Temperature dependence of critical current in high-temperature superconductors with the low-angle boundaries of crystalline blocks

The model of critical current restriction (limitation) in quite perfect HTSC crystals and epitaxial films having the block structure is considered for the case of small misorientation angles θ of the crystalline blocks, when the distance d between the edge dislocations in the grain boundaries exceeds the coherence length ξ(T). It is shown, that under these conditions the transparency of the low-angle grain boundaries for superconducting current carriers is independent of θ and T in the vicinity of tire critical temperature Tc. As a result, the depairing current j0(T) varies directly as (1 - T/Tc)3/2 is the only factor responsible for the temperature dependence of the critical current density jc(T). In the vicinity of Tc, when ξ(T) > d, the dependence jc(T) [similar to] (1 - T/Tc)3/2 changes into jc(T) [similar to] (1 - T/Tc)2. Such behavior of jc(T) agrees well with experimental measurements of critical currents in thin epitaxial films of YBa2Cu3O7-δ.