Predication of topological states in the allotropes of group-IV elements

TL;DR

This paper predicts new stable allotropes of Ge and Sn that are topological insulators at room temperature, highlighting their potential for quantum materials and applications in electronics.

Contribution

It introduces the first room-temperature stable 3D allotropes of Ge and Sn with topological states, expanding the class of group-IV topological insulators.

Findings

T5-Ge(Sn) are the first room-temperature stable topological insulators among Ge and Sn allotropes.

These allotropes are highly anisotropic Dirac semimetals without SOC.

Their C and Si counterparts are metastable semiconductors.

Abstract

Three-dimensional topological insulators have been studied for approximately fifteen years, but those made from group-IV elements, especially Ge and Sn, seem particularly attractive owing to their nontoxicity, sizable intrinsic spin-orbit coupling (SOC) strength and natural compatibility with the current semiconductor industry. However, group-IV elemental TIs have rarely been reported, except for the low temperature phase of alpha-Sn under strain. Here, based on first-principles calculations, we propose new allotropes of Ge and Sn, named T5-Ge(Sn), as desirable TIs. These new allotropes are also highly anisotropic Dirac semimetals if the SOC is turned off. To the best of our knowledge, T5-Ge(Sn) are the first 3D allotropes of Ge(Sn) that possess topological states in their equilibrium state at room temperature. Additionally, their isostructures of C and Si are metastable indirect and direct semiconductors. Our work not only reveals two promising TIs, but more profoundly, we justify the advantages of group-IV elements as topological quantum materials (TQMs) for fundamental research and potential practical applications, and thus reveal a new direction in the search for desirable TQMs.