction\, with a significant increase of the conductance d
ue to excitations.
DTSTART;TZID=Europe/Berlin:20170815T140000
DTEND;TZID=Europe/Berlin:20170815T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Spin detection and doping of metallocenes on copper substrates (Nic
olas Bachellier\, Institut de Physique et Chimie des Matériaux de Strasbou
rg (IPCMS))
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5004Dz2ruO@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Thermal fluctuations have always been a topic of interest in mi
cromagnetism. Theoretical descriptions already date back to the fifties as
W. F. Brown derived and presented the statistical properties of the rando
mly fluctuating thermal field required to physically describe the switchin
g behaviour of single-domain nanoparticles. In this talk\, I present the r
esults of 2 studies on the measurement and simulation of thermally driven
magnetization dynamics. In the first part\, the switching of magnetic nano
particles is investigated via an experimental study\, introducing a new me
thod for magnetic nanoparticle characterization: Thermal magnetic noise sp
ectroscopy. Typically\, particle characterization is performed by measurin
g the particles response to an external excitation like an applied field.
However\, such excitations are known to alter the nanoparticles aggregat
ion state and thus affect the characterization results. Recently\, we demo
nstrated the feasibility of measuring the thermal magnetic noise emitted b
y magnetic nanoparticles in the absence of any excitation. The magnetic pa
rticles noise spectrum was recorded using a SQUID in a magnetically shiel
ded environment and the recorded spectra could then be interpreted in orde
r to characterize the magnetic nanoparticles. The second part of the talk
deals with the thermally activated motion of domain walls in a magnetic na
nowire. Because each finite-difference cell in micromagnetic simulations c
an be considered as a single-domain particle\, the thermal field describ
ed by Brown can be added as an effective field term in the Landau-Lifshitz
-Gilbert equation. Using large- scale micromagnetic simulations\, we explo
re the current-driven creep regime of a transverse domain wall in disorder
ed Permalloy nanostrips. Our results show that the domain wall creep veloc
ity exhibits a simple linear dependence on the current density instead of
the highly non-linear creep scaling law usually encountered in rough elast
ic systems. To explain this\, we derived an equation describing the motion
of a current-driven domain wall in a disordered nanowire at finite temper
atures. In contrast to the creep scaling law found in elastic systems\, th
is equation is only valid for domain walls sufficiently small to be descri
bed as rigid objects. We validated this equation against experimental data
and our micromagnetic simulations and could conclude that the domain wall
s under study can indeed be described as a rigid object instead of an elas
tic line. The ongoing miniaturization of spintronic devices dictates that
thermal effects will become increasingly important in micromagnetic resear
ch\, and the two presented systems show that they can accurately be taken
into account in numerical studies and can even be exploited in technologic
al applications.
DTSTART;TZID=Europe/Berlin:20170822T140000
DTEND;TZID=Europe/Berlin:20170822T150000
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
SUMMARY:Thermally driven micromagnetic systems (Jonathan Leliaert\, Dept. o
f Solid State Sciences\, Universität Gent\, Belgien)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5035FCe1ot@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The formation of a spin-disordered state due to the local momen
t fluctuations at elevated temperatures strongly affects the ground state
electronic properties of magnetic materials. In particular\, we investigat
e how the spectral function changes as a function of temperature in select
ed Heusler alloys. Furthermore\, we focus on the spin disorder effect on t
he thermoelectric and spin-caloric transport properties in various magneti
c nanostructures. This is motivated by the miniaturization of spintronics
devices and by recent suggestions that magnetic nanostructures can lead to
extraordinary thermoelectric effects due to quantum confinement [1]. In o
ur approach\, the electronic structure is calculated within the full-poten
tial Korringa-Kohn-Rostoker Green function (KKR-GF) framework [2] using th
e local density approximation. The Monte-Carlo methodology is used to simu
late the effect of temperature induced spin disorder and the set of spin-d
isordered configurations is fed back in the KKR-GF method to obtain the st
atistical average of the relevant material properties [3-5]. [1] N. Vu et
al.\, APEX 4\, 015203 (2011). [2] N. Papanikolaou et al.\, J. Phys.: Conde
ns. Matter 14\, 2799\, (2002)\, also see: kkr-gf.org. [3] Ph. Mavropoulos
et al.\, Phys. Rev. B 69\, 125104\, (2004). [4] R. Kováčik et al.\, Phys.
Rev. B 89\, 134417\, (2014). [5] R. Kováčik et al.\, Phys. Rev. B 91\, 014
421\, (2015).
DTSTART;TZID=Europe/Berlin:20171017T140000
DTEND;TZID=Europe/Berlin:20171017T150000
LOCATION:Galilei Room\, 01-128 (Staudinger Weg 9)
SUMMARY:Spin disorder effect on the electronic and transport properties in
magnetic materials from first principles (Roman Kováč\;ik\, Peter Grün
berg Institut and Institute for Advanced Simulation\, Forschungszentrum Jü
lich and JARA)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-50546Urxuv@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:In this talk\, I will speak about magnetic textures including d
omain walls and skyrmions in one and two dimensions from a macroscopic poi
nt of view. Among all the possible configurations\, there is a set of magn
etic textures with topological properties and a rather rigid structure. We
analyze the minimum requirements for the existence and creation of these
textures. We will present an effective Hamiltonian formalism that describe
s the low energy excitation of the topological textures. This formalism is
independent of microscopic details and external perturbations. We show ho
w interactions may be easily introduced and consider also antiferromagneti
c materials. Future developments and potential applications will be discus
sed.
DTSTART;TZID=Europe/Berlin:20171024T140000
DTEND;TZID=Europe/Berlin:20171024T150000
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
SUMMARY:Effective description of topological magnetic textures (Davi R. Rod
rigues\, Department of Physics & Astronomy\, Texas A&M University)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5068xG4nrG@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Recently the phenomenon of negative magnetoresistance (MR) is a
ttracting renewed interest due to its occurrence in Weyl semimetals becaus
e of the chiral anomaly. In other systems a large MR typically relates to
magnetism. In this talk a novel mechanism leading to a large negative MR w
ill be presented that is based not on magnetism\, but on disorder. In the
newly synthesized bulk- insulating topological insulator material T1BixSb1
-xTe2 we find a suppression of the resistivity by up to 98 % in 14 T at lo
w temperature. From transport data and numerical simulations\, this gigant
ic negative MR is understood by a percolation of charge puddles formed in
the disordered bulk.
DTSTART;TZID=Europe/Berlin:20171107T140000
DTEND;TZID=Europe/Berlin:20171107T150000
LOCATION:Galileo room\, 01-128 (Staudinger Weg 9)
SUMMARY:Gigantic negative magnetoresistance in a disordered Topological Ins
ulator (Oliver Breunig\, University of Cologne)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5080C8UA5v@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:First-principles calculations based on density functional theor
y (DFT) appeared to be valuable tools to compute the strength of the magne
toelectric response of materials and to understand its microscopic origin.
The methods are becoming sufficiently reliable and predictive to be used
in the search for new magnetoelectric materials. In this talk I will prese
nt the state of the art of the different first-principles techniques that
can be used to compute the magnetoelectric response of a crystal under ele
ctric or magnetic fields. I will show their applications on several system
s such as the prototypical magnetoelectric material Cr2O3\, LiFePO4 and th
e troilite phase of FeS. For each of these systems\, I will discuss the di
fferent microscopic mechanisms that drive their response: electronic versu
s lattice mediated and spin versus orbital origins. Then\, I will present
two original examples of strain engineered ferroelectric and magnetoelectr
ic responses in initially non-functional materials: CaMnO3 and NaMnF3. I
will also profit the occasion to introduce some related and exotic featur
es of magnetoelectricity: magnetoelectric monopoles and (ferro)toroidal mo
ments.
DTSTART;TZID=Europe/Berlin:20171122T150000
DTEND;TZID=Europe/Berlin:20171122T160000
LOCATION:ComZone 01-620 (Staudinger Weg 7)
SUMMARY:Magnetoelectric response from first- principles: microscopic unders
tanding and design rules (Eric Bousquet\, Universitée de Lièges)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5097T7Pn9A@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The spin-orbit interaction (SOI) is at the heart of spin orbitr
onics and gives rise to unique physical effects. The vision is to exploit
SOI for the generation\, transport and detection of spin currents without
magnetic fields\, i.e.\, the all-electric control of the electron spin\, o
r to stabilize new magnetic states with non-trivial topology and novel pro
perties. Crucial from a materials perspective how much lattice defects\, i
mpurities and in general symmetry breaking alter such important spin-orb
it effects like spin-relaxation\, the Hall effects and Dzyaloshinskii-Mori
ya interaction (DMI). I will introduce the Korringa-Kohn-Rostoker (KKR) me
thod and focus on our new developments for the calculation of aforemention
ed spintronic effects with predictive power. I will show selected examples
to highlight the capabilities of our approach\, starting from our discove
ry of a colossal anisotropy of spinrelaxation in metals [1-3]\, which orig
inates from a pure band-structure effect. By explicitly including scatteri
ng properties off impurities\, we predict the electron skew-scattering con
tribution to the Hall effects in ferromagnets for the first time [4] and a
nalyze complex disorder in the L10-ordered alloy FePt [5]. Finally\, I wil
l turn to magnetic interactions and highlight the importance of symmetry-b
reaking for an anisotropic DMI\, which leads in a double-layer Fe on W(110
) to the stabilization of anti-skyrmions rather than skyrmions [6]. To con
clude\, I will analyze the effect of intermixing on the DMI at the promine
nt Co/Pt interface employing the powerful Coherent Potential Approximation
(CPA) for a disordered system [7]. [1] Zimmermann et al.\, Phys Rev. Lett
. 109\, 236603 (2012)\, [2] Zimmermann et al.\, Phys. Rev. B 93\, 144403 (
2016)\, [3] Long et al.\, Phys. Rev. B 90\, 064406 (2014)\, [4] Zimmermann
et al.\, Phys. Rev. B 90\, 220403(R) (2014)\, [5] Zimmermann\, et al.\, P
hys. Rev. B 94\, 060406(R) (2016)\, [6] Hoffmann et al.\, Nature Commun. 8
\, 308 (2017)\, [7] Zimmermann\, et al.\, in preparation. All interested a
re cordially welcome!
DTSTART;TZID=Europe/Berlin:20171205T140000
DTEND;TZID=Europe/Berlin:20171205T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Spin-orbit effects from ab-initio theory: from electron scattering
to chiral spin textures (Bernd Zimmermann\, Peter Grünberg Institut and In
stitute for Advanced Simulation\, Forschungszentrum Jülich and JARA)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5123OP3Ih0@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:
DTSTART;TZID=Europe/Berlin:20180109T140000
DTEND;TZID=Europe/Berlin:20180109T150000
LOCATION:Galilei room\, 01-128 (Staudinger Weg 9)
SUMMARY:Master thesis talk: Specialization seminar (Wojciech Morawiec\, Joh
annes Gutenberg-Universität)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5129G8wfad@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Magnetic skyrmions in ultrathin films require a strong chiral i
nteraction. It is usually provided by the Dzyaloshinskii-Moriya interactio
n\, of the interfacial type for ultrathin films. For single films\, in an
asymmetrical architecture\, it has been shown that the skyrmion size and s
tability depend extremely sensitively on all sample parameters. Multilayer
s with typically 10 repetitions of an asymmetrical structure have also bei
ng studied\, showing robust skyrmions but\, as realized recently\, a degra
ded chirality of the domain wall due to magnetostatic effects. In order to
retain\, by construction\, the benefits of both the magnetostatic interac
tion and the Dzyaloshinskii-Moriya interaction\, we have studied symmetric
bilayers of ultrathin films\, each in an asymmetric structure. In such a
system\, we obtain robust skyrmions with a typical 100 nm diameter\, show
that they can be nucleated by localized current injection using sharp elec
trodes\, measure their current-induced propagation with up to 60 m/s longi
tudinal velocity\, and observe their transverse deflection according to th
e gyrovector sign. These experiments were performed inside a magnetic forc
e microscope. In addition\, high-resolution skyrmion shapes have been syst
ematically mapped using the NV-center magnetic microscope and the measured
distributions have been compared to micromagnetic simulations\, using a p
hysical description of magnetic disorder based on magnetic layer thickness
fluctuations. [1] Current-induced skyrmion generation and dynamics in sym
metric bilayers\, A. Hrabec\, J. Sampaio\, M. Belmeguenai\, I. Gross\, R.
Weil\, S.M. Cherif\, A. Stashkevich\, V. Jacques\, A. Thiaville\, and S. R
ohart\, Nat. Commun. 8\, 15765 (2017). [2] Skyrmion morphology in ultrathi
n magnetic films\, I. Gross\, W. Akhtar\, A. Hrabec\, J. Sampaio\, L. J. M
artinez\, S. Chouaieb\, B. J. Shields\, P. Maletinsky\, A. Thiaville\, S.
Rohart\, and V. Jacques\, arXiv:1709.06027 (2017).
DTSTART;TZID=Europe/Berlin:20180122T130000
DTEND;TZID=Europe/Berlin:20180122T140000
LOCATION:Media Raum\, 03-431 (Staudinger Weg 7)
SUMMARY:Skyrmions in symmetric bilayers (André Thiaville\, Université Paris
-Sud)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5152HIGCvI@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:Formation of unusual textures of polarization is imminent for n
ano-scale ferroelectric samples\, films\, rods\, and granules\, where the
depolarization surface effects play the crucial role. The topologically pr
otected stability of such textures is coming from polarization vorticity\,
provided by condition of absence of the energetically-unfavorable depolar
ization charge. Polarization domains that alternate the surface charge dis
tribution\, first proposed by Landau and Kittel in contents of ferromagnet
ism can be formed in ferroelectric thin films as an effective mechanism to
confine the depolarization field to the near-surface layer and diminish t
he depolarization energy. However\, their existence have long been conside
red as barely possible until the direct theoretical predictions and experi
mental evidences thin oxide-based superlattices. Very recently we have dem
onstrated that the effective capacitance of ferroelectric layers with doma
ins is negative. This effect is explained by the opposite orientation of t
he depolarizing field with respect to the field-induced averaged polarizat
ion. This phenomenon is currently considered as the platform for realizati
on of the dissipationfree high performance nano-circuits. Moreover\, in su
b-THz region the resonance plasmonic effect can be induced by oscillating
domain walls and can be suitable for design of the ultrasmall low-energy T
Hz chips. Multi-vortex and skyrmion states can be formed inside ferroelect
ric cylindrical nano-dots and nanorods to reduce the depolarization energy
. We study the stability of such states and demonstrate that the topologic
al class of the most stable topological excitations can be driven by the g
eometrical and electrical parameters of the system\, external field and te
mperature. We target the multi-domain and topological excitations in FE na
nodots as a platform for multivalued logic units\, breaking ground for neu
romorphic computing. All interested are cordially welcome!
DTSTART;TZID=Europe/Berlin:20180123T140000
DTEND;TZID=Europe/Berlin:20180123T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Topological excitations in nano-scale ferroelectrics (Igor Lukyanch
uk\, Laboratory of Condensed Matter Physics\, University of Picardie\, Fra
nce)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5176EKxrg7@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:
DTSTART;TZID=Europe/Berlin:20180130T140000
DTEND;TZID=Europe/Berlin:20180130T150000
LOCATION:Galilei room 01-128 (Staudinger Weg 9)
SUMMARY:Universal fluctuations of Floquet topological invariants at low fre
quencies (Babak Seradjeh\, Indiana University)
END:VEVENT
BEGIN:VEVENT
UID:20180226T023506CET-5183gpGBMB@42.seminar.physik.uni-mainz.de
DTSTAMP:20180226T013506Z
DESCRIPTION:The last decade has seen nearly exponential growth in the scien
ce and technology of two-dimensional (2D) materials. Beyond graphene\, the
re is a great variety of new monolayer materials\, which can adjust their
properties from insulators to superconductors. On the other hand\, the sta
cking of different materials also allows an additional 'dimensionality' in
the design of new semiconductor and superconductor heterostructures. In t
his talk\, I will discuss recent breakthroughs in the theoretical characte
rization of two-dimensional materials\, including the new 2D nitrides. In
particular\, starting from the wurtzite phase of gallium nitride (GaN)\; m
echanical\, electronic and optical properties of a novel 2D phase (type of
graphene\, known as g-GaN) is debated. The structural and vibrational sta
bility of g-GaN is presented within the density functional theory (DFT) fr
amework [1]. It is also shown a comparative study to reveal how their phys
ical properties are modified by the dimensionality and doping [2]. [1] P.
Giannozzi\, et al\, J. Phys.: Condens. Matter\, (2009)\, 21\, 395502 [2] R
. González\, W. López-Pérez\, Á. González-García\, M. Moreno-Armenta\, R.
González-Hernández\, Applied Surface Science\, (2018) 433\, 1049 All inter
ested are cordially welcome!
DTSTART;TZID=Europe/Berlin:20180227T140000
DTEND;TZID=Europe/Berlin:20180227T150000
LOCATION:Galilei Raum\, 01-128 (Staudinger Weg 9)
SUMMARY:Computational modeling of 2D materials beyond graphene (Rafael Gonz
alez-Hernandez\, Universidad del Norte\, Barranquilla\, Colombia)
END:VEVENT
END:VCALENDAR