DYNAMIC STUDY OF CONDUCTION CARRIERS IN YBA2CU3O7-DELTA THIN-FILMS USING A PULSED-LASER-INDUCED TRANSIENT-THERMOELECTRIC-EFFECT METHOD

The pulsed-laser-induced transient thermoelectric effect (TTE) has been measured for c-axis-oriented YBa2Cu3O7-delta thin films over a wide time range (50 ns to 2 ms) and temperature range (10-300 K). The analysis of the decay curves of TTE voltages has revealed that the YBa2Cu3O7-delta system has multiple conduction carriers, the semiconducting holes in the one-dimensional (1D) CuO chains and two types of holes (light-mass and heavy-mass holes) arising from the metallic 2D CuO2-derived band. From the observed relaxation times for thermal diffusions of light and heavy holes, we have estimated their mobilities, which show a "critical slowing-down"-like anomaly near the superconducting transition temperature T(c). The temperature dependence of the hole mobilities can be reasonably explained by considering a critical divergent nature of the diffusion coefficients for conduction holes and a "quasiparticle lifetime" tau* in the superconducting state. In the superconducting state we have observed the stepwise-, shunt-, and plateau-type TTE signals above and/or below a characteristic temperature T(c)* (= 35 K). The presence of T(c)* is indicative of an additional superconducting transition from phase I to II of the quasiparticle system.