Fast Diffusion Process in Quenched hcp Dilute Solid 3^3He-4^4He Mixture

The study of phase structure of dilute $^3$He - $^4$He solid mixture of different quality is performed by spin echo NMR technique. The diffusion coefficient is determined for each coexistent phase. Two diffusion processes are observed in rapidly quenched (non-equilibrium) hcp samples: the first process has a diffusion coefficient corresponding to hcp phase, the second one has huge diffusion coefficient corresponding to liquid phase. That is evidence of liquid-like inclusions formation during fast crystal growing. It is established that these inclusions disappear in equilibrium crystals after careful annealing.Comment: 7 pages, 3 figures, QFS200

On The Mobile Behavior of Solid 4^4He at High Temperatures

We report studies of solid helium contained inside a torsional oscillator, at temperatures between 1.07K and 1.87K. We grew single crystals inside the oscillator using commercially pure $^4$He and $^3$He-$^4$He mixtures containing 100 ppm $^3$He. Crystals were grown at constant temperature and pressure on the melting curve. At the end of the growth, the crystals were disordered, following which they partially decoupled from the oscillator. The fraction of the decoupled He mass was temperature and velocity dependent. Around 1K, the decoupled mass fraction for crystals grown from the mixture reached a limiting value of around 35%. In the case of crystals grown using commercially pure $^4$He at temperatures below 1.3K, this fraction was much smaller. This difference could possibly be associated with the roughening transition at the solid-liquid interface.Comment: 15 pages, 6 figure

The Geyser effect in the expansion of solid helium into vacuum

The mechanism behind the intensity oscillations accompanying the flow of solid helium through a micron-sized orifice into vacuum, called the geyser effect, is investigated by measuring the pressure pulses at various locations in the entire flow system. The new results reveal that the source chamber pressure pulses have the same shape as the external detector pulses monitored in the previous experiments [G. Benedek et al., Phys. Rev. Lett. 95, 095301 (2005)]. New experiments in which the external gas reservoir is isolated from the pressure regulator provide direct information on the mechanism of the collapse leading to the geyser pulses. Thus each geyser pulse is triggered by the breakdown of a plug located upstream of the source chamber. The flow of liquid through the orifice determines the shape of the subsequent geyser pulse. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010

Elementary excitations in solid and liquid He-4 at the melting pressure.

Recent discovery of a nonclassical rotational inertia (NCRI) in solid He-4 below 0.2 K by Kim and Chan has revived great interest in the problem of supersolidity and initiated intensive study on the properties of solid He-4. A direct proof that the onset of NCRI corresponds to the supersolid transition would be the observation of a corresponding drop of the entropy of solid He-4 below the transition temperature. We have measured the melting pressure of ultrapure He-4 in the temperature range from 0.01 to 0.45 K with several single crystals grown at different pressures and with the accuracy of 0.5 mu bar. In addition, supplementary measurements of the pressure in liquid He-4 at constant volume have been performed, which allowed us to eliminate the contribution of the temperature-dependent properties of the pressure gauge from the measured melting pressure data. With the correction to the temperature-dependent sensitivity of the pressure gauge, the variation of the melting pressure of He-4 below 320 mK obeys the pure T-4 law due to phonons with the accuracy of 0.5 mu bar, and no sign of the transition is seen (Todoshchenko et al. in JETP Lett. 85:454, 2007). This sets the upper limit of similar to 5 center dot 10(-8) R for a possible excess entropy in high-quality He-4 crystals below 320 mK. At higher temperatures the contribution from rotons in the superfluid He-4 has been observed. The thermal expansion coefficient of the superfluid He-4 has been measured in the range from 0.01 to 0.7 K with the accuracy of similar to 10(-7) 1/K, or by two orders of magnitude better than in previous measurements. The roton contributions to the melting pressure and to the pressure in liquid at a constant volume are consistent and yield the value of 6.8 K for the roton gap, which is very close to the values obtained with other methods. As no contribution due to weakly interacting vacancies to the melting pressure of He-4 has been observed, the lower limit of about 5.5 K for their activation energy can be set

Spin-spin correlation effect on the thermodynamic properties of the polarized liquid 3 He at finite temperature

We have used the lowest order constrained variational (LOCV) method to calculate some thermodynamic properties of the polarized liquid 3He at finite temperature with the spin-dependent correlation function. For each value of the temperature and density we have shown that the main contribution to the potential energy comes from the spin-triplet state. For the polarized liquid 3He, we have seen that the differences between the thermodynamic properties of the spin-dependent and the spin-independent cases decrease by increasing both polarization and temperature. For all relevant temperatures and densities, our results do not show any ferromagnetic phase transition

Thermodynamic and electrical properties of laser-shocked liquid deuterium

Liquid deuterium at high pressure and temperature has been observed to undergo significant electronic structural changes. Reflectivity and temperature measurements of liquid deuterium up to around 70 GPa were obtained using a quartz standard. The observed specific heat of liquid deuterium approaches the Dulong-Petit limit above 1 eV. Discussions on specific heat indicate a molecular dissociation below 1 eV and fully dissociated above 1.5 eV. Also, the electrical conductivity of deuterium estimated from reflectivity reaches ~1.3 × 105 (Ω⋅m)-1, proving that deuterium in this condition is a conducting degenerate liquid metal and undergo an insulator-metal transition. The results from specific heat, carrier density and conductivity agreed well with each other, which might be a reinforcement of the insulator-metal transition and the molecular dissociation. In addition, a new correction method of reflectivity in temperature calculation was proposed to improve the accuracy of temperature results. A new “dynamic calibration” was introduced in this work to make the experiments simpler and more accurate