Non-Linear Effects on the Spin Dynamics of Polaritons in II–VI Microcavities

Abstract

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 (LPB) for negative detuning and the upper polaritons branch (UPB) for positive detuning. The time dependence of the polarization, which represents the spin dynamics of the polaritons, shows a very rich and novel behavior in this non-linear regime, as compared to that under low excitation conditions. In the latter case, the polarization decays exponentially to zero after a pulsed excitation, in a similar way to that known for bare excitons in quantum wells, while in the non-linear regime the polarization reaches its maximum at 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.