Controlling Vortex Lattice Structure of Binary Bose-Einstein Condensates via Disorder Induced Vortex Pinning

TL;DR

This paper investigates how disorder and pinning potentials influence the vortex lattice structures in rotating binary Bose-Einstein condensates, revealing structural transitions and melting processes through numerical simulations.

Contribution

It demonstrates the effects of impurities and periodic potentials on vortex lattice configurations and melting in binary BECs, including novel two-step melting mechanisms.

Findings

Single impurity can change lattice from triangular to square.

Periodic pinning induces structural transitions to pinned lattices.

Disorder causes two-step vortex lattice melting with defect formation.

Abstract

We study the vortex pinning effect on the vortex lattice structure of the rotating two-component Bose-Einstein condensates (BECs) in the presence of impurities or disorder by numerically solving the time-dependent coupled Gross-Pitaevskii equations. We investigate the transition of the vortex lattice structures by changing conditions such as angular frequency, the strength of the inter-component interaction and pinning potential, and also the lattice constant of the periodic pinning potential. We show that even a single impurity pinning potential can change the unpinned vortex lattice structure from triangular to square or from triangular to a structure which is the overlap of triangular and square. In the presence of periodic pinning potential or optical lattice, we observe the structural transition from the unpinned vortex lattice to the pinned vortex lattice structure of the optical lattice. In the presence of random pinning potential or disorder, the vortex lattice melts following a two-step process by creation of lattice defects, dislocations, and disclinations, with the increase of rotational frequency, similar to that observed for single component Bose-Einstein condensates. However, for the binary BECs, we show that additionally the two-step vortex lattice melting also occurs with increasing strength of the inter-component interaction.