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We have studied the frequency dependence of superfluid response for He confined in a one-dimension nano-porous medium, FSM16, with 2.8-nm channel. The measurements were performed for an identical sample at two frequencies of 2000 and 500 Hz, by means of a double torsional oscillator. It was made clear that the rapid growth of superfluid response for the low frequency mode occurs at several tens mK lower than those for the high frequency mode. The difference between the two frequency modes is enhanced by the application of pressure. The observed frequency dependence suggests a dynamical superfluid peculiar to one dimension. [ABSTRACT FROM AUTHOR]

We consider He particles confined in a quasi-one-dimensional nanoscale channel in the range of liquid density, and numerically calculate the energy per particle by the imaginary time path integral Monte Carlo method. When the channel diameter becomes less than 1.6 nm, T, at which the energy drops due to the particle exchange effect, shifts to lower temperature, and disappears below 0.48 nm. The diameter dependence of T is similar to the behavior of the superfluid onset temperature, T, for mesoporous materials FSM16 observed by the torsional oscillator. [ABSTRACT FROM AUTHOR]

The gravity on the Earth ( g) has not been taken seriously to mask the fundamental phenomena on quantum solids, though there are some important studies on the critical phenomena of superfluid He under microgravity. We are planning to investigate the effect of gravity on the equilibrium shape of solid He. Since we had a chance to do such an experiment on a small jet plane through the ground based program by JAXA, we got started to construct a cryostat which could cool down as low as 500 mK and meet severe restrictions of experiments on a jet plane. The main part of the refrigerator was a usual He-evaporator pumped by a scroll pump. A small GM refrigerator was installed to provide 4 K stage. 1 K pot was also put in which was also pumped by another scroll pump to condense He gas and sample He. The cryostat was designed to have two optical windows to be able to observe solid He under microgravity. In the test flight for the refrigerator, the minimum temperature of 690 mK was kept during the entire flight of two hours in which 7 to 8 times parabolic flight was performed. Each parabolic flight includes about 20 seconds microgravity and 20 seconds 1.5 to 2.0 g period before and after the microgravity. We did some preliminary experiments with bcc solid He under microgravity. The crystal remained stuck to the bottom of the sample cell even in the 20 seconds microgravity condition. [ABSTRACT FROM AUTHOR]

We have performed the freezing pressure and heat capacity measurements for He confined in a nano-porous medium FSM16 which possesses a one-dimensional 2.8-nm straight channel, in the pressure region above the bulk freezing pressure. At 2.8 MPa, where He in the channel remains a non-superfluid liquid down to the lowest temperature, the heat capacity decreases monotonically with decreasing temperature. It is in contrast to the heat capacity at 0.03 MPa with a broad bump at the temperature higher than the superfluid onset. At around the freezing onset in the channel, no clear heat capacity peak was observed. It suggests that the latent heat of the liquid-solid transition in the channel is quite small. [ABSTRACT FROM AUTHOR]

We have carried out quartz-crystal microbalance (QCM) experiments of 32 kHz quartz tuning fork for He films adsorbed on Grafoil, and have measured the temperature dependence of the resonance frequency and Q value for various areal densities. It was found that the frequency does not decrease exactly in proportion to the areal density. This means that the film still undergoes decoupling partly, although it is strongly suppressed from that of 5 MHz QCM measurements. Above the three-atom thick film, the decoupling due to the superfluidity of the overlayer is observed. In addition, we found that the competition between the superfluidity and the slippage takes place for a large oscillation amplitude. From the comparison with 5 MHz QCM measurements, it is concluded that the acceleration of substrate plays an important role in the slippage. [ABSTRACT FROM AUTHOR]

Sound velocity of solid3 He with an almost single magnetic domain was measured in the nuclear-ordered U2D2 phase and the paramagnetic phase along the melting curve using 10.98MHz longitudinal ultra-sound. The sound velocity increased with temperatures as T4 in the U2D2 phase and jumped about 0.1% at the nuclear-ordered temperature TN . Above TN , it increased gradually, going through a maximum around 4mK, and then decreased as temperature increased. The temperature dependence of the sound velocity is attributed to two parts, the change in density of the solid along the melting curve and the temperature dependent internal energy of the nuclear spin. The nuclear spin contribution to the temperature dependent sound velocity agreed qualitatively with measured thermodynamical quantities. Attenuation of the sound at 10.98MHz was smaller than 0.2(cm−1 ). [ABSTRACT FROM AUTHOR]

The mechanical responses of physisorbed films to the vibration of a substrate were investigated by measuring the sound velocity and attenuation of a two-dimensional mesoporous hectorite. The sound velocity of a pellet with adsorbed3 He films increased drastically at low temperatures accompanied by the attenuation. The temperature dependence of the sound velocity and attenuation can be described by the thermally activated relaxation process, and the increase in sound velocity was found to be proportional to the amount of adsorbed3 He. The most plausible explanation for this behavior is that3 He films decouple from the vibrating substrate at low temperatures. [ABSTRACT FROM AUTHOR]

We measured the interfacial tension of3 He-4 He mixtures at several pressures up to 21 atm down to 0.18 K as well as the number densities of the4 He-rich and3 He-rich liquids at the phase-separation line. The interfacial tension was proportional to T2 up to about 0.4 K without respect to pressure, and the coefficient of this T2 -dependence did not depend strongly on pressure. The extrapolated values of the interfacial tension at absolute zero decreased drastically up to 3 atm, and at this level the decrease about 15% of the value at the saturated vapor pressure σi = 23.9 ± 1.0 μN/m. However, this tension was unchanged above 7 atm. From the pressure dependence of the absolute value the adsorption of3 He relative to the Gibbs dividing surface of4 He component was calculated. [ABSTRACT FROM AUTHOR]

We report the growth kinetics of the4He crystals with a small amount of3He impurities around 0.8 K. The growth resistance was measured using the response of the charged interface with respect to an externally applied voltage. In 5 ppm and 10 ppm3He mixtures, it is found that (1) the relaxation process can be expressed as an exponential behavior, (2) the growth resistance becomes larger compared to pure4He and does not have a strong3He concentration dependence, and (3) the temperature dependence of the growth resistance is much the same as pure4He. We discuss several possible explanations of the present experiment. [ABSTRACT FROM AUTHOR]

The interfacial tension of3He−4He mixtures at saturated vapor pressure has been measured precisely down to 0.15 K by means of the resonance of the interfacial wave. We found that the decrease of the interfacial tension from the value at absolute zero can be described as 56.8 T2 mdyne/cm up to about 0.4 K and that the extrapolated value at absolute zero is 23.9±1.0 mdyne/cm. The large temperature dependence in the low temperature region may be explained by the effect of the change in density difference between the two phases. [ABSTRACT FROM AUTHOR]