Charge Kondo anomalies in PbTe doped with Tl impurities

We investigate the properties of PbTe doped with a small concentration $x$ of Tl impurities acting as acceptors and described by Anderson impurities with negative onsite correlation energy. We use the numerical renormalization group method to show that the resulting charge Kondo effect naturally accounts for the unusual low temperature and doping dependence of normal state properties, including the self-compensation effect in the carrier density and the non-magnetic Kondo anomaly in the resistivity. These are found to be in good qualitative agreement with experiment. Our results for the Tl s-electron spectral function provide a new interpretation of point contact data.Comment: 5 pages, 3 figures; published versio

ELECTRONIC STRUCTURE OF FeSi

The full set of high-energy spectroscopy measurements including X-ray photoelectron valence band spectra and soft X-ray emission valence band spectra of both components of FeSi (Fe K_beta_5, Fe L_alpha, Si K_beta_1,3 and Si L_2,3) are performed and compared with the results of ab-initio band structure calculations using the linearized muffin-tin orbital method and linearized augmented plane wave method.Comment: 11 pages + 3 PostScript figures, RevTex3.0, to be published in J.Phys.:Cond.Matte

Charge Kondo Effect in Thermoelectric Properties of Lead Telluride doped with Thallium Impurities

We investigate the thermoelectric properties of PbTe doped with a small concentration $x$ of Tl impurities acting as acceptors and described by Anderson impurities with negative on-site (effective) interaction. The resulting charge Kondo effect naturally accounts for a number of the low temperature anomalies in this system, including the unusual doping dependence of the carrier concentration, the Fermi level pinning and the self-compensation effect. The Kondo anomalies in the low temperature resistivity at temperatures $T\leq 10\, {\rm K}$ and the $x$-dependence of the residual resistivity are also in good agreement with experiment. Our model also captures the qualitative aspects of the thermopower at higher temperatures $T>300\, {\rm K}$ for high dopings ($x>0.6$) where transport is expected to be largely dominated by carriers in the heavy hole band of PbTe.Comment: chapter contributed to 'New Materials for Thermoelectric Applications: Theory and Experiment' Springer Series: NATO Science for Peace and Security Series - B: Physics and Biophysics, pp. 67-80, ed. Veljko Zlati\'c, and Alex Hewson (Editor). ISBN: 978-94-007-4983-2 (2013