Topological superconductivity from doping a triplet quantum spin liquid in a flat-band system

We explore superconductivity in strongly interacting electrons on a decorated honeycomb lattice (DHL). An easy-plane ferromagnetic interaction arises from spin-orbit coupling in the Mott insulating phase, which favors a triplet resonance valence bond spin liquid state. Hole doping leads to partial occupation of a flat band and to triplet superconductivity. The order parameter is highly sensitive to the doping level and the interaction parameters, with p + ip, f , and p + f superconductivity found, as the flat band leads to instabilities in multiple channels. Typically, first-order transitions separate different superconducting phases, but a second-order transition separates two time-reversal symmetry breaking p + ip phases with different Chern numbers (nu = 0 and 1). The Majorana edge modes in the topological (nu = 1) superconductor are almost localized due to the strong electronic correlations in a system with a flat band at the Fermi level. This suggests that these modes could be useful for topological quantum computing. The hybrid p + f state does not require two phase transitions as temperature is lowered. This is because the symmetry of the model is lowered in the p-wave phase, allowing arbitrary admixtures of f-wave basis functions as overtones. We show that the multiple sites per unit cell of the DHL, and hence multiple bands near the Fermi energy, lead to very different nodal structures in real and reciprocal space. We emphasize that this should be a generic feature of multisite/multiband superconductors.

Automated summary

In this paper, we investigate superconductivity in strongly interacting electrons on a decorated honeycomb lattice. We find that spin-orbit coupling induces an easy-plane ferromagnetic interaction, and hole doping leads to partial occupation of a flat band, resulting in highly sensitive order parameters for superconductivity. We also explore different superconducting phases under various interaction parameters, and observe both first-order and second-order phase transitions. Additionally, we show that the multiple sites per unit cell in the lattice and multiple bands near the Fermi energy give rise to distinct nodal structures in real and reciprocal space.