Phonon Scattering in Disordered Systems

摘要: It is well known that glasses, which are completely disordered homogeneous solids, display acoustic and thermal properties at low temperature deviate markedly from those of crystals [1]. This especially (but not exclusively) true below 1 K, these differences explained by the presence low-lying excitations, described as “Two-Level Systems” (TLS) with a constant energy density states. The TLS supposed to be caused tunnelling motion group atoms in double-well asymmetric potential [2]. experiments have shown long wavelength phonons exist large range frequency, strongly scattered via resonant relaxation processes has also been established responsible for heat transport [3], scattering leading T2 dependence conductivity K(T) K. tunneling model gives satisfactory phenomenological description anomalies but microscopic nature still unknown. On other hand, there no definitively accepted describe above plateau around 10 In view two unresolved problems, great deal work done during last years search “glassy” either “model” systems where units or partly systems.