MIFP RESEARCH MIFP PUBLICATIONS

MIFP PUBLICATIONS

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    Excitonic lasing of strain-free InP(As) quantum dots in AlInAs microdisk

    Uploaded:
    20.03.17
    Modified:
    20.03.17
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    1 MB

    D. V. Lebedev, M. M. Kulagina, S. I. Troshkov, A. S. Vlasov, V. Y. Davydov, A. N. Smirnov, A. A. Bogdanov, J. L. Merz, J. Kapaldo, A. Gocalinska, G. Juska, S. T. Moroni, E. Pelucchi, D. Barettin, S. Rouvimov, and A. M. Mintairov


    Formation, emission, and lasing properties of strain-free InP(As)/AlInAs quantum dots (QDs) embedded in AlInAs microdisk (MD) cavity were investigated using transmission electron microscopy and photoluminescence (PL) techniques. In MD structures, the QDs have the nano-pan-cake shape with the height of ˜2 nm, the lateral size of 20–50 nm, and the density of ˜5x109 cm-2. Their emission observed at ˜940 nm revealed strong temperature quenching, which points to exciton decomposition. It also showed unexpected type-I character, indicating In-As intermixing as confirmed by band structure calculations. We observed lasing of InP(As) QD excitons into whispering gallery modes in MD having the diameter of ˜3.2 lm and providing a free spectral range of ˜27 nm and quality factors up to Q˜13 000. Threshold of ˜50 W/cm2 and spontaneous emission coupling coefficient of ˜0.2 were measured for this MD-QD system.

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    Fast 3C 279 γ flares by a merging medium size black hole jet aligned to the AGN one by tidal torque?

    Uploaded:
    17.10.16
    Modified:
    17.10.16
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    4 MB

    D. Fargion, P. Oliva


    The shorter-than-Schwarzschild 3C 279 variability flare on June 2015 is very puzzling. Its nature cannot be due to any NS merging nor to a medium sized (˜ 102 M) BH collapse. Our preliminary model is based on the long-life (˜ 107 s) merging of a medium size BH (˜ 102 M) spiralling towards the more massive AGN (BH) that is tidally dragging the medium size BH jet in alignment with the jet of the more massive BH of AGN 3C 279. The tidal torque is aligning both jets towards Earth. The twin overlapping blazars may offer at once a long and a short scale variability consistent with the surprising Fermi discoveries.

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    Nano-carbon pixels array for ionizing particles monitoring

    Uploaded:
    31.08.16
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    31.08.16
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    629 KB

    S. Salvatori, P. Oliva, M. Pacilli, P. Allegrini, G. Conte, M. Komlenok, A.A. Khomich, A. Bolshakov, V. Ralchenko, V. Konov


    The paper deals on the response of a polycrystalline diamond sensor, 500 μm thick, to particles from a Sr β-source. 21×21 nano-carbon pads, with 0.18 mm×0.18 mm area each, were realized by ArF excimer laser irradiation on one diamond face, whereas a 7×7 mm2 backside contact was fabricated and used for sensor biasing during characterization of sensor under β-source irradiation. The carbon pads embrace a number of grains, which show different degrees of surface graphitization dependent on the grain orientations. Each carbon pad exhibits a linear I(V) response up to 200 V. The average number of charge carriers collected by a single pixel, as well as the distribution of pixels involved by the impinging particle tracking, is analyzed as a function of the applied voltage recording the signals acquired by 16 pixels at a time. The pulse height distribution is not affected by reversing the bias polarity. For a single pixel, the most probable collected charge value is 1.40±0.02 fC whereas the main value gives Qcoll=1.67±0.02 fC (10430 ±120 electrons). The charge collection distance was measured tacking into account the effect induced by highenergy electrons and found to be 285±3 μm, demonstrating the absence of bulk defects induced by the laser graphitization processing. Cross-talk effects between nearest-neighbor pixels has been excluded analyzing the results obtained in a batch of more than 1000 events even if the same cannot be excluded under higher energy particles.

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    Diamond device architectures for UV laser monitoring

    Uploaded:
    01.07.16
    Modified:
    01.07.16
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    3 MB

    S Salvatori, M Girolami, P Oliva, G Conte, A Bolshakov, V Ralchenko and V Konov


    The paper reviews the status of diamond detectors for UV laser monitoring and imaging. Single pixel detectors, position sensitive architectures, optically activated switches and sensor arrays for beam positioning and imaging are analyzed. The performances of natural diamond and synthetic diamond produced by chemical vapor deposition are compared to evaluate the suitability of such an outstanding material for the described applications.

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    Enhanced thermoelectric coupling near electronic phase transition: The role of fluctuation Cooper pairs

    Uploaded:
    20.03.15
    Modified:
    20.03.15
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    164 KB

    Henni Ouerdane, Andrey A. Varlamov, Alexey V. Kavokin, Christophe Goupil, and Cronin B. Vining


    Thermoelectric energy conversion is a direct but low-efficiency process, which precludes the development of long-awaited wide-scale applications. As a breakthrough permitting a drastic performance increase is seemingly out of reach, we fully reconsider the problem of thermoelectric coupling enhancement. The cornerstone of our approach is the observation that heat engines are particularly efficient when their operation involves a phase transition of their working fluid. We derive and compute the thermoelastic coefficients of various systems, including Bose and Fermi gases, and fluctuation Cooper pairs. Combination of these coefficients yields the definition of the thermodynamic figure of merit, the divergence of which at finite temperature indicates that conditions are fulfilled for the best possible use of the thermoelectric working fluid. Here, this situation occurs in the fluctuation regime only, as a consequence of the increased compressibility of the working fluid near its phase transition. Our results and analysis clearly show that efforts in the field of thermoelectricity can now be productively directed towards systems where electronic phase transitions are possible.

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    Dispersion characteristics of electromagnetic excitations in a disordered one-dimensional lattice of coupled microresonators

    Uploaded:
    04.02.15
    Modified:
    04.02.15
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    1 MB

    V.V. Rumyantsev, S.A.Fedorov, K.V.Gumennyk, M.V.Sychanova


    Localized photonic modes are studied in a non-ideal chain of coupled microcavities with the use of the virtual crystal approximation. The approach proves sufficient to elucidate the effects of varying composition and nearest-neighbor distances on the spectrum. It permits to obtain the density of states of the studied quasiparticles as well as the dispersion dependence of collective excitation frequencies on defect concentration. Based upon the developed description of ideal photonic structures we proceed to study a non-ideal polaritonic crystal constituted by an array of spatially ordered cavities containing atomic clusters. Frequency, effective mass and group velocity of polaritons are analytically derived as functions of vacancy concentration.

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    Exciton-like electromagnetic excitations in non-ideal microcavity supercrystals

    Uploaded:
    07.11.14
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    07.11.14
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    904 KB

    Vladimir Rumyantsev, Stanislav Fedorov, Kostyantyn Gumennyk, Marina Sychanova, Alexey Kavokin


    We study localized photonic excitations in a quasi-two-dimensional non-ideal binary microcavity lattice with use of the virtual crystal approximation. The effect of point defects (vacancies) on the excitation spectrum is investigated by numerical modelling. We obtain the dispersion and the energy gap of the electromagnetic excitations which may be considered as Frenkel exciton-like quasiparticles and analyze the dependence of their density of states on the defect concentrations in a microcavity supercrystal.

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    Spin Currents in a Coherent Exciton Gas

    Uploaded:
    08.07.13
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    08.07.13
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    1 MB

    A. A. High, A. T. Hammack, J. R. Leonard, Sen Yang, L.V. Butov, T. Ostatnicky, M. Vladimirova, A.V. Kavokin, T. C. H. Liew, K. L. Campman, and A. C. Gossard


    We report the observation of spin currents in a coherent gas of indirect excitons. The realized longrange spin currents originate from the formation of a coherent gas of bosonic pairs—a new mechanism to suppress the spin relaxation. The spin currents result in the appearance of a variety of polarization patterns, including helical patterns, four-leaf patterns, spiral patterns, bell patterns, and periodic patterns. We demonstrate control of the spin currents by a magnetic field. We also present a theory of coherent exciton spin transport that describes the observed exciton polarization patterns and indicates the trajectories of the spin currents.

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    Nonlinear effects in multi-photon polaritonics

    Uploaded:
    08.07.13
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    08.07.13
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    1 MB

    A. A. Pervishko, T. C. H. Liew, V. M. Kovalev, I. G. Savenko, and I. A. Shelykh


    We consider theoretically nonlinear effects in a semiconductor quantum well embedded inside a photonic microcavity. Two-photon absorption by a 2p exciton state is considered and investigated; the matrix element of two-photon absorption is calculated. We compute the emission spectrum of the sample and demonstrate that under coherent pumping the nonlinearity of the two photon absorption process gives rise to bistability.

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    Stochastic Gross-Pitaevskii Equation for the Dynamical Thermalization of Bose-Einstein Condensates

    Uploaded:
    08.07.13
    Modified:
    08.07.13
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    500 KB

    I. G. Savenko, T. C. H. Liew, and I. A. Shelykh


    We present a theory for the description of energy relaxation in a nonequilibrium condensate of bosonic particles. The approach is based on coupling to a thermal bath of other particles (e.g., phonons in a crystal, or noncondensed atoms in a cold atom system), which are treated with a Monte Carlo type approach. Together with a full account of particle-particle interactions, dynamic driving, and particle loss, this offers a complete description of recent experiments in which Bose-Einstein condensates are seen to relax their energy as they propagate in real space and time. As an example, we apply the theory to the solid-state system of microcavity exciton polaritons, in which nonequilibrium effects are particularly prominent.

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