Flat-band-induced superconductivity in synthetic bilayer optical lattices

TL;DR

This paper demonstrates that synthetic bilayer optical lattices can exhibit enhanced superconductivity due to flat-band effects, with tunable inter- and intra-layer interactions influencing the superconducting state.

Contribution

It introduces a novel synthetic bilayer optical lattice model that mimics twisted bilayer graphene, revealing flat-band-induced superconductivity and tunable interlayer pairing.

Findings

Strong pairing gap enhancement at flat bands

Switchable inter- and intra-layer superconductivity

Re-entrant superconductivity with interaction tuning

Abstract

Stacking two layers of graphene with a relative twist angle gives rise to moir\'e patterns, which can strongly modify electronic behavior and may lead to unconventional superconductivity. A synthetic version of twisted bilayers can be engineered with cold atoms in optical lattices. Here, the bilayer structure is mimicked through coupling between atomic sublevels, and the twist is achieved by a spatial modulation of this coupling. In the present paper, we investigate the superconducting behavior of fermionic atoms in such a synthetic twisted bilayer lattice. Attractive interactions between the atoms are treated on the mean-field level, and the superconducting behavior is analyzed via the self-consistently determined pairing gap. A strong enhancement of the pairing gap is found, when a quasi-flat band structure occurs at the Fermi surface, reflecting the prominent role played by the twist on the superconductivity. The tunability of interactions allows for the switching of superconducting correlations from intra (synthetic) layer to inter (synthetic) layer. This includes also the intermediate scenario, in which the competition between inter- and intra-layer coupling completely destroys the superconducting behavior, resulting in re-entrant superconductivity upon tuning of the interactions