Bose-Einstein Condensates in Spin-Orbit Coupled Optical Lattices: Flat Bands and Superfluidity

TL;DR

This paper explores the emergence of flat bands and superfluid stability in spin-orbit coupled Bose-Einstein condensates within one-dimensional optical lattices, revealing a new platform for topological flat band physics.

Contribution

It demonstrates the formation of isolated flat bands in SO coupled BECs in optical lattices and analyzes their stability, extending understanding of topological flat band systems.

Findings

Flat bands can form in 1D SO coupled optical lattices.

The flat band remains stable under mean field interactions.

Superfluidity persists across the entire flat band.

Abstract

Recently spin-orbit (SO) coupled superfluids in free space or harmonic traps have been extensively studied, motivated by the recent experimental realization of SO coupling for Bose-Einstein condensates (BEC). However, the rich physics of SO coupled BEC in optical lattices has been largely unexplored. In this paper, we show that in suitable parameter region the lowest Bloch state forms an isolated flat band in a one dimensional (1D) SO coupled optical lattice, which thus provides an experimentally feasible platform for exploring the recently celebrated topological flat band physics in lattice systems. We show that the flat band is preserved even with the mean field interaction in BEC. We investigate the superfluidity of the BEC in SO coupled lattices through dynamical and Landau stability analysis, and show that the BEC is stable on the whole flat band.