Type-II Dirac nodal chain semimetal CrB4

TL;DR

This paper predicts that CrB4 is an ideal type-II Dirac nodal chain semimetal with protected surface states and multiple nodal rings, providing a promising platform for experimental exploration of exotic topological properties.

Contribution

The study identifies CrB4 as the first experimentally feasible material hosting a type-II Dirac nodal chain semimetal with unique topological features.

Findings

CrB4 hosts two nodal rings protected by symmetries.

CrB4 exhibits topologically protected drumhead surface states.

CrB4 shows potential for large magnetoresistance due to Dirac fermions.

Abstract

Dirac nodal line semimetals with topologically protected drumhead surface states have attracted intense theoretical and experimental attention over a decade. However, the study of type-II Dirac nodal line semimetals is rare, especially the type-II nodal chain semimetals have not been confirmed by experiment due to the lack of ideal material platform. In this study, based on symmetry analysis and the first-principles electronic structure calculations, we predict that CrB4 is an ideal type-II Dirac nodal chain semimetal protected by the mirror symmetry. Moreover, there are two nodal rings protected by both space-inversion and time-reversal symmetries in CrB4. More importantly,in CrB4 the topologically protected drumhead surface states span the entire Brillouin zone at the Fermi level. On the other hand, the electron-hole compensation and the high mobility of Dirac fermions can result in large magnetoresistance effects in CrB4 according to the two-band model.Considering the fact that CrB4 has been synthesized experimentally and the spin-orbit coupling is very weak, CrB4 provides an ideal material platform for studying the exotic properties of type-II Dirac nodal chain semimetals in experiment.