  We detail the influence of a magnetic field on exciton-polaritons inside a
semiconductor microcavity. Magnetic field can be used as a tuning parameter for
exciton and photon resonances. We discuss the change of the exciton energy, the
oscillator strength and redistribution of the polariton density along the
dispersion curves due to the magnetically-induced detuning. We have observed
that field-induced shrinkage of the exciton wave function has a direct
influence not only on the exciton oscillator strength, which is observed to
increase with the magnetic field, but also on the polariton linewidth. We
discuss the effect of the Zeeman splitting on polaritons which magnitude
changes with the exciton Hopfield coefficient and can be modelled by
independent coupling of the two spin components of excitons with cavity
photons.

Mesoscale and Nanoscale Physics