Effects of an anisotropic superstructure on surface phonons: The Bi-O surface of Bi2Sr2CaCu2O8.

Abstract

The high-{ital T}{sub {ital c}} compound Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} exhibits an anisotropic superstructure. Helium atom scattering (HAS) has revealed unusual characteristics in the surface phonons of the Bi-O surface, namely occurrence of apparently dispersionless surface modes, and unusual similarity of surface modes in different directions on the surface. With a shell model calculation we account for the HAS results and show that these unusual features are direct consequences of the anisotropic superstructure at the surface. {copyright} {ital 1996 The American Physical Society.}