Lorenz function of Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ superlattices

TL;DR

This study investigates the anisotropic Lorenz function in Bi2Te3/Sb2Te3 superlattices using first-principles calculations and Boltzmann transport, revealing complex deviations from classical behavior due to quantum well effects.

Contribution

It provides the first detailed analysis of the Lorenz function in these superlattices, highlighting quantum effects influencing thermoelectric properties.

Findings

Lorenz function deviates from classical limits in bulk materials.

Superlattices show oscillatory Lorenz function deviations at high carrier concentrations.

Quantum well effects are responsible for these deviations.

Abstract

Combining first principles density functional theory and semi-classical Boltzmann transport, the anisotropic Lorenz function was studied for thermoelectric Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ superlattices and their bulk constituents. It was found that already for the bulk materials Bi$_{2}$Te$_{3}$ and Sb$_{2}$Te$_{3}$, the Lorenz function is not a pellucid function on charge carrier concentration and temperature. For electron-doped Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ superlattices large oscillatory deviations for the Lorenz function from the metallic limit were found even at high charge carrier concentrations. The latter can be referred to quantum well effects, which occur at distinct superlattice periods.