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.
Categories: cond-mat.mtrl-sci cond-mat.supr-con