Abstract
The non-local nonlinearity introduced by the dipole–dipole interaction plays a crucial role in the physics of dipolar Bose–Einstein condensates. In particular, it may distort significantly the stability of straight vortex lines due to the rotonization of the Kelvin-wave spectrum. In the present paper, we analyze this instability, showing that it leads to a second-order-like phase transition from a straight vortex line into novel helical or snake-like configurations, depending on the dipole orientation.
Highlights
The physics of ultracold atomic and molecular gases is crucially determined by the interparticle interactions
A new generation of recent experiments is opening a fascinating new research area, namely that of dipolar gases, for which the dipole-dipole interaction (DDI) plays a significant or even dominant role. These experiments include on one side those dealing with the DDI effects due to magnetic dipoles in degenerate atomic gases, as it is the case of recent exciting experiments in Chromium Bose-Einstein condensates (BECs) [1] and Rubidium spinor BECs [2]
The last term at the rhs of both equations is directly linked to the long-range character of the DDI and, as we show below, leads to novel phenomena in the physics of Kelvin modes (l = −1) in dipolar
Summary
The physics of ultracold atomic and molecular gases is crucially determined by the interparticle interactions. A new generation of recent experiments is opening a fascinating new research area, namely that of dipolar gases, for which the dipole-dipole interaction (DDI) plays a significant or even dominant role. We showed that due to the longrange character of the DDI, different parts of the vortex line interact with each other, and the 3D character of the vortices plays a much more important role in dipolar gases than in usual short-range interacting ones. We discussed that, interestingly, the DDI may severely modify the Kelvin-wave dispersion, which may even acquire a roton-like minimum This minimum may touch zero energy for sufficiently large DDI and strong lattices, leading to the instability of the straight vortex line even for those situations in which the BEC as a whole is stable.
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