Talk given by

Dr. Erwann Bocquillon
Laboratoire Pierre Aigrain
Ecole Normale Superieure
Paris, France

Abstract:

Two dimensional topological insulators coupled to superconducting and 
ferromagnetic electrodes are a candidate system for the realization of Majorana 
fermions. Majorana physics has recently attracted considerable attention in both 
theoretical and experimental studies due to the prospects for new physics 
stemming from non-Abelian exchange statistics and the associated applications to 
topological quantum computation. However, experimental studies unveiling the 
interplay between superconductivity and topological electronic transport remain 
scarce.

Here we report the observations of signatures of topological superconductivity 
induced in a HgTe quantum well, a system that exhibits the quantum spin Hall 
effect. Namely, we observe the fractional Josephson effect, in two different 
manners. When an rf excitation is applied, a doubling of the Shapiro steps is 
observed [1]. Besides, a clear emission line can be detected at half the 
Josephson frequency under dc voltage bias conditions [2]. Both features appear 
more clearly when the sample is gated towards the quantum spin Hall regime, in a 
regime where the current flows mostly along the edges of the device. These 
signatures thus point towards induced topological superconductivity in the 
quantum spin Hall edge states.

[1] E. Bocquillon et al., Nature Nanotechnology 12, 137 (2017)

[2] R.S. Deaconet al., Physical Review X 7, 021011 (2017)