RELAXATION PROCESSES IN OPTICALLY-EXCITED HIGH-TC FILMS

We have observed the transient electrical response of current-biased YBa2Cu3O7 films irradiated with 150 ps pulses from a Nd:YAG laser (λ=1.06μm). The magnitude of the response always agrees quantitatively with a simple heating model, as does the speed of the response (<2 ns) in optically thin films (<=0.2μm). However, an equally rapid response in some thicker films is faster than thermal diffusion through the film can explain. At low temperatures (<20 K), this rapid response provides indirect evidence for nonequilibrium hot-electron transport across the film on the 1 ps timescale. At higher temperatures, a similarly fast response can be achieved only by biasing the film close to the critical current, where rapid current redistribution can account for the results. © 1990, Elsevier Science Publishers B.V. (North-Holland). All rights reserved.