Perovskite ThTaN3: a Large Thermopower Topological Crystalline Insulator

TL;DR

This study predicts that ThTaN3, a cubic perovskite nitride, is a topological crystalline insulator with significant thermopower, combining topological surface states with high thermoelectric efficiency.

Contribution

It reveals that ThTaN3 exhibits topological crystalline insulating behavior with protected surface states and enhanced thermopower due to spin-orbit coupling, a novel combination for this material.

Findings

Band inversion caused by spin-orbit coupling.

Presence of topologically protected surface states.

High thermopower with Seebeck coefficient up to 400 μV/K at 150 K.

Abstract

ThTaN$_3$, a rare cubic perovskite nitride semiconductor, has been studied using {\it ab initio} methods. Spin-orbit coupling (SOC) results in band inversion and a band gap of 150 meV at the zone center. In spite of the trivial $Z_2$ indices, two pairs of spin-polarized surface bands cross the gap near the zone center, indicating that this system is a topological crystalline insulator with the mirror Chern number of $|{\cal C}_m|=2$ protected by the mirror and $C_4$ rotational symmetries. Additionally, SOC doubles the Seebeck coefficient, leading to a maximum of $\sim$400 $\mu$V/K at 150 K for carrier-doping levels of several $10^{17}$/cm$^3$. ThTaN$_3$ combines excellent bulk thermopower with parallel conduction through topological surface states that provide a platform for large engineering devices with ever larger figures of merit.