Transport properties of bi-epitaxial YBa2Cu3O7-δ grain boundary Josephson junctions:: Experimental evidence of a subdominant superconducting phase

We present the fabrication of a 45 degrees [001] tilted asymmetrical bi-epitaxial YBa2Cu3O7-delta grain boundary Josephson junction using yttria-stabilized zirconia as the seed layer. The magnetic-field dependence of the critical current, I-c(B), of these junctions was measured over a wide range of temperatures. Significant asymmetry of the I-c(B) with respect to the magnetic-field polarity was observed at low temperatures. Our measured results are compared with theoretical predictions of Josephson-junction behavior based on d-wave superconducting electrodes with the onset of a subdominant symmetry component. We estimate an imaginary subdominant symmetry greater than 20% to the d wave.