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

Abstract

Andreev reflection on the interface of ferromagnet/superconductor ([Formula: see text]) junction provides a tool for exhibiting the spin pairing symmetry in superconductors. The triplet tunneling in [Formula: see text]-wave [Formula: see text] 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 O sites yields a symmetric bound pair state [Formula: see text] with quantum numbers [Formula: see text], [Formula: see text] 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 [Formula: see text]-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 CuO[Formula: see text] layer. High-temperature superconductivity as a long-standing puzzle touches upon a hiding symmetry: the triplet state ([Formula: see text], [Formula: see text]) is indistinguishable from the singlet ([Formula: see text]) either in NMR measurements, or in muon detections, but can be identified by tunneling spectroscopy of [Formula: see text] junction.