Pairing state at an interface of Sr₂RuO₄: parity-mixing, restored time-reversal symmetry and topological superconductivity

Abstract

We investigate pairing states realized at the (001) interface of a\nspin-triplet superconductor Sr$_2$RuO$_4$ on the basis of microscopic\ncalculations. Because of a Rashba-type spin-orbit interaction induced at the\ninterface, strong parity-mixing of Cooper pairs between a spin-singlet state\nand a spin-triplet state occurs in this system. There are also strong\ninter-band pair correlations between the spin-orbit split bands, in spite of\nthe considerably large spin-orbit splitting. This is due to frustration between\nthe spin-orbit interaction and pairing interactions. In this pairing state,\ntime-reversal symmetry is restored, in contrast to the bulk Sr$_2$RuO$_4$ which\nis believed to be a chiral $p+ip$ superconductor with broken time-reversal\nsymmetry. It is demonstrated that, because of these features, the pairing state\nat the interface is a promising candidate for the recently proposed\ntime-reversal invariant topological superconductor.\n