Excitonic Theory of the Ultrafast Optical Response of 2D-Quantum-Confined Semiconductors at Elevated Densities

TL;DR

This paper develops an excitonic theoretical framework to describe the ultrafast optical response of 2D semiconductors at high densities, capturing both coherent and incoherent regimes and analyzing the effects of Coulomb interactions and excitation polarization.

Contribution

It introduces a comprehensive excitonic model applicable across different density regimes and Coulomb interaction strengths, with numerical simulations for 2D semiconductors like MoSe2.

Findings

Excitonic Rabi oscillations are weaker in Coulomb-dominated regimes.

Linear excitation suppresses excitonic Rabi oscillations.

The theory bridges coherent and incoherent optical response regimes.

Abstract

An excitonic approach to the ultrafast optical response of confined semiconductors at elevated densities below the Mott transition is presented. The theory is valid from the coherent regime, where coherent excitonic transitions and biexcitons dominate, to the incoherent regime, where excitonic occupations dominate. Numerical simulations of the $1s$ exciton dynamics during intense circularly polarized pump pulses in two different Coulomb-interaction regimes are performed for two-dimensional semiconductors: Moderate Coulomb interaction is compared with dominating Coulomb interaction with respect to the light-matter interaction strength. The different many-body contributions are disentangled and it is found, that excitonic Rabi oscillations in the Coulomb-dominated regime are considerably less strong. By also comparing circular and linear excitation in a MoSe$_2$ monolayer, it is found, that linear excitation creates a regime, where excitonic Rabi oscillations are almost completely suppressed.