Towards condensates of light and excitions at room temperature

Abstract:

In well-designed optical microcavities, non-perturbative mixing of the highly confined electromagnetic field and exciton resonances results in new quasi-particles termed exciton-polaritons. These are composite bosons with very low effective mass (~10⁻⁴ m_e). Above a certain critical density and below a critical temperature, these can undergo quantum condensation, resulting in macroscopic spontaneous coherence. Such condensates have been well documented in inorganic quantum-well microcavities such as those based on GaAs. There are also limited reports of polariton condensation in organic microcavities based on molecular semiconductors, where larger oscillator strengths and higher exciton binding energies should permit polariton condensates at higher temperature than in inorganic devices, even at room temperature. In this seminar, I will initially describe multidimensional coherent spectroscopy measurements of polariton correlations in GaAs quantum-well Fabry-Perot microcavities at 4K in order to discuss the dynamics of polariton condensate formation. These experiments measure polariton-polariton spectral correlations that produce the condensate, and their evolution on ultrafast timescales. Following the physics learned from the GaAs quantum-well devices, I will then describe our current efforts to fabricate all-solution-processed organic microcavities to pursue these exotic phases at room temperature.