title: Phonon softening, chaotic motion, and order-disorder transition in Sn/Ge(111).
abstract: The phonon dynamics of the Sn/Ge(111) interface is studied using high-resolution helium atom scattering and first-principles calculations. At room temperature we observe a phonon softening at the Kmacr; point in the (sqrt[3]xsqrt[3])R30 degrees phase, associated with the stabilization of a (3x3) phase at low temperature. That phonon band is split into three branches in the (3x3) phase. We analyze the character of these phonons and find out that the low- and room-temperature modes are connected via a chaotic motion of the Sn atoms. The system is shown to present an order-disorder transition.
authors.affiliation: Departamento de Física de la Materia Condensada and Instituto Nicolás Cabrera, Universidad Autónoma, 28049 Madrid, Spain.
authors.forename: D
authors.initials: D
authors.lastname: Farías
authors.forename: W
authors.initials: W
authors.lastname: Kamiński
authors.forename: J
authors.initials: J
authors.lastname: Lobo
authors.forename: J
authors.initials: J
authors.lastname: Ortega
authors.forename: E
authors.initials: E
authors.lastname: Hulpke
authors.forename: R
authors.initials: R
authors.lastname: Pérez
authors.forename: F
authors.initials: F
authors.lastname: Flores
authors.forename: E G
authors.initials: EG
authors.lastname: Michel