Quantum heat-bath theory of dechanneling

Abstract

Dechanneling of a particle moving swiftly in a low-index direction of a crystal is caused by its interaction with its environment, viz., the electrons and phonons of the crystal. At temperatures which are not too low the relaxation of fluctuations in the environment is rapid enough that the environment may be regarded as a quantum heat bath. In this case the Heisenberg equations for the system yield in a semiclassical limit a Fokker-Planck equation describing the dynamics of the particle prior to dechanneling. The transverse diffusion coefficient may be written compactly as a time-averaged force-force correlation function. This viewpoint of dechanneling suggests how the conventional theory may be modified to describe the low-energy regime, as well as highlighting the dechanneling problem as a prototypical example of a particle-heat bath system with nonlinear dissipation. The problem thus has wider relevance to the study of particle-environment systems in general.