Controlling soliton excitations in Heisenberg spin chain through magic angle

TL;DR

This paper investigates how applying an oblique magnetic field at a specific magic angle to an XXZ quantum spin chain can control nonlinear excitations, enabling the transition between free spin waves and solitons.

Contribution

It demonstrates that the magic angle makes the anisotropic Heisenberg chain isotropic, allowing free spin wave propagation and the emergence of bright and dark solitons at other angles.

Findings

At the magic angle, the spin chain becomes isotropic, enabling free spin wave propagation.

For angles larger or smaller than the magic angle, bright and dark solitons are observed.

The magnetic field orientation controls the type of nonlinear excitations in the chain.

Abstract

We study the nonlinear dynamics of collective excitation in a $N$-site $XXZ$ quantum spin chain, which is manipulated by an oblique magnetic field. We show that, when the tilted field is applied along the magic angle $\theta_{0} =\pm\arccos \sqrt{1/3}$, the anisotropic Heisenberg spin chain becomes isotropic and thus an free propagating spin wave is stimulated. And in the regime of the tilted angle larger and smaller then the magic angle, two types of nonlinear excitations appear, which are bright soliton and dark soliton.