Novel low-energy collective excitation at metal surfaces

arXiv:cond-mat/0402273v1A novel collective excitation is predicted to exist at metal surfaces where a two-dimensional surface state band coexists with the underlying three-dimensional continuum. This is a low-energy acoustic plasmon with linear dispersion at small wave vectors. Since new modern spectroscopies are especially sensitive to surface dynamics near the Fermi level, the existence of surface-state–induced acoustic plasmons is expected to play a key role in a large variety of new phenomena and to create situations with potentially new physics.Partial support by the University ofthe Basque Country, the Basque Unibertsitate eta Ikerketa Saila, the Spanish MCyT, and the Max Planck Research Award Funds is gratefully acknowledged.Peer reviewe