Unconventional electronic structure of silicene on Ag/H-Si(111)

We fabricated monolayer silicene on a thin silver (Ag) crystal film grown on hydrogen-terminated Si(111), and studied the crystal and the electronic structure by low-energy electron diffraction (LEED) and high-resolution angle-resolved photoemission spectroscopy (ARPES). The fabricated sample exhibits the 3 × 3 LEED pattern characteristic of silicene and the band dispersions with the periodicity of the silicene Brillouin zone, indicative of successful fabrication of silicene on Ag/H-Si(111). However, we observed no signature for the Dirac-cone state at the K point, while the observed band structure exhibits an unexpected van-Hove singularity with a saddle point at the binding energy of 1 eV. Such a singularity has not been reproduced in so-far existing band structure calculations, requesting sophisticated calculations incorporating the complicated strong hybridization between silicene and Ag orbitals.