  Moir\'e superlattices consisting of two-dimensional (2D) materials have
attracted immense attention because of emergent phenomena such as flat
band-induced Mott insulating states and unconventional superconductivity.
However, the effects of spin-orbit coupling (SOC) on them have not been fully
explored yet. Here we show that single- and double-bilayer (BL) Sb honeycomb
lattices, referred to as antimonene, forms moir\'e superlattices on a Bi(111)
substrate due to a lattice mismatch. Scanning tunnelling microscopy (STM)
measurements reveal the presence of spectral peaks near the Fermi level, which
are spatially modulated with the moir\'e period. Angle-resolved photoemission
spectroscopy (ARPES) combined with density functional theory (DFT) calculations
clarifies the surface band structure with saddle points near the Fermi level,
which allows us to attribute the observed STM spectral peaks to the van Hove
singularity. Spin-resolved ARPES measurements also shows that the observed
surface states are Rashba-type spin-polarized. The present work has significant
implications that Fermi surface instability and symmetry breaking may emerge at
low temperatures, where spin degree of freedom and electron correlation will
also play important roles.
