Substrate-induced symmetry breaking in silicene.

We demonstrate that silicene, a 2D honeycomb lattice consisting of Si atoms, loses its Dirac fermion characteristics due to substrate-induced symmetry breaking when synthesized on the Ag(111) surface. No Landau level sequences appear in the tunneling spectra under a magnetic field, and density functional theory calculations show that the band structure is drastically modified by the hybridization between the Si and Ag atoms. This is the first direct example demonstrating the lack of Dirac fermions in a single layer honeycomb lattice due to significant symmetry breaking.