Localization and magnetism of the resonant impurity states in Ti doped PbTe

TL;DR

This study investigates how Titanium impurities in PbTe create localized resonant states in the conduction band, affecting electronic and magnetic properties, and highlights the differences from Thallium doping in thermoelectric behavior.

Contribution

It provides first-principles analysis of Ti-induced resonant states in PbTe, revealing their localization and magnetic moment formation, which was not previously characterized.

Findings

Ti creates localized resonant states in PbTe's conduction band.

Ti doping induces magnetic moments on Ti atoms.

The impurity has minimal effect on thermopower compared to Tl doping.

Abstract

The problem of localization of the resonant impurity states is discussed for an illustrative example of Titanium doped Lead Telluride. Electronic structure of PbTe:Ti is studied using first principles methods, densities of states and Bloch spectral functions are analyzed. We show that Ti creates resonant states in the conduction band of PbTe, however, spectral functions of the system strongly suggest localization of these states and show poor hybridization with PbTe electronic structure. The contrast between results presented here and previously reported spectral functions for PbTe:Tl correlate very well with the different effect of those impurities on thermopower (S) of PbTe, which is large increase is S for PbTe:Tl and almost no effect on S for PbTe:Ti. Moreover, magnetic properties of the system are studied and formation of magnetic moments on Ti atoms is found, both for ordered (ferromagnetic) and disordered (paramagnetic-like) phases, showing that PbTe:Ti can be a magnetic semiconductor.