Dark exciton anti-funneling in atomically thin semiconductors

Strain engineering can manipulate the propagation of excitons in atomically thin transition metal dichalcogenides. Here, the authors observe an anti-funnelling behavior, i.e., the exciton photoluminescence moves away from high-strain regions, and attribute it to the dominating role of propagating dark excitons. Transport of charge carriers is at the heart of current nanoelectronics. In conventional materials, electronic transport can be controlled by applying electric fields. Atomically thin semiconductors, however, are governed by excitons, which are neutral electron-hole pairs and as such cannot be controlled by electrical fields. Recently, strain engineering has been introduced to manipulate exciton propagation. Strain-induced energy gradients give rise to exciton funneling up to a micrometer range. Here, we combine spatiotemporal photoluminescence measurements with microscopic theory to track the way of excitons in time, space and energy. We find that excitons surprisingly move away from high-strain regions. This anti-funneling behavior can be ascribed to dark excitons which possess an opposite strain-induced energy variation compared to bright excitons. Our findings open new possibilities to control transport in exciton-dominated materials. Overall, our work represents a major advance in understanding exciton transport that is crucial for technological applications of atomically thin materials

Nanoantenna-Enhanced Light-Matter Interaction in Atomically Thin WS2

Atomically thin transition metal dichalcogenides (TMDCs) are an emerging class of two-dimensional semiconductors. Recently, the first optoelectronic devices featuring photodetection as well as electroluminescence have been demonstrated using monolayer TMDCs as active material. However, the lightﾖmatter coupling for atomically thin TMDCs is limited by their small absorption length and low photoluminescence quantum yield. Here, we significantly increase the lightﾖmatter interaction in monolayer tungsten disulfide (WS2) by coupling the atomically thin semiconductor to a plasmonic nanoantenna. Due to the plasmon resonance of the nanoantenna, strongly enhanced optical near-fields are generated within the WS2ﾠmonolayer. We observe an increase in photoluminescence intensity by more than 1 order of magnitude, resulting from a combined absorption and emission enhancement of the exciton in the WS2monolayer. The polarization characteristics of the coupled system are governed by the nanoantenna. The robust nanoantennaﾖmonolayer hybrid paves the way for efficient photodetectors, solar cells, and light-emitting devices based on two-dimensional materials

Low-Divergence hBN Single-Photon Source with a 3D-Printed Low-Fluorescence Elliptical Polymer Microlens

Efficiently collecting light from single-photon emitters is crucial for photonic quantum technologies. Here, we develop and use an ultralow fluorescence photopolymer to three-dimensionally print micrometer-sized elliptical lenses on individual precharacterized single-photon emitters in hexagonal boron nitride (hBN) nanocrystals, operating in the visible regime. The elliptical lens design beams the light highly efficiently into the far field, rendering bulky objective lenses obsolete. Using back focal plane imaging, we confirm that the emission is collimated to a narrow low-divergence beam with a half width at half-maximum of 2.2°. Using photon correlation measurements, we demonstrate that the single-photon character remains undisturbed by the polymer lens. The strongly directed emission and increased collection efficiency is highly beneficial for quantum optical experiments. Furthermore, our approach paves the way for a highly parallel fiber-based detection of single photons from hBN nanocrystals

Large International Validation of ABSIS and PDAI Pemphigus Severity Scores

IF 6.448 (2017)International audienceThe Pemphigus Disease Area Index (PDAI) and Autoimmune Bullous Skin Disorder Intensity-Score (ABSIS) scores have been proposed to provide an objective measure of pemphigus activity. These scores have been evaluated only on already treated patients mainly with mild to moderate activity. The objective was to assess the interrater reliability of ABSIS and PDAI scores and their correlation with other severity markers in a large international study. Consecutive patients with newly diagnosed pemphigus were enrolled in 31 centers. Severity scores were recorded during a 24-month period by the same two blinded investigators. Serum was collected at each visit for ELISA measurement of anti-desmoglein antibodies. The intraclass correlation coefficient (ICC) and Spearman rank correlation coefficient were calculated. A total of 116 patients with pemphigus vulgaris (n = 84) or pemphigus foliaceus (n = 32) were included. At baseline, the ABSIS and PDAI ICCs were 0.90 (95% confidence interval [CI] = 0.85-0.93), and 0.91(95% CI = 0.87-0.94), respectively. The ICCs for PDAI were higher in moderate and extensive pemphigus (ICC = 0.82, 95% CI = 0.63-0.92 and ICC = 0.80, 95% CI = 0.62-0.90, respectively) than in patients with intermediate (significant) extent (ICC = 0.50, 95% CI = 0.27-0.68). Conversely, the ICCs for ABSIS were lower in patients with moderate extent (ICC = 0.44, 95% CI = 0.004-0.74) than in those with intermediate or extensive forms, (ICC = 0.69, 95% CI = 0.51-0.81 and ICC = 0.75, 95% CI = 0.51-0.88, respectively). During patients' follow-up, the ICCs of both ABSIS and PDAI scores remained higher than 0.70. ABSIS and PDAI skin (r = 0.71 and r = 0.75) but not mucosal (r = 0.32 and r = 0.37) subscores were correlated with the evolution of anti-DSG1 and anti-DSG3 ELISA values, respectively. ABSIS and PDAI scores are robust tools to accurately assess pemphigus activity