Voltage induced conversion of helical to uniform nuclear spin polarization in a quantum wire

TL;DR

This paper explores how applying a bias voltage to a quantum wire can convert localized helical nuclear spin polarization into a uniform polarization, revealing a voltage- and temperature-dependent behavior with potential experimental implications.

Contribution

It demonstrates that bias voltage induces a uniform nuclear spin polarization in a quantum wire, transforming the helical order and enabling control over nuclear spin states.

Findings

Bias voltage induces uniform nuclear polarization.

Nuclear spin helix rotates with polarization-dependent frequency.

Uniform polarization increases with voltage and temperature.

Abstract

We study the effect of bias voltage on the nuclear spin polarization of a ballistic wire, which contains electrons and nuclei interacting via hyperfine interaction. In equilibrium, the localized nuclear spins are helically polarized due to the electron-mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Focusing here on non-equilibrium, we find that an applied bias voltage induces a uniform polarization, from both helically polarized and unpolarized spins available for spin flips. Once a macroscopic uniform polarization in the nuclei is established, the nuclear spin helix rotates with frequency proportional to the uniform polarization. The uniform nuclear spin polarization monotonically increases as a function of both voltage and temperature, reflecting a thermal activation behavior. Our predictions offer specific ways to test experimentally the presence of a nuclear spin helix polarization in semiconducting quantum wires.