QM Seminar Speaker Christoph Fleckenstein (Institute of Theoretical Physics and Astrophysics, University of Würzburg, Germany) Wednesday, March 13

Time: 2:00 pm
Venue: LeConte 402
Title: Quantum Constrictions In Interacting Quantum Spin Hall Systems
Abstract: Quantum spin Hall insulators give rise to time-reversal protected  
helical edge modes that provide a rich platform to test an extend  
theories usually assigned to high energy physics. In particular, this  
becomes even more exciting when quantum constrictions are considered,  
such that the helical edge states of each edge interact with each  
other. Then, the effective low energy theory can be gapped without  
breaking time-reversal symmetry. For present superconducting order,  
this gives rise to Majorana Kramers pairs. Interestingly, when the  
system is gapped by Coulomb interactions, the nature of these  
bound-states changes to parafermions, which are generalizations of  
Majorana modes with richer braiding properties. Here, they can coexist  
with Majorana modes and, in contrast to many former proposals, they  
survive even in the weakly interacting regime. Remarkably, very recent  
experiments done on quantum constrictions based on HgTe/HgCdTe quantum  
wells not only imply the existence of interactions at the helical  
edge, but also indicate the presence of two-particle scattering terms,  
necessary for those parafermions.

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