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Phonon softening, chaotic motion, and order-disorder transition in Sn/Ge(111)
1Departamento de Física de la Materia Condensada and Instituto Nicolás Cabrera, Universidad Autónoma, 28049 Madrid, Spain.
Physical Review Letters
|August 9, 2003
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.