Anomalous ^{125}Te Nuclear Spin Relaxation Coincident with Charge Kondo Behavior in Superconducting Pb_{1-x}Tl_{x}Te

Abstract

We report a ^{125}Te-NMR study of single-crystalline Pb_{1-x}Tl_{x}Te for x= 0 (undoped non-superconducting "parent"), 0.35 at% (doped but on the borderline of superconductivity), and 1.0 at% (superconducting, with a critical temperature Tc ~ 1.0 K). The Knight shift in the normal state is enhanced as x increases, corresponding to an increase in the average density of states (DOS). The NMR line-width also increases significantly with increasing x, indicative of a strong spatial variation in the local DOS surrounding each Tl dopant. Remarkably, for the superconducting composition, the ^{125}Te nuclear spin relaxation rate (1/T1T) for Te ions that are close to the Tl dopants is unexpectedly enhanced in the normal state below a characteristic temperature of ~10 K. This temperature coincides with the temperature below which the normal state resistivity experiences an upturn. Such a simultaneous upturn in both the resistivity and (1/T1T) is highly anomalous, and puts Pb_{1-x}Tl_{x}Te in a distinct new class of doped semiconductors. These observations provide microscopic evidence for dynamical charge fluctuations in the absence of paramagnetism, and are consistent with expectations for charge Kondo behavior associated with the Tl dopant ions. In contrast, such anomalies were not detected in the non-superconducting samples (x=0 and 0.35 at%), suggesting a connection between dynamical valence fluctuations and the occurrence of superconductivity in Pb_{1-x}Tl_{x}Te.

arXiv comment4 pages, 3 figures

References in corpus (7)

• Evidence for charge Kondo effect in superconducting Tl-doped PbTe
• Ab initio studies of electronic structure of defects in PbTe
• Superconductivity in charge Kondo systems
• Charge Kondo anomalies in PbTe doped with Tl impurities
• Theory of Charge Kondo Effect on Pair Hopping Mechanism
• Correlation of anomalous scattering and superconductivity in Pb${}_{.99}$Tl${}_{.01}$Te doped with additional indium donors
• Quasi-localized Impurity State in Doped Topological Crystalline Insulator Sn${}_{0.9}$In${}_{0.1}$Te Probed by ${}^{125}$Te-NMR

Cited by in corpus (1)

• Direct spectroscopic evidence for mixed-valence Tl in the low carrier-density superconductor Pb${}_{1-x}$Tl${}_x$Te