RESISTIVITY AND CRITICAL-CURRENT ANISOTROPY OF UNTWINNED A-AXIS YBCO THIN-FILMS

We have pulsed laser deposited untwinned a-axis oriented YBa2Cu3O7-del ta films on (100) LaSrGaO4. From resistive measurements, the chain con tribution to the total charge carrier density was estimated to be arou nd 60%, Critical current density (J(c)) depends on the granular nature of the films and the transport across each grain boundary can be mode led as a collection of multiple parallel narrow conductive paths, Meas urements 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 fi lms, 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 crystallog raphic axes was found to be the dominant factor determining the J(c). For supercurrents flowing along the c- direction, a cross-over from gr ain boundary pinning to surface rind interface pinning was observed as temperatures approached T-c.