Fermi gap stabilization of an incommensurate two-dimensional superstructure -: art. no. 016103

The compressed, incommensurate similar to(9.5x9.5) moire superstructure of the Ag monolayer on Cu(111) displays a filled surface state band with a Fermi energy gap at the Brillouin zone boundary. By contrast, the surface band is gapless for the less compressed, commensurate (9x9) moire of two Ag layers. A simple estimate of the energy gain rendered by opening this gap gives a value similar to the elastic energy change required to modify the commensurate structure, thereby suggesting that the similar to(9.5x9.5) incommensurate phase is stabilized by such a gap opening. The possible presence of a charge density wave state is discussed.