Excited states of two-dimensional solitons supported by the spin-orbit coupling and field-induced dipole-dipole repulsion

TL;DR

This paper demonstrates the stabilization of excited semi-vortex and mixed-mode solitons in spin-orbit-coupled Bose-Einstein condensates using field-induced dipole-dipole interactions, revealing stable higher-order states up to certain vorticities.

Contribution

It introduces a method to stabilize previously unstable excited soliton states in dipolar BECs through a radially growing polarizing field, expanding the understanding of soliton stability.

Findings

Excited semi-vortex solitons are stable up to vorticity S=5.

Mixed-mode solitons with certain angular harmonics are stable if S≤4.

Characteristic size of stable solitons is about 10 micrometers.

Abstract

It was recently found that excited states of semi-vortex and mixed-mode solitons are unstable in spin-orbit-coupled Bose-Einstein condensates (BECs) with contact interactions. We demonstrate a possibility to stabilize such excited states in a setting based on repulsive dipole-dipole interactions induced by a polarizing field, oriented perpendicular to the plane in which the dipolar BEC is trapped. The strength of the field is assumed to grow in the radial direction $\sim $ $r^{4}$. Excited states of semi-vortex solitons have vorticities $S$ and $S+1$ in their two components, each being an eigenstate of the angular momentum. They are fully stable up to $S=5$. Excited state of mixed-mode solitons feature interweaving necklace structures with opposite fractional values of the angular momentum in the two components. They are stable if they are built of dominant angular harmonics $\pm S$, with $S\leq 4$. Characteristics and stability of these two types of previously unknown higher-order solitons are systematically analyzed. Their characteristic size is $\sim 10$ $\mathrm{\mu }$m, with the number of atoms $\lesssim 10^{5}$