Sub-micron sized intrinsic Josephson junctions in YBa2Cu3O7-X whiskers

To investigate the detailed junction properties of intrinsic Josephson junctions (IJJs) in YBa2Cu3O7-X (YBCO) without shunted grain boundaries and with good uniformity, we fabricated sub-micron sized IJJs in a YBCO whisker by using a focused-ion-beam etching. The sub-micron sized junctions showed clear multiple branches with a hysteresis structure in the current-voltage curve, like IJJs in Bi2Sr2CaCu2O8+X. The temperature dependence of the critical current demonstrates that the junction behaviour drastically changes from that of an SNS type to an SIS type when the critical temperature is decreased. The critical current density of the junctions, in the order of 10-100 kA cm-2, corresponds to Josephson plasma frequencies from a few hundred GHz to 1-2 THz