Collective modes and generation of a new vortex in a trapped Bose gas at finite temperature

TL;DR

This paper investigates the dynamics and collective excitations of a trapped Bose-Einstein condensate at finite temperatures using a variational HFB approach, revealing that thermal atoms partially fill vortex cores and influence their size.

Contribution

It introduces a variational time-dependent HFB formalism to study BEC dynamics at nonzero temperatures, including vortex behavior and thermal effects.

Findings

Vortex cores are partially filled by thermal atoms at finite temperatures.

Thermal fluctuations can increase vortex core size.

Condensate and anomalous density exhibit synchronized breathing oscillations.

Abstract

The dynamics of Bose-Einstein condensate (BEC) is studied at nonzero temperatures using our variational time-dependent-HFB formalism. We have shown that this approach is an efficient tool to study the expansion and collective excitations of the condensate, the thermal cloud and the anomalous correlation function at nonzero temperatures. We have found that the condensate and the anomalous density have the same breathing oscillations. We have investigated, on the other hand, the behavior of a single quantized vortex in a harmonically trapped BEC at nonzero temperatures. Generalized expressions for vortex excitations, vortex core size and Kelvin modes have been derived. An important and somehow surprising result is that the numerical solution of our equations predicts that the vortex core is partially filled by the thermal atoms at nonzero temperatures. We have shown that the effect of thermal fluctuations is important and it may lead to enhancing the size of the vortex core. The behavior of the singly anomalous vortex has also been studied at nonzero temperatures.