ELECTRONIC KAPITZA CONDUCTANCE DUE TO INELASTIC ELECTRON-BOUNDARY SCATTERING

Inelastic electron scattering at the interface between a conducting fi lm and an insulating substrate provides a new channel for energy trans fer from the film electrons to the substrate phonons. Its contribution to the Kapitza conductance is found to be (h) over bar u gamma/k(B)ta u(e-ph), where u is the sound velocity, gamma is the Sommerfeld consta nt, and tau(e-ph) is the electron-phonon energy relaxation time in the film. This mechanism is significant for conductors with strong electr on-phonon coupling, or for an interface with a small value of the phon on transparency. The results of the theory agree in order of magnitude with the observed decrease of the Kapitza conductance at the transiti on to the superconducting state. They can explain a universal minimal value of the conductance for pairs of materials with rather different acoustic impedances (metallic films on diamond substrate). This scatte ring mechanism results in the nonequilibrium component of the photores ponse with the ps decay time proportional to the film thickness that h as been recently observed in YBaCuO ultrathin films. [S0163-1829(98)52 336-3].