# AC Oscillation of a Spin Soliton Driven by a Constant Force

## TL;DR

This paper reports a novel AC oscillation phenomenon of a spin soliton in a Bose-Einstein condensate driven by a constant force, driven by nonlinear interactions and mass transitions, modeled by a quasiparticle approach.

## Contribution

It introduces a new example of AC oscillation driven by a DC force in a quantum system, highlighting the role of nonlinear interactions and mass transitions without periodic potentials.

## Key findings

- Spin soliton exhibits long-term AC oscillation under constant force.
- Nonlinear interactions induce periodic mass transitions in the soliton.
- A quasiparticle model explains the oscillation behavior effectively.

## Abstract

The phenomena of AC oscillation generated by a DC drive, such as the famous Josephson AC effect in superconductors and Bloch oscillation in solid physics, are of great interest in physics. Here we report another example of such counter-intuitive phenomenon that a spin soliton in a two-component Bose-Einstein condensate is driven by a constant force: The initially static spin soliton first moves in a direction opposite to the force and then changes direction, showing an extraordinary AC oscillation in a long term. In sharp contrast to the Josephson AC effect and Bloch oscillation, we find that the nonlinear interactions play important roles and the spin soliton can exhibit a periodic transition between negative and positive inertial mass even in the absence of periodic potentials. We then develop an explicit quasiparticle model that can account for this extraordinary oscillation satisfactorily. Important implications and possible applications of our finding are discussed.