New effects in the absorption of sound by metals in a strong magnetic field in the presence of topological restructuring of electron orbits

Resonant absorption of longitudinal sound in a pure metal in a strong magnetic field H is studied for the case when the tilting of H away from a surface perpendicular to one of the reciprocal lattice vectors by a small angle θ gives rise to a transition from open periodic electron trajectories to strongly elongated closed trajectories. It is shown that in the limit Tθ ≪ τ (Tθ is the return period of the electron along an elongated orbit, τ is the electron mean free flight time) the longitudinal (along H) dynamics of the electron is qualitatively restructured. For ql ≫ 1 (q is the wave vector of the sound, l is the electron mean free path length), this leads to anomalously rapid oscillations in the dependence of the coefficient of absorption of sound on θ and H. In addition, it turns out that for angles in the range qlθ ≪ 1 the absorption of sound loses its collisionless character, in spite of the smallness of the parameter 1/ql. An investigation of the indicated anomalies enables obtaining new information on the electronic energy spectrum of the metal.

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