Spin-vorticity coupling in viscous electron fluids

TL;DR

This paper explores how vorticity in viscous electron fluids with spin-orbit coupling can generate spin polarization, providing a new method to image electron flows and potentially produce larger spin polarizations than traditional effects.

Contribution

It derives hydrodynamic equations for spin-vorticity coupling and calculates the rotational viscosity microscopically, demonstrating the feasibility of observing this effect in experiments.

Findings

Spin-vorticity coupling can generate measurable spin polarization.

The effect can be larger than spin Hall effect in the hydrodynamic regime.

Experimental conditions for observing the effect are achievable.

Abstract

We consider spin-vorticity coupling - the generation of spin polarization by vorticity - in viscous two-dimensional electron systems with spin-orbit coupling. We first derive hydrodynamic equations for spin and momentum densities in which their mutual coupling is determined by the rotational viscosity. We then calculate the rotational viscosity microscopically in the limits of weak and strong spin-orbit coupling. We provide estimates that show that the spin-orbit coupling achieved in recent experiments is strong enough for the spin-vorticity coupling to be observed. On the one hand, this coupling provides a way to image viscous electron flows by imaging spin densities. On the other hand, we show that the spin polarization generated by spin-vorticity coupling in the hydrodynamic regime can, in principle, be much larger than that generated, e.g. by the spin Hall effect, in the diffusive regime.