Direct spectroscopic evidence for mixed-valence Tl in the low carrier-density superconductor Pb$_{1-x}$Tl$_x$Te
| Autor: | Walmsley, P., Liu, C., Palczewski, A. D., Giraldo-Gallo, P., Olson, C. G., Fisher, I. R., Kaminski, A. |
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| Rok vydání: | 2018 |
| Předmět: | |
| Zdroj: | Phys. Rev. B 98, 184506 (2018) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevB.98.184506 |
| Popis: | 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 2$e$ 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 photo emission spectroscopy measurements. It is shown via our quantitative analysis that the suppression of the carrier density at compositions exhibiting superconductivity and Kondo-like behaviour is fully accounted for by mixed valency, thus arguing strongly 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 Tl$^{3+}$ a possible third intermediate local charge-density is tentatively suggested by full fits to the data, the implications of which are discussed in the context of the charge-Kondo effect. Comment: 5 pages, 3 figures |
| Databáze: | arXiv |
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