The theory of longitudinal sound attenuation in superconductors with paramagnetic impurities

A study is made of the nonequilibrium processes associated with the propagation of a longitudinal sound wave in a superconductor with a low concentration of paramagnetic impurities (Δτ⪢ 1, Δτs⪢ 1). The longitudinal electric fields produced in this case affect the “mixing,” specific to superconductors, of the electron and hole branches of the energy spectrum. The magnetic impurities, oscillating with the lattice, on the one hand, produce a kinetic effect, namely, drag of the normal electrons and slippage of the superconducting condensate, and on the other hand, ensure paramagnetic branch mixing. Moreover, in the superconducting state the momentum transfer from electrons to impurities in collisions proves to be nonzero. The longitudinal sound attenuation calculated by taking these effects into account differs from the results of the BCS method.

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