Coherent terahertz radiation from a nonlinear oscillator of viscous electrons

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 end point 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.

Automated summary

This study numerically demonstrates that the compressible electron flow through a narrow cavity is theoretically unstable, resulting in a nonlinear hydrodynamic oscillator. This phenomenon is robust to changes in cavity structure and fluid equation of state. The emitted radiation frequency and amplitude depend on physical parameters beyond linear response theory, providing clear predictions for future experiments.