Magnetic Field Dependence of the Critical Current of Bi₂Sr₂CaCu₂O_8+δ-Based Intrinsic Josephson Junctions

Well-characterized surface intrinsic Josephson junctions (IJJs) on Bi₂Sr₂CaCu₂O_8+δ single crystals are fabricated by in situ cryogenic cleavage of the crystals and immediate evaporation of Au films on the crystal surface. Magnetic field dependences of the critical currents of the surface and inner IJJs are carefully measured. We find that the critical current behaviour of the surface IJJs in magnetic field is quite different from that of the inner junctions. The behaviour of the inner IJJs can be understood to be of large stacked junctions described by the coupled sine-Gordon equations, while the surface IJJs behave like a separate single large junction. These results indicate that the coupling between the surface IJJ and the inner IJJs is weaker than the coupling among the inner junctions.