• Progress in Superconductivity
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• 제3권1호
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• pp.70-73
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• 2001

We report the spin injection and transport properties of three terminal devices of Co/Au/$YBa_2$$Cu_3$$O_{y}$(F/N/S) tunnel junctions by injection of spin-polarized quaiparticles using a cobalt ferromagnetic injector. The observed current gain depends on the thickness of Au interlayer and is directly related to the nonequilibrium magnetization due to spin relaxation effects. The tunnel characteristic of a F/N/S tunnel junctions exhibited a zero bias conductance peak (ZBCP). The suppression of the ZBCP was observed due to the suppression of Andreev reflection at the interface, which is due to the spin scattering processes at the interface between a ferromagnetic and a d-wave superconductor.r.

• Progress in Superconductivity
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• 제2권1호
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• pp.43-46
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• 2000

We report on the tunneling spectroscopy of tunnel junctions using d-wave superconductor in relation to Andreev reflection. The zero bias conductance peak (ZBCP) which has maximum on [110] direction of ab-plane is observed on metal $Au/YBa_2Cu_3O_y$ tunnel junctions while it is suppressed on the ferromagnetic $Co/Au/YBa_2Cu_3O_y$ tunnel junctions. The effects of Andreev reflection on the differential conductance of each junction are dependent on the tunnel direction. For the $Co/Au/YBa_2Cu_3O_y$ junction, the suppression of Andreev reflection takes place by spin-polarized quasiparticles tunneling from a ferromagnetic material to a d-wave superconductor. By comparing these experimental results with recent theoretical works on Andreev reflection, the existence of Andreev bound state due to the d-wave symmetry of the pair potential is verified in high-$T_c$ superconductor.

• Progress in Superconductivity
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• 제2권2호
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• pp.57-64
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• 2001

We have calculated the tunneling density of states (TDOS) of a metal/d-wave superconductor proximity junction, where the metal stands fur the normal metal, 5-wave superconductor, and d-wave superconductor. The tunneling direction is through the ab-plane of the d-wave superconductor. Because of the sign change in the order parameter experienced in the multiple Andreev reflection, there appears a finite TDOS at zero bias for duty geometry, which results in the anomalous zero bias conductance peak(ZBCP). For $d_{x2-y2}$ geometry, however, no TDOS peak appears at zero bias. We have calculated TDOS for various crystal orientation of HTSC and compared with the experimental conductance.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.141-144
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• 2000

We report on the influence of d-wave pairing symmetry in high-T$_c$ superconductor by tunneling spectroscopy. The zerobias conductance peak(ZBCP) which is produced by tunneling through the ab-plane is observed on both of metal Au/YBa$_2$Cu$_3$O$_y$(N/S) tunnel junctions and ferromagnet Co/Au/ YBa$_2$Cu$_3$O$_y$(F/N/S) tunnel junctions. The effects of Andreev reflection on the differential conductance of each junctions are dependent on the tunnel direction. For the S/N/F junction, it appears the suppression of the ZBCP due to the suppression of Andreev reflection at the interface between a ferromagnetic material and a d-wave superconductor. By comparing these experimental results with recent theoretical works on Andreev reflection, the existence of Andreev bound state is verified in high-T$_c$ superconductor, due to the d-wave symmetry of the pair potential.