Spin singlet topological superconductivity in the attractive Rashba Hubbard model

TL;DR

This study demonstrates that Rashba spin-orbit coupling can enhance and restore superconductivity in a doped attractive Hubbard model under Zeeman magnetic field, potentially leading to topologically non-trivial superconducting states.

Contribution

It reveals how Rashba spin-orbit coupling counteracts Zeeman-induced spin imbalance, promoting topological superconductivity in a doped Hubbard model.

Findings

Rashba coupling enhances s-wave superconductivity.

It counteracts Zeeman pair-breaking effects.

Large Rashba and Zeeman fields induce topologically non-trivial states.

Abstract

Fully gapped, spin singlet superconductors with antisymmetric spin-orbit coupling in a Zeeman magnetic field provide a promising route to realize superconducting states with non-Abelian topological order and therefore fault-tolerant quantum computation. Here we use a quantum Monte Carlo dynamical cluster approximation to study the superconducting properties of a doped two-dimensional attractive Hubbard model with Rashba spin-orbit coupling in a Zeeman magnetic field. We generally find that the Rashba coupling has a beneficial effect towards s-wave superconductivity. In the presence of a finite Zeeman field, when superconductivity is suppressed by Pauli pair-breaking, the Rashba coupling counteracts the spin imbalance created by the Zeeman field by mixing the spins, and thus restores superconductivity at finite temperatures. We show that this favorable effect of the spin-orbit coupling is traced to a spin-flip driven enhancement of the amplitude for the propagation of a pair of electrons in time-reversed states. Moreover, by inspecting the Fermi surface of the interacting model, we show that for sufficiently large Rashba coupling and Zeeman field, the superconducting state is expected to be topologically non-trivial.