Bose condensation of exciton polaritons in an optical microcavity

Two methods are considered for producing traps for exciton polaritons in an optical microcavity with an embedded quantum well. The first method for controlling polaritons consists in producing a polariton trap governed by the longitudinal confinement of photons. Traps of this type can be created using an optical microcavity with a variable width. In traps of the second type, the exciton confinement is ensured by a weak potential that is applied to a quantum well with excitons or when this well is subjected to an inhomogeneous deformation. The behavior of a two-component Bose condensate of photons and excitons is analyzed theoretically. The Bose condensate is described by the coupled system of equations of the Gross-Pitaevskii type. The approximate wave functions and the spatial profiles of coupled photon and exciton condensates are obtained.     

Characteristics of exciton polaritons in a ZnO microcavity

We have investigated the characteristics of exciton polaritons in a ZnO microcavity with HfO₂/SiO₂ distributed Bragg reflectors. The results of the angle-resolved reflectance spectra were analyzed by calculating the cavity polariton dispersions with a phenomenological Hamiltonian for the coupling between the cavity photon and three kinds of excitons labeled A, B, and C peculiar to ZnO. The vacuum-Rabi-splitting energy is estimated to be ∼80 meV. The reflectance dips originating from the cavity polaritons shift to lower energy side with an increase in temperature. We discuss the temperature dependence of the cavity-polariton energies of the ZnO microcavity on the basis of the phenomenological Hamiltonian taking account of the temperature dependence of the exciton energies with Varshni’s law.     

On the mechanism of the maintenance of Rabi oscillations in the system of exciton polaritons in a microcavity

A physical mechanism of the implementation of undamped Rabi oscillations in the system of exciton polaritons in a semiconductor microcavity in the presence of nonresonant pumping has been proposed. Various mechanisms of the stimulated scattering of excitons from the reservoir have been considered. It has been shown that undamped oscillations of the population of the photon component of the condensate can be caused by the feeding of a coherent Rabi oscillator owing to the pair scattering of excitons from the reservoir to the ground state. The effect should be observed in spite of a more intense relaxation of polaritons of the upper branch observed experimentally.     

Dynamic stark effect in strongly coupled microcavity exciton polaritons

We present experimental observations of a nonresonant dynamic Stark shift in strongly coupled microcavity quantum well exciton polaritons-a system which provides a rich variety of solid-state collective phenomena. The Stark effect is demonstrated in a GaAs/AlGaAs system at 10?K by femtosecond pump-probe measurements, with the blueshift approaching the meV scale for a pump fluence of 2 mJ?cm^{-2} and 50?meV red detuning, in good agreement with theory. The energy level structure of the strongly coupled polariton Rabi?doublet remains unaffected by the blueshift. The demonstrated effect should allow generation of ultrafast density-independent potentials and imprinting well-defined phase profiles on polariton condensates, providing a powerful tool for manipulation of these condensates, similar to dipole potentials in cold-atom systems.     

Multistability of the optical response in a system of quasi-two-dimensional exciton polaritons

The nonlinear dynamic properties of a system of polaritons in a planar semiconductor microcavity under conditions of external coherent photoexcitation have been investigated. It has been shown that the interaction between polaritons with identical projections of the total angular momentum (J _z ) can give rise to multistability of the response of the excited polariton state. As a result, nonequilibrium transitions between different stability branches become possible due to fluctuations or arbitrarily smooth variations of the excitation parameters and occur with abrupt changes in the intensity and optical polarization of the field in the microcavity. It has been demonstrated that a relatively weak attraction between polaritons with opposite total angular momenta J _z leads to a possibility of spontaneously breaking the symmetry of circularly polarized field components in the microcavity under strictly linear (symmetric) polarization conditions of external excitation.     

Spin dynamics of a vortical condensate of exciton polaritons in a GaAs microcavity

The temporal dynamics of a spinor exciton-polariton condensate in a high-quality anisotropic GaAs microcavity under pulsed resonant excitation with light possessing a nonzero orbital angular momentum is investigated. The phenomenon of spatial separation of the spin components of the polariton condensate upon pumping with a coherent superposition of two beams with opposite circular polarizations and orbital angular momenta is observed. The key factors for the observation of this effect are the lateral anisotropy of the microcavity that causes a splitting between the linear components of the polariton ground state and the occurrence of opposite orbital angular momenta for the two spin components of the condensate. The experimental results are in qualitative agreement with the theoretical model of the phenomenon developed in JETP Lett. 104, 827 (2016).     

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). The text was submitted by the authors in English.     

Weak localization and nonlinear optical responses of exciton polaritons

We discuss novel nonlinear optical responses due to weak localization of exciton-polaritons (EP’s): first phase-conjugated signal induced and enhanced by the weak localization of EP’s under a single pump and a test beam which are two-photon-resonant to a biexciton. This observation will give us clear evidence of the weak localization. Second, we analyze, in terms of weak localization of EP’s, the coherent light emission in the direction normal to the surface under a single beam pumping tilted from the normal to a planar semiconductor microcavity. Fiz. Tverd. Tela (St. Petersburg) 40, 919–920 (May 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

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

The dynamics of polaritonic emission of a GaAs-based microcavity with embedded quantum wells under nonresonant optical excitation is studied. Kinetic dependences of the intensity, spectral position, and linewidth of spontaneous and stimulated emission of the microcavity are measured. It is established that the dynamics of the high-frequency shift of the emission line is qualitatively similar to the dynamics of the emission intensity, but the spectral shift attains its maximum value before the peak intensity is reached. The emission linewidth is maximal immediately after the excitation pulse. Under the conditions of spontaneous emission, the linewidth decreases steadily with time, approaching the value corresponding to low polariton densities. Under lasing conditions, the linewidth is at a minimum when the stimulated-emission intensity attains its peak value. The experimental data are analyzed on the basis of a theoretical model that describes relaxation processes taking into account exciton-exciton and exciton-free carrier interactions.     

Effect of exciton dephasing in a semiconductor microcavity

We study the interaction between delocalized excitons in a semiconductor quantum well and a longitudinal mode of the radiation field in a semiconductor microcavity with Bragg mirrors. The drastic enhancement of the spontaneous emission rate, that occurs under strong coupling conditions, is found to be surprisingly robust with respect to incoherent processes leading to dephasing of the exciton mode. Received date: 3 June 1998 / Received in final form: 19 November 1998     

Dynamics of microcavity polaritons in the Markovian limit

A master equation for the reduced density matrix of the microcavity polaritons coupled with the reservoir of high energy excitons is derived. It is allowed both the polaritons and the excitons to be self-interacting systems. Long time asymptotic properties of the polariton population is studied in the whole range of the reservoir temperatures and the corresponding decoherence effects are reported.     

Nonlinear optical excitation and dispersion relation of surface exciton polaritons in ZnO

The dispersion relation and the theory of nonlinear excitation of surface exciton polaritons are presented for a geometry consisting of a prism, and airgap and a spatially dispersive medium. We compare DeMartini et al.'s experimental results for the Cl-surface exciton polaritons in ZnO with the predictions of two models for the ABC (additional boundary conditions), i.e. P_ex = 0 and $\text{?}\text{P}{}_{\mathrm{ex}}\text{?}\text{z}\text{= 0}$ and found reasonable agreement for the second case only.     

Possible condensation of Frenkel exciton polaritons in an organic nanofiber

We theoretically investigate a phase transition of Frenkel exciton polaritons in an organic nanofiber. Assuming a phenomenological Hamiltonian, we derive a mean field equation for the condensation after finding an effective action for the phenomenon using the functional integral method and stationary phase analysis. From a solution of the mean field equation, we construct a phase diagram for the condensation and highlight features that distinguish J- and H-aggregates. We also detail a connection with the superradiant phase transition, which has been studied using the Dicke model.     

Hard mode of stimulated scattering in the system of quasi-two-dimensional exciton polaritons

Dynamics of stimulated scattering of quasi-two-dimensional exciton polaritons in a semiconductor microcavity is considered theoretically. A system possessing a bistable response to coherent excitation is studied. Being a system of weakly interacting Bose particles under strongly nonequilibrium conditions, it exhibits a complex dynamics of the development of condensate modes. It is shown that multimode instability can arise in a threshold way in the system under a smooth increase in pump intensity. In this case, rapid populating of a multitude of unstable modes leads to stochastization of scattering, and evolution to a quasi-steady macrostate is performed as self-organization in an open nonequilibrium system. Arising fluctuations lead to the occurrence of a spatial nonuniformity of the distribution of scattered states.     

Phase transition in a two-dimensional dipole-oriented exciton system

A dipole-oriented two-dimensional exciton system in electrically biased GaAs/AlGaAs coupled quantum wells has been studied through photoluminescence. The system has a sample-dependent built-in random potential which traps excitons at low temperature. The average photoluminescence photon energy shows a sudden reduction when the excitation intensity exceeds a critical value at low temperatures. This suggests a phase transition from a Bose glass to superfluid phase.     

Bragg polaritons: strong coupling and amplification in an unfolded microcavity

Periodic incorporation of quantum wells inside a one-dimensional Bragg structure is shown to enhance coherent coupling of excitons to the electromagnetic Bloch waves. We demonstrate strong coupling of quantum well excitons to photonic crystal Bragg modes at the edge of the photonic band gap, which gives rise to mixed Bragg polariton eigenstates. The resulting Bragg polariton branches are in good agreement with the theory and allow demonstration of Bragg polariton parametric amplification.     

Excitations in a nonequilibrium Bose-Einstein condensate of exciton polaritons

We develop a mean-field theory of the dynamics of a nonequilibrium Bose-Einstein condensate of exciton polaritons in a semiconductor microcavity. The spectrum of elementary excitations around the stationary state is analytically studied by means of a generalized Gross-Pitaevskii equation. A diffusive behavior of the Goldstone mode is found in the spatially homogeneous case and new features are predicted for the Josephson effect in a two-well geometry.     

Bose-Einstein condensate of cavity exciton polaritons in a trap

The properties of traps for exciton polaritons in a semiconductor microcavity with an embedded quantum well have been considered. The behavior of the two-component Bose-Einstein condensate of photons and excitons described by the coupled system of Gross-Pitaevskii equations has been investigated. The analytical solutions for weak-confinement traps have been found in the Thomas-Fermi approximation. In the case of strong confinement, the behavior of the condensate has been investigated and constraints on the possible values of the chemical potential of the system have been obtained. The wavefunctions and generally different spatial profiles of the coupled photon and exciton condensates have been found.