Coherent spin states and spin quantum beats in semiconductor microcavities

The present study evidences the influence of the strong light-matter coupling in semiconductor III–V microcavities on polariton spin dynamics at low excitation. Under resonant excitation, we observe a quenching of spin and alignment relaxation when the polariton is photon like. These behaviours are attributed, respectively, to the very small value of the long-range electron–hole exchange term of Coulomb interaction within the excitonic component of the quasi-particle and to the weakness of polariton–polariton Coulomb scattering via the inter-exciton short-range exchange interaction. Spin dynamics are also investigated under transverse magnetic field. We observe an electron–hole spin correlation within the excitonic component of the quasi-particle under resonant excitation, and an increase of the absolute value of the electron effective transverse Landé g-factor with the excitonic character of polaritons, which can be derived from a model taking into account only two classes of excitations in the lower polariton branch.