Exciton-polaritons in semiconductor quantum microcavities in high 
magnetic fields

A. Armitage, T.A. Fisher, M.S. Skolnick, D.M. Whittaker, 
P. Kinsler, J.S. Roberts.

    Department of Physics,
    University of Sheffield, 
    Sheffield S3 7RH, 
    United Kingdom.

    Phys. Rev. B55, 16395 (1997). 

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 sigma + and sigma - polarizations. 
Temperature tuning is employed to vary the exciton (|ce|2) and cavity
(|cl|2) fractions of the polariton modes throughout the resonance
regime. |ce|2 and |cl|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
InxGa1-xAs 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.  






Email: Dr.Paul.Kinsler@physics.org