Quasi-localized Impurity State in Doped Topological Crystalline Insulator Sn$_{0.9}$In$_{0.1}$Te Probed by $^{125}$Te-NMR

TL;DR

This study uses $^{125}$Te-NMR to reveal quasi-localized impurity states in In-doped SnTe, supporting the idea that In creates impurity states linked to superconductivity in topological crystalline insulators.

Contribution

It provides experimental evidence of impurity states in In-doped SnTe using NMR, highlighting the impact of In doping on electronic states relevant to topological superconductivity.

Findings

Broadening of NMR spectra indicates localized impurity states.

Temperature dependence of relaxation rate varies with magnetic field.

Impurity states are quasi-localized due to In doping.

Abstract

The In-doped topological crystalline insulator Sn$_{1-x}$In$_x$Te is a promising candidate for a topological superconductor, where it is theoretically suggested that In creates an impurity state responsible for superconductivity. We synthesized high purity Sn$_{1-x}$In$_x$Te samples and performed $^{125}$Te-nuclear magnetic resonance (NMR) measurements. The NMR spectra under a magnetic field of $H_0$ = 5 T show a broadening characteristic due to a localized impurity state. The spin-lattice relaxation rate ($1/T_1$) divided by temperature shows a Curie-Weiss like temperature-dependence under $H_0$ = 0.1 T but is temperature-independent under $H_0$ = 5 T. These results indicate the existence of quasi-localized impurity states due to In doping.