Observation of topological surface states and strong electron/hole imbalance in extreme magnetoresistance compound LaBi

Abstract

The recent discovery of the extreme magnetoresistance (XMR) in the nonmagnetic rare-earth monopnictides $\mathrm{La}X$ ($X$ = P, As, Sb, Bi,), a recently proposed new topological semimetal family, has inspired intensive research effort in the exploration of the correlation between the XMR and their electronic structures. In this work, using angle-resolved photoemission spectroscopy to investigate the three-dimensional band structure of LaBi, we unraveled its topologically nontrivial nature with the observation of multiple topological surface Dirac fermions, as supported by our $\mathit{ab} \mathit{initio}$ calculations. Furthermore, we observed substantial imbalance between the volume of electron and hole pockets, which rules out the electron-hole compensation as the primary cause of the XMR in LaBi.