Eddy Collin

Strong orientational effect of stretched aerogel on the 3 He order parameter

Deformation of aerogel strongly modifies the orientation of the order parameter of superfluid (3)He confined in aerogel. We used a radial squeezing of aerogel to keep the orbital angular momentum of the (3)He Cooper pairs in the plane perpendicular to the magnetic field. We did not find strong evidence for a polar phase, with a nodal line along the equator of the Fermi surface, predicted to occur at large radial squeezing. Instead we observed (3)He-A with a clear experimental evidence of the destruction of the long-range order by random anisotropy-the Larkin-Imry-Ma effect. In (3)He-B we observed and identified new modes of NMR, which are impossible to obtain in bulk (3)He-B. One of these modes is characterized by a repulsive interaction between magnons, which is suitable for the magnon Bose-Einstein condensation.

Counting Individual Trapped Electrons on Liquid Helium

We show that small numbers of electrons, including a single isolated electron, can be held in an electrostatic trap above the surface of superfluid helium. A potential well is created using microfabricated electrodes in a 5 μm diameter pool of helium. Electrons are injected into the trap from an electron reservoir on a helium microchannel. They are individually detected using a superconducting single-electron transistor as an electrometer. A Coulomb staircase is observed as electrons leave the trap one–by–one until the trap is empty. A design for a scalable quantum information processor using an array of electron traps is presented.

Search for supersymmetric Dark Matter with superfluid 3He (MACHe3)

Abstract MACHe3 (MAtrix of Cells of superfluid 3 He) is a project of a new detector for direct Dark Matter search, using superfluid 3 He as a sensitive medium. This Letter presents a phenomenological study done with the DarkSUSY code, in order to investigate the discovery potential of this project of detector, as well as its complementarity with existing and planned devices.

Metallic coatings of microelectromechanical structures at low temperatures: Stress, elasticity, and nonlinear dissipation

We present mechanical measurements performed at low temperatures on cantilever-based microelectromechanical structures coated with a metallic layer. Two very different coatings are presented in order to illustrate the capabilities of the present approach, namely (soft) aluminum and (hard) niobium oxide. The temperature is used as a control parameter to access materials properties. We benefit from low temperature techniques to extract a phase-resolved measurement of the first mechanical resonance mode in cryogenic vacuum. By repeating the experiment on the same samples, after multiple metallic depositions, we can determine accurately the contribution of the coating layers to the mechanical properties in terms of surface stress, additional mass, additional elasticity, and damping. Analytic theoretical expressions are derived and used to fit the data. Taking advantage of the extremely broad dynamic range provided by the technique, we can measure the anelasticity of the thin metallic film. The key parameters ...

Microfabrication of silicon vibrating wires

Abstract Superconducting vibrating wires are widely used in low-temperature measurements. We report on the fabrication of silicon micromechanical resonators covered by a superconducting layer. These resonators are designed to be vibrating wire thermometers adapted for ultra-low-temperature experiments. We describe the first tests at 4.2 K.

Topological defects and coherent magnetization precession of 3He in aerogel

Abstract We have observed for the first time the formation of the region with coherent precession of magnetization (CPM) in superfluid 3 He in aerogel covered by solid monolayers of 4 He . The signal of CPM has been observed by pulsed NMR and by CW NMR. By playing with the magnetic field gradient we were able to distinguish the spatial position of the region of CPM as well as to determine the long-scale inhomogenity of the order parameter. We have observed an evidence for existence of an enormous number of topological defects in superfluid 3 He in aerogel.

Specific heat measurement of thin suspended SiN membrane from 8 K to 300 K using the 3ω-Völklein method

We present a specific heat measurement technique adapted to thin or very thin suspended membranes from low temperature (8 K) to 300 K. The presented device allows the measurement of the heat capacity of a 70 ng silicon nitride membrane (50 or 100 nm thick), corresponding to a heat capacity of 1.4 × 10(-10) J/K at 8 K and 5.1 × 10(-8) J/K at 300 K. Measurements are performed using the 3ω method coupled to the Völklein geometry. This configuration allows the measurement of both specific heat and thermal conductivity within the same experiment. A transducer (heater/thermometer) is used to create an oscillation of the heat flux on the membrane; the voltage oscillation appearing at the third harmonic which contains the thermal information is measured using a Wheatstone bridge set-up. The heat capacity measurement is performed by measuring the variation of the 3ω voltage over a wide frequency range and by fitting the experimental data using a thermal model adapted to the heat transfer across the membrane. The experimental data are compared to a regular Debye model; the specific heat exhibits features commonly seen for glasses at low temperature.

Bolometric calibration of a superfluid 3He detector for Dark Matter search: Direct measurement of the scintillated energy fraction for neutron, electron and muon events

Abstract We report on the calibration of a superfluid 3 He bolometer developed for the search of non-baryonic Dark Matter. Precise thermometry is achieved by the direct measurement of thermal excitations using Vibrating Wire Resonators (VWRs). The heating pulses for calibration were produced by the direct quantum process of quasiparticle generation by other VWRs present. The bolometric calibration factor is analyzed as a function of temperature and excitation level of the sensing VWR. The calibration is compared to bolometric measurements of the nuclear neutron capture reaction and heat depositions by cosmic muons and low energy electrons. The comparison allows a quantitative estimation of the ultra-violet scintillation rate of irradiated helium, demonstrating the possibility of efficient electron recoil event rejection.

Slippage and Boundary Layer Probed in an Almost Ideal Gas by a Nanomechanical Oscillator

We measure the interaction between ⁴He gas at 4.2 K and a high-quality nanoelectromechanical string device for its first three symmetric modes (resonating at 2.2, 6.7, and 11 MHz with quality factor Q>0.1×10⁶) over almost 6 orders of magnitude in pressure. This fluid can be viewed as the best experimental implementation of an almost ideal monoatomic and inert gas of which properties are tabulated. The experiment ranges from high pressure where the flow is of laminar Stokes-type presenting slippage down to very low pressures where the flow is molecular. In the molecular regime, when the mean-free path is of the order of the distance between the suspended nanomechanical probe and the bottom of the trench, we resolve for the first time the signature of the boundary (Knudsen) layer onto the measured dissipation. Our results are discussed in the framework of the most recent theories investigating boundary effects in fluids (both analytic approaches and direct simulation Monte Carlo methods).

Nonlinear parametric amplification in a triport nanoelectromechanical device

We report on measurements performed at low temperatures on a nanoelectromechanical system (NEMS) under (capacitive) parametric pumping. The excitations and detection schemes are purely electrical, and enable in the present experiment the straightforward measurement of forces down to about a femtonewton, for displacements of an Angstr¨om, using standard room temperature electronics. We demonstrate that a small (linear) force applied on the device can be amplified up to more than a 100 times, while the system is truly moving. We explore the dynamics up to about 50 nm deflections for cantilevers about 200 nm thick by 3 μm long oscillating at a frequency of 7 MHz. We present a generic modeling of nonlinear parametric amplification, and give analytic theoretical solutions enabling the fit of experimental results. We finally discuss the practical limits of the technique, with a particular application: the measurement of anelastic damping in the metallic coating of the device with an exceptional resolution of about 0.5 %