Transport properties of bi-epitaxial YBa_2Cu_3O_(7-δ) grain boundary Josephson junctions: Experimental evidence of a subdominant superconducting phase

摘要

We present the fabrication of a 45° [001] tilted asymmetrical bi-epitaxial YBa_2Cu_3O_(7-δ) 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.