Multiple Dirac cones at the surface of the topological metal LaBi

TLDR

LaBi, a rare‑earth monopnictide, shows extremely large, anisotropic magnetoresistance, yet experimental evidence for its predicted topological surface states remains lacking despite band‑inversion–driven topological phase proposals. Using ARPES combined with ab initio calculations, we identified three Dirac‑cone surface states on LaBi, two at Brillouin‑zone corners and one at the center. The odd number of Dirac cones, reflecting an odd number of bulk band inversions, confirms LaBi as a topological, compensated semimetal equivalent to a time‑reversal invariant topological insulator, offering insight into its surface states and related magnetotransport.

Abstract

The rare-earth monopnictide LaBi exhibits exotic magneto-transport properties including an extremely large and anisotropic magnetoresistance. Experimental evidence for topological surface states is still missing although band inversions have been postulated to induce a topological phase in LaBi. By employing angle-resolved photoemission spectroscopy (ARPES) in conjunction with $ab~initio$ calculations, we have revealed the existence of surface states of LaBi through the observation of three Dirac cones: two coexist at the corners and one appears at the center of the Brillouin zone. The odd number of surface Dirac cones is a direct consequence of the odd number of band inversions in the bulk band structure, thereby proving that LaBi is a topological, compensated semi-metal, which is equivalent to a time-reversal invariant topological insulator. Our findings provide insight into the topological surface states of LaBi's semi-metallicity and related magneto-transport properties.