# Spin-helix states in the $XXZ$ spin chain with strong dissipation

## TL;DR

This paper studies the nonequilibrium steady states in an open XXZ spin chain, revealing a transition from diffusive to ballistic current regimes and the emergence of a pure spin-helix state under strong dissipation and parameter tuning.

## Contribution

It demonstrates how strong boundary dissipation induces a transition to a spin-helix state with a winding number proportional to system size in the XXZ chain.

## Key findings

- Resonance-like behavior of steady current with parameter changes.
- Transition from diffusive to ballistic transport regimes.
- Emergence of a pure spin-helix state characterized by a winding number.

## Abstract

We investigate the nonequilibrium steady state (NESS) in an open quantum XXZ chain with strong $XY$ plane boundary polarization gradient. Using the general theory developed in [1], we show that in the critical $XXZ$ $|\Delta|<1$ easy plane case, the steady current in large systems under strong driving shows resonance-like behaviour, by an infinitesimal change of the spin chain anisotropy or other parameters. Alternatively, by fine tuning the system parameters and varying the boundary dissipation strength, we observe a change of the NESS current from diffusive (of order $1/N$, for small dissipation strength) to ballistic regime (of order 1, for large dissipation strength). This drastic change results from an accompanying structural change of the NESS, which becomes a pure spin-helix state characterized by a winding number which is proportional to the system size. We calculate the critical dissipation strength needed to observe this surprising effect.