Reyer Jochemsen

Morphology and growth kinetics of 3He crystals below 1 mK

The shapes as well as the growth and melting properties of bcc-3He single crystals have been investigated with a low temperature Fabry-Pérot interferometer. Eleven types of facets were clearly identified during slow crystal growth at the temperature of 0.55 mK, where the solid is in the antiferromagnetically ordered u2d2 phase. The growth rates of the individual facets have been measured and the results indicate significant growth anisotropy. The observed linear dependence of the growth velocity on the driving force shows that facets grow due to the presence of screw dislocations, while the step velocity is limited by the spin wave velocity due to the strong interaction of the moving step with magnons in the solid. The measured growth rates of the facets and the assumed growth mechanism gave us the unique opportunity to obtain the step free energies for ten different types of facets observed during a single growth sequence. The dependence of the free energy of the step on the step height is compared with predictions of the weak- and strong-coupling models. Our results suggest that 3He crystals have rather strong coupling of the liquid/solid interface to the crystal lattice and that the step-step interactions are of elastic origin.

Optical observation of 3He crystals at mK-temperatures

We report on our new optical setup which employs multiple-beam interferometry for measurements on He-3 crystals. Our interferometer enables us to observe the global shape of the crystal as well as the fine details of the solid/liquid interface on a scale of less than 5 mu m. Phase measurement allows accurate studies of growth and melting kinetics. We present the first images of He-3 crystals obtained with this setup.

Considerations on the read out of low frequency NMR for 3He

For studies of the superfmid phases of 3He the technique low of frequency (500 kHz) NMR is widely used. One way to read out the NMR signal is with the continuous wave experiment. In this experiment the NMR signal is proportional with the quality factor of a tank circuit. However direct connection with a coax cable will, because of its resistivity and parasitic capacitance load the tank circuit and by that lower the quality factor In this paper two passive methods, which minimize the loading to read out the NMR signal are described and simulated. The first method reads the NMR signal over the parasitic capacitance of the coax cable, which is put in series with the tank circuit. The second method makes use of a pick up coil, which is weakly coupled to the coil of the tank circuit Both methods can preserve a high quality factor, and are optimized for best SNR

European Dissemination of the Ultra-low Temperature Scale, PLTS-2000

The first phase of the EU collaborative project on sub‐kelvin thermometry, ‘ULT Dissemination’, is nearing completion, leading to the development of several thermometers and devices, and the instrumentation needed to disseminate the new Provisional Low Temperature Scale, PLTS‐2000, to users. Principal among these are a current‐sensing noise thermometer (CSNT), a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second‐sound acoustic thermometer and a superconductive reference device SRD‐1000. Several partners have set up 3He melting‐pressure thermometers to realise the PLTS‐2000, and will check it using Pt‐NMR, CMN and other thermometers. The scale, which was formally adopted by the Comite International des Poids et Mesures in October 2000, covers the range of temperature from 1 K down to 0.9 mK, and is defined by an equation for the melting pressure of 3He. The SRD employs novel fabrication and detection techniques with up to 10 samples, and is expected to meet the requirement...

First Prototypes of the Superconductive Reference Device SRD1000

In the framework of the European Project “Ultra‐Low Temperature Dissemination (ULT),” a superconductive reference device (SRD1000) and dedicated external measurement electronics were developed to provide direct traceability to the new Provisional Low Temperature Scale (PLTS‐2000). The SRD1000 includes 10 reference points in the temperature range 15 mK to 1 K: W (TC = 15 mK), Be (TC = 23 mK), Ir80Rh20 (TC ≈ 35 mK), Ir92Rh08 (TC ≈ 65 mK), Ir (TC = 100 mK), AuAl2 (TC = 160 mK), AuIn2 (TC = 208 mK), Cd (TC = 520 mK), Zn (TC = 850 mK) and Al (TC = 1180 mK). After extensive research and development in the preparation and in the ultra‐low temperature characterization of superconductive reference materials during the past years, eventually a final selection of the materials to be included in the first SRD1000 prototype sensors was made. In this paper, the superconducting transitions observed for the selected materials and the sample preparations are reported, the SRD1000 sensor and external electronics technology...

EU dissemination of the provisional ultra-low-temperature scale, PLTS-2000

Following the introduction of the provisional low-temperature scale from 0.9 mK to 1K, PLTS-2000, there is a need for primary and secondary thermometers and fixed points, which can disseminate the scale to users. This paper reports on the progress, within the EU collaborative project ‘ULT Dissemination’, in the development and evaluation of several devices with associated instrumentation. Principal among them are a current-sensing noise thermometer, a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second-sound thermometer, a 3He melting pressure thermometer for a direct realisation of the PLTS-2000. A superconductive reference device has also been developed, as a replacement for the NBS SRM-768 which is no longer available.

SRD1000: a superconductive reference device for thermometry below 1 K

A superconductive reference device (SRD1000), providing 10 reference points in the temperature range 10 mK–1 K with dedicated measurement electronics, has been developed and tested to provide direct traceability to the new provisional low temperature scale (PLTS-2000). We report on the repeatability of the transition temperatures of samples of IrxRh100−x alloys (with transition temperatures between 20 and 100 mK) and some single crystals (Cd, Zn, AuIn2,AuAl2 and W).

Faceting on 3He crystals

It has been predicted by Landau that, ideally at low temperatures, crystals should show many different types of facets, i.e., flat smooth faces on their surface, but this so-called “devils staircase” phenomenon has been difficult to observe experimentally. In this paper we describe our recent experiments, in which altogether 11 different types of facets have been identified on growing 3He crystals at the temperature of 0.55 mK by using a unique low-temperature Fabry–Pérot interferometer. Previously only 3 types of facets had been seen in this system. We have also measured the growth velocities of different facets, and our interpretation of the obtained results yields the conclusion that 3He has much stronger coupling of the liquid–solid interface to the crystal lattice than has been expected. After an introduction we present a short theoretical background about the equilibrium crystal shape and the roughening transitions, which is followed by the description of our experimental results and discussion.

Quasi-2D Flows of 3He – 4He Mixtures

Transport in degenerate 3He-4He mixtures in quasi-2D flow channels is discussed. The quasiparticle mean free path combines particle-wall and particle-particle collisions including the interference between them. The temperature, concentration, and polarization dependences of the transport coefficients allow easy extraction of the correlation parameters of random surface roughness from transport data.

On the Possibility of Observing Third Sound on 3He

This paper focuses on the hydrodynamics of third sound on a superfluid3He film. We solve the hydrodynamical equations in the limit of thick films with weak interaction with the substrate. The surface tension at the free interface is shown to have a large effect on the third sound velocity and on the attenuation for frequencies larger than 1Hz. In the case of a diffusely scattering substrate a ripplon-like dispersion relation is found for this frequency range.