Superconductivity in Sn$_{1-x}$In$_{x}$Te thin films grown by molecular beam epitaxy

TL;DR

This paper reports the successful growth of high-quality Sn$_{1-x}$In$_{x}$Te thin films via molecular beam epitaxy, revealing evidence of both bulk and surface superconductivity, which may be topologically nontrivial.

Contribution

It introduces a new method for growing high-quality superconducting Sn$_{1-x}$In$_{x}$Te films and provides experimental evidence of coexistence of bulk and surface superconductivity.

Findings

Observation of two superconducting gaps indicating bulk and surface superconductivity

Surface superconductivity likely has topological p-wave character

Films grown using Bi$_2$Te$_3$ buffer layer are of high quality

Abstract

The superconductor Sn$_{1-x}$In$_{x}$Te is derived from the topological crystalline insulator SnTe and is a candidate topological superconductor. So far, high-quality thin films of this material have not been available, even though such samples would be useful for addressing the nature of its superconductivity. Here we report the successful molecular beam epitaxy growth of superconducting Sn$_{1-x}$In$_{x}$Te films by using Bi$_2$Te$_3$ as a buffer layer. The data obtained from tunnel junctions made on such films show the appearance of two superconducting gaps, which points to the coexistence of bulk and surface superconductivity. Given the spin-momentum locking of the surface states, the surface superconductivity is expected to be topological with an effective $p$-wave character. Since the topological surface states of SnTe consist of four Dirac cones, this platform offers an interesting playground for studying topological surface superconductivity with additional degrees of freedom.