Variational Monte Carlo Optimization of Topological Chiral Superconductors

TL;DR

This paper uses variational Monte Carlo to explore topological chiral superconductivity driven by Coulomb interactions, revealing conditions under which such phases are energetically favored in systems like rhombohedral graphene.

Contribution

It demonstrates that topological chiral superconducting phases can be stabilized by Coulomb interactions without Fermi surface pairing, especially near flat band bottoms.

Findings

Chiral superconductivity can be favored over Fermi liquids in certain parameter regimes.

Superconductivity may arise from repulsive Coulomb interactions without traditional pairing.

Preference for chiral phases is strongest when the dispersion parameter c_2 is between zero and negative.

Abstract

We perform the variational Monte Carlo calculation for recently proposed chiral superconducting states driven by strong Coulomb interactions. We compare the resulting energetics of these electronic phases for the electron dispersion relation $E_k = c_2 k^2+c_4 k^4$. Motivated by the recent discovery of chiral superconductivity in rhombohedral graphene systems, we apply our analysis to relevant parameter regimes. We demonstrate that topological chiral superconducting phases (including a spin-unpolarized state) can be energetically favored over the spin-valley polarized Fermi liquid above the density of Wigner crystal phase. Our results show that the preference for chiral superconductivity is strongest when $c_2$ lies between zero and a negative value, corresponding to a system on the verge of forming a hole pocket around $k=0$. This finding suggests that superconductivity can arise from pure repulsive Coulomb interactions in systems with an almost flat band bottom, without relying on the pairing instability of a Fermi surface. This mechanism opens a new pathway to superconductivity beyond the conventional BCS mechanism.