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Register a new userElectroluminescence emission from polariton states in GaAs-based semiconductor microcavities
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Added by
Dmitriy Krizhanovskii Dr
Publication date
2008
fields
Physics
and research's language is
English
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The authors report the observation of electroluminescence from GaAs-based semiconductor microcavities in the strong coupling regime. At low current densities the emission consists of two peaks, which exhibit anti-crossing behaviour as a function of detection angle and thus originate from polariton states. With increasing carrier injection we observe a progressive transition from strong to weak coupling due to screening of the exciton resonance by free carriers. The demonstration that polariton emission can be excited by electrical injection is encouraging for future development of polariton lasers.
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The dynamics of optical switching in semiconductor microcavities in the strong coupling regime is studied using time- and spatially-resolved spectroscopy. The switching is triggered by polarised short pulses which create spin bullets of high polariton density. The spin packets travel with speeds of the order of 106 m/s due to the ballistic propagation and drift of exciton-polaritons from high to low density areas. The speed is controlled by the angle of incidence of the excitation beams, which changes the polariton group velocity.
Based on a microscopic many-particle theory we investigate the influence of excitonic correlations on the vectorial polarization state characteristics of the parametric amplification of polaritons in semiconductor microcavities. We study a microcavity with perfect in-plane isotropy. A linear stability analysis of the cavity polariton dynamics shows that in the co-linear (TE-TE or TM-TM) pump-probe polarization state configuration, excitonic correlations diminish the parametric scattering process whereas it is enhanced by excitonic correlations in the cross-linear (TE-TM or TM-TE) configuration. Without any free parameters, our microscopic theory gives a quantitative understanding how many-particle effects can lead to a rotation or change of the outgoing (amplified) probe signals vectorial polarization state relative to the incoming ones.
We investigate the interactions between exciton-polaritons in N two-dimensional semiconductor layers embedded in a planar microcavity. In the limit of low-energy scattering, where we can ignore the composite nature of the excitons, we obtain exact analytical expressions for the spin-triplet and spin-singlet interaction strengths, which go beyond the Born approximation employed in previous calculations. Crucially, we find that the strong light-matter coupling enhances the strength of polariton-polariton interactions compared to that of the exciton-exciton interactions, due to the Rabi coupling and the small photon-exciton mass ratio. We furthermore obtain the dependence of the polariton interactions on the number of layers N, and we highlight the important role played by the optically dark states that exist in multiple layers. In particular, we predict that the singlet interaction strength is stronger than the triplet one for a wide range of parameters in most of the currently used transition metal dichalcogenides. This has consequences for the pursuit of polariton condensation and other interaction-driven phenomena in these materials.
Semiconductor microcavities operating in the polaritonic regime are highly non-linear, high speed systems due to the unique half-light, half-matter nature of polaritons. Here, we report for the first time the observation of propagating multi-soliton polariton patterns consisting of multi-peak structures either along (x) or perpendicular to (y) the direction of propagation. Soliton arrays of up to 5 solitons are observed, with the number of solitons controlled by the size or power of the triggering laser pulse. The break-up along the x direction occurs due to interplay of bistability, negative effective mass and polariton-polariton scattering, while in the y direction the break-up results from nonlinear phase-dependent interactions of propagating fronts. We show the experimental results are in good agreement with numerical modelling. Our observations are a step towards ultrafast all-optical signal processing using sequences of solitons as bits of information.
Using a microscopic many-particle theory, we propose all-optical switching in planar semiconductor microcavities where a weak beam switches a stronger signal. Based on four-wave-mixing instabilities, the general scheme is a semiconductor adaptation of a recently demonstrated switch in an atomic vapor [Dawes et al., Science 308, 672 (2005)].
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