Lattice Properties of PbX (X = S, Se, Te): Experimental Studies and ab initio Calculations Including Spin-Orbit Effects

TL;DR

This study combines experimental measurements and ab initio calculations to analyze the lattice properties of lead chalcogenides, focusing on isotopic effects and the influence of spin-orbit coupling on phonon behavior and specific heat.

Contribution

It provides a systematic investigation of isotopic and spin-orbit effects on lattice properties of PbS, PbSe, and PbTe using both experiments and advanced calculations including spin-orbit interactions.

Findings

Including spin-orbit coupling improves agreement between theory and experiment.

Isotopic variations significantly affect the specific heat of lead chalcogenides.

Spin-orbit effects alter phonon dispersion and lattice parameters.

Abstract

During the past five years the low temperature heat capacity of simple semiconductors and insulators has received renewed attention. Of particular interest has been its dependence on isotopic masses and the effect of spin- orbit coupling in ab initio calculations. Here we concentrate on the lead chalcogenides PbS, PbSe and PbTe. These materials, with rock salt structure, have different natural isotopes for both cations and anions, a fact that allows a systematic experimental and theoretical study of isotopic effects e.g. on the specific heat. Also, the large spin-orbit splitting of the 6p electrons of Pb and the 5p of Te allows, using a computer code which includes spin-orbit interaction, an investigation of the effect of this interaction on the phonon dispersion relations and the temperature dependence of the specific heat and on the lattice parameter. It is shown that agreement between measurements and calculations significantly improves when spin-orbit interaction is included.