Hydrodynamic magnetotransport in two-dimensional electron systems with macroscopic obstacles

TL;DR

This paper investigates magnetotransport in viscous electron fluids with obstacles, revealing strong negative magnetoresistance and Hall resistance modifications, and compares theoretical models with experimental data in high-quality GaAs quantum wells.

Contribution

It introduces and compares hydrodynamic and quasi-hydrodynamic models for electron flow around obstacles, highlighting their effects on magnetoresistance and Hall resistance in high-quality conductors.

Findings

Longitudinal magnetoresistivity is strongly negative.

Hall resistivity is unaffected by rough edges but slightly corrected by smooth edges due to Hall viscosity.

Theoretical results agree well with experimental data in GaAs quantum wells.

Abstract

In high-quality conductors, the hydrodynamic regime of electron transport has been recently realized. In this work we theoretically investigate magnetotransport of a viscous electron fluid in samples with electron-impermeable obstacles. We use the two approaches to describe the fluid flow. The first one is based on the equations of hydrodynamics of a charged fluid, which assume that the kinetic equation takes into account the two harmonics of the electron distribution function. The second approach is based on the equations that are obtained by taking into account three harmonics of the distribution function (''quasi-hydrodynamics''). Within the hydrodynamic approach, we consider the cases of the rough and the smooth edges of the disks, on which the electron scattering is diffusive or specular, respectively. The longitudinal magnetoresistivity turns out to be strong and negative, the same for both rough and smooth discs edges to within small corrections. For rough discs, the Hall resistivity is equal to its standard value. For smooth discs the Hall resistance acquire a small correction to the standard value, proportional to the Hall viscosity. In the quasi-hydrodynamic approach, we considered the case of smooth discs and small magnetic fields. In the regime when the flow is substantially different from the hydrodynamic one, the longitudinal resistivity does not depend on the shear stress relaxation time (but depends on the relaxation time of the third angular harmonic), while the correction to the standard Hall resistivity does not depend on both relaxation times. We compare the results of the hydrodynamic calculation of the longitudinal resistance with the experimental data on magnetotransport in high-quality GaAs quantum wells with macroscopic defects. A good agreement of theory and experiment evidences in favor of the realization of the hydrodynamic transport regime in such systems.