CaTe: a new topological node-line and Dirac semimetal

TL;DR

This paper predicts that CaTe is a topological node-line semimetal without spin-orbit coupling, and becomes a Dirac semimetal with robust Dirac points protected by symmetry, which can transition to a topological insulator if symmetry is broken.

Contribution

It introduces CaTe as a new topological semimetal with unique surface states and symmetry-protected Dirac points, expanding the class of topological materials.

Findings

CaTe is a topological node-line semimetal without SOC.

Inclusion of SOC leads to Dirac points protected by C4 symmetry.

Breaking symmetry transforms CaTe into a topological insulator.

Abstract

Topological semimetals recently stimulate intense research activities. Combining first-principles calculations and effective model analysis, we predict that CaTe is topological node-line semimetal when spin-orbit coupling (SOC) is ignored. We also obtain the nearly flat surface state which has the drumhead characteristic. When SOC is included, three node lines evolve into a pair of Dirac points along the $M-R$ line. These Dirac points are robust and protected by $C_{4}$ rotation symmetry. Once this crystal symmetry is broken, the Dirac points will be eliminated, and the system becomes a strong topological insulator.