Effect of boundaries and impurities on electron-phonon dephasing

Electron scattering from boundaries and impurities destroys the single-particle picture of the electron-phonon interaction. We show that quantum interference between `pure' electron-phonon and electron-boundary/impurity scattering may result in the reduction as well as to the significant enlargement of the electron dephasing rate. This effect crucially depends on the extent, to which electron scatterers, such as boundaries and impurities, are dragged by phonons. Static and vibrating scatterers are described by two dimensionless parameters q_Tl and q_TL, where q is the wavevector of the thermal phonon, l is the total electron mean-free path, L is the mean-free path due to scattering from static scatterers. According to the Pippard ineffectiveness condition, without static scatterers the dephasing rate at low temperatures is slower by the factor l/ql than the rate in a pure bulk material. However, in the presence of static potential the dephasing rate turns out to be l/qL times faster. Thus, at low temperatures electron dephasing and energy relaxation may be controlled by electron boundary/impurity scattering in a wide range.