Coulomb blockade in an atomically thin quantum dot coupled to a tunable Fermi reservoir

Gate-tunable quantum-mechanical tunnelling of particles between a quantum confined state and a nearby Fermi reservoir of delocalized states has underpinned many advances in spintronics and solid-state quantum optics. The prototypical example is a semiconductor quantum dot separated from a gated contact by a tunnel barrier. This enables Coulomb blockade, the phenomenon whereby electrons or holes can be loaded one-by-one into a quantum dot. Depending on the tunnel-coupling strength, this capability facilitates single spin quantum bits or coherent many-body interactions between the confined spin and the Fermi reservoir. Van der Waals (vdW) heterostructures, in which a wide range of unique atomic layers can easily be combined, offer novel prospects to engineer coherent quantum confined spins, tunnel barriers down to the atomic limit or a Fermi reservoir beyond the conventional flat density of states. However, gate-control of vdW nanostructures at the single particle level is needed to unlock their potential. Here we report Coulomb blockade in a vdW heterostructure consisting of a transition metal dichalcogenide quantum dot coupled to a graphene contact through an atomically thin hexagonal boron nitride (hBN) tunnel barrier. Thanks to a tunable Fermi reservoir, we can deterministically load either a single electron or a single hole into the quantum dot. We observe hybrid excitons, composed of localized quantum dot states and delocalized continuum states, arising from ultra-strong spin-conserving tunnel coupling through the atomically thin tunnel barrier. Probing the charged excitons in applied magnetic fields, we observe large gyromagnetic ratios (~8). Our results establish a foundation for engineering next-generation devices to investigate either novel regimes of Kondo physics or isolated quantum bits in a vdW heterostructure platform.Comment: Published in Nature Nanotechnology. 7 pages + 14 supplementary information pages. 14 figure

Improved detection of intestinal helminth infections with a formalin ethyl-acetate-based concentration technique compared to a crude formalin concentration technique

Intestinal helminth infections are the most prevalent neglected tropical diseases, predominantly affecting rural and marginalised populations. The mainstay of diagnosis is the microscopic examination of faecal samples to detect parasites in the form of eggs, larvae and cysts. In an effort to improve the standard of care, the comparative accuracy in detecting helminth infections of the hitherto used formalin-based concentration method (FC) was compared to a previously developed formalin ethyl-acetate-based concentration technique (FECT), prior to the systematic deployment of the latter at a research and humanitarian unit operating on the Thailand-Myanmar border. A total of 693 faecal samples were available for the comparison of the two diagnostic methods. The FECT was superior in detecting hookworm, Trichuris trichiura and small liver flukes. Interestingly, there was no significant difference for Ascaris lumbricoides, possibly due to the high observed egg density. Despite the minor increase in material cost and the fact that the FECT is somewhat more time consuming, this method was implemented as the new routine technique

Application of third generation synchrotron source to studies of noncrystalline materials : In-Se amorphous films

The local structure of vacuum evaporated In-Se amorphous films, containing 50, 60, and 66 at .% Se, was studied using differential anomalous X -ray scattering and extended X -ray absorption fine structure. Both intensity and absorption spectra were measured in the vicinity of the absorption K -edge of Se. The differential anomalous X -ray scattering data were converted to real space by the inverse Fourier transform yielding the differential radial distribution functions. The obtained results provide evidence for the presence of Se-In spatial correlations for In5 0 Se50 and Se-In and Se-Se correlations for In40 Se60 and In34 Se66 within the first coordination sphere

Is phytoextraction a suitable green treatment for metal-contaminated sediments ?

International audienceThe cleaning of waterways by regular dredging generates great volumes of sediments and, owing to human activities, these sediments often contain large amounts of metals. These materials are usually spread on landfill sites. Phytoremediation could be a stategy for the reclamation of these polluted sediments. To our knowledge, phytoextraction with hyperaccumulating plants has been few tested on contaminated sediment. This work focuses on the mechanisms of Cd accumulation in Arabidopsis halleri, a Cd and Zn hyperaccumulator, and the effects of this species on a metal polluted sediment

Out-of-plane orientation of luminescent excitons in atomically thin indium selenide flakes

Van der Waals materials offer a wide range of atomic layers with unique properties that can be easily combined to engineer novel electronic and photonic devices. A missing ingredient of the van der Waals platform is a two-dimensional crystal with naturally occurring out-of-plane luminescent dipole orientation. Here we measure the far-field photoluminescence intensity distribution of bulk InSe and two-dimensional InSe, WSe$_2$ and MoSe$_2$. We demonstrate, with the support of ab-initio calculations, that layered InSe flakes sustain luminescent excitons with an intrinsic out-of-plane orientation, in contrast with the in-plane orientation of dipoles we find in two-dimensional WSe$_2$ and MoSe$_2$ at room-temperature. These results, combined with the high tunability of the optical response and outstanding transport properties, position layered InSe as a promising semiconductor for novel optoelectronic devices, in particular for hybrid integrated photonic chips which exploit the out-of-plane dipole orientation.Comment: Published in Nature Communications. 12 pages, 5 figures. Link: https://www.nature.com/articles/s41467-019-11920-

A coumaroyl-ester-3-hydroxylase insertion mutant reveals the existence of nonredundant meta-hydroxylation pathways and essential roles for phenolic precursors in cell expansion and plant growth

Cytochromes P450 monooxygenases from the CYP98 family catalyze the meta-hydroxylation step in the phenylpropanoid biosynthetic pathway. The ref8 Arabidopsis (Arabidopsis thaliana) mutant, with a point mutation in the CYP98A3 gene, was previously described to show developmental defects, changes in lignin composition, and lack of soluble sinapoyl esters. We isolated a T-DNA insertion mutant in CYP98A3 and show that this mutation leads to a more drastic inhibition of plant development and inhibition of cell growth. Similar to the ref8 mutant, the insertion mutant has reduced lignin content, with stem lignin essentially made of p-hydroxyphenyl units and trace amounts of guaiacyl and syringyl units. However, its roots display an ectopic lignification and a substantial proportion of guaiacyl and syringyl units, suggesting the occurrence of an alternative CYP98A3-independent meta-hydroxylation mechanism active mainly in the roots. Relative to the control, mutant plantlets produce very low amounts of sinapoyl esters, but accumulate flavonol glycosides. Reduced cell growth seems correlated with alterations in the abundance of cell wall polysaccharides, in particular decrease in crystalline cellulose, and profound modifications in gene expression and homeostasis reminiscent of a stress response. CYP98A3 thus constitutes a critical bottleneck in the phenylpropanoid pathway and in the synthesis of compounds controlling plant development. CYP98A3 cosuppressed lines show a gradation of developmental defects and changes in lignin content (40% reduction) and structure (prominent frequency of p-hydroxyphenyl units), but content in foliar sinapoyl esters is similar to the control. The purple coloration of their leaves is correlated to the accumulation of sinapoylated anthocyanins

FAME : A new beamline for X-ray absorption investigations of very-diluted systems of environmental, material and biological interests

International audienceFAME is the French Absorption spectroscopy beamline in Material and Environmental sciences at the ESRF (France), operational since September 2002. Technically speaking, the source is a 0.85 T bending magnet and the main optical element is a two-crystals monochromator using either Si(111) or Si(220) monocrystals so that the available energy ranges from 4 to 40 keV. The first crystal is liquid nitrogen cooled in order to avoid a thermal bump and thus preserve the energy resolution. The second crystal is dynamically bent during the energy scan in order to focus the beam in the horizontal plane. Two bendable mirrors are located before and after the monochromator, for beam-collimation (to optimize the energy resolution) and vertical focalization, respectively. During scans, the beam on the sample is kept constant in position and size (around 150 × 200 μm2, V × H). The high flux on the sample combined with the sensitivity of our 30-elements fluorescence detector allow to decrease the detection limit down to 10 ppm or around less than a monolayer. Moreover, quick-EXAFS acquisition is operational: the acquisition time may be reduced down to 30s

Extensive Copy-Number Variation of Young Genes across Stickleback Populations

MM received funding from the Max Planck innovation funds for this project. PGDF was supported by a Marie Curie European Reintegration Grant (proposal nr 270891). CE was supported by German Science Foundation grants (DFG, EI 841/4-1 and EI 841/6-1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Manslaughter by Fake Artesunate in Asia—Will Africa Be Next?

Fake artesunate could compromise the hope that artemisinin-based combination therapy offers for malaria control in Africa and Asia