Resistivity and critical current anisotropy of untwinned a-axis YBCO thin films

We have pulsed laser deposited untwinned a-axis oriented YBa2Cu3O7-delta films on (100) LaSrGaO4. From resistive measurements, the chain contribution to the total charge carrier density was estimated to be around 60%, Critical current density (J(c)) depends on the granular nature of the films and the transport across each grain boundary can be modeled as a collection of multiple parallel narrow conductive paths, Measurements in fields up to 6 T indicate that the behavior of J(c) vs, B along the b- and c-directions is similar to that of standard c-axis films, with no significant weak link effects from the grain boundaries, We have also measured the temperature and magnetic field dependence of the critical current density (J(c)) along b- and c- directions of our films, The direction of magnetic field with respect to the crystallographic axes was found to be the dominant factor determining the J(c). For supercurrents flowing along the c- direction, a cross-over from grain boundary pinning to surface rind interface pinning was observed as temperatures approached T-c.