Stability and structure of an anisotropically trapped dipolar Bose-Einstein condensate: angular and linear rotons

TL;DR

This paper theoretically investigates the stability, structure, and excitations of anisotropically trapped dipolar Bose-Einstein condensates, revealing density-oscillating states, collapse conditions, and excitation classifications.

Contribution

It provides a detailed mapping of parameter space for dipolar BECs, identifying density-oscillating states and their relation to excitations and stability, which is novel.

Findings

Density-oscillating condensate states occur in specific parameter regions.

Condensate collapse happens at high dipolar interactions, linked to excitation softening.

Excitations are classified by linear and angular properties, with unstable excited solutions.

Abstract

We study theoretically Bose-Einstein condensates with polarized dipolar interactions in anisotropic traps. We map the parameter space by varying the trap frequencies and dipolar interaction strengths and find an irregular-shaped region of parameter space in which density-oscillating condensate states occur, with maximum density away from the trap center. These density-oscillating states may be biconcave (red-blood-cell-shaped), or have two or four peaks. For all trap frequencies, the condensate becomes unstable to collapse for sufficiently large dipole interaction strength. The collapse coincides with the softening of an elementary excitation. When the condensate mode is density-oscillating, the character of the softening excitation is related to the structure of the condensate. We classify these excitations by linear and angular characteristics. We also find excited solutions to the Gross-Pitaevskii equation, which are always unstable.