Electronic evidence of asymmetry in the Si(111)sqrt3xsqrt3-Ag structure

Our photoemission spectroscopy results clearly demonstrate that symmetry breakdown in atomic arrangement brings about a lift of degeneracy in electronic states, leading to settle a long-standing controversy on a surface superstructure. We provide unambiguous evidences that Si(111)sqrt3xsqrt3-Ag has the inequivalent triangle structure (IET), excluding a long-lived honeycomb-chained triangle model. We also give critical experimental proof that the surface exhibits a disorder-order phase transition by cooling; the thermally fluctuating IET structure is frozen.