ON THE MAGNETIC-FIELD DEPENDENCE OF CRITICAL-CURRENT DENSITY IN SINGLE-CRYSTALS OF HIGH-T(C) SUPERCONDUCTORS

The critical current density, J(c), is discussed theoretically to expl ain the exponential dependence of J(c) on the flux density, B, given t ypically by J(c) is-proportional-to exp(-B/B0(T)), which has been wide ly observed for single crystals of high-T(c) superconductors in an ext ernal magnetic field parallel to the crystal c-axis. It is pointed out that J(c) shows an exponential-type dependence, J(c) is-proportional- to exp(-f(B, T)), when the tilt modulus, C44, Of fluxoids shows a rema rkable softening for higher values of the wave number. It is also show n that the present expression of J(c) is reduced to the observed B dep endence of f(B, T) congruent-to B/B0(T) by taking account of the effec ts of the layered crystal structure on C44 and the correlation length, l44.