Fabrication and characterization of Nb/MgO/Bi2Sr2CaCu2Ox tunnel junctions using a single crystal

This paper reports on Nb/MgO/Bi2Sr2CaCu2Ox (BSCCO) tunnel junctions using both amorphous and crystalline MgO barriers fabricated using a BSCCO single crystal in order to compare their superconducting states of interface. Both MgO thin films, 4-8 nm thick and with full coverage, were deposited onto BSCCO single crystals using the MBE method. The junctions using amorphous and crystalline MgO films were found to have gap opening structures at a bias voltage of about 38 mV and 25 mV at 5.2 K, respectively. The gap opening of the junction using an amorphous MgO barrier occurred below 86 K, corresponding very closely with the Tc for the BSCCO single crystal. Its characteristics showed a BCS-like temperature dependence