Dipolar condensates with tilted dipoles in a pancake-shaped confinement

TL;DR

This paper investigates how the orientation of dipoles affects the stability, excitation spectrum, and nonlinear structures of dipolar Bose-Einstein condensates in a pancake-shaped trap, revealing tunable roton features and novel dynamical behaviors.

Contribution

It introduces the impact of dipole tilting on stability and excitations in quasi-2D condensates, and explores self-trapped states and anisotropic solitons in dipolar BECs.

Findings

Tilted dipoles induce tunable roton minima in excitation spectrum.

Long-wavelength excitations are unstable at the magic angle without contact interactions.

Transient stripe patterns form after roton instability and can be stabilized with parameter tuning.

Abstract

The effect of dipolar orientation with respect to the condensate plane on the mean-field dynamics of dipolar Bose-Einstein condensates in a pancake-shaped confinement is discussed. The stability of a quasi-two-dimensional condensate, with respect to the tilting angle, is found to be different from a two-dimensional layer of dipoles, indicating the relevance of the transverse extension while characterizing two-dimensional dipolar systems. An anisotropic excitation spectrum exhibiting a highly tunable, rotonlike minimum can arise entirely from the dipole-dipole interactions, by tilting the dipoles. At the magic angle and in the absence of contact interactions, the long-wavelength excitations are not phononlike and always unstable. The post-roton-instability dynamics, in contrast to phonon instability, in a uniform condensate, is featured by a transient, defect-free, stripe pattern, which eventually undergoes local collapses, and driving the condensate back into the stable regime can make them sustained for longer. Hopping between stripes has been observed before it melts into a uniform state in the presence of dissipation. Finally, we discuss a class of solutions, in which a quasi-two-dimensional condensate is self-trapped in one direction, as well as a regime of interaction parameters, including attractive short-range interactions, at which a two-dimensional anisotropic soliton can be stabilized, and we show that a chromium condensate with a relatively small number of atoms is well suited for this.