Tunneling spectra of Co/I/BiSrCaCuO tunnel junctions

Ferromagnet/insulator/superconductor (F/I/S) tunnel junctions consisting of Co and Bi2Sr2CaCu2Ox (BSCCO) have been fabricated in order to study whethe r the superconducting properties are affected by the spin-polarized current . Co is a ferromagnetic metal with a spin polarization of approximately 35% , and BSCCO is a high-T-c superconductor with critical temperature (T-c) of 80-90 K. The junctions with 100 x 100 mu m(2) have been fabricated using p hotolithography on the cleaved BSCCO single crystal. As a reference, Au/I/B SCCO tunnel junctions have also been fabricated in the same manner. In both junctions, gap structures were clearly observed in dI/dV spectra. However, the gap energy of 28 mV obtained at 30 K for the Co/I/BSCCO junction was s maller than that obtained for the Au/I/BSCCO junction. The zero-bias conduc tance peak (ZBCP) was observed clearly for the Au/I/BSCCO junction. It is c onsidered that these differences between the Co/I/BSCCO and the Au/I/BSCCO junctions are due to the spin-polarized current flowing through the junctio ns.