Fabrication of YBa/sub 2/Cu/sub 3/O/sub 7//AlO/sub x//Nb quasiparticle tunnel junctions

The authors have fabricated superconductor-insulator-normal metal (SIN) tunnel junctions with c-axis-oriented YBCO thin films as the superconducting electrodes and studied the tunneling characteristics of the junctions by measuring the zero-bias junction resistance as a function of temperature and dI/dV as a function of the bias voltage. Measured junction resistance showed characteristic tunneling properties with a strong semiconducting background, which is ascribed to the imperfect tunnel barrier. dI/dV curves indicated gap structures at 27 mV and 4.5 mV, respectively, with a parabolic background. >