Spatial order in a two-dimensional spin-orbit-coupled spin-1/2 condensate: superlattice, multi-ring and stripe formation

TL;DR

This paper investigates the formation of various spatially-ordered states, including superlattice, multi-ring, and stripe patterns, in a quasi-2D spin-orbit-coupled Bose-Einstein condensate using mean-field theory.

Contribution

It reveals the existence and characteristics of multiple stable spatially-ordered states, including a novel superlattice state with supersolid properties, in spin-orbit-coupled BECs.

Findings

Multi-ring states with vorticity for weak SO coupling

Stripe states with no total density modulation for intermediate SO coupling

Superlattice states with square-lattice patterns, resembling supersolids

Abstract

We demonstrate the formation of stable spatially-ordered states in a {\it uniform} and also {\it trapped} quasi-two-dimensional (quasi-2D) Rashba or Dresselhaus spin-orbit (SO) coupled pseudo spin-1/2 Bose-Einstein condensate using the mean-field Gross-Pitaevskii equation. For weak SO coupling, one can have a circularly-symmetric $(0,+1)$- or $(0,-1)$-type multi-ring state with intrinsic vorticity, for Rashba or Dresselhaus SO coupling, respectively, where the numbers in the parentheses denote the net angular momentum projection in the two components, in addition to a circularly-asymmetric degenerate state with zero net angular momentum projection. For intermediate SO couplings, in addition to the above two types, one can also have states with stripe pattern in component densities with no periodic modulation in total density. The stripe state continues to exist for large SO coupling. In addition, a new spatially-periodic state appears in the uniform system: a superlattice state, possessing some properties of a supersolid, with a square-lattice pattern in component densities and also in total density. In a trapped system the superlattice state is slightly different with multi-ring pattern in component density and a square-lattice pattern in total density. For an equal mixture of Rashba and Dresselhaus SO couplings, in both uniform and trapped systems, only stripe states are found for all strengths of SO couplings. In a uniform system all these states are quasi-2D solitonic states.