Highly nonlinear trion-polaritons in a monolayer semiconductor.

Highly nonlinear optical materials with strong effective photon-photon interactions are required for ultrafast and quantum optical signal processing circuitry. Here we report strong Kerr-like nonlinearities by employing efficient optical transitions of charged excitons (trions) observed in semiconducting transition metal dichalcogenides (TMDCs). By hybridising trions in monolayer MoSe2 at low electron densities with a microcavity mode, we realise trion-polaritons exhibiting significant energy shifts at small photon fluxes due to phase space filling. We find the ratio of trion- to neutral exciton-polariton interaction strength is in the range from 10 to 100 in TMDC materials and that trion-polariton nonlinearity is comparable to that in other polariton systems. The results are in good agreement with a theory accounting for the composite nature of excitons and trions and deviation of their statistics from that of ideal bosons and fermions. Our findings open a way to scalable quantum optics applications with TMDCs.

Transition from Propagating Polariton Solitons to a Standing Wave Condensate Induced by Interactions.

We explore phase transitions of polariton wave packets, first, to a soliton and then to a standing wave polariton condensate in a multimode microwire system, mediated by nonlinear polariton interactions. At low excitation density, we observe ballistic propagation of the multimode polariton wave packets arising from the interference between different transverse modes. With increasing excitation density, the wave packets transform into single-mode bright solitons due to effects of both intermodal and intramodal polariton-polariton scattering. Further increase of the excitation density increases thermalization speed, leading to relaxation of the polariton density from a solitonic spectrum distribution in momentum space down to low momenta, with the resultant formation of a nonequilibrium condensate manifested by a standing wave pattern across the whole sample.

Backward Cherenkov radiation emitted by polariton solitons in a microcavity wire.

Exciton-polaritons in semiconductor microcavities form a highly nonlinear platform to study a variety of effects interfacing optical, condensed matter, quantum and statistical physics. We show that the complex polariton patterns generated by picosecond pulses in microcavity wire waveguides can be understood as the Cherenkov radiation emitted by bright polariton solitons, which is enabled by the unique microcavity polariton dispersion, which has momentum intervals with positive and negative group velocities. Unlike in optical fibres and semiconductor waveguides, we observe that the microcavity wire Cherenkov radiation is predominantly emitted with negative group velocity and therefore propagates backwards relative to the propagation direction of the emitting soliton. We have developed a theory of the microcavity wire polariton solitons and of their Cherenkov radiation and conducted a series of experiments, where we have measured polariton-soliton pulse compression, pulse breaking and emission of the backward Cherenkov radiation.

Exciton-polaritons in van der Waals heterostructures embedded in tunable microcavities.

Layered materials can be assembled vertically to fabricate a new class of van der Waals heterostructures a few atomic layers thick, compatible with a wide range of substrates and optoelectronic device geometries, enabling new strategies for control of light-matter coupling. Here, we incorporate molybdenum diselenide/hexagonal boron nitride (MoSe2/hBN) quantum wells in a tunable optical microcavity. Part-light-part-matter polariton eigenstates are observed as a result of the strong coupling between MoSe2 excitons and cavity photons, evidenced from a clear anticrossing between the neutral exciton and the cavity modes with a splitting of 20 meV for a single MoSe2 monolayer, enhanced to 29 meV in MoSe2/hBN/MoSe2 double-quantum wells. The splitting at resonance provides an estimate of the exciton radiative lifetime of 0.4 ps. Our results pave the way for room-temperature polaritonic devices based on multiple-quantum-well van der Waals heterostructures, where polariton condensation and electrical polariton injection through the incorporation of graphene contacts may be realized.

Spatial Patterns of Dissipative Polariton Solitons in Semiconductor Microcavities.

We report propagating bound microcavity polariton soliton arrays consisting of multipeak structures either along (x) or perpendicular (y) to the direction of propagation. Soliton arrays of up to five solitons are observed, with the number of solitons controlled by the size and power of the triggering laser pulse. The breakup along the x direction occurs when the effective area of the trigger pulse exceeds the characteristic soliton size determined by polariton-polariton interactions. Narrowing of soliton emission in energy-momentum space indicates phase locking between adjacent solitons, consistent with numerical modeling which predicts stable multihump soliton solutions. In the y direction, the breakup originates from inhomogeneity across the wave front in the transverse direction which develops into a stable array only in the solitonic regime via phase-dependent interactions of propagating fronts.

Two-dimensional metal-chalcogenide films in tunable optical microcavities.

Integration of quasi-two-dimensional (2D) films of metal-chalcogenides in optical microcavities permits new photonic applications of these materials. Here we present tunable microcavities with monolayer MoS2 or few monolayer GaSe films. We observe significant modification of spectral and temporal properties of photoluminescence (PL): PL is emitted in spectrally narrow and wavelength-tunable cavity modes with quality factors up to 7400; a 10-fold PL lifetime shortening is achieved, a consequence of Purcell enhancement of the spontaneous emission rate.

Effects of spin-dependent interactions on polarization of bright polariton solitons.

We report on the spin properties of bright polariton solitons supported by an external pump to compensate losses. We observe robust circularly polarized solitons when a circularly polarized pump is applied, a result attributed to phase synchronization between nondegenerate TE and TM polarized polariton modes at high momenta. For the case of a linearly polarized pump, either σ+ or σ- circularly polarized bright solitons can be switched on in a controlled way by a σ+ or σ- writing beam, respectively. This feature arises directly from the widely differing interaction strengths between co- and cross-circularly polarized polaritons. In the case of orthogonally linearly polarized pump and writing beams, the soliton emission on average is found to be unpolarized, suggesting strong spatial evolution of the soliton polarization. The observed results are in agreement with theory, which predicts stable circularly polarized solitons and unstable linearly polarized solitons.

Effect of a GaAsP shell on the optical properties of self-catalyzed GaAs nanowires grown on silicon.

We realize the growth of self-catalyzed core-shell GaAs/GaAsP nanowires (NWs) on Si substrates using molecular-beam epitaxy. Transmission electron microscopy of single GaAs/GaAsP NWs demonstrates their high crystal quality and shows domination of the GaAs zinc-blende phase. Using continuous-wave and time-resolved photoluminescence (PL), we make a detailed comparison with uncapped GaAs NWs to emphasize the effect of the GaAsP capping in suppressing the nonradiative surface states. Significant PL enhancement in the core-shell structures exceeding 3 orders of magnitude at 10 K is observed; in uncapped NWs PL is quenched at 60 K, whereas single core-shell GaAs/GaAsP structures exhibit bright emission even at room temperature. From analysis of the PL temperature dependence in both types of NW we are able to determine the main carrier escape mechanisms leading to the PL quench.

Polarization bistability and resultant spin rings in semiconductor microcavities.

The transmission of a pump laser resonant with the lower polariton branch of a semiconductor microcavity is shown to be highly dependent on the degree of circular polarization of the pump. Spin dependent anisotropy of polariton-polariton interactions allows the internal polarization to be controlled by varying the pump power. The formation of spatial patterns, spin rings with a high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on effective semiclassical equations of motion provides a good description of the experimental results. Inclusion of interactions with the incoherent exciton reservoir, which provides spin-independent blueshifts of the polariton modes, is found to be essential.

Glomerular extracellular matrix and growth factors in diffuse mesangial sclerosis.

UNLABELLED: Diffuse mesangial sclerosis, isolated (IDMS) or observed in the context of Denys-Drash syndrome (DDS) due to WT1 mutation, is characterized by early onset nephrotic syndrome progressing to renal failure. A striking morphological feature is the rapid development of glomerulosclerosis. THE AIMS OF OUR STUDY WERE: (1) to analyze the glomerular distribution of extracellular matrix (ECM) antigens at the early stage of DMS, (2) to determine the composition of the ECM accumulated within the mesangial areas and leading to glomerular sclerosis, and (3) to analyze the expression of growth factors, transforming growth factor-beta 1 (TGF beta 1) and platelet-derived growth factor A (PDGFA). In glomeruli of patients with IDMS and DDS, the glomerular basement membrane (GBM) expression of the heparan sulfate chain of heparan sulfate proteoglycan (HSPG) was decreased from the early stage of DMS, at a time when ECM proteins retained a normal distribution. In fully developed lesions, mesangial and subendothelial accumulation of collagenous and noncollagenous glycoproteins normally expressed in the mesangial area (types IV [alpha 1(IV)2 alpha 2(IV)] and VI collagen, beta 1 laminin, fibronectin, tenascin, and perlecan) increased with progression of mesangial sclerosis. This was associated with mesangial expression of proteins normally restricted to the GBM (agrin, alpha 1/alpha 5, beta 2, and gamma 1 laminin chains) and with accumulation of chondroitin sulfate proteoglycan. The distribution of the alpha 3-alpha 5 chains of type IV collagen was normal. Focal accumulation of types I, III, and V collagen was seen only in severely sclerotic glomeruli. Expression of growth factors TGF beta 1 and PDGFA was increased in 9 of 10 and 5 of 10 patients, respectively. Early decreased GBM expression of the heparan sulfate chain of HSPG could play a role in the proteinuria of DMS patients. Changes in the composition of the ECM accumulated within the mesangial areas are not specific. We speculate that deregulation of the expression of growth factors normally downregulated by WT1, is one of the factors responsible for the rapid and massive mesangial deposition of basement membrane material in DDS.

MR lymphography using iron oxide nanoparticles in rats: pharmacokinetics in the lymphatic system after intravenous injection.

The objective of the study was to quantify the kinetics of the superparamagnetic nanoparticle ferumoxtran (AMI 227, Sinerem(R), Combidex(R)) in the efferent lymph of the subdiaphragmatic lymph nodes and in various node groups of the rat to elucidate the uptake mechanism. The thoracic lymph duct was catheterized in 24 rats after an IV injection of 40 micromol Fe/kg ferumoxtran. Three rats were studied at several time points between 1.5 and 24 hours. At each time point, 0.3 ml of lymph were collected over 45 minutes. Lymph nodes were differentiated into five groups. The iron concentration in the samples and in plasma was measured by relaxometry at 0.47 T and atomic absorption spectrometry. Cytology was performed on the lymph. High concentrations of nanoparticles were found in the thoracic lymph soon after injection (90 minutes). No particle was found in the lymph cells, indicating that ferumoxtran was extracellular in the lymph fluid. The maximum concentration was reached later in all node groups, at 12 hours, and then plateaued. The transcapillary pathway and subsequent lymph drainage of the particles seem to play a major role in the delivery to the lymph nodes.

Distribution of iron oxide nanoparticles in rat lymph nodes studied using electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI).

Superparamagnetic iron nanoparticles have been developed as contrast agents for magnetic resonance lymphography. The kinetics of uptake of these particles has not yet been accurately determined. We have therefore monitored the distribution of individual iron particles (ferumoxtran, AMI-227, Sinerem) in rat lymph nodes 1.5, 3, 6, 12, and 24 hours after i.v. injection (two rats per time point). The ultrastructural distribution of the iron was determined by energy-filtered transmission electron microscopy (EFTEM). This method allows the identification of elements using element-specific energy-loss electrons. Iron was identified by the Fe-L(2,3) edge (EELS), and iron maps were obtained using iron-specific electrons for imaging (ESI). The background was calculated by simplex optimization (EELS) and by the two-window method (ESI). Ferumoxtran particles were regularly observed at the periphery of the lymph nodes but not in their centers. Isolated iron particles were seen extracellularly within lymph vessels and, 3 hours after injection, as small dots in phagocytic cells. Numerous dense clusters appeared within the cells at later times (6 and 12 hours after injection). These results suggest that the contrast agent moves rapidly across the capillary wall to the lymph and is then taken up by phagocytic cells. J. Magn. Reson. Imaging 2000;12:505-509.

Collagen distribution in focal and segmental glomerulosclerosis: an immunofluorescence and ultrastructural immunogold study.

Focal and segmental glomerulosclerosis (FSGS) is a non-specific scarring process of the glomerulus, initially described in idiopathic nephrotic syndrome. The distribution of types I, III, IV, V, and VI collagen and of the alpha 1, alpha 3, alpha 4, alpha 5, and alpha 6 chains of type IV collagen was studied by immunohistochemistry in sclerotic lesions of nine nephrotic children. Dual immunofluorescence and high-resolution immunogold labelling were used to determine the precise distribution of the antigens. No changes were detected in normal glomeruli of patients compared with controls. In FSGS, type IV collagen [alpha 1(IV)2 alpha 2(IV)], and to a lesser degree type VI, accumulates in the two components of the lesion: the enlarged mesangial matrix and the material deposited between the pushed-out podocytes and the alpha 3-alpha 5(IV)-positive glomerular basement membrane. Staining for alpha 6(IV) and types I, III, and V collagen was practically negative. These results suggest that the matrix components of the sclerotic lesion are produced solely by glomerular cells. Changes in the relative distribution of type IV collagen chains, characterized by the presence of collagen [alpha 1(IV)2 alpha 2(IV)] in close contact with the podocytes, strongly suggest a switch in the podocyte programme of collagen synthesis.

Collagen distribution in human membranous glomerulonephritis.

In membranous glomerulonephritis (MGN), thickening of the glomerular basement membrane (GBM) is partly due to the accumulation of basement membrane material between and around immune deposits located on the epithelial aspect of the GBM. We investigated the distribution of type IV collagen chains (alpha 1/alpha 2, alpha 3, alpha 4, alpha 5, alpha 6) and of types I, III, V, and VI collagen in the glomeruli from 16 patients, by indirect immunofluorescence in 13 and the high-resolution immunogold technique in 6. No changes were detected in stage I MGN. The spiky projections of the GBM in stage II MGN and the basement membrane layers encircling immune deposits in stage III contained the alpha 3, alpha 4, and alpha 5 chains of type IV collagen. In contrast, the alpha 1/alpha 2 chains of type IV, as well as type VI collagen accumulated in the subendothelial aspect of the GBM. No significant staining for types I, III, and V collagens or for the alpha 6 chain of type IV collagen was detected. The results show that, as in the normal glomeruli, the different chains of type IV collagen are not co-distributed in the glomerular extracellular matrix in MGN. They also indicate that type IV collagen chains and type IV collagen play an important role in the thickening of the GBM in human MGN.

Effects of epidermal growth factor on calf renal glomerular cells in vitro.

Epidermal growth factor (EGF) stimulates the mitosis and differentiation of a variety of cellular types. It also delays the cell senescence in vitro. Because of its multiple functions, the effects of EGF on cells from isolated, explanted calf renal glomeruli have been studied. The cell types emerging from glomeruli cultured with and without EGF were compared and identified by morphological, immunofluorescence and electron microscopy criteria. Two cell types: visceral epithelial cells or podocytes (type I) and mesangial cells (type II) emerged from glomeruli cultivated without EGF. A third cell type, called type III cells, appeared only in the presence of EGF. These cells divided, were mobile and had prolonged lifespan in culture. They appeared pavement-like, and acquired progressively the morphological features and cytoskeletal components of type I cells. They also showed certain characteristics of podocytes in vivo. We suggest that type III epithelial-like cells are precursor cells of podocytes, that EGF triggers their emergence from glomeruli and their subsequent proliferation and differentiation in vitro. EGF also prolongs their lifetime in culture.

Ontogenesis of angiotensin-I converting enzyme in human kidney.

The kidney distribution of angiotensin-I converting enzyme (ACE) was studied in 14 fetuses (11 to 30 weeks old) and 7 children (2 days to 13 years old) by immunohistochemistry using specific antibodies to human kidney ACE. Immunohistochemical techniques included indirect immunofluorescence on cryostat sections of frozen tissue, immunoperoxidase and immunofluorescence of fixed tissue embedded in Paraplast, and immunoelectron microscopy. The ACE distribution in the fetal kidneys was independent of the age of the fetus. ACE was detected in two locations: 1) on the basolateral membranes and primary apical microvilli of epithelial cells from early differentiating proximal tubules; the labeling was intense in brush borders of fully developed proximal tubules; and 2) on glomerular endothelial cells; cells were lined by reaction product as soon as capillaries invaded the inferior cleft of the S-shaped body. Tubular ACE distribution was identical in the postnatal kidneys. The staining of the glomerular endothelium was extremely inconstant. The presence of ACE in proximal tubular cells and glomerular endothelial cells at the beginning of nephron differentiation may indicate that it is involved in the development of nephron function and renal hemodynamic.

Ontogenesis of 28 kDa vitamin D-induced calcium-binding protein in human kidney.

The kidney distribution of 28 kDa vitamin D-induced calcium binding protein (CaBP) was studied in 15 fetuses (11 to 33 weeks old), six children and adults (12 days to 32 years old) by immunocytochemistry using a specific antibody to rat renal 28 kDa CaBP. Similar results were obtained on frozen and fixed tissues. Kidneys from one adult and three fetuses were studied by immunoelectronmicroscopy for antigen localization at the subcellular level using the indirect immunoperoxidase technique. The 28 kDa CaBP was present in all kidneys from the eleventh week of gestation. At that stage, all deep parts of collecting ducts were homogeneously stained and a few distal tubules located in the deep cortex were intensely labeled. No labeling was observed in the early stage of nephron differentiation (S-body). 28 kDa CaBP distribution changed with kidney maturation. There was a progressive reduction of the deep part of collecting duct labeling and a concomitant increase in the number and intensity of stained distal tubular cells. At the ultrastructural level, 28 kDa CaBP was observed in the cytosol and the nuclear euchromatin. Our study demonstrates the early cellular synthesis of 28 kDa CaBP and its transient expression by deep collecting duct cells during early fetal life, at a time when only a few distal convoluted tubular cells synthetize it.

Complement activation in acute glomerulonephritis in children.

Serial determinations of complement components (C1q, C4, C3, C5 and factor B) were performed in 32 children with acute glomerulonephritis. Low levels of C3 were found in 30 patients and low levels of C5 in 26. The findings of reduced C1q and/or C4 levels (25 patients) in the first days of the disease suggest activation of the classical pathway. Depressed Factor B levels were found rarely (4 patients). In all patients, the presence of a C3 splitting activity and/of a C3 nephritic factor-like activity was investigated. Both activities were demonstrated in 7 patients whereas in another patient, only C3 splitting activity was noted. A disappearance of both activities was observed in all patients. In 3 patients tested, the C3 nephritic factor-like activity was heat-labile and was therefore not related to true C3 nephritic factor. Both pathways are implicated in the early phases of the disease but continued C3 depression is probably through alternate pathway.

[Complement and nephritic activity in membranoproliferative glomerulonephritis]. / Complément et activité néphritique dans les glomérulonéphrites membranoprolifératives.

A study of complement profiles and of "nephritic activity" (NeF activity) has been carried out in 33 children presenting with membranoproliferative glomerulonephritis (MPGN), in order to determine the pathway of complement activation. By morphological studies two varieties of MPGN have been distinguished. In MPGN with subendothelial deposits, immunofluorescent studies and complement profiles show an activation by the classical pathway. The demonstration of NeF activity in 7 of 20 patients suggests that there is recruitment of the amplification pathway. In MPGN with dense deposits, immunopathological studies indicate an activation of the complement system through the alternate pathway, NeF activity being present in 10 of 13 patients. With the functional tests used, it is not possible to ascertain that the factors responsible for the NeF activity in MPGN with subendothelial deposits are identical to the C3NeF identified in MPGN with dense deposits and/or partial lipodystrophy.