Talk given by

Prof. Ronny Thomale
Theoretische Physik I
University of Würzburg

Abstract:

Since its discovery in HgTe/CdTe quantum wells in 2007, the quantum spin Hall 
effect has become a central source of stimulation and inspiration for the 
growing field of topological phases in condensed matter systems. For by now more 
than a decade, one central challenge has been to diversify the range of 
experimental systems in which the quantum spin Hall effect could be 
unambiguously observed, and in particular to elevate the operating temperature 
to a level that would render quantum spin Hall devices technologically 
accessible. We report on recent progress in realizing one-dimensional step edge 
modes in the topological crystalline insulator Pb(Sn,Se) [Sessi et al., Science 
354, 1269 (2016)], where the Berry phase slip at odd step edges ensures robust 
spin-polarized edge states at elevated temperatures. The theoretical mechanism 
is unprecedented, as it imposes a d-2 dimensional edge termination of a d 
dimensional bulk, as opposed to the usual d-1 to d bulk boundary correspondence 
in topological phases. We further propose a generalized Kane-Mele model to 
optimize the spin-orbit induced bulk gap in quantum spin Hall candidate 
materials. We apply the model to the heterostructure Bi/SiC [Reis et al., 
Science 10.1126/science.aai8142 (2017)], where local spectroscopy yields a bulk 
spectral gap of 670 meV. We find Bi/SiC to be a prime candidate material for 
room temperature quantum spin Hall effect.​