Exciton polaritons in semiconductor quantum microcavities in a high magnetic field

Abstract

Exciton-photon polariton coupled mode spectra in (In)GaAs-GaAs-(Al)GaAs semiconductor quantum-microcavity structures are studied in magnetic fields up to 14 T. Very-well-resolved spectra are observed with large vacuum Rabi splittings of 7.1 meV being found due to the enhanced exciton oscillator strength in a high magnetic field. The spectra exhibit strong circular polarization with marked Zeeman splitting observed between the ${\mathrm{\ensuremath{\sigma}}}^{+}$ and ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{\ensuremath{-}}}$ polarizations. Temperature tuning is employed to vary the exciton (|${\mathrm{c}}_{\mathrm{e}}$${\mathrm{|}}^{2}$) and cavity (|${\mathrm{c}}_{\mathrm{l}}$${\mathrm{|}}^{2}$) fractions of the polariton modes throughout the resonance regime. |${\mathrm{c}}_{\mathrm{e}}$${\mathrm{|}}^{2}$ and |${\mathrm{c}}_{\mathrm{l}}$${\mathrm{|}}^{2}$ are deduced as a function of detuning, from fitting of the observed peak positions as a function of temperature to a two-level coupled-mode model. The two-level model is found to explain the variation of Zeeman splitting with detuning very well, with the on-resonance Zeeman splitting being one half of the unperturbed exciton splitting. Anomalous narrowing of the lower polariton branch is found through the resonance regime. The observations are found to be in good agreement with a motional narrowing model for the polariton linewidths. The Zeeman splittings are investigated as a function of In composition in the quantum wells. Reasonable agreement with literature values for bare quantum wells is found, with a sign reversal of the polarization for GaAs relative to ${\mathrm{In}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As quantum wells being observed. Finally, coupling of the cavity mode to exciton excited states corresponding to higher Landau levels is seen, with vacuum Rabi splittings in good agreement with the results of exciton oscillator strength calculations.