Negative magnetoresistance in viscous flow of two-dimensional electrons

TL;DR

This paper investigates how viscous electron flow in ultra-clean 2D materials causes negative magnetoresistance, explaining recent experimental observations through a hydrodynamic model.

Contribution

It introduces a theoretical framework for viscous electron flow in magnetic fields, linking viscosity changes to negative magnetoresistance in 2D electron systems.

Findings

Viscosity coefficients depend on magnetic field and temperature.

Negative magnetoresistance arises from decreasing diagonal viscosity.

Viscous effects explain giant negative magnetoresistance in GaAs quantum wells.

Abstract

At low temperatures, in very clean two-dimensional (2D) samples the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature- and size dependent. Our analysis demonstrates that the viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultra-high-mobility GaAs quantum wells. We conclude that 2D electrons in that structures in moderate magnetic fields should be treated as a viscous fluid.