Decoupling of vortex-antivortex pairs: a possible explanation for nonequilibrium microwave response of YBa2Cu3O7-delta granular films

A two-dimensional Josephson-junction array has been employed as a model sys tem for YBa2Cu3O7-delta (YBCO) granular films. Based on this model, the dis sociation process of the vortex-antivortex pairs is discussed in terms of a pplied current activation, and the unbinding vortices distribution n(T, I) is calculated as a function of temperature and applied current. When I/I-c << 1 is satisfied, the value of the n(T, I) could only be observed within t he temperature region of (2/3)T-KT < T < T-KT, this behavior is analogous t o that of photoresponse dissipation measured from the granular YBCO films. This similitude implies that the unbinding process of the vortex pairs migh t be responsible for the nonequilibrium photoresponse dissipation in granul ar superconducting films. (C) 2001 Elsevier Science B.V. All rights reserve d.