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The recent field measurements of katabatic winds on steep alpine slopes provide a unique database for theoretical analysis of the mean flow development and the determination of mixing properties. The theory is based on the depth-integrated momentum and heat equations, and demonstrates an increase in mean velocity $U$ with downstream distance $x$ according to $x^{n}$ ( $n\leq 1/2$ ). An equation for the mean wind velocity is established, expressing its dependency on the buoyancy flux, related to the heat flux to the ground, entrainment and bottom friction. No ambient stratification, and ambient wind and constant ground surface temperature, lead to $U{\sim} x^{1/2}$ , while constant heat flux to the ground leads to $U{\sim} x^{1/3}$ and requires that the reduced gravity decreases as $x^{-1/3}$ . Stable ambient stratification $N$ causes, in addition to small-amplitude mean flow oscillations, a decrease in reduced gravity with $x$ , in which case the assumption of constant surface heat flux along $x$ is only an approximation. The turbulent fluxes are a function of gradient Richardson number $Ri$ with the ratio of turbulent diffusivity to viscosity $K_h/K_m$ changing from nearly $1.4$ to approximately $0.5$ at $Ri\approx 0.5$ . A new mixing efficiency is introduced that includes turbulence kinetic energy production or consumption by along-slope turbulent buoyancy flux. It increases with $Ri$ up to $0.25$ at $Ri\approx 0.5$ and then remains nearly constant. The measurements allowed us to determine the bottom drag coefficients and interfacial entrainment, with the ground surface heat flux being determined from the mean buoyancy flux.

Katabatic winds are generated by the combination of a vertical density gradient, slope and gravity, when the surface radiative budget is negative. We presently analyse some results of a campaign led in the French Alps in 2019 (Charrondière et al. 2022) in order to study katabatic flows over a steep snowy alpine slope of about 30°, that develop during winter anticyclonic conditions. In the topographic and meteorological configuration of the experiment, these downslope flows have a jet shape, with a maximum wind speed height zj very close to the surface, at about 30 cm height.A 3D pitot type sensor allowed measurements of wind speed down to 3 cm height above the surface, at a high sampling frequency of 1250 Hz. Sonic anemometers placed on a fixed bracket allowed to capture for the first time the 3D velocity of the katabatic flows (f=20 Hz) in the topographic coordinate system, whereas previous studies are in the streamline coordinate system. We focus mainly on the inner region of the jet, below zj. The turbulent momentum flux is decreasing with height, and its variation can be derived from a simplification of the along-slope momentum equation where the gravity term balances the turbulent momentum flux gradient to first order, as shown in Denby and Smeets (2000).We compare the inner region of the jet with a neutral turbulent boundary layer in terms of wind speed profile, and derive a correction of the classical log-law that considers the gravity effect on the along-slope velocity. This correction is different from the well-known Monin-Obukhov stability correction, which is negligible for the present flow because of relative low turbulent sensible heat fluxes compared to turbulent momentum fluxes.We also show that the slope-normal velocity is negative and as high as 10-15% of the maximum wind speed in the inner region of the jet. The slope-normal momentum equation behavior in this region of the jet is consistent with the observations and confirms that a gravity source term directs the flow to the ground. We finally analyze the impact of gravity on the temperature equation: the mean temperature profile and the turbulent sensible heat flux are also modified by it. All these modifications have implications on the turbulent Prandtl number, which behaves differently from what we expect on a neutral turbulent boundary layer cooled at the surface.Charrondière, C., Brun, C., Cohard, JM. et al. Katabatic Winds over Steep Slopes: Overview of a Field Experiment Designed to Investigate Slope-Normal Velocity and Near-Surface Turbulence. Boundary-Layer Meteorol 182, 29–54 (2022). Denby B, Smeets CJPP (2000) Derivation of turbulent flux profiles and roughness lengths from katabatic flow dynamics. Journal of Applied Meteorology 39(9):1601–1612

We describe a new field campaign over a steep, snowy $$30^{\circ }$$ alpine slope, designed to investigate three recurrent issues in experimental studies of steep-slope katabatic winds. (1) Entrainment is known to be present in katabatic jets and has been estimated at the interface between the jet and the boundary layer above it. However, to our knowledge, the slope-normal velocity component has never been measured in the katabatic jet. (2) It is hard to accurately measure turbulence in the first tens of centimetres above the surface using standard sonic anemometry due to the filtering effect of the long instrument path. The present field experiment used a three-dimensional multi-hole pitot-type probe with a high sampling frequency (1250 Hz) that was positioned as close to the surface as 3 cm. It provides three-dimensional mean velocity and Reynolds stress tensor from which dissipation can be estimated, as well as spectra for the turbulent quantities. Energy spectra reveal a well-developed inertial range and capture the inertial scales and some of the dissipative scales. (3) Measuring turbulence on a mast usually provides information about mean and turbulent quantities at certain discrete heights because the sensors are sparsely located inside the jet. We present the first measurements of well-developed katabatic flows where the full wind-speed and temperature profiles acquired, from tethered balloon are available at the location of the measurement mast, which comprises three-dimensional anemometry and thermometry.

We report on structural and electronic properties of superconducting nanohybrids made of Pb grown in the ultrahigh vacuum on the atomically clean surface of single crystals of topological Bi2Te3. In situ scanning tunneling microscopy and spectroscopy demonstrated that the resulting network is composed of Pb-nanoislands dispersed on the surface and linked together by an amorphous atomic layer of Pb, which wets Bi2Te3. As a result, the superconducting state of the system is characterized by a thickness-dependent superconducting gap of Pb-islands and by a very unusual position-independent proximity gap between them. Furthermore, the data analysis and DFT calculations demonstrate that the Pb-wetting layer leads to significant modifications of both topological and trivial electronic states of Bi2Te3, which are responsible for the observed long-range proximity effect.

We report on structural and electronic properties of superconducting nanohybrids made of Pb grown in the ultrahigh vacuum on the atomically clean surface of single crystals of topological Bi

We present an experimental and numerical study of the turbulent boundary layer at $$1200< Re_{\theta}

International audience; We present results from a highly resolved large-eddy simulation of a freely developing Blasius profile over a concave boundary in a large spanwise domain. Due to the large initial Reynolds and Görtler numbers (Reθ,0 = 1175, Gθ,0 = 75), we observe the onset of two dominant wavelengths: the first dominating in the linear/transition region, λ1, and the second dominating in the turbulent region, λ2. Extending previous linear stability analysis (LSA) to higher Görtler numbers and non-dimensional wavenumbers, both dominant wavelengths of the Görtler instability correspond to predictions of LSA, the latter comparable to laminar theory by replacing the kinematic viscosity with the turbulent viscosity in the definition of the Görtler number. The predicted spatial modes compare well with the computed profiles for both λ1 and λ2. The skin friction coefficient Cf is found heterogeneous in the spanwise direction according to the emerging wavelengths λ1 and λ2 of the Görtler instability. We report a smooth increase in Cf from the theoretical predictions of a laminar boundary layer to those for a turbulent boundary layer over a flat plate. The values only slightly overshoot these predictions in the domain of existence of the second dominant wavelength λ2, very different from that reported at lower Reynolds numbers.

International audience; Transition metal dichalcogenides (TMDs) display a rich variety of instabilities such as spin and charge orders, Ising superconductivity, and topological properties. Their physical properties can be controlled by doping in electric double‐layer field‐effect transistors (FET). However, for the case of single layer NbSe2, FET doping is limited to ≈1 × 1014 cm−2, while a somewhat larger charge injection can be obtained via deposition of K atoms. Here, by performing angle‐resolved photoemission spectroscopy, scanning tunneling microscopy, quasiparticle interference measurements, and first‐principles calculations it is shown that a misfit compound formed by sandwiching NbSe2 and LaSe layers behaves as a NbSe2 single layer with a rigid doping of 0.55–0.6 electrons per Nb atom or ≈6 × 1014 cm−2. Due to this huge doping, the 3 × 3 charge density wave is replaced by a 2 × 2 order with very short coherence length. As a tremendous number of different misfit compounds can be obtained by sandwiching TMDs layers with rock salt or other layers, this work paves the way to the exploration of heavily doped 2D TMDs over an unprecedented wide range of doping.

Hybrid interfaces where organic molecules are adsorbed on metallic substrates are very interesting to understand the fundamental interactions that might modify the chemical-physical properties of molecules or substrate. Here, we explore the adsorption of manganese phthalocyanines (MnPcs) on different structural phases of a Pb monatomic layer, namely, the √7 × √3-Pb and the striped incommensurate phase (SIC-Pb) phase, grown on Si(111). Surprisingly, the deposition of a minute amount of MnPc molecules (∼0.18 molecules/100 nm2) nucleates a macroscopic structural transition of the √7 × √3-Pb phase into the SIC-Pb phase. Our combined scanning tunneling microscopy, low-energy electron diffraction, and density functional theory study revealed that the mechanism behind this surface transformation is related to a strong and local molecule-substrate interaction. The structural phase transition is finally driven by the strained nature of the Pb phases and the energetic stability of the MnPc/SIC-Pb/Si(111) system with respect to the MnPc/√7 × √3-Pb/Si(111) one. The molecule-substrate interaction found in the present study is stronger than the one observed on Pb(111) bulk or thin films, highlighting the implication of the Pb/Si(111) interface in the interaction process. Hence, our results reveal that playing with the substrate dimensionality to tune the molecule-substrate coupling has strong impact on the electronic/magnetic properties of organic hybrid systems., We gratefully acknowledge F. Thibout (Kastler Brossel Laboratory) for the realization of the glass crucibles used during the experiments of this study. N.L. gratefully acknowledges financial support from the Spanish MICINN (project RTI2018-097895-B-C44) and FEDER funds. N.W. gratefully acknowledges the financial support of Labex Matisse and Investissement d’Avenir. C.B. gratefully acknowledges financial support from the French ANR Rodesis (project ANR-16-CE30-0011-01). The computational work was granted access to the HPC resources of GENCI (TGCC and CINES) under Grant No. A0050807364.

Katabatic winds are gravity flows that develop over sloping terrain due to radiative cooling at the surface. They have been extensively studied, but experimental works have generally been performed over gentle slopes. Some recent papers (eg. [3]) focused on the combined effect of surface angle and buoyancy on turbulence over steep slopes. In such configurations, the vertical component of the turbulent sensible heat flux may differ a lot from the slope-normal component, suggesting that buoyancy may act on turbulent quantities in an unusual way when katabatic jets develop over steep slopes. Such behavior seems to affect stability parameters used in Monin-Obukhov similarity theory applied in most meteorological models.We study the buoyancy production term in the continuity of the work from [3], drawing on temperature and wind speed measurements acquired during 10 nights in November 2012 [1]. In situ measurements were performed under stable anticyclonic conditions, over an alpine slope of around 21° (French Alps) on a 4 level mast up to 6.5m, at a frequency sampling of 10 to 20Hz.We conclude that turbulent kinetic energy and turbulent momentum flux are damped below the maximum wind speed height as expected from stably stratified atmospheric boundary layer. Conversely, turbulent kinetic energy can be locally reinforced by buoyancy in the external part of the katabatic jet, which confirms the results from [3]. Buoyancy may also produce turbulent momentum flux around the maximum wind speed due to the asymmetry of the jet. Results compare well with recent numerical modeling of a katabatic jet along a curved alpine slope under similar meteorological conditions [2].Another field experiment took place during 16 nights in February 2019, over a snow-covered slope of around 34° in a similar location. The 11 wind speed levels and 17 temperature levels up to 12m, associated with a change of the surface level due to packing and melting of the snow, widen the range of analysis of the vertical profile. These data are associated with meteorological measurements and with a tethered balloon up to 50-100m above the ground surface.Wind velocity measurements with a multi-hole pressure probe (cobra type) close to the ground provided more information than the previous dataset at a high frequency sampling of 1250 Hz. We show that the classical turbulent boundary layer wind speed profile applies well to the inner-layer region of katabatic jets, in spite of the presence of a maximum on the vertical streamwise velocity profiles. We find no significative changes caused by buoyancy on this profile. Roughness effect due to the snow on the surface will be discussed as well.[1] Blein (2016), PhD[2] Brun et al. (2017), JAS[3] Oldroyd et al. (2016), BLM

We study the unconventional superconducting correlations caused by a single isolated magnetic impurity in a conventional s-wave superconductor. Due to the local breaking of time-reversal symmetry, the impurity induces unconventional superconductivity which is even in both space and spin variables but odd under time inversion. We derive an exact proportionality relation between the even-frequency component of the local electron density of states and the imaginary part of the odd-frequency local pairing function. By applying this relation to scanning tunneling microscopy spectra taken on top of magnetic impurities immersed in a Pb/Si(111) monolayer, we show experimental evidence of the occurrence of the odd-frequency pairing in these systems and explicitly extract its superconducting function from the data., Comment: 6 pages, 3 figures, revised version

International audience; Katabatic winds are very frequent but poorly understood or simulated over steep slopes. This study focuses on a katabatic jet above a steep alpine slope. We assess the buoyancy terms in both the turbulence kinetic energy (TKE) and the Reynolds shear stressbudgetequations.We specifically focus on the contribution of the slope-normal and along-slope turbulent sensible heat fluxes to these terms. Four levels of measurementsbelowandabovethemaximumwin - speed height enable analysis of the buoyancy effect along the vertical profile as follow: (i) buoyancy tends to destroy TKE, as expected in stable conditions, and the turbulent moment m flux in the inner-layer region of the jet below the maximum wind-speed height z j ; (ii) results also suggest buoyancy contributes to the production of TKE in the outer-layer shear region of the jet (well above z j ) while consumption of the turbulent momentum flux is observed in the same region; (iii) In the region around the maximum wind speed where mechanical shear production is marginal, buoyancy tends to destroy TKE and our results suggest it tends to increase the momentum flux. The present study also provides an analytical condition for the limit between production and consumption of the turbulent momentum flux due to buoyancy as a function of the slope angle, similar to the condition already proposed for TKE. We reintroduce the stress Richardson number, which is the equivalent of the flux Richardson number for the Reynolds shear-stress budget. We point out that the flux Richardson number and the stress Richardson number are complementary stability parameters for characterizing the katabatic flow apart from the region around the maximum wind-speed height.

Majorana zero modes are fractional quantum excitations appearing in pairs, each pair being a building block for quantum computation. Some signatures of Majorana zero modes have been reported at endpoints of one-dimensional systems, which are however required to be extremely clean. An alternative are two-dimensional topological superconductors, such as the Pb/Co/Si(111) system shown recently to be immune to local disorder. Here, we use scanning tunneling spectroscopy to characterize a disordered superconducting monolayer of Pb coupled to underlying Co-Si magnetic islands. We show that pairs of zero modes are stabilized: one zero mode positioned in the middle of the magnetic domain and its partner extended all around the domain. The zero mode pair is remarkably robust, isolated within a hard superconducting gap. Our theoretical scenario supports the protected Majorana nature of this zero mode pair, highlighting the role of magnetic or spin-orbit coupling textures., It is predicted that Majorana zero modes can appear locally around topological defects in a two-dimensional system. Here, the authors observe pairs of zero modes stabilized in the middle and around the magnetic domains in a disordered superconducting Pb monolayer.

Josephson vortices play an essential role in superconducting quantum electronics devices. Often seen as purely conceptual topological objects, 2π-phase singularities, their observation and manipulation are challenging. Here we show that in Superconductor—Normal metal—Superconductor lateral junctions Josephson vortices have a peculiar magnetic fingerprint that we reveal in Magnetic Force Microscopy (MFM) experiments. Based on this discovery, we demonstrate the possibility of the Josephson vortex generation and manipulation by the magnetic tip of a MFM, thus paving a way for the remote inspection and control of individual nano-components of superconducting quantum circuits., Josephson vortices (JVs) play an important role in superconducting quantum devices, but they remain difficult to be observed and manipulated. Here, Dremov et al. report magnetic fingerprint of JVs in magnetic force microscopy experiments, which paves a way to generate and control JVs.

There is presently a tremendous activity around the field of topological superconductivity and Majorana fermions. Among the many questions raised, it has become increasingly important to establish the topological or non-topological origin of features associated with Majorana fermions such as zero-bias peaks. Here, we compare in-gap features associated either with isolated magnetic impurities or with magnetic clusters strongly coupled to the atomically thin superconductor Pb/Si(111). We study this system by means of scanning tunneling microscopy and spectroscopy (STM/STS). We take advantage of the fact that the Pb/Si(111) monolayer can exist either in a crystal-ordered phase or in an incommensurate disordered phase to compare the observed spectroscopic features in both phases. This allows us to demonstrate that the strongly resolved in-gap states we found around the magnetic clusters in the disordered phase of Pb have a clear topological origin., 11 pages, 5 figures. To be published in European Physical Journal Special Topics.dedicated to the conference FQMT'17

International audience; An experimental study conducted in a wind tunnel on the mixing of moist air by a scaled wind turbine is presented. The experimental setupallows us to generate stable stratification conditions with respect to relative humidity and temperature in a closed-loop wind tunnel. The flowand its thermodynamic properties were characterized using a Cobra probe (a multi-hole pitot tube) and a sensor of local temperature and rel-ative humidity, both used simultaneously to obtain vertical profiles. The flow and its stratification were measured downstream of a scaledrotor at two different streamwise distances (1 and 10 rotor diameters) and two Reynolds numbers based on the diameter of the wind turbinerotor (22000 and 44000, respectively). This was then compared to the inflow conditions. The wake mean structure and the humidity andtemperature stratifications of the flow are found to be affected by the presence of the rotor. In particular, the stratification was always smallerone diameter downstream from the model (when compared to the empty test section case), and then was mostly recovered in the far wake(10 diameters downstream). This effect depended not only on the streamwise distance, but also on the Reynolds number of the flow. Finally,the bulk Richardson number R b was found to be an appropriate parameter to quantify this effect.

With their attractive intrinsic properties, such as morphology, autoassembling properties, and tailorability, nano-objects could provide alternative and innovative routes to current microelectronics and nanoelectronics. Further insight on their electrical properties, especially in terms of statistics and reproducibility, as well as on their potential integration into silicon-based electronics is, however, often required to be able to fully exploit their potential. This paper proposes an innovative approach using a generic structure allowing the study of nano-objects electrical properties. Regarding the nano-objects integration, a homogeneous approach is presented with the in situ fabrication of atomic wires as a possible planar interconnection system. A heterogeneous approach is described as well with the characterization and preliminary integration of biological material, such as deoxyribonucleic acid-based nanowires or amyloid fibers.

DNA nanotechnology is currently widely explored and especially shows promises for advanced lithography due to its ability to define nanometer scale features. We demonstrate a 9 × 14 nm(2) hole pattern transfer from DNA origami into an SiO2 layer with a sub-10-nm resolution using anhydrous HF vapor in a semiconductor etching machine. We show that the resulting SiO2 pattern inherits its shape from the DNA structure within a process time ranging from 30 to 60 s at an etching rate of 0.2 nm/s. At 600 s of etching, the SiO2 pattern meets corrosion and the overall etching reaction is blocked. These results, in addition to the entire surface coverage by magnesium occurring on the substrate at a density of 1.1 × 10(15) atom/cm(2), define a process window, fabrication rules, and limits for DNA-based lithography.

Microelectronics industry aims at pushing the scaling of MOSFET devices, with a lot of challenges to solve for front-end and back-end processes. These challenges are also new opportunities, as for co-integration between silicon components and biological objects. In particular, bio-inspired nano objects such as DNA-based nanowires and protein-based nanowires have generated a huge interest based on their promising electrical properties [1, 2] and their size at the nanoscale. They could indeed bring a rich evolution in the nanotechnology community. This paper presents a common work performed by microelectronic biology and characterization teams which aims at describing the design, and the fabrication of a characterization platform dedicated to bio-inspired objects, and the first electrical measurements acquired on amyloid fibers. The design of this characterization platform takes into account biological and microelectronic constraints. Regarding biological constraints, special attention has been paid to materials choice and device fabrication in order to be biocompatible and to enable drop deposition for both wet and dry experiments. Dedicated patterns have been designed in order to measure electrical parameters such as contact resistance and resistivity of the bio-inspired objects. Regarding the fabrication step, the characterization platform has taken advantage from microelectronic technologies, especially in terms of size (nanoscale), reproducibility and robustness taken into account the specific environment. These aspects will be further discussed in this paper, as well as the first electrical measurements. To properly understand the electrical characteristics of bio-inspired objects, one critical point is the measurement of the linear conductivity of these objects, which implies the discrimination from contact resistance. Another important point is the conduction mechanism. Table 1 presents two patterns used to investigate the conduction mechanisms. To realize a complete electrical study, we have thus decided to design specific test structures as Transmission Line Matrix (TLM) and Van der Pauw patterns, structures with a variable electrode gap, and different contact areas structures. Figure 1 shows SEM images of the electrodes fabricated with this specific layout. The inter-electrode distance has been measured at 1µm and 70µm x 70µm square pads have been obtained. The figure 2 presents a cross section view of the fabricated electrodes. Electrode thickness is equal to 200nm and the width is equal to 1.7µm. Material impact and electrochemical properties of bio-inspired objects have also been investigated. Working with biological object at the nanoscale requires further restrictions. The main constraint is the use of biocompatible material to pattern all the layers in contact with the bio-inspired object. We have decided to use (i) platinum and gold because these metals are commonly used in biological measurements, and (ii) ruthenium due to its anisotropic etching properties. Another requirement relies on back gate electrode to enable the field effect investigation of bio-inspired object. To deal with wet measurement and to control the film deposition at the desirable position we have decided to engineer further cavities. Regarding packaging solutions, standard microelectronic metallic pads have been patterned to allow automated electrical characterization. Bioelectrical investigations as electrochemistry or control atmosphere measurements require the design of an “easy to plug” device enabling drop deposition and a very simple electrical connection adapted to electrical probers. This “easy to plug” device has been fabricated including a patterned silicon die assembled with a conductive glue on a Side-brazed Ceramic Dual In-inline Package (SCDIP) and wire-bonding. A SCDIP has been especially chosen to be easily carried and plugged inside biological equipment such as climatic chamber and glove box. Large package have been used in order to connect the maximum of patterns but also to provide an important protein-based nanowires density on the top of the electrodes. Figure 3 presents photography picture of the characterization platform used to perform the conduction measurements in biological equipment. The figure 4 presents the first electrical signal of the bio-inspired nano object which confirms that the characterization platform has been correctly fabricated and can be able to study the electrical properties of the protein film. This papers aims at presenting more details on (i) the design, (ii) the fabrication of silicon die in clean room (iii) the packaging adapted to the biological environment and (iv) results of electrical characterization of the bio-inspired objects at the nanoscale. References [1] D. V. Lim, M. M. Simpson, E. A. Kearns et al., Clin. Microbiol. Rev., vol. 18, no. 4, pp. 583–607, Oct. 2005. [2] F. S. Ligler and J. S. Erickson, Nature, vol. 440, no. 7081, pp. 159–160, Mar. 2006. Figure 1

Vortices in quantum condensates exist owing to a macroscopic phase coherence. Here we show, both experimentally and theoretically, that a quantum vortex with a well-defined core can exist in a rather thick normal metal, proximized with a superconductor. Using scanning tunneling spectroscopy we reveal a proximity vortex lattice at the surface of 50 nm—thick Cu-layer deposited on Nb. We demonstrate that these vortices have regular round cores in the centers of which the proximity minigap vanishes. The cores are found to be significantly larger than the Abrikosov vortex cores in Nb, which is related to the effective coherence length in the proximity region. We develop a theoretical approach that provides a fully self-consistent picture of the evolution of the vortex with the distance from Cu/Nb interface, the interface impedance, applied magnetic field, and temperature. Our work opens a way for the accurate tuning of the superconducting properties of quantum hybrids., Quantum condensates may penetrate from one material to another due to the proximity effect. Here, Stolyarov et al. report the spatial evolution of quantum vortices from a superconducting Nb layer to a 50 nanometer thick diffusive metallic Cu-film, which is quite thick away from the interface.

We investigate the 1/3 monolayer α-Pb/Si(111) surface by scanning tunneling spectroscopy (STS) and fully relativistic first-principles calculations. We study both the high-temperature sqrt[3]×sqrt[3] and low-temperature 3×3 reconstructions and show that, in both phases, the spin-orbit interaction leads to an energy splitting as large as 25% of the valence-band bandwidth. Relativistic effects, electronic correlations, and Pb-substrate interaction cooperate to stabilize a correlated low-temperature paramagnetic phase with well-developed lower and upper Hubbard bands coexisting with 3×3 periodicity. By comparing the Fourier transform of STS conductance maps at the Fermi level with calculated quasiparticle interference from nonmagnetic impurities, we demonstrate the occurrence of two large hexagonal Fermi sheets with in-plane spin polarizations and opposite helicities.

International audience; The quantum coupling of fully different degrees of freedom is a challenging path towards new functionalities for quantum electronics [1–3]. Here we show that the localized classical spin of a magnetic atom immersed in a superconductor with a two-dimensional electronic band structure gives rise to a long range coherent magnetic quantum state. We experimentally evidence coherent bound states with spatially oscillating particle-hole asymmetry extending tens of nanometers from individual iron atoms embedded in a 2H-NbSe 2 crystal. We theoretically elucidate how reduced dimensionality enhances the spatial extent of these bound states and describe their energy and spatial structure. These spatially extended magnetic states could be used as building blocks for coupling coherently distant magnetic atoms in new topological superconducting phases [4–11].

Large-eddy simulation is performed to study a katabatic jet along a convexly curved slope with a maximum angle of about 35.5°. The design of this numerical simulation of turbulent shear flow is discussed, and a qualitative assessment of the method is proposed. The katabatic flow is artificially generated by ground surface cooling, and a stable atmospheric boundary layer with constant stratification is considered as a reference state. A quantitative statistical analysis is used to describe the present turbulent flow, with a focus on the outer-layer shear of the katabatic jet, which extends about 50 m above the jet maximum. The Prandtl model for a katabatic jet is applied to the present results, and revisited versions of the model found in the literature are discussed, with an emphasis on specific momentum and turbulent heat diffusion. The vertical and downslope variability of the turbulent kinetic energy budget is also discussed, and it is shown that advection and production contributions in the downslope direction are far from negligible in katabatic flows along curved slopes. A specific effect that the convex curvature has on the katabatic jet is one of centrifugal deceleration and an increase of the flow’s turbulent production and turbulent intensity in the outer-layer shear. A strong thickening of the outer layer is also observed.

International audience; Metallic conductive nanowires (NWs) with DNA bundle core are achieved, thanks to an original process relying on double-stranded DNA alignment and physical vapor deposition (PVD) metallization steps involving a silicon substrate. First, bundles of DNA are suspended with a repeatable process between 2 aem high parallel electrodes with separating gaps ranging from 800 nm to 2 mu m. The process consists in the drop deposition of a DNA lambda-phage solution on the electrodes followed by a naturally evaporation step. The deposition process is controlled by the DNA concentration within the buffer solution, the drop volume, and the electrode hydrophobicity. The suspended bundles are finally metallized with various thicknesses of titanium and gold by a PVD e-beam evaporation process. The achieved NWs have a width ranging from a few nanometers up to 100 nm. The electrical behavior of the achieved 60 and 80 nm width metallic NWs is shown to be Ohmic and their intrinsic resistance is estimated according to different geometrical models of the NW section area. For the 80 nm width NWs, a resistance of about few ohms is established, opening exploration fields for applications in microelectronics.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

International audience

International audience

International audience; The purpose of this review is to focus from an experimental point-of-view on the new physical properties of some of the thinnest superconducting films that can be fabricated and studied in situ nowadays with state-of-the-art methods. An important characteristic of the films we address is that the underlying electronic system forms a two-dimensional electron gas (2DEG). Up to now there are only few of these systems. Such true 2D superconductors can be divided into two classes: surface-confined or interface-confined films. Because the second types of films are burried below the surface, they are not accessible to purely surface-sensitive techniques like angular-resolved photoemission spectroscopy (ARPES) or scanning tunneling spectroscopy (STS). As a consequence the bandstructure characteristics of the 2DEG cannot be probed nor the local superconducting properties. On the other hand, in situ prepared surface-confined films are nowadays accessible not only to ARPES and STS but also to electrical transport measurements. As a consequence surface-confined systems represent at present the best archetypes on which can be summarized the new properties emerging in ultimately thin superconducting films hosting a 2DEG, probed by both macroscopic and microscopic measurement techniques. The model system we will widely refer to consists of a single atomic plane of a conventional superconductor, like for example lead (Pb), grown on top of a semiconducting substrate, like Si(111). In the introductory part 1 we first introduce the topic and give historical insights into this field. Then in the section 2, we introduce useful concepts worked out in studies of so-called 'granular' and 'homogeneous' superconducting thin films that will be necessary to understand the role of non-magnetic disorder on 2DEG superconductors. In this section, we also briefly review the superconducting properties of crystalline Pb/Si(111) ultrathin films grown under ultrahigh vacuum (UHV) conditions in order to illustrate their specific properties related to quantum-size effects. In the next section 3 we review the growth methods and structural properties of the presented 2DEG surface-confined superconductors. In section 4, we review the electronic structure and Fermi surface properties as measured by macroscopic ARPES and confront them to ab initio DFT calculations based on the characterized atomic structures of the monolayers. The following section 5 reviews the macroscopic properties inferred from in situ electrical transport measurements methods, including attempts to study the Berezinsky–Kosterlitz–Thouless 2D regime. In the last section 6, we summarize the emerging local spectroscopic properties measured by STS. These latter demonstrate variations of the local superconducting properties at a scale much shorter than the superconducting coherence length due to a combined effect of non-magnetic disorder and two-dimensionality. Further peculiar local spectroscopic effects are presented giving evidence for the presence of a mixed singlet-triplet superconducting order parameter induced by the presence of a strong Rashba spin–orbit coupling term at the surface. These local signatures will be discussed along with ARPES and transport measurements in parallel high magnetic field on closely related systems. Finally, we present in anisotropic Pb and In monolayers the peculiar role played by atomic steps on vortex properties, leading to the observation by STS of mixed Abrikosov–Josephson vortices in agreement with in situ macroscopic transport measurements. From the overview of all recent experimental and theoretical results it appears that these surface 2D superconductors, such as one monolayer of Pb on Si(111), are ideal templates to engineer and realize topological superconductivity.

This article presents the formal design of a functional algorithm which computes the convex hull of a finite set of points incrementally. This algorithm, specified in Coq, is then automatically extracted into an OCaml program which can be plugged into an interface for data input (point selection) and graphical visualization of the output. A formal proof of total correctness, relying on structural induction, is also carried out. This requires to study many topologic and geometric properties. We use a combinatorial structure, namely hypermaps, to model planar subdivisions of the plane. Formal specifications and proofs are carried out in the Calculus of Inductive Constructions and its implementation: the Coq system.

Carbon nanotubes (CNTs) are a unique group of materials with high aspect ratio, mechanical and electrical properties, which are of great interests in the field of interconnects, and radio frequency applications. In order to incorporate CNTs into any of these applications successfully, one important issue that has to be resolved is the critical parameters (temperature and reactant gases) associated with the growth of the CNTs. As such, the effect of these growth requirements on the adjacent components should be studied. In this work, we examined specifically the effect of carbon nanotubes growth on the underlying metallization, in particular gold, dedicated for radio-frequency-based applications. The gold coplanar lines were annealed at 800°C in a plasma-enhanced chemical vapor deposition (PECVD) system to simulate the worst-case condition. The reflection and transmission parameters were analyzed using a probe station connected to a vector network analyzer. Carbon nanotubes grown on different barrier layers were also characterized using a scanning electron microscope and Raman spectroscopy to identify a suitable barrier layer for gold. Our results showed that it is promising to integrate carbon nanotubes grown using PECVD onto Au coplanar waveguide without degrading the S-parameters measurements up to 20 GHz.

The synthesis of two novel glycosyl-nucleoside fluorinated amphiphiles (GNFs) derived from the 2H,2H,3H,3H-perfluoro-undecanoyl hydrophobic chain is described. The GNF amphiphiles, which feature either β- d -glucopyranosyl or β- d -lactopyranosyl moieties linked to a thymine base via a 1,2,3 triazole linker, were prepared using a ‘double click’ chemistry route. Surface tension measurements, gelation properties, and TEM studies show that GNFs spontaneously assemble into supramolecular structures. Similarly to their hydrocarbon analogues (GNLs), the GNFs have unique gelation properties in water. A minimum hydrogelation concentration of 0.1% (w/w), was determined in the case of the β- d -glucopyranosyl derivative. Cell viability studies indicate that fluorocarbon GNF 5 was not toxic for human cells (Huh7), whereas hydrocarbon analogue GNL is toxic above 100 μm.

Large Eddy Simulations of a constant-density flow carrying a passive scalar around a square cylinder at Reynolds numbers Re = 1000 and Re = 1500 are performed. We describe the three-dimensional topology of the turbulent flow in terms of intense longitudinal counter-rotating coherent vortices. We show also a change of regime concerning spanwise Kelvin–Helmholtz (KH) vortices. At the lower Reynolds number, they roll up downstream of the obstacle to form the von Karman vortex street (VK). At higher Reynolds, they form immediately in the separating shear layer on the two sides of the cylinder. The role of vortices in the passive-scalar mixing is also looked at. To cite this article: C. Brun, T. Goossens, C. R. Mecanique 336 (2008).

The microscopic nature of an insulating state in the vicinity of a superconducting state, in the presence of disorder, is a hotly debated question. While the simplest scenario proposes that Coulomb interactions destroy the Cooper pairs at the transition, leading to localization of single electrons, an alternate possibility supported by experimental observations suggests that Cooper pairs instead directly localize. The question of the homogeneity, granularity, or possibly glassiness of the material on the verge of this transition is intimately related to this fundamental issue. Here, by combining macroscopic and nano-scale studies of superconducting ultrathin NbN films, we reveal nanoscopic electronic inhomogeneities that emerge when the film thickness is reduced. In addition, while thicker films display a purely two-dimensional behaviour in the superconducting fluctuations, we demonstrate a zero-dimensional regime for the thinner samples precisely on the scale of the inhomogeneities. Such behavior is somehow intermediate between the Fermi and Bose insulator paradigms and calls for further investigation to understand the way Cooper pairs continuously evolve from a bound state of fermionic objects into localized bosonic entities., 29 pages 9 figures

Les conditions anticycloniques hivernales (ciel clair, nuits froides) conduisent a la formation de couches stables persistantes qui favorisent les episodes de pollution, particulierement en terrain montagneux. La vallee de l’Arve est tres sensible a ce phenomene, en particulier pres de la ville de Passy (Haute-Savoie), situee a 20 kilometres en aval de Chamonix-Mont-Blanc, ou la qualite de l’air est l’une des moins bonnes de France. Au-dela du suivi de la qualite de l’air, tel que realise par Atmo Auvergne-Rhone-Alpes ou par le projet DECOMBIO pilote par l’Institut des Geosciences et de l’Environnement (IGE), il est primordial d’ameliorer la connaissance de la dynamique atmospherique a l’echelle de la vallee en conditions stables pour mieux comprendre comment, couplee au cycle et a la geographie des emissions, elle pilote la dispersion des polluants. C’est la motivation du projet Passy, initie en 2014. Ce projet s’appuie sur les observations de la campagne Passy-2015, presentees dans cet article avec quelques premiers resultats. L’objectif general de cette campagne est de documenter la dynamique atmospherique au sein de la vallee de l’Arve lors des episodes de pollution hivernale. Les travaux menes dans le cadre du projet et de l’analyse des donnees de la campagne s’inscrivent au sein d’une collaboration sur plusieurs annees entre les differents partenaires. Ils contribueront a affiner la prevision du temps et de la qualite de l’air dans ce type de vallee, et plus generalement en conditions stables. Il s’agit en particulier d’ameliorer la capacite a prevoir des phenomenes critiques, comme les temperatures minimales, le verglas, le brouillard, les evenements de pollution ou encore les zones de pollution intense.

A new extended inner scaling is proposed for the wall layer of wall-bounded flows under the influence of both wall shear stress and streamwise pressure gradient. This scaling avoids problems of the classical wall coordinates close to flow separation and reattachment. Based on the proposed extended velocity and length scales a universal nondimensional family of velocity profiles is derived for the viscous region in the vicinity of a wall that depend on wall distance and a parameter α quantifying the importance of the streamwise pressure gradient with respect to the wall shear stress in the momentum balance. The performance of the proposed extended scaling is investigated in two different flow fields, a separating and reattaching turbulent boundary layer and a turbulent flow over a periodic arrangement of smoothly contoured hills. Both flows are results of highly resolved direct numerical simulation (DNS). The results show that the viscous assumptions are valid up to about two extended wall units. If the profiles are scaled by the extended inner coordinates, they seem to behave in a universal way. This gives rise to the hope that a universal behavior of velocity profiles can be found in the proposed extended inner coordinates even beyond the validity of the extended viscous law of the wall.

Inhomogenities of the b* surface component of the CDW wave vector, probed by LT-UHV-STM, were observed at the (-201) surface of quasi-1D blue bronze Rb0.3MoO3cleaved in-situ. Whereas on the scale of tens of nanometers, the CDW wave vector might be constant, significant changes were observed on the scale of microns in STM measurement. On the basis of first-principles DFT calculations, it is found that these inhomogenities could be due to a change in the stoichiometry of surface alkali atoms taking place after the cleavage process. It is shown that differences in the stoichiometry of surface alkali atoms change the filling of the partially filled bands of the top most layer. Consequently, in equilibrium with the bulk layers, this results in a local surface potential that changes the surface nesting vector and hence the periodicity of the CDW modulation. The DFT predictions for the changes in surface nesting vector are consistent with the observed experimental inhomogenities probed by STM.

The paper presents near-wall scaling in incompressible and compressible flows. It concen- trates on flows with streamwise pressure gradients which render traditional scaling inapplicable. For incompressible flows a scaling for the velocity profiles is introduced based on both the friction velocity and the pressure gradient. For compressible flows a scaling is developed for the velocity and the tem- perature. This scaling is based on wall friction, pressure gradient and wall heat flux. We define two new parameters α and β where α defines a measure for the ratio between wall friction and pressure gra- dient and β defines the ratio between wall heat flux and pressure gradient. For zero pressure gradient flows the traditional scaling is recovered. A priori tests are performed by means of Direct Numerical Simulations (DNS). The compressible scaling is analyzed on channel flow with non-adiabatic walls and adverse pressure gradient. The incompressible scaling is analyzed on channel flow with periodic hill constrictions. Finally a wall model based on the new scaling is tested a posteriori by means of Large Eddy Simulation (LES).

We have studied the superconducting state of 2H−NbSe2 by scanning tunneling spectroscopy along two different crystal orientations, the c and the a/b axes. Along the c axis a large gap is dominant in the spectra, while a smaller gap is measured along the a/b axis. We show that these spectra are accurately described by the McMillan model where the small gap is induced through the coupling to the band associated with the large gap. In order to assign the small and large gaps to specific parts of the 2H−NbSe2 Fermi surface, the electronic structure was studied using first-principles calculations. While we cannot exclude the possibility of intrinsic anisotropy of the gaps, we propose that the large gap opens in the Fermi surface cylinders located around the corner K points while the sheets located around Γ are associated with the small gap. An additional component of the Fermi surface, a selenium based pocket, plays an essential role in the tunneling process. The role of the charge density wave occurring in this material is also discussed. Finally, we are able to give a coherent description of the observed characteristics of the tunneling spectra of 2H−NbSe2 as well as the differences with 2H−NbS2 where no charge density wave state is present. Further experimental work, such as high-resolution ARPES, would be very useful to confirm our interpretation. The approach and modeling developed here could also be relevant for other compounds of the dichalcogenide family.

Dans les années 1870, le mouvement anarchiste apparaît dans le paysage politique de l’Europe occidentale et de l’Amérique du Nord, où il ne cesse de s’étoffer jusqu’à la Première Guerre mondiale. Il connaît dans les années 1880, puis surtout au cours des années 1890, deux pics successifs de notoriété. Si les procès anarchistes tenus à Paris dans les années 1890-1910 ont suscité depuis longtemps une « littérature d’audiences » significative, en revanche, les enquêtes et procès des années 1880 ...

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This paper focuses on the use of CNTs for new mm-to-THz interconnects for nanopackaging. To successfully integrate CNT to be in line with nanoelectronics trends, new growth processes and modeling approaches are proposed. Several experimental works are presented such as millimeter-wave flip-chip bonding. In addition, novel THz 3-D wireless interconnect, based on CNT monopole antennas, working at 200 and 300 GHz are designed, simulated, and fabricated.

A new subgrid scale (SGS) modelling concept for large-eddy simulation (LES) of incompressible flow is proposed based on the three-dimensional spatial velocity increment δ u i . The new model is inspired by the structure function formulation developed by Metais and Lesieur [39] and applied in the context of the scale similarity type formulation. First, the similarity between the SGS stress tensor τ ij and the velocity increment tensor Q ij = δ u i δ u j is analyzed analytically and numerically using a priori tests of fully developed pipe flow at Re τ = 180. Both forward and backward energy transfers between resolved and unresolved scales of the flow are well predicted with a SGS model based on Q ij . Secondly, a posteriori tests are performed for two families of turbulent shear flows. LES of fully developed pipe flow up to Re τ = 520 and LES of round turbulent jet at Re D = 25000 carried out with a dynamic version of the model provide promising results that confirm the power of this approach for wall-bounded and free shear flows.

We report experimental results obtained on cleaved (-201) surface of Rb 0.3 MoO 3 using low temperature scanning tunnelling microscopy under ultra-high vacuum (UHV-LT-STM). Molecular resolution has been obtained at 63 K, 78 K and 300K. At low temperatures, both the molecular lattice and CDW superlattice were observed simultaneously in topographical constant current images.

Wakes, and their interaction behind two parallel cylinders lying in a plane perpendicular to the flow, have been investigated experimentally in the sub-critical Reynolds number regime. The experiments were performed in a water channel using laser Doppler velocimetry. The gap between the two cylinders was less than the cylinder diameter, a geometry referred to as strong interaction configuration. In this case the blockage is strong and a gap-jet appears between the cylinders. Two flow regimes of the near wake region have been identified: one below a critical Reynolds number Re c ∈]1000;1700[, where the gap jet is stably deflected to one side and the double near-wake becomes asymmetric; the other, above Re c, where the gap-jet deflection is unstable and a random flopping phenomenon takes place. When ReRe c, a third frequency appears in the near wake, related to the development of Kelvin-Helmholtz vortices in the separated shear layer of the cylinders [Prasad A, Williamson CHK (1997) J Fluid Mech 333:375]. The observed flopping behavior is attributed to the birth of these Kelvin-Helmholtz instabilities and their intermittent nature. Further downstream, beyond about five cylinder diameters, the random flopping flow phenomena disappear while a slightly asymmetric single wake persists. It is characterized by a Strouhal number St=0.13, a value that one would normally measure behind a single cylinder of twice its diameter.

International audience; Superconducting correlations may propagate between two superconductors separated by a tiny insulating or metallic barrier, allowing a dissipationless electric current to flow(1,2). In the presence of a magnetic field, the maximum supercurrent oscillates(3) and each oscillation corresponding to the entry of one Josephson vortex into the barrier(4). Josephson vortices are conceptual blocks of advanced quantum devices such as coherent terahertz generators(5) or qubits for quantum computing(6), in which on-demand generation and control is crucial. Here, we map superconducting correlations inside proximity Josephson junctions(7) using scanning tunnelling microscopy. Unexpectedly, we find that such Josephson vortices have real cores, in which the proximity gap is locally suppressed and the normal state recovered. By following the Josephson vortex formation and evolution we demonstrate that they originate from quantum interference of Andreev quasiparticles(8), and that the phase portraits of the two superconducting quantum condensates at edges of the junction decide their generation, shape, spatial extent and arrangement. Our observation opens a pathway towards the generation and control of Josephson vortices by applying supercurrents through the superconducting leads of the junctions, that is, by purely electrical means without any need for a magnetic field, which is a crucial step towards high-density on-chip integration of superconducting quantum devices.

With the blooming demand for wireless and mobile applications, the needs to develop existing RF technologies are increasing. For example, there is a need for RF technologies that can operate at much higher frequencies, which can be potentially used for satellite or tetra-hertz imaging applications. Thus, there is a strong interest for novel materials, which can have more reliable and stable high-frequency performance. Flip chip is one of the technology offering lower insertion loss, compact packages, and low-cost fabrication. The use of carbon nanotube (CNT) bumps to replace existing materials or applications is not unheard of. In this chapter, demonstration of a successfully CNT flip chip device at high frequency will be done. A parametric study using hybrid EM/analytical modeling of the device will be conducted.

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International audience; We have performed scanning tunneling microscopy experiments in the quasi-one dimensional charge density wave (CDW) system NbSe3, where we could image and study in detail individual solitons corresponding to the self-trapping of a single electron. Our analysis shows that the type of soliton we observed is an ``Amplitude Soliton'', characterized by a vanishing CDW amplitude at the soliton center and by a pi-shift of its phase along the chain direction. Pairs of solitons or multiple solitons were also observed. Such observations could be made only in the high-temperature COW phase. Additionally, one-dimensional Friedel oscillations around charged defects could also be imaged and are found to be superimposed to the COW. The distinction between amplitude solitons and Friedel oscillations can be made without any ambiguity. (C) 2014 Elsevier B.V. All rights reserved.