Static structure factor of two-dimensional liquid 3He adsorbed on graphite

International audienceLiquid 3He is a model system for strongly correlated Fermi liquids. For this reason, many X-ray and neutron scattering experiments have been performed to understand the structure and dynamics of this quantum fluid. We have recently shown that two-dimensional liquid 3He sustains long-lived zero-sound excitations at large wave-vectors (Nature 483, 576, 2012). Here we show that its static structure factor can be obtained with reasonable accuracy by integrating the experimental S(Q,ω) over a suitable energy range. A good agreement is found between the static structure factor deduced from the experiment and theoretical models: Quantum Monte Carlo simulations and Dynamical Many Body Theory (DMBT). At high wave-vectors, the experimental values are underestimated because of the limited accessible phase space; nevertheless, even at atomic wave-vectors a semiquantitative agreement is observed with the theoretical predictions

Evidence for magnon BEC in superfluid 3He-A

International audienceThe phenomenon of phase-coherent precession of magnetization in superfluid 3He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different states of coherent precession have been observed in 3He-B: homogeneously precessing domain (HPD); persistent signal formed byQ-balls at very low temperatures; coherent precession with fractional magnetization; and two new modes of the coherent precession in compressed aerogel. Here we demonstrate the evidence of magnons Bose-Einstein condensation in 3He-A in a compressed aerogel

Modal Decomposition in Goalpost Micro/nano Electro-mechanical Devices

We have studied the first three symmetric out-of-plane flexural resonance modes of a goalpost silicon micro-mechanical device. Measurements have been performed at 4.2K in vacuum, demonstrating high Qs and good linear properties. Numerical simulations have been realized to fit the resonance frequencies and produce the mode shapes. These mode shapes are complex, since they involve distortions of two coupled orthogonal bars. Nonetheless, analytic expressions have been developed to reproduce these numerical results, with no free parameters. Owing to their generality they are extremely helpful, in particular to identify the parameters which may limit the performances of the device. The overall agreement is very good, and has been verified on our nano-mechanical version of the device.Comment: Journal of Low Temperature Physics (2013

Pulse-tube dilution refrigeration below 10 mK for Astrophysics

International audienceAstroparticle bolometric detectors often rely on the use of dilution refrigerators providing a large cooling power at millikelvin temperatures. Conventional machines, however, need a systematic supply of cryogenic fluids, complicating and making more expensive their operation, particularly in underground laboratories. We describe here novel cryogen-free dilution units, able to cool down large detectors to millikelvin temperatures, and where cooling and warming times have been optimised

Experimental results on the free cooling power available on 4K pulse tube coolers

International audienceWe report experimental results on the free cooling power available at the level of the second stage regenerator of a 4K pulse tube cooler. By using two localised heat exchangers we obtained additional cooling power, in the range 400 and 600mW at 4.8K or between 500 and 700mW at 18K. We have investigated in detail the thermal behavior of the system. In this manuscript we report on the evolution of the temperature of the heat exchangers and the pulse tube stages under different distributions of the total heat load

Pulse-tube dilution refrigeration below 10 mK

International audienceWe report the design, realization and performance of dilution refrigerators using a pulse-tube cooler as a first cryogenic stage. The absence of a Dewar containing cryogenic fluids makes this new type of refrigerators particularly versatile. The system provides relatively high cooling power, and reaches temperatures well below 10 mK

ULTIMA: Magnetic field dependence of the calibration factor

International audienceULTIMA is a project which proposes to use superfluid 3He as a sensitive medium for direct dark matter search. In this paper we report on new, detailed calibrations of our bolometric cells as a function of the magnetic field. An influence on the order of 20% is observed for magnetic fields up to 330 mT. Simultaneous measurements of neutron capture and heater events, releasing both a well defined energy, show that the effect is similar for both, and that it is possible to maintain a good calibration by an appropriate correction