Condensed-Matter Physics seminars: Fall 2008

Wednesdays in the Physics Reading Room

Date & timeSpeaker & 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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Leonid Pryadko <my first name at landau dot ucr dot edu>
Last modified: Mon Apr 27 10:16:30 PDT 2009