Correlation of anomalous scattering and superconductivity in Pb$_{.99}$Tl$_{.01}$Te doped with additional indium donors

TL;DR

This study investigates how doping with indium affects the charge-Kondo effect and superconductivity in Pb$_{1-x}$Tl$_x$Te, revealing their common origin and the influence of chemical potential on these phenomena.

Contribution

It demonstrates that indium doping suppresses both superconductivity and Kondo-like behavior, supporting the negative U model linking them in Pb$_{1-x}$Tl$_x$Te.

Findings

Both $T_c$ and resistance anomalies decrease with indium doping.

Superconductivity and Kondo-like physics are correlated and originate from the same mechanism.

Chemical potential tuning influences the emergence of superconductivity and Kondo effects.

Abstract

Recent evidence for a charge-Kondo effect in superconducting samples of Pb$_{1-x}$Tl$_x$Te [1] has brought renewed attention to the possibility of negative U superconductivity in this material, associated with valence fluctuations on the Tl impurity sites [2]. Here, we use indium as an electron-donor to counterdope Pb$_{.99}$Tl$_{.01}$Te and study the effect of the changing chemical potential on the Kondo-like physics and on the superconducting critical temperature, $T_c$. We find that, as the chemical potential moves away from the value where superconductivity, Kondo-like physics, and chemical potential pinning are expected, both $T_c$ and the low-temperature resistance anomaly are suppressed. This provides further evidence that both the superconductivity and the Kondo-like behavior are induced by the same source, as anticipated in the negative U model.