Dispersion mapping of spin-dependent polariton dynamics in CdTe microcavities

We have studied the polarization of the light emitted by a semiconductor microcavity as a function of the detuning between the cavity mode and the exciton. Under high excitation conditions, when the cavity is in a non-linear regime, the emission originates from the cavity-like branch of the polaritons, i.e. the lower polariton branch for negative detuning and the upper polariton branch for positive detuning. The time dependence of the polarization, which represents the spin dynamics of the polaritons, shows a very rich and novel behaviour in this non-linear regime. The polarization initially is not at its maximum, like in the linear regime, but reaches it after a finite time and, furthermore, its sign is strongly dependent on the cavity–exciton detuning (δ = E_C − E_X): it is positive for δ > 0 and negative for δ < 0. The negative polarization is directly related with an energy splitting between the σ⁺- and σ⁻-polarized components of the emission, which appears when the excitation density drives the cavity into the non-linear regime.