Faraday rotation in photoexcited semiconductors: an excitonic many-body effect

TL;DR

This paper explains Faraday rotation in photoexcited semiconductors as a result of Pauli interactions between real and virtual excitons, introducing a new many-body theory with Shiva diagrams to clarify the underlying physics.

Contribution

It introduces a new many-body theory for interacting excitons and links Faraday rotation to the exciton optical Stark effect using Shiva diagrams.

Findings

Pauli interactions cause Faraday rotation in semiconductors.

New many-body theory with Shiva diagrams elucidates exciton interactions.

Faraday rotation relates to the exciton optical Stark effect.

Abstract

This letter assigns the Faraday rotation in photoexcited semiconductors to ``Pauli interactions'', \emph{i}. \emph{e}., carrier exchanges, between the real excitons present in the sample and the virtual excitons coupled to the $\sigma_{\pm}$ parts of a linearly polarized light. While \emph{direct Coulomb} interactions scatter bright excitons into bright excitons, whatever their spins are, \emph{Pauli} interactions do it for bright excitons \emph{with same spin only}. This makes these Pauli interactions entirely responsible for the refractive index difference, which comes from processes in which the virtual exciton which is created and the one which recombines are formed with different carriers. To write this difference in terms of photon detuning and exciton density, we use our new many-body theory for interacting excitons. Its multiarm ``Shiva'' diagrams for $N$-body exchanges make transparent the physics involved in the various terms. This work also shows the interesting link which exists between Faraday rotation and the exciton optical Stark effect.