Photoinduced magneto-optic Kerr effects in asymmetric semiconductor microcavities D. Pereda Cubian, 1,2 M. Haddad, 3 R. Andre ´ , 4 R. Frey, 1 G. Roosen, 1 J. L. Arce Diego, 2 and C. Flytzanis 5 1 Laboratoire Charles Fabry de l’Institut d’Optique (CNRS UMR 8501), Universite´ Paris Sud, Baˆt. 503, F-91403 Orsay Ce´dex, France 2 Departamento de Tecnologia Electronica e Ingenieria de Sistemas y Automatica, Universidad de Cantabria, E-39005 Santander, Espania 3 Laboratoire d’Optique Quantique, Ecole Polytechnique and CNRS, F-91128 Palaiseau Ce´dex, France 4 Laboratoire de Spectrome´trie Physique (CNRS UMR 558), Universite´ J. Fourier-Grenoble, B.P. 87, F-38402 Saint Martin d’He`res Ce´dex, France 5 Laboratoire de Physique de la Matie`re Condense´e, Ecole Normale Supe´rieure and CNRS, 24 Rue L’Homond, F-75231 Paris Ce´dex, France ~Received 24 May 2002; revised manuscript received 12 September 2002; published 14 January 2003! Giant photoinduced magneto-optic Kerr effects are predicted and measured in asymmetric semiconductor microcavities with a totally reflecting rear mirror operated in the limit of the strong coupling regime. The microcavity is modeled by two coupled Fabry-Perot cavities and use is made of the optical scattering matrices to derive its characteristics. The giant photoinduced rotations and phase changes are traced to the saturation, blueshift, and pseudo-Zeeman splitting of the exciton transition. Modeling the lower and upper polariton transitions by two different two-level systems qualitatively accounts for the main spectral features: the photo- induced Kerr rotations and phase changes are due to the modifications of the coupling existing between the cavity and exciton modes, due to the photoinduced changes of the exciton characteristics. The influence of spin relaxation on the rotation and ellipticity spectra is also analyzed; it confirms the gyrotropic nature of the interaction which depends strongly on the difference between the densities of counter-rotating circularly po- larized excitons and only weakly on their sum as is the case in previous isotropic studies. Measurements of photoinduced Kerr rotations performed at a temperature of 50 K in a microcavity containing a single semi- magnetic semiconductor quantum well confirm the effectiveness of the effect with polarization rotations of 10° around the lower polariton frequency at a pump fluence of only 2 mJ/cm 2 . DOI: 10.1103/PhysRevB.67.045308 PACS number~s!: 78.67.De, 42.65.2k I. INTRODUCTION The study of exciton-polariton modes received a renewed attention in the recent years with the use of quantum micro- cavities where the material ~exciton! and electromagnetic ~photon! components can be independently and artificially modified through appropriate tailoring of microcavities and quantum well characteristics. 1,2 The coupling of the exciton and cavity modes in these so-called cavity polariton modes can be easily modified by static electric 2,3 and magnetic 4–9 fields. The modification of the cavity-polariton characteris- tics by intense laser pulses has also been investigated and revealed polariton bleaching and many-body interaction effects. 10 In these studies only the isotropic ~scalar! part of these interactions could be assessed since the gyrotropic part is canceled out in the chosen configurations. Here we assess the gyrotropic part of these photoinduced changes through an experimental and theoretical study of the polarization effects occurring at high exciton densities in a microcavity operated in the strong coupling regime. In this nonlinear process, a circularly polarized pump pulse induces polarization changes on a linearly polarized incident probe beam due to the huge polarization dependent modifications of the light induced cavity-exciton coupling. In Sec. II we schematically present the experimental configuration used in our study. In Sec. III we present the setup used in our ex- periment and show that polarization rotations of a weak probe beam as large as 10° can be photoinduced by 2 mJ/cm 2 fluence circularly polarized pump pulses. In Sec. IV we de- scribe the principle of the calculations based on optical scat- tering matrices which allow the determination of the magneto-optic Kerr rotation and phase change photoinduced by a circularly polarized pump pulse. In Sec. V we apply the model to the case of resonant optical nonlinearities resulting from the photogeneration of polarized excitons. The nonlin- earities considered in this section, i.e., saturation, blueshift, and pseudo-Zeeman splitting of the exciton transition in- duced by circularly polarized pump pulses are considered decoupled from population and spin relaxation processes. The corresponding photoinduced polarization rotation and ellipticity spectra are compared and their physical interpreta- tion given in terms of the shift of the polariton frequencies due to the modifications of the exciton transition character- istics. The role played by spin relaxation processes on the photoinduced Kerr rotations and phase changes is analyzed in Sec. VI in two particular cases: for synchroneous pump and probe pulses when the exciton spin relaxation time is of the order of the pulse durations and for delayed short dura- tion probe pulses in the case of long-lived exciton spins. II. EXPERIMENTAL CONFIGURATION The device considered in this study is an asymmetric mi- crocavity operated in the strong coupling regime ~see Fig. 1!. A circularly polarized short duration pump pulse is sent onto the device at some small angle in order to generate polarized excitons. The frequency of the pump pulse is resonant with one of the polariton modes in order to instantaneously gen- PHYSICAL REVIEW B 67, 045308 ~2003! 0163-1829/2003/67~4!/045308~8!/$20.00 ©2003 The American Physical Society 67 045308-1