Observation of Symmetry-Protected Dirac States in Nonsymmorphic $\alpha$-Antimonene

TL;DR

This paper reports the discovery of symmetry-protected Dirac states in nonsymmorphic alpha-antimonene, a 2D material synthesized via molecular beam epitaxy, revealing new spin-orbit coupled Dirac physics beyond graphene.

Contribution

It demonstrates the existence of symmetry-protected Dirac states in alpha-antimonene, expanding the family of 2D Dirac materials with spin-orbit interactions.

Findings

Observation of two anisotropic Dirac cones via ARPES

Dirac states are symmetry-protected by nonsymmorphic symmetries

Dirac states in alpha-antimonene are spin-orbit type

Abstract

Two-dimensional (2D) Dirac states with linear band dispersion have attracted enormous interest since the discovery of graphene. However, to date, 2D Dirac semimetals are still very rare due to the fact that 2D Dirac states are generally fragile against perturbations such as spin-orbit couplings. Nonsymmorphic crystal symmetries can enforce the formation of Dirac nodes, providing a new route to establishing symmetry-protected Dirac states in 2D materials. Here we report the symmetry-protected Dirac states in nonsymmorphic alpha-antimonene. The antimonene was synthesized by the method of molecular beam epitaxy. Two Dirac cones with large anisotropy were observed by angle-resolved photoemission spectroscopy. The Dirac state in alpha-antimonene is of spin-orbit type in contrast to the spinless Dirac states in graphene. The result extends the 'graphene' physics into a new family of 2D materials where spin-orbit coupling is present.