EXCITON POLARITONS IN SEMICONDUCTOR QUANTUM MICROCAVITIES IN A HIGH MAGNETIC-FIELD

Exciton-photon polariton coupled mode spectra in (In)GaAs-GaAs-(Al)GaA s 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 exc iton oscillator strength in a high magnetic field. The spectra exhibit strong circular polarization with marked Zeeman splitting observed be tween the sigma(+) and sigma(-) polarizations. Temperature tuning is e mployed to vary the exciton (\c(e)\(2)) and cavity (\c(l)\(2)) fractio ns of the polariton modes throughout the resonance regime. \c(e)\(2) a nd \c(l)\(2) are deduced as a function of detuning, from fitting of th e observed peak positions as a function of temperature to a two-level coupled-mode model. The two-level model is found to explain the variat ion 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 th e resonance regime. The observations are found to be in good agreement with a motional narrowing model for the polariton linewidths. The Zee man splittings are investigated as a function of In composition in the quantum wells. Reasonable agreement with literature values for bare q uantum wells is found, with a sign reversal of the polarization for Ga As relative to InxGa1-xAs quantum wells being observed. Finally, coupl ing of the cavity mode to exciton excited states corresponding to high er Landau levels is seen, with vacuum Rabi splittings in good agreemen t with the results of exciton oscillator strength calculations.