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 (Formula available in paper), which is insensitive to the variations in T and x. In contrast, the maximum superconducting gap ((Delta) d) in YBa2Cu3O7-(delta ) and La2-xSrxCuO4-(delta ) scales with the superconducting transition temperature (Tc), and the ratio of (2 (Delta) d/kBTc) increases with decreasing doping level. The dominance of dx2-y2 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 YBa2Cu3O7-(delta ) single crystal. To further elucidate the nature of the pairing state, the c-axis spin- polarized quasiparticle transport in the superconducting state of YBa2Cu3O7-(delta ) is investigated by studying the critical currents and STS under the injection of electrical currents from the underlying ferromagnetic La0.7Sr0.3MnO3 layer in various ferromagnet-insulator-superconductor (F-I-S) heterostructures. The temperature dependent spin diffusion length ((delta) s) and signatures of nonequilibrium quasiparticle distribution under spin injection in d-wave superconductors are determined for the first time.