# Spontaneous generation of spin current from the vacuum by strong electric fields

## TL;DR

This paper demonstrates that strong electric fields can spontaneously generate a spin current from the vacuum through a mechanism involving the Schwinger effect and spin-orbit coupling, with relativistic effects influencing the current's properties.

## Contribution

It provides a numerical evaluation of vacuum spin current generation under combined electric fields, revealing relativistic effects on spin polarization and direction.

## Key findings

- Spin current flows mainly in the longitudinal direction.
- Relativistic helicity conservation affects spin current polarization.
- Vacuum expectation value of spin current can be explicitly computed.

## Abstract

We discuss spontaneous spin current generation from the vacuum by strong electric fields as a result of interplay between the Schwinger mechanism and a spin-orbit coupling. By considering a homogeneous slow strong electric field superimposed by a fast weak transverse electric field, we explicitly evaluate the vacuum expectation value of a spin current (the Bargmann-Wigner spin current) by numerically solving the Dirac equation. We show that a non-vanishing spin current polarized in the direction perpendicular to the electric fields flows mostly in the longitudinal direction. We also find that a relativistic effect due to the helicity conservation affects direction/polarization of spin current.