Coherent Terahertz Radiation from a Nonlinear Oscillator of Viscous Electrons

TL;DR

This paper demonstrates that viscous electron flow in a narrow cavity can produce stable nonlinear oscillations that generate Terahertz radiation, with potential for experimental realization.

Contribution

It introduces a nonlinear hydrodynamic oscillator model for viscous electrons, predicting Terahertz emission beyond linear response and robustness to inhomogeneity.

Findings

Oscillations are stable nonlinear hydrodynamic states.

Frequency and amplitude depend on viscosity, relaxation rate, and bias current.

Predictions are made for experimental parameters.

Abstract

Compressible electron flow through a narrow cavity is theoretically unstable, and the oscillations occurring during the instability have been proposed as a method of generating Terahertz radiation. We numerically demonstrate that the endpoint of this instability is a nonlinear hydrodynamic oscillator, consisting of an alternating shock wave and rarefaction-like relaxation flowing back and forth in the device. This qualitative physics is robust to cavity inhomogeneity and changes in the equation of state of the fluid. We discuss the frequency and amplitude dependence of the emitted radiation on physical parameters (viscosity, momentum relaxation rate, and bias current) beyond linear response theory, providing clear predictions for future experiments.