Spin quantum beats in semiconductor microcavities in the strong coupling regime

We have observed polariton spin quantum beats under transverse magnetic field and circular polarization excitation (Voigt configuration) by time-resolved photoluminescence spectroscopy. The temporal behaviour of the beats strongly differs depending on whether the excitation is resonant or not with the lower polariton branch. As in bare quantum wells, we show that this is the consequence of the hole spin instability under non-resonant excitation. In both cases, we evidence a dependence on the cavity detuning δ of the electron effective Landé g-factor (geff). This is attributed to strong coupling regime, where the bare electron Landé g-factor is depends on the polariton exciton component. All these characteristics are well described by a simplified model, which takes into account the transfer dynamics between two classes of polaritons.