Spin-twisted Optical Lattices: Tunable Flat Bands and Larkin-Ovchinnikov Superfluids

TL;DR

This paper explores how twisting two atomic spin-dependent optical lattices creates flat bands and induces a Larkin-Ovchinnikov superfluid phase, revealing new quantum phenomena in cold atomic systems.

Contribution

It introduces a new type of moiré system with spin-dependent optical lattices, demonstrating the emergence of flat bands and a novel superfluid phase with finite momentum pairing.

Findings

All twist angles up to 6 degrees support flat bands.

Weak attractive interactions can induce superfluidity.

The superfluid phase is a Larkin-Ovchinnikov state with finite momentum pairing.

Abstract

Moir\'{e} superlattices in twisted bilayer graphene and transition-metal dichalcogenides have emerged as a powerful tool for engineering novel band structures and quantum phases of two-dimensional quantum materials. Here we investigate Moir\'{e} physics emerging from twisting two independent hexagonal optical lattices of atomic (pseudo-)spin states (instead of bilayers), which exhibits remarkably different physics from twisted bilayer graphene. We employ a momentum-space tight-binding calculation that includes all range real-space tunnelings, and show that all twist angles $\theta \lesssim 6^{\circ }$ can become magic that support gapped flat bands. Due to greatly enhanced density of states near the flat bands, the system can be driven to superfluid by weak attractive interaction. Strikingly, the superfluid phase corresponds to a Larkin-Ovchinnikov state with finite momentum pairing, resulting from the interplay between flat bands and inter-spin interactions in the unique single-layer spin-twisted lattice. Our work may pave the way for exploring novel quantum phases and twistronics in cold atomic systems.