Matter-wave dark solitons and their excitation spectra in spin-orbit coupled Bose-Einstein condensates

TL;DR

This paper explores three types of dark solitons in spin-orbit coupled Bose-Einstein condensates, analyzing their stability and excitation spectra, and discovering a second anomalous mode linked to the system's double well structure.

Contribution

It introduces three types of dark solitons in spin-orbit coupled BECs and uncovers a novel second anomalous mode in their excitation spectra.

Findings

Two soliton types are always stable, third is conditionally stable.

Discovery of a second anomalous mode related to the double well spectrum.

The second mode causes density stripes or out-of-phase oscillations.

Abstract

We present three types of dark solitons in quasi-one-dimensional spin-orbit coupled repulsive Bose-Einstein condensates. Among these families, two are always stable, while the third one is only stable sufficiently close to the linear regime. The solitons' excitation spectra reveal the potential existence of a second anomalous mode. While the first such mode describes the soliton oscillatory motion in a parabolic trap, the second, when present, reflects the double well structure of the underlying single-particle spectrum. This novel mode results in moving density stripes in the vicinity of the soliton core, or in an out-of-phase oscillation of the constituent components, with little effect on the nearly stationary striped total density of the composite soliton.