Negative conductivity and anomalous screening in two-dimensional electron systems subjected to microwave radiation

TL;DR

This paper investigates how microwave radiation induces negative conductivity in 2D electron systems under magnetic fields, revealing that diffusion can stabilize such states and lead to unique electrostatic and domain structures.

Contribution

It demonstrates that negative conductivity can coexist with positive diffusion and shows how finite system size influences electrostatic stability in microwave-driven 2D electron systems.

Findings

Negative conductivity can coexist with positive diffusion.

System size smaller than divergence of screening length stabilizes negative conductivity.

System splits into regions with opposite electric fields in the negative conductivity regime.

Abstract

A 2D electron system in a quantized magnetic field can be driven by microwave radiation into a non-equilibrium state with strong magnetooscillations of the dissipative conductivity. We demonstrate that in such system a negative conductivity can coexist with a positive diffusion coefficient. In a finite system, solution of coupled electrostatic and linear transport problems shows that the diffusion can stabilize a state with negative conductivity. Specifically, this happens when the system size is smaller than the absolute value of the non-equilibrium screening length that diverges at the point where the conductivity changes sign. We predict that a negative resistance can be measured in such a state. Further, for a non-zero difference between the work functions of two contacts, we explore the distribution of the electrostatic potential and of the electron density in the sample. We show that in the diffusion-stabilized regime of negative conductivity the system splits into two regions with opposite directions of electric field. This effect is a precursor of the domain structure that has been predicted to emerge spontaneously in the microwave-induced zero-resistance states.