Observation of Unpinned 2D Dirac States in ??-Antimonene

The discovery of graphene has stimulated enormous interest in two-dimensional (2D) electron gas with linear band structures. 2D Dirac materials possess many intriguing physical properties such as high carrier mobility and zero-energy Landau level thanks to the relativistic dispersion and chiral spin/pseudospin texture. 2D Dirac states discovered so far are exclusively pinned at high-symmetry points of the Brillouin zone, for example, surface Dirac states at Γ in topological insulators Bi₂Se(Te)₃ and Dirac cones at K and K′ in graphene. In this work, we report the realization of 2D Dirac states at generic k-points in ??-antimonene films with black phosphorus-like structures. These Dirac points in generic k-points are experimentally discovered for the first time, which is protected by the sublattice symmetry from gap opening in the absence of spin-orbit coupling. The unpinned nature enables a multitude of ways to control the locations of the Dirac points in momentum space. In addition, dispersions around the unpinned Dirac points exhibit intrinsically anisotropic behaviors due to the reduced symmetry of generic momentum points. These properties make the ??-antimonene films a promising platform for exploring interesting physics in unpinned 2D Dirac fermions that are distinct from the conventional Dirac states in graphene.