Direct spectroscopic evidence for mixed-valence Tl in the low carrier-density superconductor Pb1−xTlxTe
P. Walmsley, C. Liu, A. D. Palczewski, P. Giraldo-Gallo, C. G. Olson, I. R. Fisher, A. Kaminski
DOI 10.1103/PhysRevB.98.184506 · Physical Review B
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Abstract
Upon doping with Tl the narrow band-gap semiconductor PbTe exhibits anomalously high-temperature superconductivity despite a very low carrier-density as well as signatures of the Kondo effect despite an absence of magnetic moments. These phenomena have been explained by invoking 2e fluctuations of the valence of the Tl dopants, but a direct measurement of the mixed valency implied by such a mechanism has not been reported to date. In this work we present the unambiguous observation of multiple valences of Tl in Tl-doped PbTe via photoemission spectroscopy measurements. It is shown via a quantitative analysis that the suppression of the carrier density in compositions exhibiting superconductivity and Kondo-like behavior can be accounted for by mixed valency, thus arguing against a self-compensation scenario proposed elsewhere for this material and strengthening the case for valence fluctuation models. In addition to the identification of Tl+ and Tl3+ a possible third intermediate local charge-density is suggested by full fits to the data, the origins of which are also discussed but remain unclear.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Pb1-xTlxTe Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 1.5 | Pressure not reported | onset |
| Pb1-xTlxTe Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 1.5 | Pressure not reported | onset |
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