Thermal fluctuations of vortex clusters in quasi-two-dimensional Bose-Einstein condensate

TL;DR

This paper investigates how thermal fluctuations affect vortex arrangements in small clusters within a rotating Bose-Einstein condensate, revealing temperature-dependent order-disorder transitions and effects of trap anisotropy.

Contribution

It introduces a detailed analysis of vortex cluster melting and decoupling phenomena, emphasizing the role of shell commensurability and trap anisotropy in these processes.

Findings

Order-disorder transition occurs via shell decoupling.

Melting temperature depends on vortex shell commensurability.

Thermal fluctuations can cause vortex decoupling from trap deformation.

Abstract

We study the thermal fluctuations of vortex positions in small vortex clusters in a harmonically trapped rotating Bose-Einstein condensate. It is shown that the order-disorder transition of two-shells clusters occurs via the decoupling of shells with respect to each other. The corresponding "melting" temperature depends stronly on the commensurability between numbers of vortices in shells. We show that "melting" can be achieved at experimentally attainable parameters and very low temperatures. Also studied is the effect of thermal fluctuations on vortices in an anisotropic trap with small quadrupole deformation. We show that thermal fluctuations lead to the decoupling of a vortex cluster from the pinning potential produced by this deformation. The decoupling temperatures are estimated and strong commensurability effects are revealed.