Valley polarization fluctuations, bistability, and switching in two-dimensional semiconductors

TL;DR

This paper theoretically investigates nonlinear valley polarization dynamics in atom-thin semiconductors, revealing bistability, noise effects, and switching behavior between polarized states driven by exciton interactions.

Contribution

It introduces a theoretical framework for understanding valley polarization bistability and noise-induced switching in two-dimensional semiconductors.

Findings

Demonstrates bistability of valley polarization with low and high states.

Shows high-amplitude, long-relaxation fluctuations in high-polarization regime.

Finds high valley polarization state is favored over a wide range of pumping rates.

Abstract

We study theoretically nonlinear valley polarization dynamics of excitons in atom-thin semiconductors. The presence of significant polarization slows down valley relaxation due to an effective magnetic field resulting from exciton-exciton interactions. We address temporal dynamics of valley polarized excitons and study the steady states of the polarized exciton gas. We demonstrate bistability of the valley polarization where two steady states with low and high valley polarization are formed. We study the effects of fluctuations and noise in such system. We evaluate valley polarization autocorrelation functions and demonstrate that for a high-polarization regime the fluctuations are characterized by high amplitude and long relaxation time. We study the switching between the low- and high-valley polarized states caused by the noise in the system and demonstrate that the state with high valley polarization is preferential in a wide range of pumping rates.