Odd-parity multipole fluctuation and unconventional superconductivity in locally noncentrosymmetric crystal

Abstract

A microscopic calculation and symmetry argument reveal superconductivity in the vicinity of parity-violating magnetic order. In a crystal structure lacking local space inversion symmetry, an augmented cluster magnetic multipole order may break global inversion symmetry, and therefore it is classified into an odd-parity multipole order. We investigate unconventional superconductivity induced by an odd-parity magnetic multipole fluctuation in a two-dimensional two-sublattice Hubbard model motivated by ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$. We find that even-parity superconductivity is more significantly suppressed by spin-orbit coupling than that in a globally noncentrosymmetric system. Consequently, two odd-parity superconducting states are stabilized by magnetic multipole fluctuations in a large spin-orbit coupling region. Both of them are identified as ${Z}_{2}$ topological superconducting states. The obtained gap function of intersublattice pairing shows a gapped or nodal structure protected by nonsymmorphic symmetry. Our finding implies a family of odd-parity topological superconductors. Candidate materials are discussed.