Electronic structures and stability investigation of the new class of large band gap topological insulators MTl$_4$Te$_3$ (M = Cd, Hg)

TL;DR

This study predicts that the new compounds M Tl4 Te3 (M = Cd, Hg) are stable, topologically nontrivial insulators with large band gaps, suitable for spintronic applications, based on phase diagram, phonon, and electronic structure calculations.

Contribution

It introduces a new class of stable, large band gap topological insulators derived from Tl5Te3 with detailed theoretical validation.

Findings

M Tl4 Te3 compounds are thermodynamically and dynamically stable.

A topological band gap of about 0.13 eV is confirmed in CdTl4Te3.

These materials are promising for spintronic devices.

Abstract

By means of ternary chemical potential phase diagram and phonon spectrum calculations, we propose that $M$Tl$_4$Te$_3$ ($M$ = Cd, Hg), the derivatives of Tl$_5$Te$_3$, are thermodynamically and dynamically stable in the body centered tetragonal crystal structure with $I$4/$mcm$ symmetry. Our electronic structures calculations confirm that a robust $s$-$p$ band inversion occurs near the Fermi level in $M$Tl$_4$Te$_3$, and a topological band gap about 0.13 eV in CdTl$_4$Te$_3$ is induced by the spin-orbit coupling. These results suggest that $M$Tl$_4$Te$_3$ are a new class of large band gap 3D strong topological insulators that are stable and synthesizable in experiments, which could be used to design efficient spin torque equipment and spin device.