Spin-polarized quasiparticle injection into YBCO

Abstract

FET-type devices have been fabricated by using trilayers of Nd/sub 0.7/Sr/sub 0.3/MnO/sub 3/LaNiO/sub 3/ (NSMO) or LaNiO/sub 3/ (LNO) (gate)/LaAlO/sub 3/ (LAO) (barrier)/YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) (channel) in order to investigate effect of quasiparticle injection into YBCO. Here, NSMO and LNO were used as gate electrodes for injection of spin-polarized and spin-unpolarized quasiparticles into the superconducting channel, respectively. When injecting along the c-axis of YBCO, the critical current was suppressed with spin-polarized quasiparticles 30 times more efficiently than with spin-unpolarized quasiparticles. Differential current gain, defined as a differential change of the critical current to injection current change, has been achieved up to /spl sim/16 for c-axis YBCO. If the response time is limited by quasiparticle relaxation time of /spl sim/10 ps, the device may be useful for fast electronics. Preliminary high-speed measurements indicate that part of the critical current suppression may be caused by quasiparticle injection, not all by heating. When injecting along a-axis, no significant dependence on quasiparticle polarization was observed. Other superconductors such as Pr/sub 1.85/Ce/sub 0.15/CuO/sub 4/ (PCCO) and PbIn have been tested in similar devices for comparison.