Presence of Exotic Electronic Surface States in LaBi and LaSb

TL;DR

This study uses ARPES to identify Dirac-like surface states in LaBi and LaSb, suggesting their topological nature and potential role in the materials' high magnetoresistance, making them promising for topological research.

Contribution

The paper provides direct experimental evidence of topological surface states in LaBi and LaSb using ARPES, highlighting their potential role in magnetoresistance phenomena.

Findings

Multiple Dirac-like surface states observed near the Fermi level.

Circular dichroism detected in surface and near-surface bulk bands.

Surface states may contribute to the materials' high magnetoresistance.

Abstract

Extremely high magnetoresistance (XMR) in the lanthanum monopnictides La$X$ ($X$ = Sb, Bi) has recently attracted interest in these compounds as candidate topological materials. However, their perfect electron-hole compensation provides an alternative explanation, so the possible role of topological surface states requires verification through direct observation. Our angle-resolved photoemission spectroscopy (ARPES) data reveal multiple Dirac-like surface states near the Fermi level in both materials. Intriguingly, we have observed circular dichroism in both surface and near-surface bulk bands. Thus the spin-orbit coupling-induced orbital and spin angular momentum textures may provide a mechanism to forbid backscattering in zero field, suggesting that surface and near-surface bulk bands may contribute strongly to XMR in La$X$. The extremely simple rock salt structure of these materials and the ease with which high-quality crystals can be prepared suggests that they may be an ideal platform for further investigation of topological matter.