Proximity effect at the superconducting-topological insulator interface from first principles*

A topological insulator (TI) film in contact with an s-wave superconducting
(SC) substrate has been extensively studied due to the possibility of hosting
zero-energy Majorana states using the proximity effect. So far, theoretical
studies have been carried out based on effective models. Experimental
studies of TI-SC heterostructures showed inconsistent results on
a dependence of the induced SC gap size on TI film thickness as well as
on the proximity effect for the TI bulk states. The Fermi level is likely to
cross both TI bulk and Dirac surface states. Here we investigate the
proximity-induced SC gap at the interface TI and top TI surface states and
bulk TI states, considering a Bi2Se3 film on a PdTe SC substrate within
first-principles calculations. In this study, we solve the fully relativistic
Kohn-Sham-Dirac-Bogoliubov-de Gennes equations for the heterostructure
by introducing Cooper pairs within the screened Korringa-Kohn-Rostoker (SKKR)
method. We present our results on the induced SC gap arising from TI bulk and
surface states and its dependence on TI film thickness at several chemical
potential values.