Nonlinear emission dynamics of a GaAs microcavity with embedded quantum wells

The emission dynamics of a GaAs microcavity at different angles of observation with respect to the sample normal under conditions of nonresonant picosecond-pulse excitation is measured. At sufficiently high excitation densities, the decay time of the lower-polariton emission increases with the polariton wavevector; at low excitation densities the decay time is independent of the wavevector. The effect of additional nonresonant continuous illumination on the emission originating from the bottom of the lower polariton branch is investigated. The additional illumination leads to a substantial increase in the emission intensity (considerably larger than the intensity of the photoluminescence excited by this illumination alone). This fact is explained in terms of acceleration of the polariton relaxation to the radiative states due to scattering by charge carriers created by the additional illumination. The results obtained show, that at large negative detunings between the photon and exciton modes, polariton-polariton and polariton-free carrier scattering are the main processes responsible for the filling of states near the bottom of the lower polariton branch.Comment: 10 pages, 6 figures. This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics: Condesed Matter. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Dynamics of spatial coherence and momentum distribution of polaritons in a semiconductor microcavity under conditions of Bose-Einstein condensation

The study was supported by the Russian Foundation for Basic Research (project nos. 12-02-33091, 13-02-12197, and 14-02-01073) and the Presidium of the Russian Academy of Sciences. The work of V.V.B. was supported in part by a scholarship of the President of the Russian Federation.The dynamics of spatial coherence and momentum distribution of polaritons in the regime of Bose-Einstein condensation in a GaAs microcavity with embedded quantum wells under nonresonant excitation with picosecond laser pulses are investigated. It is shown that the establishment of the condensate coherence is accompanied by narrowing of the polariton momentum distribution. At the same time, at sufficiently high excitation densities, there is significant qualitative discrepancy between the dynamic behavior of the width of the polariton momentum distribution determined from direct measurements and that calculated from the spatial distribution of coherence. This discrepancy is observed at the fast initial stage of the polariton system kinetics and, apparently, results from the strong spatial nonuniformity of the phase of the condensate wavefunction, which equilibrates on a much longer time scale.Publisher PDFPeer reviewe

Addressing the exciton fine structure in colloidal nanocrystals: the case of CdSe nanoplatelets

We study the band-edge exciton fine structure and in particular its bright-dark splitting in colloidal semiconductor nanocrystals by four different optical methods based on fluorescence line narrowing and time-resolved measurements at various temperatures down to 2 K. We demonstrate that all these methods provide consistent splitting values and discuss their advances and limitations. Colloidal CdSe nanoplatelets with thicknesses of 3, 4 and 5 monolayers are chosen for experimental demonstrations. The bright-dark splitting of excitons varies from 3.2 to 6.0 meV and is inversely proportional to the nanoplatelet thickness. Good agreement between experimental and theoretically calculated size dependence of the bright-dark exciton slitting is achieved. The recombination rates of the bright and dark excitons and the bright to dark relaxation rate are measured by time-resolved techniques

Exciton localization and drift in tailored-potential quantum nanowires

Exciton recombination dynamics in tailored-potential, site-controlled AlGaAs quantum wires (QWRs) are studied. Time-resolved photoluminescence spectra evidence exciton localization in weakly disordered "uniform" QWRs, whereas deterministic bandgap grading is shown to suppress localization and promote exciton drift along the potential gradient. Measured exciton transit times between two quantum dot probes placed at opposite ends of the potential gradient yield the effective 1D exciton mobility as >1300 cm(2)/(eVs). (C) 2014 AIP Publishing LLC

Multiexciton dynamics in tailored band-gap quasi-one-dimensional systems

Optoelectronic properties of site-controlled AlGaAs/GaAs quasi-one-dimensional structures are investigated. Controllable linear variation of the band gap along the vertical axis of the quantum wire, symmetrical with respect to its center, results in a set of closely separated (by a few meV) confined electron and hole states giving rise to multiple excitonic lines well resolved in the photoluminescence spectra. Exciton recombination and relaxation dynamics in this multilevel system is studied by time-resolved and photon correlation spectroscopy and described with a master-equation model. Increasing carrier occupation in the higher-energy levels results in appearance of new multiexciton lines in the emission from the lowest-energy states. Typical features of quantum dot multiexciton dynamics such as antibunching photon statistics and cascaded biexciton-exciton emission are observed for the ground state. Pronounced bunching photon statistics and strong temporal correlations between photons emitted from the different excited states indicate sequential photon emission from multiple discrete energy levels. These structures thus represent a class of quasi-one-dimensional systems with tailored energy levels and photon emission statistics

Dynamics of spatial coherence and momentum distribution of polaritons in a semiconductor microcavity under conditions of Bose-Einstein condensation

The dynamics of spatial coherence and momentum distribution of polaritons in the regime of Bose-Einstein condensation in a GaAs microcavity with embedded quantum wells under nonresonant excitation with picosecond laser pulses are investigated. It is shown that the establishment of the condensate coherence is accompanied by narrowing of the polariton momentum distribution. At the same time, at sufficiently high excitation densities, there is significant qualitative discrepancy between the dynamic behavior of the width of the polariton momentum distribution determined from direct measurements and that calculated from the spatial distribution of coherence. This discrepancy is observed at the fast initial stage of the polariton system kinetics and, apparently, results from the strong spatial nonuniformity of the phase of the condensate wavefunction, which equilibrates on a much longer time scale

Coherence Expansion and Polariton Condensate Formation in a Semiconductor Microcavity

The dynamics of the expansion of the first order spatial coherence g(1) for a polariton system in a high-Q GaAs microcavity was investigated on the basis of Young's double slit experiment under 3 ps pulse excitation at the conditions of polariton Bose-Einstein condensation. It was found that in the process of condensate formation the coherence expands with a constant velocity of about 10^8 cm/s. The measured coherence is smaller than that in thermally equilibrium system during the growth of condensate density and well exceeds it at the end of condensate decay. The onset of spatial coherence is governed by polariton relaxation while condensate amplitude and phase fluctuations are not suppressed.Comment: 5 pages, 3 figure