Mixed-pairing superconductivity in 5d Mott insulators with antisymmetric exchange: Application to Sr2IrO4

Abstract

We study the symmetry of the potential superconducting order parameter in $5d$ Mott insulators with an eye toward hole-doped ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$. Using a mean-field method, a mixed singlet-triplet superconductivity, $d+p$, is observed due to the antisymmetric exchange originating from a quasi-spin-orbit coupling. Our calculation on ribbon geometry shows the possible existence of the topologically protected edge states, because of the nodal structure of the superconducting gap. These edge modes are spin polarized and emerge as zero-energy flat bands, supporting a symmetry-protected Majorana state, verified by evaluation of the winding number and ${\mathbb{Z}}_{2}$ topological invariant. At the end, a possible experimental approach for observation of these edge states and determination of the superconducting gap symmetry is discussed based on the quasiparticle interference technique.