Two-dimensional solitons in dipolar Bose-Einstein condensates with spin-orbit coupling

TL;DR

This paper demonstrates the existence of stable, spatially asymmetric vortex solitons in two-dimensional dipolar Bose-Einstein condensates with spin-orbit coupling, revealing new soliton behaviors and stability conditions.

Contribution

It introduces a new class of stable asymmetric vortex solitons supported by dipole-dipole interactions in spin-orbit coupled BECs, expanding understanding of soliton dynamics in such systems.

Findings

Stable asymmetric vortex solitons exist with a maximum offset.

Kicked solitons exhibit negative effective mass and spiral drift.

Semi-vortices can follow magnetic field rotation up to a critical angular velocity.

Abstract

We report families of two-dimensional (2D) composite solitons in spinor dipolar Bose-Einstein condensates, with two localized components linearly mixed by the spin-orbit coupling (SOC), and the intrinsic nonlinearity represented by the dipole-dipole interaction (DDI) between atomic magnetic moments polarized in-plane by an external magnetic field. Recently, stable solitons were predicted in the form of \textit{semi-vortices} (composites built of coupled fundamental and vortical components) in the 2D system combining the SOC and contact attractive interactions. Replacing the latter by the anisotropic long-range DDI, we demonstrate that, for a fixed norm of the soliton, the system supports a \emph{continuous family} of stable spatially asymmetric vortex solitons (AVSs), parameterized by an offset of the pivot of the vortical component relative to its fundamental counterpart. The offset is limited by a certain maximum value, while the energy of the AVS practically does not depend on the offset. At small values of the norm, the vortex solitons are subject to a weak oscillatory instability. In the present system, with the Galilean invariance broken by the SOC, the composite solitons are set in motion by a kick whose strength exceeds a certain depinning value. The kicked solitons feature a negative effective mass, drifting along a spiral trajectory opposite to the direction of the kick. A critical angular velocity, up to which the semi-vortices may follow rotation of the polarizing magnetic field, is found too.