The tilt effect in the electron-phonon interaction with finite relaxation times of the electrons

A theoretical study of the tilt effect is presented namely the dependence of the longitudinal sound absorption and velocity on the angle between the magnetic field and the propagation vector. As has been shown, the tilt effect is a strong nonadiabatic effect which does not contain the small parameter s/v. The influence of the finite electron relaxation time on the singularities of the absorption and of the sound velocity is investigated. The tilt effect proves to be well-distinguishable if the condition ωτ > 1 is satisfied.