Polariton states bound to defects in GaAs/AlAs planar microcavities

We report on polariton states bound to defects in planar GaAs/AlAs microcavities grown by molecular beam epitaxy. The defect types relevant for the spatial polariton dynamics in these structures are cross-hatch misfit dislocations, and point-like defects extended over several micrometers. We attribute the latter defects to Ga droplets emitted occasionally by the Ga cell during the growth. These defects, also known as oval defects, result in a dome-like local modulation of surface, which is translated into the cavity structure and leads to a lateral modulation of the cavity polariton energy of up to 15\,meV. The resulting spatially localized potential landscape for the in-plane polariton motion creates a series of bound states. These states were characterized by spectrally resolved transmission imaging in real and reciprocal space, and reveal the spatial potential created by the defects. Interestingly, the defect states exhibit long lifetimes in the 10ps range, which we attribute to a spatially smooth confinement potential

Parametric scattering of microcavity polaritons into ghost branches

Polaritons of defined momentum and energy are excited resonantly on the lower polariton branch of a planar semiconductor microcavity in the strong coupling regime, and the spectrally and momentum resolved emission is analyzed. We observe ghost branches from scattering within the lower polariton branch, as well as from scattering to the middle polariton branch, showing the nonlinear mixing between different branches. Extending the theoretical treatment of spontaneous parametric luminescence developed in Ciuti et al. [Phys. Rev. B 63, 041303 (2001)], the eigenmodes of the driven polariton system and its photoluminescence are modeled. A quantitative agreement with the measured branch positions and a qualitative agreement with the branch intensities is found

Temperature dependency of resonance fluorescence from InAs/GaAs quantum dots : dephasing mechanisms

We report a study on temperature-dependent resonant fluorescence from InAs/GaAs quantum dots. We combined spectral and temporal measurements in order to identify sources of dephasing. In the spectral domain, we observed temperature-dependent broadening of the zero-phonon line as 0.3 μeV/K, and a temperature-dependent phonon broadband. Time-resolved autocorrelation measurements revealed temperature-dependent spin pumping times between T1,s = 6 ns (4 K) and 0.5 ns (15 K). These results are compared against theoretical modeling with a master equation for a four-level system coupled to phonon and spin baths. We explained the results by phonon-mediated hole-spin scattering between two excited states, with the piezophonons as a dominant mechanism.Publisher PDFPeer reviewe

Microcavity polaritons propagation, scattering, and localization

Strong coupling between a Fabry-Perot cavity mode and a quantum well exciton give rise to the new quasi-particles microcavity exciton-polaritons. Microcavity polaritons were for the first time demonstrated in 1992 in Ref [1] and since then, the field developed dramatically. Fundamental physics was explored in these systems including a quantum phase transitions of microcavity polaritons [2–4], demonstration of quantized vortices [5] and superfluidity [6]. Concerning applications [7], properties of microcavity polaritons are explored in optoelectronic devices e.g. low threshold electrically pumped polariton lasers, polarization sensitive optical bistable switches, spin memories and spin logic gates. Main research interest of this work concerned the field of quantum phase transitions and the many-body physics of microcavity polaritons which are relatively easily accessible experimentally as compared to similar physics in cold-atoms systems [8] from the point of view of equipment complexity. However, in polariton physics, samples with desirable properties play a crucial role. Microcavity samples commonly suffer from disorder, for both the exciton and the photon components of the polaritons, which strongly modifies polariton quantum effects and makes them difficult to interpret. This fact emphasizes the importance of the further development in the field of the sample design and growth, and this was one of the goals of this contribution. In particular, we worked to identify and suppress disorder in microcavity samples and to develop reproducible growth receipts providing samples with long photon lifetime. Photonic disorder was identified as cross-hatch dislocations and point-like-defects. A novel cross-hatch suppressing sample design was proposed and demonstrated, providing samples with long polariton propagation lengths in the order of millimeters in which genuine quantum fluid effects can be explored. Moreover, the origin behind the point-like-defects formation was identified as Ga nano-droplets deposited in microcavity during the molecular-beam epitaxial growth. These states were investigated using surface (differential-interference contrast microscopy, scanning-electron microscopy, chemical etching) and volume (focused-ion beam milling) techniques. Point-like-defect resulted in 0-dimensional polariton states exhibiting quantized energy levels which we have characterized in real and reciprocal space. The second part of this work was the investigation of quantum many-body effects in low disorder microcavities. In particular, we investigated polariton parametric scattering and demonstrated experimentally and theoretically scattering into ”ghost” branches which arises due to energy and momentum conservation of polaritons. Finally, we theoretically modeled quantum fluid effects of polaritons using Gross- Pitaievskii equation reproducing superfluid transition and bistability for spin independent polariton interactions

Platelets augment respiratory burst in neutrophils activated by selected species of gram-positive or gram-negative bacteria.

Neutrophils and platelets circulate in blood system and play important physiological roles as part of immunological system. Neutrophils are the first line of host defense against various intruders, and platelets are satellite cells cooperating with other components of defense system. Recent studies report about the cooperation among these types of cells. We analyzed the effect of platelets on oxygen burst in neutrophils triggered by Staphylococcus aureus and Escherichia coli bacteria in vitro. The effect of platelets on oxygen burst in neutrophils was measured by luminol enhanced chemiluminescence. Opsonized and non-opsonized bacteria were used as activators. Activation of neutrophils with live non-opsonized and opsonized bacteria in the presence of platelets increased the oxygen burst as compared to the same system without platelets. The gram-positive bacteria (Staphylococcus aureus) were causing higher activation than gram-negative bacteria (Escherichia coli). This work demonstrate that platelets potentate the response of neutrophils augmenting their respiratory burst in vitro when triggered by bacteria

Season\u27s influence on the relationship between mass concentrations of sulphur dioxide and sulphate in the air

Studiran je odnos masenih koncentracija (p) sumpor-dioksida i sulfata u prirodnim uvjetima, tj. u dvije gradske sredine s različitim razinama atmosferskog onečišćenja tijekom zimskog i ljetnog razdoblja. Na svakom mjernom mjestu tijekom sezone sakupljeno je i analizirano pedesetak uzoraka sumpor-dioksida, dima·i lebdećih čestica. U uzorcima lebdećih čestica određivana je ukupna masena koncentracija lebdećih čestica, sulfata, kalcija, olova, željeza, mangana i bakra. Studirana je korelacija po sezonama između masenih koncentracija sulfata i sumpor-dioksida, lebdećih čestica, dima, te pojedinih komponenata lebdećih čestica. Dobivena je dobra korelacija između masenih koncentracija sulfata i lebdećih čestica. Razine masenih koncentracija sumpor-dioksida, dima, sulfata i lebdećih čestica značajno su više tijekom zimskog razdoblja u obim sredinama. Na obim je mjestima dobiven gotovo jednak prosječni maseni udjel (w) sulfata (oko 10) u lebdećim česticama i tijekom zimskog i ljetnog razdoblja. Izračunate jednadžbe regresije za odnos između sulfatnog S i ukupnog S (sulfati i sumpor-dioksid) za ljetno i zimsko razdoblje međusobno se razlikuju. Izgleda da se taj sezonski utjecaj na odnos masenih koncentracija sumpor-dioksida i sulfata može dovesti u vezu s različitim porijeklom i različitim razinama masenih koncentracija lebdećih čestica u zraku.The relationship between sulphur dioxide and sulphate was studied in natural conditions, in two urban areas with different levels of air pollution during the winter and summer periods. About fifty samples of sulphur dioxide, smoke and suspended particulates were collected and analysed on each measuring site during the season. In the sample of suspended particulates the total mass concentration of suspended particulates, sulphate, calcium, lead, iron, manganese and copper was determined. The correlation between sulphate and sulphur dioxide, suspended particulates, smoke and some suspended particulate\u27s components was studied by seasons. A good correlation was found between the concentration of sulphate and suspended particulates. The concentration levels of sulphur dioxide, smoke, sulphate and suspended particulates were significantly higher during the winter period in both areas. On both locations the average mass fraction of sulphate (about 10%) in suspended particulates was nearly the same during the winter and summer periods. The calculated equation regressions for the relationship between sulphate S and total S (sulphate and sulphur dioxide) for the summer and winter period are reciprocally different. It seems that the season\u27s influence on the relationship between sulphur dioxide and sulphate might be due to a different origin and different levels of suspended particulates in the air

Health related values and preferences regarding meat intake : a cross-sectional mixed-methods study

Background. In addition to social and environmental determinants, people's values and preferences determine daily food choices. This study evaluated adults' values and preferences regarding unprocessed red meat (URM) and processed meat (PM) and their willingness to change their consumption in the face of possible undesirable health consequences. Methods. A crosssectional mixed-methods study including a quantitative assessment through an online survey, a qualitative inquiry through semi-structured interviews, and a follow-up assessment through a telephone survey. We performed descriptive statistics, logistic regressions, and thematic analysis. Results. Of 304 participants, over 75% were unwilling to stop their consumption of either URM or PM, and of those unwilling to stop, over 80% were also unwilling to reduce. Men were less likely to stop meat intake than women (odds ratios < 0.4). From the semi-structured interviews, we identified three main themes: the social and/or family context of meat consumption, healthand non-health-related concerns about meat, and uncertainty of the evidence. At three months, 63% of participants reported no changes in meat intake. Conclusions. When informed about the cancer incidence and mortality risks of meat consumption, most respondents would not reduce their intake. Public health and clinical nutrition guidelines should ensure that their recommendations are consistent with population values and preferences