Fabrication and properties of Nb/MgO/Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ tunnel junctions using crystalline and amorphous MgO films grown by the MBE method

The properties of tunnel-type junctions have been improved by using the Nb/MgO/Au/BSCCO structure. Tunneling spectroscopy was examined in junctions such as Nb/MgO/BSCCO and Nb/MgO/Au/BSCCO. MgO films for tunnel barriers were grown by molecular-beam epitaxy (MBE). In a Nb/MgO/BSCCO junction with no Au layer, the superconducting gap parameters, Delta , of BSCCO single crystals with crystalline and amorphous MgO barriers were estimated to be 25 meV and 38 meV, respectively. Nb/MgO/Au/BSCCO junctions with a 20-nm-thick Au layer indicated a clear gap structure induced by the proximity effect at 30 meV. These junction characteristics were confirmed to be closely related to the existence of interdiffusion between BSCCO and other materials.<
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