Generation of odd-frequency surface superconductivity with spontaneous spin current due to the zero-energy Andreev bound state

Abstract

We propose that the odd-frequency s wave (= s odd wave) superconducting gap function, which is usually unstable in bulk, naturally emerges at the edge of d wave superconductors. This prediction is based on the surface spin fluctuation pairing mechanism owing to the zero-energy surface Andreevbound state (SABS). The interference between bulk and edge gap functions triggers the d + s odd state, and the generated spin current is a useful signal for uncovering the "hidden" odd-frequency gap. In addition, the edge s odd gap can be determined via the proximity effect into the diffusive normal metal. Furthermore, this study provides a decisive validation of the "Hermite odd-frequency gap function," which has been an open fundamental challenge to this field.