Flow bistability in non-Newtonian electron fluid

Abstract

Modern two dimensional conductors with low defect densities and strong electron-electron scattering are favorable platforms for formation of a viscous fluid of conduction electrons. Electric properties of these systems are determined by the hydrodynamic regime of charge transport distinguished by many experimental signatures: a decrease in sample resistance with increasing temperature (the Ghurzhi effect), strong negative magnetoresistance and others. Here we consider the flow of 2D electron fluid in the nonlinear regime characterized by non-Newtonian viscosity which depends on spatial gradients of hydrodynamic velocity. We derive a simplified version of the dynamic equations for the non-Newtonian electron fluid and consider the specific underlying mechanism associated with local electron heating. Recent works have demonstrated that this may be one of the main mechanisms for nonlinearity in 2D electron fluids. We show that in a certain range of parameters, the two steady-state flow configurations coexist for the narrow channel geometry, and this bistability leads to an S-shaped current-voltage characteristic. By solving the derived time-dependent dynamic equations, we trace the transient response to a step variation of the longitudinal voltage and demonstrate how the current switching and hysteresis occur in samples with the non-Newtonian electron fluid.