Superconductivity, pairing symmetry, and disorder in the doped topological insulator Sn$_{1-x}$In$_x$Te for x $\geq$ 0.10

TL;DR

This study investigates the superconducting properties of doped topological insulator Sn$_{1-x}$In$_x$Te, revealing fully gapped behavior and showing that disorder does not enhance the critical temperature, thus informing the understanding of pairing mechanisms.

Contribution

The paper provides experimental evidence that doping and disorder do not induce unconventional pairing or increase $T_c$ in Sn$_{1-x}$In$_x$Te, clarifying the nature of its superconductivity.

Findings

Superconductivity shows fully gapped BCS-like behavior.

Disorder via proton irradiation does not increase $T_c$.

Critical field values are below 1 K.

Abstract

The temperature dependence of the London penetration depth $\Delta\lambda(T)$ in the superconducting doped topological crystalline insulator Sn$_{1-x}$In$_x$Te was measured down to 450 mK for two different doping levels, x $\approx$ 0.45 (optimally doped) and x $\approx$ 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. The introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance $T_c$, indicating that ferroelectric interactions do not compete with superconductivity.