3He Temperature Research Articles

The Provisional Low Temperature Scale from 0.9 mK to 1 K, PLTS-2000

An internationally-accepted ultra-low temperature scale is needed to provide the basis for reliable thermometry in the temperature range in which commercial dilution refrigerators operate, and in experiments investigating the properties of 3He and other condensed matter. Several laboratories have developed 3He melting-pressure scales, but there are substantial differences even between the most recent of them. These amount to about 0.3% of T near 500 mK, rising to about 6% of T at 0.9 mK. In 1996 a collaboration was initiated between low temperature physicists in national laboratories and elsewhere to derive an equation for the melting pressure of 3He which could be accepted for international use from 1 K to 0.9 mK, the Neel temperature of solid 3He. After an open workshop in Leiden in 1998, discussions took place to see if thermodynamic calculation of 3He melting pressures could resolve the differences. In January 2000 the authors (apart from ALR and GS) met at NIST and were able to reach a compromise on the Provisional Low Temperature Scale, PLTS-2000. Its 1-sigma uncertainty is estimated to be 0.3% of T (up to a maximum of 0.5 mK), but this rises to about 2% of T at 0.9 mK. The provisional status recognizes that the PLTS-2000 is a compromise, rather than a true consensus, but it is likely to be some years before it can be replaced by a more accurate scale. The scale was announced at the Quantum Fluids and Solids conference in Minnesota, USA, in June 2000, and was formally adopted by the Comite International des Poids et Mesures in October 2000.

Semisuperfluidity of 3He in aerogel?

According to hydrodynamic, acoustic, and NMR studies the superfluid transition temperature of 3He in aerogel ( T(a)(c)) is significantly suppressed with respect to that of bulk 3He. We have found in the range of temperatures between T(c) and T(a)(c) a large and unexpected NMR satellite line attributable to the liquid inside the aerogel. We propose that this anomalous behavior of liquid 3He corresponds to a new type of superfluid ordering related to magnetic and possibly orbital coherence.

Superfluidity of 3He contained in aerogel

It is known that the critical temperature of superfluid 3He confined within aerogel is suppressed, however, the exact nature of the superfluid phase is currently undetermined. We have designed an experiment in which the aerogel is surrounded by bulk superfluid of a known phase. Owing to the dipole–dipole interaction the bulk superfluid precesses at a frequency shifted from the Larmor frequency. The surface solid and the confined liquid components of the 3He inside the aerogel are in fast exchange and precess near the Larmor frequency. We have observed an additional NMR signal near the frequency of the bulk 3He from the aerogel.

Scaling of the superfluid fraction and T(c) of 3He in aerogel

We have investigated the superfluid transition of 3He in different samples of silica aerogel. By comparing new measurements on a 99.5% sample with previous observations on the behavior of 3He in 98% porous aerogel, we have found evidence for a scaling of the transition temperature and superfluid density of 3He to the correlation length of the aerogel.

Phase diagram of the A-B transition of superfluid 3He

We have measured the A-B phase transition temperature of superfluid 3He at pressures from zero to 29 bars, and in all magnetic fields up to the highest field limit of the B phase (∼0.59 Tesla). We have also devised a simple function which accurately describes the entire pressure-temperature-magnetic field phase diagram of the A-B transition. This function intrinsically satisfies all correct asymptotic behaviors in the low- and high-field limits. Using thermodynamic identities we can measure properties which previously could not be directly measured.

Suppression of the Critical Current and Transition Temperature of Superfluid 3He in a Single Submicron Cylindrical Channel

The flow of superfluid 3He through a single cylindrical channel of 0.7 micron diameter is studied. Suppresion of the transition temperature and of the depairing critical current density are observed indicating that the boundary condition at the wall is that for diffuse quasiparticle scattering. The suppresions agree reasonably well with model calculations for this geometry using the diffuse scattering boundary conditions. Some evidence for dissipation of superflow due to thermal activation of 2π phase slips of the order parameter inside the channel is seen.

Miniature liquid-3He refrigerator

The use of a cryopump and high-pressure, internal storage of the cryogen makes it possible to miniaturize a one-shot recyclable 3He refrigerator while at the same time improving its performance. Because of their simplified interface requirements, such refrigerators are readily incorporated into existing 4He cryostats, allowing a convenient extension of their operating range down to 0.3 K. An analysis of the parameters describing refrigerator performance (condensation time, heat transfer to the 4He bath, lifetime, and refrigeration power) leads to the definition of an optimized refrigerator. Measured performance characteristics of a miniature [2-l standard temperature and pressure (STP) of 3He] refrigerator used in laboratory and stratospheric balloon-borne experiments are given.

A Temperature Controller for Experiments Using Adiabatic Demagnetization

An apparatus has been designed to control and stabilize temperature in the range 2–20 mK using the adiabatic demagnetization technique. Using a standard CMN demagnetization cell, the temperature of liquid 3He was stabilized within ±0.5 µK.

Fourth sound, size effects, and healing length in superfluid 3He

Fourth sound was used to measure the depressions of the superfluid component density and the transition temperature of superfluid 3He confined in resonators filled with packed powders. The observed magnitude of the size effects in 3He is much greater than that in 4He [M. Kriss and I. Rudnick, J. Low Temp. Phys. 3, 339 (1970)]. The depression in transition temperature was measured as a function of pressure (12–30 bar) and pore size (0.1–5 μm) and it is found to be consistent with theoretical estimates of healing length. The Q of a fourth sound resonance was also measured as a function of temperature over a limited range. The maximum Q observed was 40. The magnitude of Q appears to be too small to be accounted for by the normal component motion alone. [Work supported by NSF.]

Static magnetization and ordering temperature of solid 3He at various molar volumes

Abstract The magnetization of solid 3He has been measured at three molar volumes from 10 mK down to 0.4 mK. Near the ordering temperature, the magnetization increases with decreasing temperature more rapidly than the Curie-Weiss behaviour. The ordering temperature TN decreases linearly with decreasing molar volume V with the slope, dTN/dV = 0.57 mKmole/cm3. This value leads to the pressure change ΔP = 14.7 mbar at the transition (constant volume) along the melting curve.

Suppression of P-wave superfluidity in long, narrow pores

The transition temperature of superfluid 3He is calculated as a function of the size of an infinitely long cylindrical pore or an infinite slab container with diffusely scattering walls. We present the exact asymptotic behavior for large and small containers and a full numerical calculation for intermediate sizes.

Self diffusion in solid 3He at very low temperature

Multiple spin echoes in solid 3He, which are due to the demagnetizing field effect, have been reconsidered by taking into account the spin diffusion. The analysis is applied to the experimental results obtained earlier at very low temperature. The spin diffusion coefficient D remains constant in the whole temperature range 10.5 mK-1.07 mK, even close to the spin ordering temperature of solid 3He. The susceptibility values χ obtained have a higher precision than those previously published [3].

Interpretation of the elastic debye temperature of bcc 3He

It is argued that the temperature dependence of the elastic constants of bcc 3He is not large enough to explain the discrepancy between the elastic and the extrapolated calorimetric Debye temperatures.