The Effect of Magnetic Flux Focusing on the Current–Voltage Characteristics of YBa2Cu3O7-δ Grain Boundary Josephson Junctions

In order to obtain experimental evidence for the influence of flux focusing effect on the characteristics of planar grain boundary (GB) Josephson junctions, we measured the current-voltage characteristics and magnetic-field-dependent current-voltage steps of integrated YBa₂Cu₃O_7-δ bicrystal GB Junctions with different junction widths. Under the self-magnetic field, the critical current of the GB junction is proportional to the square root of the junction width, which is different from the traditional linear relationship between the critical current and the junction width. When a vertical magnetic field is applied, the flux flow current-voltage step could be observed, and the step voltage increases monotonously with an increase in the junction width. When a magnetic field rotating in the bc plane is applied, the voltage value of the flux flow step decreases slowly as the magnetic field inclined angle increases when the field inclined angle is relatively large. Based on these results, we demonstrate the presence of the magnetic flux focusing effect on YBa₂Cu₃O_7-δ GB Josephson junctions. The size of flux focusing in the GB is closely associated with the width of the junctions and the orientation of the magnetic field.