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

TL;DR

This paper explores how odd-parity multipole fluctuations in locally noncentrosymmetric crystals can induce unconventional, topologically nontrivial superconductivity, revealing new potential materials with such properties.

Contribution

It demonstrates that odd-parity magnetic multipole fluctuations can stabilize topological superconducting states in a two-dimensional Hubbard model with strong spin-orbit coupling.

Findings

Odd-parity superconducting states are stabilized by magnetic multipole fluctuations.

Both states are identified as $Z_2$ topological superconductors.

The gap function exhibits a nonsymmorphic symmetry-protected structure.

Abstract

A microscopic calculation and symmetry argument reveal superconductivity in the vicinity of parity-violating magnetic order. An augmented cluster magnetic multipole order in a crystal lacking local space inversion parity may break global inversion symmetry, and then, 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 Sr$_2$IrO$_4$. We find that even-parity superconductivity is more significantly suppressed by a 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 inter-sublattice pairing shows a gapped/nodal structure protected by nonsymmorphic symmetry. Our finding implies a new family of odd-parity topological superconductors. Candidate materials are discussed.