| The narrow gap semiconductor Lead Telluride (PbTe) is one of the most interesting materials for thermoelectric applications. When doped with a small concentration x of Thallium (Tl) impurities, superconductivity appears at surprisingly low carrier densities. The carrier density saturates for x > 0.3 at % Tl, when Kondo like anomalies of non-magnetic nature manifest themselves in static and transport properties. By combining band structure aspects of PbTe with a description of Tl impurities as negative-U centres we provide a semi-quantitative description of these anomalies. |
|