Triplet FFLO Superconductivity in the doped Kitaev-Heisenberg Honeycomb Model

TL;DR

This paper demonstrates the existence of spin-triplet FFLO superconductivity in a doped Kitaev-Heisenberg honeycomb model, revealing novel pairing mechanisms and spatially modulated order parameters driven by strong spin-orbit coupling.

Contribution

It provides the first analytical and numerical evidence of triplet FFLO superconductivity with non-zero momentum pairing in this model, highlighting the role of spin-orbit coupling and multiple degenerate ground states.

Findings

Identification of 6 inversion symmetry centers at non-zero momenta

Observation of spatial modulation of the superconducting order parameter

Existence of three degenerate ground states with distinct spin-triplet pairings

Abstract

We provide analytical and numerical evidence of a spin-triplet FFLO superconductivity in the itinerant Kitaev-Heisenberg model (anti-ferromagnetic Kitaev coupling and ferromagnetic Heisenberg coupling) on the honeycomb lattice around quarter filling. The strong spin-orbit coupling in our model leads to the emergence of 6 inversion symmetry centers for the Fermi surface at non zero momenta in the first Brillouin zone. We show how the Cooper pairs condense into these non-trivial momenta, causing the spatial modulation of the superconducting order parameter. Applying a Ginzburg-Landau expansion analysis, we find that the superconductivity has three separated degenerate ground states with three different spin-triplet pairings. This picture is also supported by exact diagonalizations on finite clusters.