Bose-Einstein condensate in Bloch bands with off-diagonal periodic potential

TL;DR

This paper demonstrates the realization of Bose-Einstein condensates in Bloch bands with off-diagonal periodic potential, revealing tunable spin textures and phase transitions, and proposing a three-band model for understanding these phenomena.

Contribution

It introduces a new system with off-diagonal periodic potential that combines spin-orbit coupling and Zeeman field, enabling control over condensate phases and spin textures.

Findings

Transition from plane wave to stripe phase in BECs.

Observation of multiple momentum peaks reflecting periodic structure.

Proposal of a three-band effective model for analysis.

Abstract

We report the Bose-Einstein condensate (BEC) in the Bloch bands with off-diagonal periodic potential (ODPP), which simultaneously plays the role of spin-orbit coupling (SOC) and Zeeman field. This model can be realized using two independent Raman couplings in the same three level system, in which the time-reversal symmetry ensures the energy degeneracy between the two states with opposite momenta. We find that these two Raman couplings can be used to tune the spin polarization in momentum space, thus greatly modifies the effective scatterings over the Bloch bands. We observe a transition from the Bloch plane wave phase with condensate at one wave vector to the Bloch stripe phase with condensates at the two Bloch states with opposite wave vectors. These two phases will exhibit totally different spin textures and density modulations in real space, which are totally different from that in free space. In momentum space multiple peaks differ by some reciprocal lattice vectors can be observed, reflecting the periodic structure of the ODPP. A three-band effective model is proposed to understand these observations. This system can provide a new platform in investigating of various physics, such as collective excitations, polaron and topological superlfuids, over the Bloch bands.