Electron spin-vorticity coupling in low and high Reynolds number pipe flows

TL;DR

This study experimentally investigates electron spin-vorticity coupling in pipe flows across a wide Reynolds number range, confirming theoretical predictions in laminar flow and validating a scaling law in turbulent flow.

Contribution

It extends the Reynolds number range for spin hydrodynamic coupling experiments and verifies theoretical and scaling laws in both laminar and turbulent regimes.

Findings

Linear voltage-flow velocity relation in laminar flow

Universal behavior regardless of pipe shape in laminar regime

Validation of the scaling law up to Re=21,500 in turbulent flow

Abstract

Spin hydrodynamic coupling is a recently discovered method to directly generate electricity from an electrically conducting fluid flow in the absence of Lorentz forces. This method relies on a collective coupling of electron spins - the internal quantum mechanical angular momentum of the electrons - with the local vorticity of a fluid flow. In this work, we experimentally investigate the spin hydrodynamic coupling in circular and non-circular capillary pipe flows and extend a previously obtained range of Reynolds numbers to smaller and larger values, 20<Re<21,500, using the conducting liquid metal alloy GaInSn as the working liquid. In particular, we provide experimental evidences for the linear dependence of the generated electrical voltage with respect to the bulk flow velocity in the laminar regime of the circular pipe flow as predicted by Matsuo et al. [Phys. Rev. B. 96, 020401 (2017)]. Moreover, we show analytically that this behavior is universal in laminar regime regardless of the cross-sectional shape of the pipe. Finally, the proposed scaling law by Takahashi et al. [Nat. Phys. 12, 52 (2016)] for the generated voltage in turbulent circular pipe flows is experimentally evaluated at Reynolds numbers higher than in previous studies. Our results verify the reliability of the proposed scaling law for Reynolds numbers up to Re=21,500 for which the flow is in a fully developed turbulent state.