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Published September 6, 2000 | Published
Book Section - Chapter Open

Pairing symmetry and spin-polarized quasiparticle transport in high-temperature superconducting cuprates

Abstract

The pairing symmetry and the superconducting gap in high- temperature superconducting cuprates are investigated as a function of the hole doping level (x) and temperature (T), using directional scanning tunneling spectroscopy (STS). It is found that the predominant pairing symmetry is (d_(x^2 - y^2)), which is insensitive to the variations in T and x. In contrast, the maximum superconducting gap (Δ_d) in YBa_2Cu_3O_(7-∂) and La_(2-x)Sr_xCuO_(4-∂) scales with the superconducting transition temperature (T_c), and the ratio of (2Δ_d/k_BT)c) increases with decreasing doping level. The dominance of d_(x^2 - y^2) pairing is consistent with strong spatial variations in the local quasiparticle spectra near non-magnetic impurities such as Zn and Mg in a (Zn,Mg)-doped YBa_2Cu_3O_(7-∂) single crystal. To further elucidate the nature of the pairing state, the c-axis spin- polarized quasiparticle transport in the superconducting state of YBa_2Cu_3O_(7-∂) is investigated by studying the critical currents and STS under the injection of electrical currents from the underlying ferromagnetic La_(0.7)Sr_(0.3)MnO_3 layer in various ferromagnet-insulator-superconductor (F-I-S) heterostructures. The temperature dependent spin diffusion length (∂_s) and signatures of nonequilibrium quasiparticle distribution under spin injection in d-wave superconductors are determined for the first time.

Additional Information

© 2000 Society of Photo-Optical Instrumentation Engineers (SPIE). The work performed at Caltech is jointly supported by NSF Grant #DMR-9705171 and NASA/OSS. Part of the research was performed by the Center for Space Microelectronics Technology, Jet Propulsion Laboratory, Caltech, through an agreement with the National Aeronautics and Space Administration. The work performed at SRL/ISTEC in Japan has been partially supported by NEDO.

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