| Date & time | Speaker & affiliation | Talk title & abstract |
| Apr 1 4:00pm | TBA | |
| Apr 8 4:00pm | TBA | |
| Apr 15 4:00pm | Xiaoling Qi (Stanford) | Fractional charge and spin-charge separation in
quantum spin Hall insulators
Abstract:
The existence of fractional charge and spin-charge separation are two
related fractionalization phenomena in condensed matter physics. One
of the simplest realizations of these phenomena is given by the Su-
Schrieffer-Heeger model describing a one-d chain with bond or site
CDW
order. In this talk, I will show how both effects are realized in the
recently discovered two-dimensional quantum spin Hall (QSH) insulator
system. The QSH insulator is a topological state of matter, which has
a bulk gap and counter-propagating gapless edge states protected by
the time-reversal symmetry. Firstly, a half charge is trapped when an
anti-phase domain wall configuration of a magnetic field is applied to
the one-d edge of the QSH system. We propose an experimental device
to
measure such a half charge, using the concept of single electron
transistor. Secondly, the spin-charge separation effect can be
realized when a π flux is threaded into the bulk of a QSH insulator.
Under very general preconditions of time-reversal symmetry and non-
degenerate ground state, we show that the spin-charge separation is
always well-defined and topologically protected, and the presence of
this effect can act as a generic definition of QSH insulator, which is
applicable to most generic systems with interaction and disorder.
Physically, this effect can be realized in a heterostructure between a
QSH insulator and a type II superconductor. Besides providing a two-d
realization of fractionalization effects, these two effects proposed
here also provide qualitative observable criteria to distinguish the
QSH insulator from a trivial band insulator.
|
| Apr 22 4:00pm | Paco Guinea (Instituto de Ciencia de Materiales de Madrid, Spain) | Electronic properties and structural deformations in
graphene
Abstract: Graphene is a two dimensional material which
shows many unusual properties, not observed in other two dimensional
metals. Among others, the graphene lattice can be corrugated, and these
corrugations induce on the electrons effective gauge fields. We discuss the
way in which the electronic properties are modified by random, and induced
lattice deformationes.
|
| Apr 27 (Monday) 4:00pm | Krishnendu Sengupta (Indian Association for the Cultivation of Sciences, Kolkata, India) | Aspects of many-body physics in graphene
Abstract: Graphene, due to the Dirac nature of its low-energy
quasiparticle, exhibits a host of unconventional
electronic properties. In this talk, I would concentrate on
two of these, namely, i) physics of superconducting junctions and
ii) magnetic impurities in graphene.
I would discuss the unconventional nature of the
physics involved for both the cases and show that the
helicity of the gapless low-energy Dirac-like quasiparticles
in graphene is at the heart of this unconventional
behavior.
|
| Apr 29 4:00pm | Sasha Chernyshev (UCI) | Frustrated, Degenerate, and Breaking Apart:
The Bright Side of Life in Triangular Lattice
Abstract: We demonstrate that the spin-wave
excitations in a wide class of frustrated antiferromagnets are unstable
with respect to spontaneous two-magnon decays leading to the overdamped
spectra. Their spectra also exhibit threshold singularities which lead to
strong enhancement of the decay rates along special contours in the momentum
space. Such singularities can serve as fingerprints of magnon decays, which
should help future experiments to distinguish the decay-induced spin-wave
broadening from the other scenarios that may yield broad spectra of spin
excitations.
|
| May 4 4:00pm | Revaz Ramazashvilli (U. Paris-Sud, France) | |
| May 6 4:00pm | Vladimir Cvetkovic (Johns Hopkins) | |
| May 13 4:00pm | TBA | |
| May 20 4:00pm | Dmitrii Maslov (U of Florida) | |
| May 27 4:00pm | TBA | |
| Jun 3 4:00pm | TBA | |
| Jun 10 4:00pm | TBA |
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