[en] A study of plastic flow of solid 3He through a metallized porous elastic polymer film, the frozen-in crystal, is carried out in the temperature range of 0.1-1 K. The flow was caused by mechanical stresses in the crystal, which created by an external electrical power. The velocity of the solid helium plastic flow was determined by measuring changes in capacitance of the measuring capacitor, in which the metallized surface of the film served as a movable electrode. Two areas can be clearly identified on the temperature dependence of the flow velocity V. Above approx 200 mK the value of V decreases exponentially with decreasing of temperature, which corresponds to the thermally activated regime of plastic flow. At lower temperatures the velocity V does not depend on temperature, indicating a quantum plastic flow. A detailed analysis of experimental data is performed in the thermally activated region. The empirical values of the following parameters are defined: activation volume, the activation energy and the threshold stress above which there is a macroscopic plastic flow. It is found that the value of the activation volume in 3070 times more than the atomic volume, indicating that the scale of the structural rearrangements in the crystal at the elementary acts of plastic flow is significantly higher than the atomic size. In this case the activation energy is close to the value of the vacancy activation energy. The experimental results are analyzed in the framework of the diffusion-vacancy and dislocation models of plastic flow. In the dislocation model we estimated the temperature below which dislocations overcome barriers Peierls by quantum tunneling. The appendix discusses the physical foundations of the methodology used and the results of the theory of the dislocation motion in the Peierls relief, which were used to analyze the characteristics of the plastic flow of solid "3He.

[en] NMR and pressure have been measured during phase separation in solid ³He-⁴He mixtures. Spin echoes were used to observe bounded diffusion and to estimate the diffusion coefficient, size and nuclei concentration in the ³He-enriched phase. The characteristic phase separation time constant of the mixture was found from pressure measurements. The results argue convincingly for homogeneous nucleation. The surface tension of the nuclei is found independently from NMR and from pressure measurements; the two determinations agree well and yield a surface tension coefficient of 4.9x10^-6 J m^-2

[en] The kinetics of the phase separation in ³He-⁴He superfluid solutions is studied from anomaly in the first sound velocity and the dielectric constant. The histogram of experiments on solution supersaturation is obtained and used to study of phase separation probability. It was shown that above 50 mK the obtained temperature dependence of the supersaturation is qualitatively in accord with the thermal activation mechanism of nucleation. Below 50 mK the data may point towards a transition from classical to quantum mechanism of nucleation

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[en] The kinetics of BCC-HCP phase transition along the ⁴He melting curve is studied in the temperature range of 1.25 to 2.0 K in the vicinity of triple points (BCC-HCP-He II and BCC-HCP-He I). The samples are produced by the capillary blocking technique, and the kinetics is investigated by the precise pressure measurements. It is found that far from the triple points the variation in the pressure with the temperature along the melting curve can be described by the exponential dependences. When passing though the triple points, the behavior of pressure and temperature becomes anomalous, favouring the assumption of crystal remelting under structure phase transition

[en] Phase separation kinetics and growth of the new phase in supersaturated superfluid ³He-⁴He solutions was studied using the method of continuous change of ³He concentration in situ and developed theory. Simultaneous measurements of the first sound velocity and the dielectric constant were carried out during the change of concentration. The velocity and attenuation of the first sound and the dielectric constant in supersaturated metastable solutions were calculated on the assumption that the excess ³He in the solution is in the form of both atoms and droplets of the new phase. It was shown that the sound velocity, unlike the dielectric constant, is very sensitive to the formation of droplets. Comparison of the theory and the experimental data allowed the authors to elucidate the growth dynamics of the nuclei of the new phase from the metastable supersaturated mixture

[en] The velocity of fast and slow collective modes of 90, 94 and 98% porosity aerogels filled with superfluid helium were measured by means of low-frequency resonant technique at temperatures 0.5-2.5 K. The temperature dependences of velocities of both modes are compared with the hydrodynamic theory which was modified taking into account the mobility of the aerogel matrix, porosity of media and tortuosity of an acoustic way. It has been found that the fast and slow modes in an aerogel are coupled much stronger than the first and second sounds in bulk He II.

[en] A review of experimental and theoretical studies of the plastic flow of solid helium in the temperature range 0.1–1.0 K is presented. The most reliable and interesting results were obtained in two scientific groups where a plastic flow was observed between interconnected chambers with solid helium that occurred after an overpressure in one of the chambers, in which the direct contact of solid helium with the superfluid phase was excluded in the measuring cell. A significantly different nature of plastic flow was found in solid 4 He and 3 He: if in solid 4 He, the plastic flow rate decreases with decreasing temperature, which corresponds to a thermally activated process, then in solid 3 He at temperatures below ≈ 0.2 K, quantum creep was first recorded when the flow rate ceases to depend on temperature. Only in one group in experiments conducted near the melting curve, an increase in the flow rate of 4 He was observed with decreasing temperature, which allowed the authors to conclude that some form of superfluidity manifested itself. In the thermally activated region of the plastic flow of 4 He and 3 He, the values of the activation energy were found and also the activation volume were estimated, which are 30–70 times higher than the atomic volume. The analysis of the possible physical mechanisms of plastic flow of solid helium was carried out. (author)

[en] The precision barometry measurements have revealed an unusual behavior of pressure in solid ³He-⁴He solutions of concentration ∼ 30% ³He: in the pre separation region the pressure increases with decreasing temperature long before the onset of the phase transition. This anomaly is found to be associated with correlation effects in the impuriton subsystem that cause large-scale fluctuations of the impurity concentration. In this case the fluctuation contribution to the pressure far exceeds the phonon contribution. It is established that the experimental data are in quantitative agreement with the proposed theory. It is shown that the temperature behavior of pressure in the pre separation and metastable regions can be explained only with correct account for the long-range behavior of the interimpurity interaction