Transient response of YBaCuO granular films submitted to optical or electrical pulses

This paper reports on superconducting YBaCuO films, current-driven in the resistive regime, that were submitted to nanosecond laser pulses. Our films responded by a fast rise of the resistivity, followed by a much slower quasi-exponential decay, whose characteristic time is very little dependent upon bias current, magnetic field, or laser fluence. On the contrary, the decay time shows a striking non-monotonic variation with temperature, indicative of electron-lattice decoupling at low T. The resistivity change following the application of a fast-rising step function of the current was also monitored in the same conditions. Unlike metallic superconductors (e.g. Sn, Pb or Nb), YBCO films exhibit very fast transition times, of the order of 0.2 nsec or less, which could not be resolved in time