Anderson localization and the pseudogap in the energy spectrum of holes in PbTe: Tl under resonant scattering

This paper reports on a comprehensive study of the effect of additional doping with the Na acceptor impurity on the low-temperature resistivity of PbTe samples doped with Tl (2 at %), an impurity producing a band of resonant states within the valence-band spectrum. By additional doping with Na, we have shifted the Fermi level within the band of the resonant states of Tl in PbTe and varied the hole filling (k _h ) of the thallium impurity states. The larger part of the PbTe: (Tl,Na) samples transfers to the superconducting state with a critical temperature T _c = 0.4–2.3 K. The T _c (k _h ) relation obtained argues for the fact that, in the region of resonant states in PbTe: Tl, Anderson localization of holes and a pseudogap in the density of delocalized states are observed.