Third harmonic generation on exciton-polaritons in bulk semiconductors subject to a magnetic field

TL;DR

This study investigates how magnetic fields influence third harmonic generation in exciton-polaritons within bulk semiconductors, revealing a significant enhancement in GaAs due to increased oscillator strength, with less effect in CdTe and ZnSe.

Contribution

It provides the first comprehensive experimental and theoretical analysis of magnetic field effects on THG in exciton-polaritons across multiple semiconductors.

Findings

THG intensity in GaAs increases fiftyfold at 10 T magnetic field.

Enhancement is moderate in CdTe and negligible in ZnSe.

The increase is mainly due to magnetic field-induced oscillator strength enhancement.

Abstract

We report on a comprehensive experimental and theoretical study of optical third harmonic generation (THG) on the exciton-polariton resonances in the zinc-blende semiconductors GaAs, CdTe, and ZnSe subject to an external magnetic field, representing a topic that had remained unexplored so far. In these crystals, crystallographic THG is allowed in the electric-dipole approximation, so that no strong magnetic-field-induced changes of the THG are expected. Therefore, it comes as a total surprise that we observe a drastic enhancement of the THG intensity by a factor of fifty for the $1s$-exciton-polariton in GaAs in magnetic fields up to 10 T. In contrast, the corresponding enhancement is moderate for CdTe and almost neglectful for ZnSe. In order to explain this strong variation, we develop a microscopic theory accounting for the optical harmonics generation on exciton-polaritons and analyze the THG mechanisms induced by the magnetic field. The calculations show that the increase of THG intensity is dominated by the magnetic field enhancement of the exciton oscillator strength which is particularly strong for GaAs in the studied range of field strengths. The much weaker increase of THG intensity in CdTe and ZnSe is explained by the considerably larger exciton binding energies, leading to a weaker modification of their oscillator strengths by the magnetic field.