Acoustic wave spread in superconducting–normal–superconducting sandwich

Abstract

The acoustic wave spread, perpendicular to the boundaries between superconducting and normal metals in superconducting–normal–superconducting (SNS) sandwich has been considered. The alternate current flow sound induced by the Green function method has been found and the coefficient of the acoustic wave transmission through the junction γ=( S 1− S 2)/ S 1, (where S 1 and S 2 are average energy flows formed on the first and second boundaries) as a function of the phase difference between superconductors has been investigated. It is shown that while the SNS sandwich is almost transparent for acoustic waves ( γ⪡1) at the phase differences φ= π(2 n+1+ τ 0/ τ), n=0,1,2,… (where τ 0/ τ is the ratio of the broadening of the quasiparticle energy levels in impurity normal metal as a result of scattering of the carriers by impurities 1/ τ to the spacing between energy levels 1/ τ 0), γ=2, ( S 2=− S 1), which corresponds to the full reflection of the acoustic wave from SNS sandwich. This result is valid for the limit of a pure normal metal but in the main impurity case there are two amplification and reflection regions for acoustic waves. The result obtained shows promise for the SNS sandwich as an ideal mirror for acoustic wave reflection.