Orientational anomalies of sound absorption by metals under magnetic breakdown

We consider the oscillations of longitudinal sound absorption by metals under a stochastic magnetic breakdown (MB). The case studied is a typical one when the magnetic field H forms a small angle θ with the plane perpendicular to the reciprocal lattice vector b and the MB configuration constitutes weakly aperiodic chains of electron orbits linked by small orbits (so-called quantum gates that are characterized by a 2 π-periodic dependence of the effective probability ω of magnetic breakdown on the quasiclassical phase φ = cS/eHℏ, where S is the area of a small orbit). We demonstrate that for θ≳x~1°, where eℏH/cb2 is the quasiclassicality parameter, the MB oscillations of sound absorption are very sensitive to the structure of nonuniform distribution of ψ phases over the MB configuration. The amplitude of MB oscillations in this range of angles is low except for a small neighborhood of selected values θ=θk≡(4πHk/S‖)1/2(k=1,2,…;S‖=|∂2S/∂pz2|), in which it is comparable with the smooth part of the absorption.

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