TEMPERATURE PULSE INDUCED THERMAL-INSTABILITY IN Y1BA2CU3O7-DELTA SUPERCONDUCTORS

As a common effect of a large and variable temperature gradient and a temperature pulse, a thermal instability of a new type has been observ ed in high-T-c, superconductors. The primary effect is the temporal ch ange of local energy density, that causes a dynamic state of simultane ously coexisting normal and superconducting domains, establishing a sp atial and temporal variation of superconducting and normal states. The fluctuation of the ratio of the superconducting and normal volume fra ctions can be detected by the oscillation of DC and AC voltages measur ed on the samples. Supposing that every jump of the AC voltage represe nts the transformation of a single coherent domain, it leads to the av erage value of the linear dimension of domains as 2.1 mm, characterist ic time of the transformation as 7.5 s and velocity of the propagation of this effect as 0.3 mm/s in the case of Y1Ba2Cu3O7-delta specimens. The macroscopic consequence of the thermal disturbance introduced int o the sample is the appearance of a giant flux creep, Its existence is confirmed by comparison of our measurements to others, by analytical and numerical calculations of the forces acting on the vortices and by evaluation of the effect of the huge fluctuation created in the sampl es by our experiments. (C) 1997 Elsevier Science B.V.