Orbital Limit and Gaussian Fluctuation Effects in Flat Band Superconductors with PseudoMagnetic Fields

TL;DR

This paper investigates how pseudomagnetic fields in flat band superconductors, created by strain in molecular graphene on a superconductor, significantly enhance the orbital limit and influence fluctuation effects, revealing new physical insights.

Contribution

It demonstrates that pseudomagnetic fields greatly increase the orbital limit and analyzes Gaussian fluctuation effects in flat band superconductors with vanishing bandwidth.

Findings

Pseudomagnetic fields lock orbital angular momenta, suppressing orbital magnetization.

Orbital limit is substantially enhanced by pseudomagnetic fields.

Gaussian fluctuations lower critical temperatures in the dilute limit.

Abstract

In this work, we study a molecular graphene model on the top of a superconductor in the presence of pseudomagnetic fields induced by coplanar strain fields. With the pseudomagnetic fields and the attractive interaction induced from the substrate, a flat band superconductor can be achieved according to mean field analysis on the effective Hamiltonian. Based on a semiclassical approximation, we first show that the orbital limit is hugely enhanced by the pseudomagnetic fields. The physical reason is that the orbital angular momenta locking at $K$ and $K'$ valleys due to the pseudomagnetic fields suppress the orbital magnetization from external magnetic fields. Considering the vanishing band width in this system, we then study the effects of Gaussian fluctuations in both Hartree and pairing channels. We show that in the dilute limit, the phase transition is dominated by collective modes with critical temperatures much lower than the mean field results. At half filling, our method gives no corrections to the mean field critical temperatures.