Evidence of topological insulator state in the semimetal LaBi

TL;DR

This study provides experimental evidence that LaBi exhibits a topological insulator state characterized by Dirac surface states and band inversion, expanding the understanding of topological phases in rare-earth monopnictides.

Contribution

The paper demonstrates the existence of a topological insulator state in LaBi through combined ARPES and first-principles calculations, revealing band inversion and Dirac surface states.

Findings

Presence of band inversion along the Γ-X direction

Existence of a massless Dirac cone at the X point

LaBi is analogous to a Z2 nontrivial topological insulator

Abstract

By employing angle-resolved photoemission spectroscopy combined with first-principles calculations, we performed a systematic investigation on the electronic structure of LaBi, which exhibits extremely large magnetoresistance (XMR), and is theoretically predicted to possess band anticrossing with nontrivial topological properties. Here, the observations of the Fermi-surface topology and band dispersions are similar to previous studies on LaSb [Phys. Rev. Lett. 117, 127204 (2016)], a topologically trivial XMR semimetal, except the existence of a band inversion along the $\Gamma$-$X$ direction, with one massless and one gapped Dirac-like surface state at the $X$ and $\Gamma$ points, respectively. The odd number of massless Dirac cones suggests that LaBi is analogous to the time-reversal $Z_2$ nontrivial topological insulator. These findings open up a new series for exploring novel topological states and investigating their evolution from the perspective of topological phase transition within the family of rare-earth monopnictides.