# Evolution of electronic states and emergence of superconductivity in the polar semiconductor GeTe by doping valence-skipping In

## TL;DR

This study explores how doping GeTe with indium induces a transition from a semiconductor to a superconductor, revealing a critical doping level where structural, electronic, and valence properties change significantly, highlighting valence fluctuations' role in superconductivity.

## Contribution

It uncovers a doping-induced superconductor-semiconductor transition in GeTe and identifies a critical doping point with notable structural and electronic changes, including valence state shifts of indium.

## Key findings

- Critical doping at x=0.12 causes structural transition from polar-rhombohedral to cubic.
- Resistivity increases sharply near the critical doping level.
- Valence state of indium shifts from In^{3+} to In^{1+} with doping.

## Abstract

GeTe is a chemically simple IV-VI semiconductor which bears a rich plethora of different physical properties induced by doping and external stimuli. These include, among others, ferromagnetism, ferroelectricity, phase-change memory functionality, and comparably large thermoelectric figure of merits. Here we report a superconductor - semiconductor - superconductor transition controlled by finely-tuned In doping. Our results moreover show the existence of a critical doping concentration around $x = 0.12$ in Ge$_{1-x}$In$_{x}$Te, where various properties take either an extremum or change their characters: The structure changes from polarly-rhombohedral to cubic, the resistivity sharply increases by orders of magnitude, the type of charge carriers changes from holes to electrons, and the density of states diminishes at the dawn of an emerging superconducting phase. By core-level photoemission spectroscopy we find indications of a change in the In-valence state from In$^{3+}$ to In$^{1+}$ with increasing $x$, suggesting that this system is a new promising playground to probe valence fluctuations and their possible impact on superconductivity.