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FeSe x Te 1 − x compounds display a rich phase diagram, ranging from the nematicity of FeSe to the ( π , π ) magnetism of FeTe. We focus on FeSe0.4Te0.6, and exploit tr-ARPES to study its ultrafast electron dynamics following photoexcitation by near-infrared pump pulses. By exploiting probe-polarization-dependent matrix element effects, we reveal a photoinduced long-lived state, lasting for a few tens of picoseconds, showing features compatible with a nematic state. The possibility to induce a long-lived state in this compound by using ultra-short pulses might shed a new light on the driving force behind the nematic symmetry breaking in iron-based superconductors. With the aid of a phenomenological model, we illustrate how our results possibly question the common belief that a low-energy coupling with fluctuations is a necessary condition to stabilize the nematic order. On the contrary, the tendency towards orbital differentiation due to strong electronic correlations induced by the Hund’s coupling could be at the origin of the nematic order in iron-based superconductors.

Sporozoite forms of the malaria parasite Plasmodium are transmitted by mosquitoes and first infect the liver for an initial round of replication before parasite proliferation in the blood. The molecular mechanisms involved during sporozoite invasion of hepatocytes remain poorly understood. Two receptors of the Hepatitis C virus (HCV), the tetraspanin CD81 and the scavenger receptor class B type 1 (SR-B1), play an important role during the entry of Plasmodium sporozoites into hepatocytic cells. In contrast to HCV entry, which requires both CD81 and SR-B1 together with additional host factors, CD81 and SR-B1 operate independently during malaria liver infection. Sporozoites from human-infecting P. falciparum and P. vivax rely respectively on CD81 or SR-B1. Rodent-infecting P. berghei can use SR-B1 to infect host cells as an alternative pathway to CD81, providing a tractable model to investigate the role of SR-B1 during Plasmodium liver infection. Here we show that mouse SR-B1 is less functional as compared to human SR-B1 during P. berghei infection. We took advantage of this functional difference to investigate the structural determinants of SR-B1 required for infection. Using a structure-guided strategy and chimeric mouse/human SR-B1 constructs, we could map the functional region of human SR-B1 within apical loops, suggesting that this region of the protein may play a crucial role for interaction of sporozoite ligands with host cells and thus the very first step of Plasmodium infection.IMPORTANCEMalaria is caused by Plasmodium parasites and remains one of the deadliest parasitic diseases worldwide. The parasite is transmitted by a blood feeding mosquito and first invades the liver for an initial, obligatory and silent round of replication. The liver infection is an attractive target for antimalarial vaccine strategies, however the molecular mechanisms of parasite invasion of hepatocytes remain to be fully elucidated. Two hepatocyte surface proteins are known to be important for parasite entry into hepatocytes, the tetraspanin CD81 and the scavenger receptor class B type 1 (SR-B1). These receptors constitute independent gateways depending on the Plasmodium species. Here, we identified the structural determinants of SR-B1, an important hepatocyte entry factor for human-infecting P. vivax. This study paves the way toward a better characterization of the molecular interactions underlying the crucial early stages of infection, a pre-requisite for the development of novel malaria vaccine strategies.

Progress in health has occurred in the past decades in Cambodia, in terms of health service access and interventions, but several indicators, including the prevalence of malnourished children, remain alarming. The causes of undernutrition are often linked to inadequate access to water, sanitation and hygiene services but limited evidence exists on the direct association between poor WASH practices and children&rsquo, s&rsquo, nutritional statuses. This study investigates the relationship between water, sanitation and hygiene practices, defined as the child-sensitive composite score, and the nutritional status of children under five years old, measured as the weight-for-height z-score, mid-upper arm circumference or height-for-age z-score in six districts of Cambodia. The analysis used data from a longitudinal study, comprising extensive data collection on anthropometry, health, nutrition, WASH, and cognitive development. Chronological trends in wasting and stunting were described cross-sectionally, whereas the effect of WASH practices on the nutritional status of children over up to three consecutive study visits was examined with a linear mixed-effects model. The prevalence of wasting decreased during the study while stunting prevalence increased. A small, but significant, association was found between the WASH child-sensitive composite scores and the wasting child anthropometry indicators: weight-for-height z-score or mid-upper arm circumference. Evidence for an association with height-for-age z-score, detecting stunted children, was found when the independent variable was quantified according to global, but not national, guidelines. This study reinforces discordant existing evidence towards a direct association between WASH practices and children&rsquo, s nutritional status, suggesting the need to align nutrition and WASH programmes.

A novel ultrafast photoemission technique unveils the Mottness of antinodal quasiparticles in superconducting copper oxides., Many puzzling properties of high–critical temperature (Tc) superconducting (HTSC) copper oxides have deep roots in the nature of the antinodal quasiparticles, the elementary excitations with wave vector parallel to the Cu–O bonds. These electronic states are most affected by the onset of antiferromagnetic correlations and charge instabilities, and they host the maximum of the anisotropic superconducting gap and pseudogap. We use time-resolved extreme-ultraviolet photoemission with proper photon energy (18 eV) and time resolution (50 fs) to disclose the ultrafast dynamics of the antinodal states in a prototypical HTSC cuprate. After photoinducing a nonthermal charge redistribution within the Cu and O orbitals, we reveal a dramatic momentum-space differentiation of the transient electron dynamics. Whereas the nodal quasiparticle distribution is heated up as in a conventional metal, new quasiparticle states transiently emerge at the antinodes, similarly to what is expected for a photoexcited Mott insulator, where the frozen charges can be released by an impulsive excitation. This transient antinodal metallicity is mapped into the dynamics of the O-2p bands, thus directly demonstrating the intertwining between the low- and high-energy scales that is typical of correlated materials. Our results suggest that the correlation-driven freezing of the electrons moving along the Cu–O bonds, analogous to the Mott localization mechanism, constitutes the starting point for any model of high-Tc superconductivity and other exotic phases of HTSC cuprates.

Here we report on experiments performed by linear-dichroism angle resolved photoelectron spectroscopy (LD-ARPES) on septuple layers (SL) topological insulator GeBi2Te4. The linear dichroic signals, both for the valence band states and in the topologically protected surface state are interpreted as a probe of the symmetry of the states. The observation of a change in the LD-ARPES spectrum at the top of VB is attributed to the band parity inversion which is predicted by theory for all materials entering the topologically protected phase. Finally, the opening of a gap in the surface state dispersion along the non-high symmetry direction is reported. This is proposed to originated from the interaction between the surface state and the VB, leading to the formation of surface resonances.

International audience; Plasmodium sporozoites are deposited in the host skin by Anopheles mosquitoes. The parasites migrate from the dermis to the liver, where they invade hepatocytes through a moving junction (MJ) to form a replicative parasitophorous vacuole (PV). Malaria sporozoites need to traverse cells during progression through host tissues, a process requiring parasite perforin-like protein 1 (PLP1). We find that sporozoites traverse cells inside transient vacuoles that precede PV formation. Sporozoites initially invade cells inside transient vacuoles by an active MJ-independent process that does not require vacuole membrane remodeling or release of parasite secretory organelles typically involved in invasion. Sporozoites use pH sensing and PLP1 to exit these vacuoles and avoid degradation by host lysosomes. Next, parasites enter the MJ-dependent PV, which has a different membrane composition, precluding lysosome fusion. The malaria parasite has thus evolved different strategies to evade host cell defense and establish an intracellular niche for replication.

The prediction of Weyl fermions in the low-temperature noncentrosymmetric $1{T}^{\ensuremath{'}}$ phase of ${\mathrm{MoTe}}_{2}$ still awaits clear experimental confirmation. Here, we report angle-resolved photoemission (ARPES) data and ab initio calculations that reveal a surface state arc dispersing between the valence and the conduction band, as expected for a Weyl semimetal. However, we find that the arc survives in the high-temperature centrosymmetric $1{T}^{\ensuremath{'}\ensuremath{'}}$ phase. Therefore, a surface Fermi arc is not an unambiguous fingerprint of a topologically nontrivial phase. We have also investigated the surface state spin texture of the $1{T}^{\ensuremath{'}}$ phase by spin-resolved ARPES, and identified additional topologically trivial spin-split states within the projected band gap at higher binding energies.

Physical review / B 96(24), 241408 (2017). doi:10.1103/PhysRevB.96.241408, $MoTe_2$ has recently been shown to realize in its low-temperature phase the type-II Weyl semimetal (WSM). We investigated by time- and angle- resolved photoelectron spectroscopy (tr-ARPES) the possible influence of the Weyl points on the electron dynamics above the Fermi level $E_F$, by comparing the ultrafast response of $MoTe_2$in the trivial and topological phases. In the low-temperature WSM phase, we report an enhanced relaxation rate of electrons optically excited to the conduction band, which we interpret as a fingerprint of the local gap closure when Weyl points form. By contrast, we find that the electron dynamics of the related compound $WTe_2$is slower and temperature independent, consistent with a topologically trivial nature of this material. Our results shows that tr-ARPES is sensitive to the small modifications of the unoccupied band structure accompanying the structural and topological phase transition of $MoTe_2$., Published by Inst., Woodbury, NY

The electronic structure of ZrTe5 has been matter of renewed interest aimed at clarifying, along with its topological character, the temperature dependence of the unusual transport properties of this material. Here, we report an extensive high resolution Angle Resolved Photoelectron Spectroscopy (ARPES) study unveiling a non-monotonic shift of the bands, when the sample temperature is varied between 16 K and 300 K. Moreover, the present conventional ARPES and circularly dichroic ARPES measurements reveal the presence of two states at the top of the valence band. The strong ARPES dichroic signal detected in proximity of the Fermi energy has been interpreted as the indication of the presence of spin polarized states, in agreement with the predicted strong topological character of this material. published

Summary Plasmodium sporozoites are transmitted by Anopheles mosquitoes and first infect the liver of their mammalian host, where they develop as liver stages before the onset of erythrocytic infection and malaria symptoms. Sporozoite entry into hepatocytes is an attractive target for anti-malarial prophylactic strategies but remains poorly understood at the molecular level. Apicomplexan parasites invade host cells by forming a parasitophorous vacuole that is essential for parasite development, a process that involves secretion of apical organelles called rhoptries. We previously reported that the host membrane protein CD81 is required for infection by Plasmodium falciparum and Plasmodium yoelii sporozoites. CD81 acts at an early stage of infection, possibly at the entry step, but the mechanisms involved are still unknown. To investigate the role of CD81 during sporozoite entry, we generated transgenic P. yoelii parasites expressing fluorescent versions of three known rhoptry proteins, RON2, RON4 and RAP2/3. We observed that RON2 and RON4 are lost following rhoptry discharge during merozoite and sporozoite entry. In contrast, our data indicate that RAP2/3 is secreted into the parasitophorous vacuole during infection. We further show that sporozoite rhoptry discharge occurs only in the presence of CD81, providing the first direct evidence for a role of CD81 during sporozoite productive invasion.

Summary Plasmodium sporozoites are transmitted by mosquitoes and first infect hepatocytes of their mammalian host, wherein they develop as liver stages, surrounded by the parasitophorous vacuole membrane (PVM). The parasite must rapidly adapt to its changing environment after switching host. Shortly after invasion, the PVM is remodelled by insertion of essential parasite proteins of the early transcribed membrane protein family such as UIS4. Here, using the rodent malaria model Plasmodium berghei, we show that transcripts encoding UIS4 are stored in a translationally repressed state in sporozoites, allowing UIS4 protein synthesis only after host cell invasion. Using a series of reporter transgenic parasite lines we could demonstrate that the open reading frame of UIS4 mRNA is critical for gene silencing, whereas the 5′ and 3′ untranslated regions are dispensable. Our data further indicate that the UIS4 translational repression machinery is present only in mature sporozoites in the mosquito salivary glands, and that premature expression of UIS4 protein results in a loss of parasite infectivity. Our findings reveal the importance of specific post-transcriptional control in sporozoites, and establish that host switch requires high levels of translationally silent UIS4 RNA, which permits stage conversion, yet avoids premature expression of this liver stage-specific protein.

Scientific reports 6, 38796 (2016). doi:10.1038/srep38796, In the past few years, we have been witnessing an increased interest for studying materials properties under non-equilibrium conditions. Several well established spectroscopies for experiments in the energy domain have been successfully adapted to the time domain with sub-picosecond time resolution. Here we show the realization of high resolution resonant inelastic X-ray scattering (RIXS) with a stable ultrashort X-ray source such as an externally seeded free electron laser (FEL). We have designed and constructed a RIXS experimental endstation that allowed us to successfully measure the d-d excitations in KCoF3 single crystals at the cobalt M$_{2,3}$-edge at FERMI FEL (Elettra-Sincrotrone Trieste, Italy). The FEL-RIXS spectra show an excellent agreement with the ones obtained from the same samples at the MERIXS endstation of the MERLIN beamline at the Advanced Light Source storage ring (Berkeley, USA). We established experimental protocols for performing time resolved RIXS experiments at a FEL source to avoid X ray-induced sample damage, while retaining comparable acquisition time to the synchrotron based measurements. Finally, we measured and modelled the influence of the FEL mixed electromagnetic modes, also present in externally seeded FELs, and the beam transport with ~120 meV experimental resolution achieved in the presented RIXS setup., Published by Nature Publishing Group, London

The complex electronic properties of ${\mathrm{ZrTe}}_{5}$ have recently stimulated in-depth investigations that assigned this material to either a topological insulator or a 3D Dirac semimetal phase. Here we report a comprehensive experimental and theoretical study of both electronic and structural properties of ${\mathrm{ZrTe}}_{5}$, revealing that the bulk material is a strong topological insulator (STI). By means of angle-resolved photoelectron spectroscopy, we identify at the top of the valence band both a surface and a bulk state. The dispersion of these bands is well captured by ab initio calculations for the STI case, for the specific interlayer distance measured in our x-ray diffraction study. Furthermore, these findings are supported by scanning tunneling spectroscopy revealing the metallic character of the sample surface, thus confirming the strong topological nature of ${\mathrm{ZrTe}}_{5}$.

International audience; SmB6 is a mixed valence Kondo system resulting from the hybridization between localized f electrons and delocalized d electrons. We have investigated its out-of-equilibrium electron dynamics by means of time- and angle-resolved photoelectron spectroscopy. The transient electronic population above the Fermi level can be described by a time-dependent Fermi-Dirac distribution. By solving a two-temperature model that well reproduces the relaxation dynamics of the effective electronic temperature, we estimate the electron-phonon coupling constant lambda to range from 0.13 +/- 0.03 to 0.04 +/- 0.01. These extremes are obtained assuming a coupling of the electrons with either a phonon mode at 10 or 19 meV. A realistic value of the average phonon energy will give an actual value of lambda within this range. Our results provide an experimental report on the material electron-phonon coupling, contributing to both the electronic transport and the macroscopic thermodynamic properties of SmB6.

The quest for investigating the non-equilibrium dynamics of the band structure of strongly-correlated materials over their entire Brillouin zone is a primary objective. However, the actual ultrafast UV light sources are not suitable for addressing several critical questions in the field. Here we report on a novel light source generating sub-250 fs, 9.3 eV photon energy light pulses at 250 kHz repetition rate, obtained via third-harmonic generation in Xe of frequency-doubled 50 fs laser pulses at 1.55 eV. By reporting the measured band dispersion of a Cu(111) crystal and the non-equilibrium dynamics of the Bi2Se3 topological insulator, we prove that this source is suitable for studying the non-equilibrium dynamics of the entire Fermi surface of several complex materials, with high signal statistics and limited space-charge effect. (C) 2015 Elsevier B.V. All rights reserved.

International audience; Experimental genetics have been widely used to explore the biology of the malaria parasites. The rodent parasites Plasmodium berghei and less frequently P. yoelii are commonly utilised, as their complete life cycle can be reproduced in the laboratory and because they are genetically tractable via homologous recombination. However, due to the limited number of drug-selectable markers, multiple modifications of the parasite genome are difficult to achieve and require large numbers of mice. Here we describe a novel strategy that combines positive-negative drug selection and flow cytometry-assisted sorting of fluorescent parasites for the rapid generation of drug-selectable marker-free P. berghei and P. yoelii mutant parasites expressing a GFP or a GFP-luciferase cassette, using minimal numbers of mice. We further illustrate how this new strategy facilitates phenotypic analysis of genetically modified parasites by fluorescence and bioluminescence imaging of P. berghei mutants arrested during liver stage development.

Plasmodium sporozoites are transmitted by Anopheles mosquitoes and first infect the liver of their mammalian host, where they develop as liver stages before the onset of erythrocytic infection and malaria symptoms. Sporozoite entry into hepatocytes is an attractive target for anti-malarial prophylactic strategies but remains poorly understood at the molecular level. Apicomplexan parasites invade host cells by forming a parasitophorous vacuole that is essential for parasite development, a process that involves secretion of apical organelles called rhoptries. We previously reported that the host membrane protein CD81 is required for infection by Plasmodium falciparum and Plasmodium yoelii sporozoites. CD81 acts at an early stage of infection, possibly at the entry step, but the mechanisms involved are still unknown. To investigate the role of CD81 during sporozoite entry, we generated transgenic P. yoelii parasites expressing fluorescent versions of three known rhoptry proteins, RON2, RON4 and RAP2/3. We observed that RON2 and RON4 are lost following rhoptry discharge during merozoite and sporozoite entry. In contrast, our data indicate that RAP2/3 is secreted into the parasitophorous vacuole during infection. We further show that sporozoite rhoptry discharge occurs only in the presence of CD81, providing the first direct evidence for a role of CD81 during sporozoite productive invasion.

The relaxation dynamics of unaligned multi-walled carbon nanotubes decorated with metallic nanoparticles have been studied by using transient optical measurements. The fast dynamics due to the short-lived free-charge carriers excited by the pump are not affected by the presence of nanoparticles. Conversely, a second long dynamics, absent in bare carbon nanotubes, appears only in the decorated samples. A combination of experiment and theory allows us to ascribe this long dynamics to relaxation channels involving electronic states localized at the tube-nanoparticle interface.

The possibility to inject spin currents in topological insulators (TIs) by ultrashort optical pulses has stimulated intense studies of their out-of-equilibrium electronic properties. However, a comprehensive description of the electronic relaxation dynamics has been elusive, so far. In order to reveal the role of the bulk and surface states in the microscopic scattering mechanisms, we have investigated, by means of time- and angle-resolved photoemission spectroscopy, a wide set of TIs. These have been selected in order to display different positions of the Fermi energy (${E}_{\text{F}}$) within the bulk band structure. When three-dimensional bulk states lie at ${E}_{\text{F}}$, we observe a fast relaxation dynamics with a characteristic time scale of a few picoseconds (ps). On the contrary, a long lasting excited state is recorded when only the two-dimensional surface state crosses ${E}_{\text{F}}$. These findings suggest the important role played by spatial diffusion in the direction orthogonal to the surface in governing the relaxation mechanisms. We propose that this electron diffusive mechanism is driven by the optically induced temperature gradient that is at play only for electrons residing in bulk states.