The spin pairing symmetry of d-wave superconductor indicated by tunneling spectroscopy

Abstract

Andreev reflection on the interface of ferromagnet/superconductor (F/S) junction pro 7) vides a tool for exhibiting the spin pairing symmetry in superconductors. The triplet tunneling in F/d-wave S junction observed in recent experiments revived a fundamental interest: the pairing mechanism of the superconducting cuprate. Here we show that in a doped cuprate, the effective spin coupling between the doped holes on the 0 sites yields a symmetric bound pair state In vertical bar up arrow down arrow vertical bar + vertical bar up arrow down arrow vertical bar, with quantum numbers S = 1, S-z = 0 in the CuO2 layer, which explains the origin of the resonating valence bound state in cuprates, as well as the tunneling experiments. In addition, the d-wave is consistent with the triplet pairing since the observable orbital wavefunction is a projection from the total odd-frequency wavefunction onto the quasi-2D superconducting CuO2 layer. High-temperature superconductivity as a long-standing puzzle touches upon a hiding symmetry: the triplet state (S = 1, S-z = 0) is indistinguishable from the singlet (S = 0) either in NMR measurements, or in muon detections, but can be identified by tunneling spectroscopy of F/S junction.