Picosecond spin conversion in quasi two dimensional exciton-polariton systems
Quasi two dimensional exciton polaritons are composite bosons that emerge through strong exciton-photon coupling in flat semiconductor microresonators. Spin-related polariton-polariton interaction results in multistability and allows fast resonator response switching when the field values in the active layer reach their critical point. The physical reason for polariton multistability lays in spectrum renormalization with a shift of effective resonance frequency that significantly surpasses the resonance spectral width.
Normally, such conditions can only be achieved in a strong exciton-photon coupling mode. They make polariton multistability effect qualitatively different from the previously studied optical multistability phenomena in lasers and other nonlinear media.
One of the key distinctions here is the strong sensitivity of the system to the initial resonance position which leads to new non-equilibrium transition scenarios in anisotropic or chiral polariton systems with split self-modes, for instance, due to Zeeman effect in the magnetic field.
We theoretically predicted and experimentally observed (see Fig.1) the effect of threshold spin-anisotropic spectrum renormalization of chiral exciton-polariton systems that related to the condensate mode occupation number. This effect lead to excited mode spin inversion at the scale of several polariton lifetimes (tens of picoseconds) under the conditions of resonance optical pumping with gradually changing intensity and constant polarization.
Due to this newly-discovered effect, a new type of compact and quick-operating optical switches and logic elements based on microresonators with a strong exciton-photon coupling can emerge.
Fig.1. The upper part shows a diagram of the system steady-state response depending on the optical pumping power, its circular polarization degree being rс=0.5 (circular polarization degree of the transmission signal is marked by color), and a chart of anticipated transitions between different stability branches (polarization is shown by ellipses). The lower part of the Figure represents the measured and calculated time dependences of the intensity of right- and left-hand-polarized components of the resonator optical field, the pulsed pumping duration being 70 ps in magnetic field B=6 Т for W=2W0 (reversible polarization transition 1-2_-1), and W=4W0 (irreversible polarization transition with spin inversion); W0 is the threshold power of the instability development.
(Laboratory of Non-equilibrium Electronic Processes, RAS Associate Member V. D. Kulakovsky)
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