Fermi surface and electron dispersions of PbTe doped with resonant Tl impurity from KKR-CPA calculations

We present results of detailed study on the electron dispersions and Fermi surface of lead telluride doped with $2\%$ of thallium, which is resonant impurity in PbTe. Using the KKR--CPA method, Bloch spectral functions (BSFs), which replace the dispersion relations in alloys, are calculated, and BSFs intensity maps over the Brillouin zone (alloy Fermi surface cross-sections) are presented. It is shown, that close to the valence band edge, Tl does not create an isolated impurity band, but due to its resonant character, strongly disturbs the host electronic bands, leading to disappearance of sharp and well defined electronic energy bands. Consequences of this effect on the transport properties are discussed and new qualitative explanation of the improvement in thermoelectric properties of PbTe:Tl is suggested.