Quasiparticle energy relaxation in the cuprate superconductors

Abstract

At high flux-flow velocities in the mixed state of a type-II superconductor the nonequilibrium distribution of the quasiparticles is shifted to higher energies. As shown theoretically by Larkin and Ovchinnikov, a distinct signature of this nonequilibrium effect is an electronic instability, resulting in a sharp kink in the current-voltage characteristic at a critical vortex velocity (Formula presented) From measurements of (Formula presented) the quasiparticle-energy relaxation rate (Formula presented) can be found. We have measured this instability point for epitaxial (Formula presented) axis oriented films of (Formula presented) and (Formula presented) In both cuprates the observed temperature dependence of (Formula presented) could be well fitted with the function (Formula presented) suggesting that the electron-electron recombination process, perhaps in combination with the emission of another excitation, is crucial. As an example of a low-(Formula presented) superconductor we have also studied amorphous (Formula presented) films and found that (Formula presented) can be fitted by a function similar to that we have used for the cuprates, again indicating the importance of the electron-electron interaction. © 1997 The American Physical Society.