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

TL;DR

This paper investigates how doping a triplet quantum spin liquid in a flat band system on a decorated honeycomb lattice induces various topological superconducting phases, revealing complex phase transitions and potential for topological quantum computing.

Contribution

It demonstrates the emergence of multiple topological superconducting phases, including $p+ip$, $f$, and $p+f$, driven by doping in a flat band system with strong correlations, and analyzes their properties and transitions.

Findings

Multiple topological superconducting phases identified.

Majorana edge modes are highly localized in the topological phase.

Different nodal structures arise due to multi-band effects.

Abstract

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 multi-site/multi-band superconductors.