Evidence of incoherent carriers associated with resonant impurity levels and their influence on superconductivity in the anomalous superconductor Pb$_{1-x}$Tl$_x$Te

TL;DR

This study combines experimental and theoretical methods to show that resonant impurity states at the Fermi level in Pb$_{1-x}$Tl$_x$Te are linked to its high-temperature superconductivity, highlighting the role of incoherent carriers.

Contribution

It provides evidence that resonant impurity levels at the Fermi energy are responsible for superconductivity in Pb$_{1-x}$Tl$_x$Te, a novel insight into impurity-induced pairing mechanisms.

Findings

Resonant impurity states align with the Fermi energy beyond a critical Tl concentration.

No additional valence band maximum is present at the Fermi level.

Impurity states at the Fermi energy are linked to high-temperature superconductivity.

Abstract

We present a combined experimental and theoretical study of the evolution of the Fermi surface of the anomalous superconductor Pb$_{1-x}$Tl$_x$Te as a function of thallium concentration, drawing on a combination of magnetotransport measurements (Shubnikov de Haas oscillations and Hall coefficient), Angle Resolved Photoemission Spectroscopy (ARPES), and density functional theory (DFT) calculations of the electronic structure. Our results indicate that for Tl concentrations beyond a critical value the Fermi energy coincides with resonant impurity states in Pb$_{1-x}$Tl$_x$Te, and we rule out the presence of an additional valence band maximum at the Fermi energy. Through comparison to non-superconducting Pb$_{1-x}$Na$_x$Te we argue that the presence of these states at the Fermi energy provides the pairing interaction and thus also the anomalously high temperature superconductivity in this material.