Intrinsic Stabilization of High-Order Van Hove Singularity in 2D Rashba Superconductor

Electronic correlations in two-dimensional (2D) systems are strongly governed by Van Hove singularities, which generate divergences in the density of states and enhance correlation effects. Although high-order Van Hove singularities (HOVHSs) are typically associated with engineered band structures that require external tuning, their intrinsic emergence in realistic crystalline materials remains largely unexplored. We report on an interface-driven mechanism that intrinsically stabilizes a type-II HOVHS (emerged at nonregular points of the Brillouin zone) in an atomically thin Pb monolayer epitaxially grown on Si(111). Combining angle-resolved photoemission spectroscopy, scanning tunneling spectroscopy, and state-of-the-art ab initio calculations, we demonstrated that the HOVHS forms in close proximity to the Fermi level within Rashba-split surface states and produces a pronounced power-law divergence of the density of states exceeding that of conventional saddle points. We show that HOVHS arises without any external control and is stabilized by strong spin-orbit coupling and orbital hybridization at the Pb/Si interface. Our results establish an interface-driven mechanism for generating HOVHSs in spin-orbit coupled two-dimensional superconductors.