Crossover between integer and fractional vortex lattices in coherently coupled two-component Bose-Einstein condensates

TL;DR

This paper explores how vortex lattices in two-component Bose-Einstein condensates evolve from fractional to integer vortices as the internal Rabi coupling increases, revealing complex bound states and lattice transformations.

Contribution

It uncovers the transition mechanisms of vortex lattices under Rabi coupling, including formation of multi-vortex bound states and partner exchanges leading to Abrikosov lattices.

Findings

Fractional vortices form multi-dimer bound states at low Rabi coupling.

Bound states break into dimers at intermediate Rabi coupling.

Vortices reorganize into integer vortex lattices at high Rabi coupling.

Abstract

We study effects of the internal coherent (Rabi) coupling in vortex lattices in two-component BECs under rotation. We find how the vortex lattices without the Rabi coupling known before are connected to the Abrikosov lattice of integer vortices with increasing the Rabi coupling. We find that 1) for small Rabi couplings, fractional vortices in triangular or square lattice for small or large inter-component coupling constitute hexamers or tetramers, namely multi-dimer bound states made of six or four vortices, respectively, 2) these bound states are broken into a set of dimers at intermediate Rabi couplings, and 3) vortices change their partners in various ways depending on the inter-component coupling to organize themselves for constituting the Abrikosov lattice of integer vortices at strong Rabi couplings.