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We observe and comprehend the dynamical Coulomb blockade suppression of the electrical conductance across an electronic quantum channel submitted to a temperature difference. A broadly tunable, spin-polarized Ga(Al)As quantum channel is connected on-chip, through a micron-scale metallic node, to a linear $RC$ circuit. The latter is made up of the node's geometrical capacitance $C$ in parallel with an adjustable resistance $R\in \{1/2,1/3,1/4\}\times h/e^2$ formed by 2--4 quantum Hall channels. The system is characterized by three temperatures: a temperature of the electrons in the large electrodes ($T$) and in the node ($T_\mathrm{node}$), and a temperature of the electromagnetic modes of the $RC$ circuit ($T_\mathrm{env}$). The temperature in the node is selectively increased by local Joule dissipation, and characterized from current fluctuations. For a quantum channel in the tunnel regime, a close match is found between conductance measurements and tunnel dynamical Coulomb blockade theory. In the opposite near ballistic regime, we develop a theory that accounts for different electronic and electromagnetic bath temperatures, again in very good agreement with experimental data. Beyond these regimes, for an arbitrary quantum channel set in the far out-of-equilibrium situation where the temperature in the node significantly exceeds the one in the large electrodes, the equilibrium (uniform temperature) prediction for the conductance is recovered, albeit at a rescaled temperature $\alpha T_\mathrm{node}$., Comment: Submitted

When assembling individual quantum components into a mesoscopic circuit, the interplay between Coulomb interaction and charge granularity breaks down the classical laws of electrical impedance composition. Here we explore experimentally the thermal consequences, and observe an additional quantum mechanism of electronic heat transport. The investigated, broadly tunable test-bed circuit is composed of a micron-scale metallic node connected to one electronic channel and a resistance. Heating up the node with Joule dissipation, we separately determine, from complementary noise measurements, both its temperature and the thermal shot noise induced by the temperature difference across the channel (`delta-$T$ noise'). The thermal shot noise predictions are thereby directly validated, and the electronic heat flow is revealed. The latter exhibits a contribution from the channel involving the electrons' partitioning together with the Coulomb interaction. Expanding heat current predictions to include the thermal shot noise, we find a quantitative agreement with experiments., Minor differences with published article: additional reference [29], more explicit identification 'thermal shot noise' - 'delta-T noise', includes the supplementary figures

Transmitting quantum states The coherence of electrons in mesoscopic structures is thought to be unlikely to survive in a disordered environment. Duprez et al. show that this is not necessarily the case. They studied a metallic island as an example of a disordered environment. They made an electron interferometer and incorporated the island in one of the two paths through the interferometer. At sufficiently low temperatures and in the quantum Hall regime, they observed a clear interference pattern, indicating successful transmission of the electrons' quantum state across the island. Science , this issue p. 1243

The quantum coherence of electronic quasiparticles underpins many of the emerging transport properties of conductors at small scales. Novel electronic implementations of quantum optics devices are now available with perspectives such as 'flying' qubit manipulations. However, electronic quantum interferences in conductors remained up to now limited to propagation paths shorter than $30\,\mu$m, independently of the material. Here we demonstrate strong electronic quantum interferences after a propagation along two $0.1\,$mm long pathways in a circuit. Interferences of visibility as high as $80\%$ and $40\%$ are observed on electronic analogues of the Mach-Zehnder interferometer of, respectively, $24\,\mu$m and $0.1\,$mm arm length, consistently corresponding to a $0.25\,$mm electronic phase coherence length. While such devices perform best in the integer quantum Hall regime at filling factor 2, the electronic interferences are restricted by the Coulomb interaction between copropagating edge channels. We overcome this limitation by closing the inner channel in micron-scale loops of frozen internal degrees of freedom, combined with a loop-closing strategy providing an essential isolation from the environment., Comment: To be published in PRX

The Tomonaga-Luttinger liquid (TLL) concept is believed to generically describe the strongly-correlated physics of one-dimensional systems at low temperatures. A hallmark signature in 1D conductors is the quantum phase transition between metallic and insulating states induced by a single impurity. However, this transition impedes experimental explorations of real-world TLLs. Furthermore, its theoretical treatment, explaining the universal energy rescaling of the conductance at low temperatures, has so far been achieved exactly only for specific interaction strengths. Quantum simulation can provide a powerful workaround. Here, a hybrid metal-semiconductor dissipative quantum circuit is shown to implement the analogue of a TLL of adjustable electronic interactions comprising a single, fully tunable scattering impurity. Measurements reveal the renormalization group `beta-function' for the conductance that completely determines the TLL universal crossover to an insulating state upon cooling. Moreover, the characteristic scaling energy locating at a given temperature the position within this conductance renormalization flow is established over nine decades versus circuit parameters, and the out-of-equilibrium regime is explored. With the quantum simulator quality demonstrated from the precise parameter-free validation of existing and novel TLL predictions, quantum simulation is achieved in a strong sense, by elucidating interaction regimes which resist theoretical solutions., To be published in Phys. Rev. X

Quantum phase transitions are ubiquitous in many exotic behaviors of strongly-correlated materials. However the microscopic complexity impedes their quantitative understanding. Here, we observe thoroughly and comprehend the rich strongly-correlated physics in two profoundly dissimilar regimes of quantum criticality. With a circuit implementing a quantum simulator for the three-channel Kondo model, we reveal the universal scalings toward different low-temperature fixed points and along the multiple crossovers from quantum criticality. Notably, an unanticipated violation of the maximum conductance for ballistic free electrons is uncovered. The present charge pseudospin implementation of a Kondo impurity opens access to a broad variety of strongly-correlated phenomena., Article (6 figures) with supplementary (4 figures); http://science.sciencemag.org/content/360/6395/1315

Quantum mechanics and Coulomb interaction dictate the behavior of small circuits. The thermal implications cover fundamental topics from quantum control of heat to quantum thermodynamics, with prospects of novel thermal machines and an ineluctably growing influence on nanocircuit engineering. Experimentally, the rare observations thus far include the universal thermal conductance quantum and heat interferometry. However, evidences for many-body thermal effects paving the way to markedly different heat and electrical behaviors in quantum circuits remain wanting. Here we report on the observation of the Coulomb blockade of electronic heat flow from a small metallic circuit node, beyond the widespread Wiedemann-Franz law paradigm. We demonstrate this thermal many-body phenomenon for perfect (ballistic) conduction channels to the node, where it amounts to the universal suppression of precisely one quantum of conductance for the transport of heat, but none for electricity. The inter-channel correlations that give rise to such selective heat current reduction emerge from local charge conservation, in the floating node over the full thermal frequency range ($\lesssim$temperature$\times k_\mathrm{B}/h$). This observation establishes the different nature of the quantum laws for thermal transport in nanocircuits., Letter: 5 pages including 3 figures; Methods: 3 pages and 4 figures

Quantum physics emerge and develop as temperature is reduced. Although mesoscopic electrical circuits constitute an outstanding platform to explore quantum behaviour, the challenge in cooling the electrons impedes their potential. The strong coupling of such micrometre-scale devices with the measurement lines, combined with the weak coupling to the substrate, makes them extremely difficult to thermalize below 10 mK and imposes in situ thermometers. Here we demonstrate electronic quantum transport at 6 mK in micrometre-scale mesoscopic circuits. The thermometry methods are established by the comparison of three in situ primary thermometers, each involving a different underlying physics. The employed combination of quantum shot noise, quantum back action of a resistive circuit and conductance oscillations of a single-electron transistor covers a remarkably broad spectrum of mesoscopic phenomena. The experiment, performed in vacuum using a standard cryogen-free dilution refrigerator, paves the way towards the sub-millikelvin range with additional thermalization and refrigeration techniques., Mesoscopic electrical circuits are an ideal platform to explore quantum phenomena, but this requires cooling the electrons to very low temperature, which is challenging. Here, the authors employ three different in situ thermometers to report electronic quantum transport at 6mK in a micrometer-scale circuit.

In 1909, Millikan showed that the charge of electrically isolated systems is quantized in units of the elementary electron charge e. Today, the persistence of charge quantization in small, weakly connected conductors allows for circuits where single electrons are manipulated, with applications in e.g. metrology, detectors and thermometry. However, quantum fluctuations progressively reduce the discreteness of charge as the connection strength is increased. Here we report on the full quantum control and characterization of charge quantization. By using semiconductor-based tunable elemental conduction channels to connect a micrometer-scale metallic island, the complete evolution is explored while scanning the entire range of connection strengths, from tunnel barrier to ballistic contact. We observe a robust scaling of charge quantization as the square root of the residual electron reflection probability across a quantum channel when approaching the ballistic critical point, which also applies beyond the regimes yet accessible to theory. At increased temperatures, the thermal fluctuations result in an exponential suppression of charge quantization as well as in a universal square root scaling, for arbitrary connection strengths, in agreement with expectations. Besides direct applications to improve single-electron functionalities and for the metal-semiconductor hybrids emerging in the quest toward topological quantum computing, the knowledge of the quantum laws of electricity will be essential for the quantum engineering of future nanoelectronic devices., Letter and Methods; See also Nature News & Views: Y. Nazarov, Nature 536, 38 (2016)

Many-body correlations and macroscopic quantum behaviors are fascinating condensed matter problems. A powerful test-bed for the many-body concepts and methods is the Kondo model which entails the coupling of a quantum impurity to a continuum of states. It is central in highly correlated systems and can be explored with tunable nanostructures. Although Kondo physics is usually associated with the hybridization of itinerant electrons with microscopic magnetic moments, theory predicts that it can arise whenever degenerate quantum states are coupled to a continuum. Here we demonstrate the previously elusive `charge' Kondo effect in a hybrid metal-semiconductor implementation of a single-electron transistor, with a quantum pseudospin-1/2 constituted by two degenerate macroscopic charge states of a metallic island. In contrast to other Kondo nanostructures, each conduction channel connecting the island to an electrode constitutes a distinct and fully tunable Kondo channel, thereby providing an unprecedented access to the two-channel Kondo effect and a clear path to multi-channel Kondo physics. Using a weakly coupled probe, we reveal the renormalization flow, as temperature is reduced, of two Kondo channels competing to screen the charge pseudospin. This provides a direct view of how the predicted quantum phase transition develops across the symmetric quantum critical point. Detuning the pseudospin away from degeneracy, we demonstrate, on a fully characterized device, quantitative agreement with the predictions for the finite-temperature crossover from quantum criticality., Letter (5 pages, 4 figures) and Methods (10 pages, 6 figures)

The three-dimensional intrinsic convection in a monodisperse dispersion of spheres settling in a vertical container of arbitrary cross section is calculated using the simple model of point forces with excluded volume near the walls, proposed by Bruneau et al. [Phys. Fluids 8, 2236 (1996)]. An exact solution of the model equations for a container with rectangular cross-section shows that corners have no significant influence on the convection. A dense suspension is modeled by assuming an equilibrium particle distribution in the near wall region. It is predicted that as a result of near wall ordering, the intrinsic convection decreases with increasing particle volume fraction.

We investigated here the micellization in water of three surfactants: (N-dodecylamino)lactitol, (N-dodecyl)lactobionamide, and (N-acetyl N-dodecyl)lactosylamine, having n-alkyl chain lengths of 12 carbon atoms and different lactose-based polar heads. The micellization is studied by small-angle neutron and X-ray scattering. The characteristic dimensions of the micelles are derived from the I(q) curve fittings. We demonstrated the existence of spherical or oblate ellipsoidal micellar structures. The differences were attributed to differences in steric hindrance of the polar head enabling or preventing formation of spherical micelles. We pointed out the particular role of steric hindrance at the junction between the hydrophobic chain and the polar head. The formation of oblate ellipsoidal micelles attests to a relatively low steric hindrance at this junction ((N-dodecylamino)lactitol and (N-dodecyl)lactobionamide) whereas the formation of spherical micelle displays an important steric hindrance as observed for (N-acetyl N-dodecyl)lactosylamine which includes a bulky linkage. The surface areas per polar head in the micelles are confronted to the minimum areas per molecules deduced from surface pressure measurements. The results are in good agreement excepted in the case of (N-dodecyl)lactobionamide. The experimental results obtained with micellar solutions of N-dodecyllactobionamide from both neutron scattering and surface pressure measurements exhibit a particular comportment of this surfactant compared with two other surfactants studied in regard to the intermicellar interactions and the minimum area per molecule at the air/aqueous solution interface. We suggest that this particular behavior could be the consequence of a very important solvation of the (N-dodecyl)lactobionamide polar heads due to the presence of an amide group in this molecule. This important solvation could modify the interactions between the micelles and the apparent size ofisolated molecules at the air/aqueous solution interface. Over parallel explanations may be suggested as formation of dimers or trimers below the critical micelle concentration (cmc) and above the cmc the existence of relatively strong intermicellar interactions stemming from the distribution of dipoles over the surface in these micelles due to the presence of the amide group.

We report here a small angle neutron scattering (SANS) study of the micellization of SDS in formamide. We show that a compound with a hydrophobic chain containing 12 carbon atoms forms micelles in formamide. The mechanism of self-association is in agreement with a multiple equilibrium model rather than a pseudophase model, as the aggregates were shown to increase in size over a large concentration domain. This was attributed to smaller solvophobic effects and lower interfacial energy in formamide than in water.

Quantum physics predicts that there is a fundamental maximum heat conductance across a single transport channel, and that this thermal conductance quantum $G_Q$ is universal, independent of the type of particles carrying the heat. Such universality, combined with the relationship between heat and information, signals a general limit on information transfer. We report on the quantitative measurement of the quantum limited heat flow for Fermi particles across a single electronic channel, using noise thermometry. The demonstrated agreement with the predicted $G_Q$ establishes experimentally this basic building block of quantum thermal transport. The achieved accuracy of below 10\% opens access to many experiments involving the quantum manipulation of heat., manuscript (5 pages, 3 figures) and supplementary materials (8 pages, 9 figures, 1 table)

In one-dimensional conductors, interactions result in correlated electronic systems. At low energy, a hallmark signature of the so-called Tomonaga–Luttinger liquids is the universal conductance curve predicted in presence of an impurity. A seemingly different topic is the quantum laws of electricity, when distinct quantum conductors are assembled in a circuit. In particular, the conductances are suppressed at low energy, a phenomenon called dynamical Coulomb blockade. Here we investigate the conductance of mesoscopic circuits constituted by a short single-channel quantum conductor in series with a resistance, and demonstrate a proposed link to Tomonaga–Luttinger physics. We reformulate and establish experimentally a recently derived phenomenological expression for the conductance using a wide range of circuits, including carbon nanotube data obtained elsewhere. By confronting both conductance data and phenomenological expression with the universal Tomonaga–Luttinger conductance curve, we demonstrate experimentally the predicted mapping between dynamical Coulomb blockade and the transport across a Tomonaga–Luttinger liquid with an impurity., When physicists study the characteristics of quantum conductors they usually take great pains to limit the resistance of other elements in the system. But Jezouin et al. show that when a single quantum channel is measured in series with a resistor, it exhibits analogous characteristics to a Tomonaga–Luttinger liquid.

In this study, we investigated the micellization in water of four surfactants from the series of (N-alkylamino)lactitols by small angle neutron and X-ray scattering. These four surfactants differed from one another by the number of carbon atoms in their alkyl chain: 8, 9, 10, or 12. The comparison of the I(q) curves of the intensity scattered from micellar solutions as a function of concentration indicated that the micelle size was weakly dispersed at small concentrations. The C8 derivative presented a singular behavior which may be attributed to the formation of premicellar aggregates. The characteristic dimensions of the micelles are derived from the I(q) curve fittings. For the calculation of scattered intensity from the micelles, three models of micelles were considered: spherical, oblate ellipsoidal, and prolate ellipsoidal. These models take into account particularities of the studied surfactants, in particular, the size of the sugar head group, which leads us to consider a nonuniform penetration ...

The Krafft temperatures and critical micellar concentrations (cmc) of N-alkylpyridinium halides (CmPyX, m = 12, 16, or 20 and X = Cl, Br, or I) in formamide were determined. The size, structure, and charge of the micelles as a function of chain length and nature of counterion were calculated from the small angle neutron scattered intensity. At a chain length of 12 carbons, only small, relatively unstructured aggregates were formed. At a chain length of 16 carbons, some micelles were also observed at a concentration of twice the cmc and above. At a chain length of 20 carbons, micelles were the sole species. The radii of the cores of the spherical micelles in formamide were always lower than the radii of the corresponding micelles in water. The micelles bear a higher charge in formamide than in water, but similar solvation effects were noted in the two solvents on changing the counterion (I-, Br-, or Cl-).

In this work we investigate lyotropic phases in different sugar-based surfactant/water systems. Studies are carried out with the (N-alkylamino)-1-deoxylactitols (C 8 , C 10 , C 12 ) and β-dodecyl maltoside. Liquid crystal phases are detected and lattice parameters determined by X-ray diffraction. The phases observed are the normal phases found in binary ionic or nonionic surfactant/water systems. Schematic diagrams show the sequences of the lyotropic phases formed by these disaccharide surfactants. The difference in behavior is accounted for by the difference in chain length, hydrophilic ability, and steric hindrance of the polar head.

We demonstrate a direct approach to investigate heat transport in the fractional quantum Hall regime. At filling factor of 4/3, we inject power at quantum point contacts and detect the related heating from the activated current through a quantum dot. The experiment reveals a chargeless heat transport from a significant heating that occurs upstream of the power injection point, in the absence of a concomitant electrical current. By tuning in-situ the edge path, we show that the chargeless heat transport does not follow the reverse direction of the electrical current path along the edge. This unexpected heat conduction demonstrates a novel aspect, yet to be elucidated, of the physics in fractional quantum Hall systems., Manuscript (5 pages, 3 figures) and supplementary material (8 pages, 9 figures); v2 includes additional supplementary material and references; to be published in Phys. Rev. Lett

What are the quantum laws of electricity in mesoscopic circuits? This very fundamental question has also direct implications for the quantum engineering of nanoelectronic devices. Indeed, when a quantum coherent conductor is inserted into a circuit, its transport properties are modified. In particular, its conductance is reduced because of the circuit back-action. This phenomenon, called environmental Coulomb blockade, results from the granularity of charge transfers across the coherent conductor. Although extensively studied for a tunnel junction in a linear circuit, it is only fully understood for arbitrary short coherent conductors in the limit of small circuit impedances and small conductance reduction. Here, we investigate experimentally the strong back-action regime, with a conductance reduction of up to 90%. This is achieved by embedding a single quantum channel of tunable transmission in an adjustable on-chip circuit of impedance comparable to the resistance quantum $R_K=h/e^2$ at microwave frequencies. The experiment reveals important deviations from calculations performed in the weak back-action framework, and matches with recent theoretical results. From these measurements, we propose a generalized expression for the conductance of an arbitrary quantum channel embedded in a linear circuit., 11 pages including supplementary information, to be published in Nature Physics

We report on low temperature conductance measurements of gold nanogaps fabricated by controlled electromigration. Fluctuations of the conductance due to quantum interferences and depending both on bias voltage and magnetic field are observed. By analyzing the voltage and magnetoconductance correlation functions we determine the type of electron trajectories generating the observed quantum interferences and the effective characteristic time of phase coherence in our device., 5 pages, 4 figures, to appear in J. Appl. Phys

We present current voltage measurements of clean electromigrated gold nanogaps at cryogenic temperatures. In all samples, we observe low voltage values $(l1\text{ }\text{V})$ for the crossover from direct tunneling to field emission regime. Two different tunneling models well explain the data with work functions values reduced with respect to the bulk ones. The influence of adsorbates on the metal work function in nanogaps is discussed.

An X-ray attenuation technique is used to obtain the local concentration of spherical particles in a polydisperse suspension as a function of vertical position and time. From these experimental data, the average velocity of sedimentation in the homogeneous part of the suspension is derived by considering the variation with time of the total volume of particles located above a given fixed horizontal plane. Measurements have been performed in suspensions of particles which differ from each other in size with a total volume concentration in particles between 0.13% and 2.5%, and also in suspensions of particles which differ from each other both in size and in density, the total volume concentration being 2%. For the first kind of suspension, the experimental hindered settling factor is plotted versus the concentration and a linear regression analysis provides the slope with its 90% confidence limits: Se = −5.3 ± 1.1. This experimental average coefficient of sedimentation is in good agreement with the theoretical average coefficient St = −5.60 obtained from the results of Batchelor & Wen (1982). The second kind of suspension, for which permanent doublets of spheres may theoretically exist, is not in the range of validity of Batchelor & Wen's results. The experimental average coefficient of sedimentation for this case is found to be much larger than the prediction obtained by extrapolating Batchelor & Wen's results out of their range of validity. This increased velocity may be experimental evidence of the existence of permanent doublets.

The creeping flow around a sphere settling along the axis of a closed axisymmetric container is obtained both theoretically and experimentally. The numerical technique for solving the Stokes equations uses the classical Sampson expansion; the boundary conditions on the sphere are satisfied exactly and those on the container walls are applied in the sense of least squares. This is an extension to the axisymmetric case of the technique for solving various two-dimensional flow problems. Two types of axisymmetric container are considered here as examples: circular cylinders closed by planes at both ends, and cones closed by a base plane. Calculated streamlines patterns show various sets of eddies, depending upon the geometry and the sphere position. Results are in agreement with earlier Stokes flow calculations of eddies in corners and in closed containers. Experiments use laser interferometry to measure the vertical displacement of a steel bead a few millimetres in diameter settling in a container filled with a very viscous silicone oil. The Reynolds number based on the sphere radius is typically of the order of 10−5. The accuracy on the vertical displacement is 50nm. Experiments show that the motion towards the apex of a cone is much slower than that towards a plane; the bead takes hours to reach the micrometre size roughness asperities on a conical wall, as compared with minutes to reach those on a plane wall. The numerical results for the drag force are in excellent agreement with experiments both for the cylindrical and the conical containers. With standard computer accuracy, the present numerical technique applies when the gap between the sphere and the nearby wall is larger than about one radius. For a sphere in the vicinity of any plane horizontal wall, these results also match with a previous analytical solution. That solution is in excellent agreement with our experimental results at small distances from the wall (typically less than a diameter, depending on the sphere size).

In order to probe quantitatively the effect of Kondo impurities on energy exchange between electrons in metals, we have compared measurements on two silver wires with dilute magnetic impurities (manganese) introduced in one of them. The measurement of the temperature dependence of the electron phase coherence time on the wires provides an independent determination of the impurity concentration. Quantitative agreement on the energy exchange rate is found with a theory by G\"{o}ppert et al. that accounts for Kondo scattering of electrons on spin-1/2 impurities., Comment: 4 pages

The intrinsic convection in a settling suspension is shown to have its origins in the buoyancy of the particle‐depleted layer next to the side walls. The convection is calculated using a simple model in which the particles are represented by an excluded volume and by point forces at their centres. A boundary layer approximation is developed for vessels which are much wider than the particle diameter. It is shown that the direction of the convection depends critically on assumptions about the formation of the particle‐depleted layer during the placement of the suspension into the vessel.

The energy dependence and intensity of Coulomb interaction between quasiparticles in metallic wires is obtained from two different methods: determination of the temperature dependence of the phase coherence time from the magnetoresistance, and measurements of the energy distribution function in out-of-equilibrium situations. In both types of experiment, the energy dependence of the Coulomb interaction is found to be in excellent agreement with theoretical predictions. In contrast, the intensity of the interaction agrees closely with theory only with the first method, whereas an important discrepancy is found using the second one. Different explanations are proposed, and results of a test experiment are presented., Submitted to Solid States Communications

A superconductor-normal metal-superconductor mesoscopic Josephson junction has been realized in which the critical current is tuned through normal current injection using a symmetric electron cooler directly connected to the weak link. Both enhancement of the critical current by more than a factor of two, and supercurrent suppression have been achieved by varying the cooler bias. Furthermore, this transistor-like device demonstrates large current gain (similar to20) and low power dissipation. (C) 2004 American Institute of Physics.

From the solution of the creeping-flow equations, the drag force on a sphere becomes infinite when the gap between the sphere and a smooth wall vanishes at constant velocity, so that if the sphere is displaced towards the wall with a constant applied force, contact theoretically may not occur. Physically, the drag is finite for various reasons, one being the particle and wall roughness. Then, for vanishing gap, even though some layers of fluid molecules may be left between the particle and wall roughness peaks, conventionally it may be said that contact occurs. In this paper, we consider the example of a smooth sphere moving towards a rough wall. The roughness considered here consists of parallel periodic wedges, the wavelength of which is small compared with the sphere radius. This problem is considered both experimentally and theoretically. The motion of a millimetre size bead settling towards a corrugated horizontal wall in a viscous oil is measured with laser interferometry giving an accuracy on the displacement of 0.1 m. Several wedge-shaped walls were used, with various wavelengths and wedge angles.From the results, it is observed that the velocity of the sphere is, except for small gaps, similar to that towards a smooth plane that is shifted down from the top of corrugations. Indeed, earlier theories for a shear flow along a corrugated wall found such an equivalent smooth plane. These theories are revisited here. The creeping flow is calculated as a series in the slope of the roughness grooves. The cases of a flow along and across the grooves are considered separately. The shift is larger in the former case. Slightly flattened tops of the wedges used in experiments are also considered in the calculations. It is then demonstrated that the effective shift for the sphere motion is the average of the shifts for shear flows in the two perpendicular directions. A good agreement is found between theory and experiment.

We have extracted the phase coherence time $\tau_{\phi}$ of electronic quasiparticles from the low field magnetoresistance of weakly disordered wires made of silver, copper and gold. In samples fabricated using our purest silver and gold sources, $\tau_{\phi}$ increases as $T^{-2/3}$ when the temperature $T$ is reduced, as predicted by the theory of electron-electron interactions in diffusive wires. In contrast, samples made of a silver source material of lesser purity or of copper exhibit an apparent saturation of $\tau_{\phi}$ starting between 0.1 and 1 K down to our base temperature of 40 mK. By implanting manganese impurities in silver wires, we show that even a minute concentration of magnetic impurities having a small Kondo temperature can lead to a quasi saturation of $\tau_{\phi}$ over a broad temperature range, while the resistance increase expected from the Kondo effect remains hidden by a large background. We also measured the conductance of Aharonov-Bohm rings fabricated using a very pure copper source and found that the amplitude of the $h/e$ conductance oscillations increases strongly with magnetic field. This set of experiments suggests that the frequently observed ``saturation'' of $\tau_{\phi}$ in weakly disordered metallic thin films can be attributed to spin-flip scattering from extremely dilute magnetic impurities, at a level undetectable by other means., Comment: 16 pages, 11 figures, to be published in Physical Review B

We have measured the tunneling density of states (DOS) in a superconductor carrying a supercurrent or exposed to an external magnetic field. The pair correlations are weakened by the supercurrent, leading to a modification of the DOS and to a reduction of the gap. As predicted by the theory of superconductivity in diffusive metals, we find that this effect is similar to that of an external magnetic field., Comment: To be published in Physical Review Letters

In order to find out if magnetic impurities can mediate interactions between quasiparticles in metals, we have measured the effect of a magnetic field B on the energy distribution function f(E) of quasiparticles in two silver wires driven out-of-equilibrium by a bias voltage U. In a sample showing sharp distributions at B=0, no magnetic field effect is found, whereas in the other sample, rounded distributions at low magnetic field get sharper as B is increased, with a characteristic field proportional to U. Comparison is made with recent calculations of the effect of magnetic-impurities-mediated interactions taking into account Kondo physics., Comment: 4 pages, 3 figures, to be published in Physical Review Letters

We have performed the tunnel spectroscopy of the energy distribution function of quasiparticles in 5-microm-long silver wires connected to superconducting reservoirs biased at different potentials. The distribution function f(E) presents several steps, which are manifestations of multiple Andreev reflections at the NS interfaces. The rounding of the steps is well explained by electron-electron interactions.

International audience; The final stage of sedimentation of a spherical particle moving along the axis of a conical vessel containing a viscous incompressible fluid is studied both theoretically by lubrication analysis and experimentally by laser interferometry. The particle settling velocity varies like d5/2, where d is the gap. There is an excellent agreement between this result from lubrication theory and experiment, the upper bound being for a gap of about 1/30 radius and the lower practical bound being at the size of the particle roughness.

Small-angle X-ray scattering has been used to study correlations between the magnetic grains of ferrofluids : for dilute colloiids, the grains look isolated or associated in dimers, trimers, etc ... depending on the nature of the ferrofluids. At higher concentration, an order appears in the spatial distribution of the grains even without magnetic field. The application of a magnetic field can generate alongated fibers of grains. An average interfiber spacing has been put in evidence. Small-angle X-ray scattering reveals as a sensitive quality test of the grain agglomeration in ferrofluids.

The size distribution and the structure of colloidal cobalt particles in toluene, as well as interparticle correlations, have been studied.