Events - Weekly
|Sunday, January 25|
|Monday, January 26|
High Energy Theory Seminar IAS - Charles Kane, University of Pennsylvania-"“The Time Reversal Invariant Fractional Josephson Effect”
Topological Superconductivity is a topic of current interest because of its potential for providing a new method for storing and manipulating quantum information. One of the most basic consequences of topological superconductivity is the fractional Josephson effect, which arises due to the coherent tunneling of single electrons between two superconductors, leading to an AC Josephson effect with half the usual Josephson frequency. In this talk we will review the theoretical foundations for the fractional Josephson effect and discuss prospects for observing it. We will then describe recent work in which we have clarified the role of time reversal symmetry. Time reversal symmetric Josephson junctions are classified by two distinct Z_2 topological invariants. One of these characterizes a junction mediated by the edge states of a quantum spin Hall insulator. In that case, we showed that electron interactions stabilize a "Z_4 fractional Josephson effect" with one quarter the usual Josephson frequency. For strong interactions this Josephson effect is associated with the tunneling of charge e/2 quasiparticles. For weak tunneling, this theory describes a fourfold ground state degeneracy that is similar to that of coupled "fractional" Majorana modes, but is protected by time reversal symmetry.
Bloomberg Lecture Hall - Institute for Advanced Study · 2:30 p.m.– 3:30 p.m.
|Tuesday, January 27|
|Wednesday, January 28|
Condensed Matter Seminar, Carlos Sa De Melo, Georgia Tech,"Effects of spin-orbit coupling on the Berezinskii-Kosterlitz-Thouless transition . . . .
We investigate the Berezinskii-Kosterlitz-Thouless (BKT) transition in a two-dimensional (2D) Fermi gas with spin-orbit coupling (SOC), as a function of the two-body binding energy and a perpendicular Zeeman field . By including a generic form of the SOC, as a function of Rashba and Dresselhaus terms, we study the evolution between the experimentally relevant equal Rashba-Dresselhaus (ERD) case and the Rashba-only (RO) case. We show that in the ERD case, at fixed non-zero Zeeman field, the BKT transition temperature TBKT is increased by the effect of the SOC for all values of the binding energy. We also find a significant increase in the value of the Clogston limit compared to the case without SOC. Furthermore, we demonstrate that the superfluid density tensor becomes anisotropic (except in the RO case), leading to an anisotropic phase-fluctuation action that describes elliptic vortices and anti-vortices, which become circular in the RO limit. This deformation constitutes an important experimental signature for superfluidity in a 2D Fermi gas with ERD SOC. Finally, we show that the anisotropic sound velocity exhibit anomalies at low temperatures in the vicinity of quantum phase transitions between topologically distinct uniform superfluid phases.
 “Effects of spin-orbit coupling on the Berezinskii-Kosterlitz-Thouless transition and the vortex-antivortex structure in two-dimensional Fermi gases”, Jeroen P. A. Devreese, Jacques Tempere, and Carlos A. R. Sá de Melo, Phys. Rev. Lett.113, 165304 (2014).
PCTS Seminar Room · 2:00 p.m.– 3:30 p.m.
|Thursday, January 29|
|Friday, January 30|
|Saturday, January 31|