Resonance-state-induced superconductivity at high Indium contents in In-doped SnTe

TL;DR

This study investigates how high indium doping induces resonance states in SnTe, leading to a transition from weakly to strongly coupled superconductivity, with electronic structure analysis revealing non-trivial In states.

Contribution

It demonstrates that In in SnTe forms hybridized states that significantly alter superconductivity, challenging the simple hole doping model.

Findings

Superconductivity evolves from weak to strong coupling with increased In content.

High In content samples are n-type, contrary to expectations.

In forms hybridized states, not just hole dopants, affecting electronic properties.

Abstract

We report a reinvestigation of superconducting Sn$_{1-x}$In$_{x}$Te at both low and high In doping levels. Analysis of the superconductivity reveals a fundamental change as a function of \textit{x}: the system evolves from a weakly coupled to a strongly coupled superconductor with increasing indium content. Hall Effect measurements further show that the carrier density does not vary linearly with Indium content; indeed at high Indium content, the samples are overall \textit{n}-type, which is contrary to expectations of the standard picture of In$^{1+}$ replacing Sn$^{2+}$ in this material. Density functional theory calculations probing the electronic state of In in SnTe show that it does not act as a trivial hole dopant, but instead forms a distinct, partly filled In 5\textit{s} - Te 5\textit{p} hybridized state centered around E$_F$, very different from what is seen for other nominal hole dopants such as Na, Ag, and vacant Sn sites. We conclude that superconducting In-doped SnTe therefore cannot be considered as a simple hole doped semiconductor.