Magnetic susceptibility of liquid 3He

International audience3He is a model of Fermi liquid, isotropic, its Fermi temperature is attainable and the interaction between atoms can be controlled by changing the pressure on the liquid. In this paper we present accurate cw-NMR measurements of the nuclear magnetic susceptibility of liquid 3He as a function of temperature and pressure. The emphasis has been placed in reliable thermometry, 3He pressure measurements directly in the cell to increase the measuring range until solidification, and an accurate characterization of the NMR spectrometer. Our measurements give effective Fermi temperatures substantially lower than former results

Magnétisme nucléaire de l'3He liquide : nouvelle détermination du paramètre de Landau F0a

3He is a model Fermi liquid, isotropic, its Fermi temperature is attainable and the interaction between atoms can be controled by changing the pressure of the liquid. In this document, we present accurate Cw-NMR measurements of the nuclear magnetic susceptibility of liquid 3He as a function of temperature and pressure. The emphasis has been placed in reliable thermometry, 3He pressure measurements directly in the cell to increase the measuring range until solidification, and an accurate characterization of the NMR spectrometer. Our measurements give an effective Fermi temperature 5% lower than former results. The Landau parameter F0a depends on the effective mass, which is determined by specific heat measurements, and consequently on the temperature scale. The re-analysis of the specific heat measurements with the PLTS-2000 temperature scale yields an effective mass increase of 4.5%. In this document, F0a is determined for two temperature scales (PLTS-2000 and Greywall). Contrarily to former measurements, the F0a density dependence does not show any saturation at high pressures.L'3He est un liquide de Fermi modèle, isotrope, pur, de température de Fermi accessible, et dont les interactions sont aisément contrôlées en faisant varier la pression du liquide. Ce manuscrit présente des mesures précises de susceptibilité magnétique nucléaire par RMN continue de l'3He liquide en fonction de la température et de la pression. Les principaux efforts expérimentaux sont portés sur la thermométrie, la mesure de la pression de l'3He in situ pour étendre les mesures jusqu'à la pression de solidification, ainsi qu'une caractérisation soigneuse du spectromètre RMN. Nos mesures remettent en cause d'environ 5% les résultats de référence pour la température de Fermi effective en fonction des interactions. L'extraction du paramètre de Landau F0a dépend aussi de la masse effective déterminée par des mesures de chaleur spécifique, et par conséquent de l'échelle de température. La ré-analyse des mesures de chaleur spécifique dans l'échelle PLTS-2000 implique une augmentation de la masse effective de 4,5%. F0a est donc déterminé dans ce manuscrit pour deux échelles de température (PLTS-2000 et Greywall). Contrairement aux résultats antérieurs, la dépendance en densité de F0a ne montre pas de saturation vers les hautes pressions

Magnétisme nucléaire de l'3He liquide (nouvelle détermination du paramètre de Landau Fa0)

L'3He est un liquide de Fermi modèle, isotrope, pur, de température de Fermi accessible, et dont les interactions sont aisément contrôlées en faisant varier la pression du liquide. Ce manuscrit présente des mesures précises de susceptibilité magnétique nucléaire par RMN continue de l'3He liquide en fonction de la température et de la pression. Les principaux efforts expérimentaux sont portés sur la thermométrie, la mesure de la pression de l'3He in situ pour étendre les mesures jusqu'à la pression de solidification, ainsi qu'une caractérisation soigneuse du spectromètre RMN. Nos mesures remettent en cause d'environ 5 % les résultats de référence pour la température de Fermi effective en fonction des interactions. L'extraction du paramètre de Landau FOa dépend aussi de la masse effective déterminée par des mesures de chaleur spécifique, et par conséquent de l'échelle de température. La ré-analyse des mesures de chaleur spécifique dans l'échelle PL T5-2000 implique une augmentation de la masse effective de 4.5 %. FOa est donc déterminé dans ce manuscrit pour deux échelles de température (PL T5-2000 et Greywall). Contrairement aux résultats antérieurs, la dépendance en densité de FOa ne montre pas de saturation vers les hautes pressions.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Fabrication and characterisation of the PiN Ge photodiode with poly-crystalline Si:P as n-type region

Germanium (Ge) PiN photodetectors are fabricated and electro-optically characterised. Unintentionally and p-type doped Ge layers are grown in a reduced-pressure chemical vapour deposition tool on a 200 mm diameter, -oriented, p-type silicon (Si) substrates. Thanks to two Ge growth temperatures and the use of short thermal cycling afterwards, threading dislocation densities down to 10⁷ cmˉ² are obtained. Instead of phosphorous (P) ion implantation in germanium, the authors use in situ phosphorous-doped poly-crystalline Si (poly-Si) in the n-type regions. Secondary ion mass spectrometry revealed that P was confined in poly-Si and did not diffuse in Ge layers beneath. Over a wide range of tested device geometries, production yield was dramatically increased, with almost no short circuits. At 30 °C and at -0.1 V bias, corresponding to the highest dynamic resistance, the median dark current of 10 μm diameter photodiodes is in the 5-20 nA range depending on the size of the n-type region. The dark current is limited by the Shockley-Read-Hall generation and the noise power spectral density of the current by the flicker noise contribution. A responsivity of 0.55 and 0.33 A/W at 1.31 and 1.55 μm, respectively, is demonstrated with a 1.8 μm thick absorption Ge layer and an optimized anti-reflection coating at 1.55 μm. These results pave the way for a cost-effective technology based on group-IV semiconductors

BRAHMS: polarimetric bolometer arrays for the SPICA observatory camera (Conference Presentation)

International audienceIn the last decades, a very large effort has been made to measure, with high sensitivity, the intensity and spectral contents of millimetric (mm) and submillimetric (submm) light from the Universe. Today this picture is in the way to be routinely completed by polarization measurements that give access to previously hidden processes, for example the traces of primordial gravitational waves in the case of CMB (mainly mm), or the effect of magnetic field for star formation mechanisms (submm and mm optical ranges). The classical way to measure the light polarization is to split the two components by a polarizer grid and record intensities with two conjugated detection setups. This approach implies the deployment of a complex instrument system, very sensitive to external constraints (vibrations, alinement, thermal expansion…), or internal ones: determine low degrees of polarization implies a large increase in sensitivity when compared with intensity measurements. The need of detector arrays, with in pixel polarization measurement capabilities, has been well understood for years: all the complexity being reported at the focal plane level. Subsequently, the instrument integration, verification and tests procedure is considerately alleviated, specially for space applications.All silicon bolometer arrays using the same micromachining techniques than the Herschel PACS modules are well suited for this type of development. New thermometers doped for 50 mK operations permit to achieve, with a new design, sensitivities close to the aW/√Hz. It is based on all-legs bolometers (ALB), where the absorbing, insulating and thermometric functions are made by the same suspended silicon structure. This ALB structure, with in this case a spiral design, permits to separate the absorption of the two electromagnetic components of the light polarization. Each pixel consists of four bolometer divided in two pairs, each sensitive to one direction of polarization. This permits to combine the bolometer bridges in a fully differential global structure with a Wheatstone bridge arrangement. Total intensity and polarization unbalance are available directly at the detector level, thanks to a cold readout circuit integrated in the detector structure. This combination of functions is achieved by above IC manufacture techniques (IC for Integrated Circuit).All these developments take place in the prospect of the joint JAXA-ESA SPICA project, to equip a 1344 pixels polarimetric and imaging camera covering three spectral bands (100, 200 and 350 µm)