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

Abstract

The pairing symmetiy and the superconducting gap in high-temperature superconducting cuprates are investigated as a function of the hole doping level (x) and temperature (7), using directional scanning tunneling spectroscopy (STS). It is found that the predominant pairing symmetry is which is insensitive to the irariations in T and x. In contrast, the maximum superconducting gap (zld) in YBa2Cu3O74 and La2SrCuO44 scales with the superconducting transition temperature (Ta), &1d the ratio of (2A,/kBT) increases with decreasing doping level. The dominance of d22 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 YBa2Cu3O74 single crystal. To further elucidate the nature of the pairing state, the c-axis spin-polarized quasiparticle transport in the superconducting state of YBa2Cu3O74 is investigated by studying the critical currents and STS under the injection of electrical currents from the underlying ferromagnetic La7Sr03MnO3 layer in various ferromagnetinsulator-superconductor (F-I-S) heterostructures. The temperature dependent spin diffusion length (5) and signatures of nonequilibrium quasiparticle distribution under spin injection in d-wave superconductors are determined for the first time.

Andreev bound states in high-Tcsuperconducting junctions

“…This was interpreted as a sign of spontaneous TRSB at the surface and evidence for a local presence of a subdominant s-wave component; see section 2.2. However, a spontaneous (zero-field) splitting of the ZBCP is not always seen (Aprili et al 1999, Yeh et al 2000. Moreover, there are other possible explanations for the splitting than that involving a subdominant s-wave component of the order parameter; see the discussion of split MGS in section 2.6.…”