Abstract
We present a combined experimental and theoretical study of the evolution of the Fermi surface of the anomalous superconductor as a function of thallium concentration, drawing on a combination of magnetotransport measurements (Shubnikov–de Haas oscillations and the Hall coefficient), angle resolved photoemission spectroscopy, and density functional theory 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 , and we rule out the presence of an additional valence band maximum at the Fermi energy. A comparison to nonsuperconducting implies that the presence of these impurity states at the Fermi energy provides the enhanced pairing interaction and thus also the anomalously high temperature superconductivity in this material.
- Received 15 November 2017
DOI:https://doi.org/10.1103/PhysRevLett.121.207001
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