Transport properties of variable-angle YBa_2Cu_3O _(7-δ) step-edge junctions in the a-b plane

摘要

The superconductor-barrier-superconductor interface in a range of YBa _2Cu_3O_(7 - δ) (YBCO) step-edge Josephson junctions was engineered to lie at angles θ other than normal to the a-b axes of the YBCO crystal. This systematic study enabled the effect of the d-wave anisotropy to be probed over the range θ = 0° ([100] direction) to θ = 45° ([110] direction) in a way not possible with junction technologies such as bicrystals. Anomalous temperature dependence of the critical current and a peak in the differential conductance at low voltage were reminiscent of features attributed elsewhere to zero-energy states in a range of [001]-tilt bicrystal and ramp-edge junctions. Moreover, I_cR _N products decreased with increasing θ, and conductance minima or gap-related structures were measured for large θ. The data reported here for variable-angle junctions are compared with results from studies of other grain boundary junctions (such as bicrystal and biepitaxial junctions) and provide support for theories developed by Shirai et al (2003 J. Phys. Soc. Japan 72 2299-307) in particular.