Exciton-polariton Systems Research Articles

Angle-Resolved Photoluminescence Spectrum of the Exciton Condensate in Electron-Hole Semiconductor Bilayers

The electron-hole semiconductor bilayer system is one of the most promising systems to search for exciton superfluid. The exciton superfluid is metastable and will eventually decay through emitting photons. Here we show that the angle-resolved photon spectrum, momentum distribution curve, energy distribution curve, and quasiparticle excitation spectrum in the exciton superfluid show many unique and unusual features not shared by any other atomic or condensed matter systems. Observing all these salient features in the photoluminescence experiments can provide convincing evidence for exciton superfluid in electron-hole semiconductor bilayers. We also comment on relevant experimental data in both exciton and exciton-polariton systems and also suggest possible future experiments to test our theoretical predictions.

Dynamics of the transition from strong to weak coupling regime in a system of exciton polaritons in semiconductor microcavities

Dynamics of the transition from strong to weak coupling regime in a system of exciton polaritons in semiconductor microcavities

On the type of a phase transition in the system of exciton polaritons in an optical microcavity

The type of a phase transition in the quasi-equilibrium system of exciton polaritons in a two-dimensional optical microcavity has been analyzed. It has been shown that, although the system contains two types of bosons undergoing mutual transformations into each other, only one phase transition to the superfluid state with the quasilong-range order occurs in the two-dimensional system. This phase transition is a Kosterlitz-Thouless phase transition. A new physical implementation—excitons in a photon crystal—has been proposed for the Bose condensation of exciton polaritons. The superfluid properties of the ordered phase are discussed, and the superfluid density and Kosterlitz-Thouless transition temperature have been calculated in the low-density approximation.

Photon Emission as a Source of Coherent Behavior of Polaritons

We show that the combined effect of photon emission and Coulomb interactions may drive an exciton-polariton system towards a dynamical coherent state, even without phonon thermalization or any other relaxation mechanism. Exact diagonalization results for a finite system (a multilevel quantum dot interacting with the lowest-energy photon mode of a microcavity) are presented in support of this statement.

Kosterlitz-Thouless phase transition in microcavity polariton system

The Kosterlitz-Thouless phase transition in a system of exciton-polaritons in a microcavity is studied. The transition temperature to superfluid state was found as a function of exciton-photon detuning. A nonquadratic dispersion law was taken into account in the framework of the self-consistent harmonic approximation (SCHA).

Quantum coherent effects in cavity exciton polariton systems

The non-linear emission from semiconductor microcavities in the strong coupling regime exhibits specific coherence properties that can be interpreted by parametric polariton four-wave mixing. In a geometry corresponding to degenerate four-wave mixing, we predict and observe a phase dependence of the amplification which is a signature of a coherent polariton wave mixing process. This process is also expected to lead to bistability and squeezed light generation. Spatial effects in the non-linear regime are evidenced, and spatial filtering is required in order to optimize the measured squeezing which is observed close to the bistability turning point. Moreover, the presence of strong coupling inside the microcavity allows to produce a new type of squeezing involving a part-light, part-matter field, the polariton.

Some Remarks on the Ground State of the Exciton and Exciton-Polariton System

A brief review of the theory of the ground state properties of the electron-hole system is presented, discussing the full density regime from isolated excitons to the electron-hole plasma. Particular attention is devoted to a discussion of coherent condensed phases, especially when excitonic recombination allows the excitonic coherence to be transferred to the light field.

Nonlinear effects in dense two-dimensional exciton polariton system

The interaction between quantum well excitons andcavity photons in semiconductor microcavities in the strongcoupling regime results in mixed 2D exciton–photon states,called exciton polaritons. The behavior of a dense polaritonsystem is of particular interest due to the fact that theseparticles have integer spin and, hence, obey Bose–Einsteinstatistics. Drastic nonlinearities have been observed both in thelow polariton (LP) emission intensity and polarization in thecase of the resonant excitation into the LP branch undercondition that 2ℏω(kex) = ℏω(k = 0) + ℏω(2kex). The experiments have shown a very strong final state stimulation of a twopolariton scattering due to the bosonic nature of the polaritons.The filling of k = 0 LP state significantly exceeding 1 has beenrealized under continuous excitation at T = 1:8 K. Thedependence of the effect on the polarization of photoexcitedlight and temperature is discussed.

Parametric luminescence of microcavity polaritons

The spectral and dispersive emission properties are analytically determined for the two-dimensional system of exciton-polaritons in microcavities excited by a resonant and coherent optical pump. New collective excitations result from the anomalous coupling between one generic polariton state and its idler, created by the scattering of two pumped polaritons. The corresponding parametric correlation is stimulated by the emitter and idler populations and drives very efficiently the luminescence. The intrinsic properties of the collective excitations determine a peculiar emission pattern.

Spatial propagation of high-density excitons localized at a stacking disorder plane inBiI3

We study spatial behavior of heavily excited excitons localized at a two-dimensional space of a specific stacking fault interface in a layered crystal ${\mathrm{BiI}}_{3}.$ Pump-and-probe absorption and resonant luminescence spectra of the exciton states were measured with an intense nanosecond laser not only at the exciting laser spot but at distant points from the exciting spot by applying space-resolved spectroscopy methods. The blueshift proportional to the exciton density was clearly observed on the probe absorption spectra even at the distant points due to high-density excitons flowing out from the exciting spot. The resonant luminescence also shows the spectral change and anomalous spatial expansion depending on the excitation density. The spatial distributions of the energy shift on the probe absorption and the luminescence intensity were analyzed on the basis of a two-dimensional exciton-flow model with dissipation processes. The analysis suggests the existence of an efficient in-phase motion of the exciton polaritons at high density. The results are discussed in terms of a new phase of the interacting high-density exciton-polariton system.

Conditions for observation of Rabi oscillations in an exciton-polariton system

The pure quantum model describing Rabi oscillations of exciton-polaritons (EP) in a micro-cavity with finite quality is considered. It is shown that the oscillations can be observed if the cavity damping rate does not exceed some critical value depending on the EP coupling constant and the detuning of the cavity mode. An explicit expression for the renormalized Rabi frequency is found. Comparison of the results with experimental data shows a good agreement.