Condensed Matter Physics

ORAL · I02 · ID: I02

We develop a microscopic mean-field theory describing superfluidity in a two-component exciton–polariton condensate formed by the simultaneous occupation of the lower and upper polariton branches in a semiconductor microcavity. Starting from the exciton–photon Hamiltonian, we derive an effective interacting polariton model that includes both intra- and interbranch scattering processes. A phenomenological population-split parameter alpha is introduced to characterize the relative occupation of the lower- and upper-polariton condensates. Within a Bogoliubov framework, we obtain analytic expressions for the collective excitation spectrum, sound velocity, and critical temperature of the coupled condensate. We show that coexistence of the two polariton branches produces tunable modifications to the superfluid properties relative to the conventional single-branch condensate. In particular, away from zero detuning the sound velocity and critical temperature depend strongly on the population imbalance between the branches, providing experimentally measurable signatures of genuine two-component polariton superfluidity. At resonance, these quantities converge to a single value independent of population distribution.

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