The nonclassical rotational inertia fraction of the identical cylindrical solid 4He below 300 mK is studied at 496 and 1173 Hz by a double resonance torsional oscillator. Below 35 mK, the fractions are the same at sufficiently low rim velocities. Above 35 mK, the fraction is greater for the higher than the lower mode. The dissipation peak of the lower mode occurs at a temperature approximately 4 mK lower than that of the higher mode. The drive dependence of the two modes shows that the reduction of the fraction is characterized by critical velocity, not amplitude or acceleration.

Frequency shifts and dissipation of a compound torsional oscillator induced by solid 4 He samples containing 3 He impurity concentrations (x3 = 0.3, 3, 6, 12 and 25 in units of 10 −6 ) have been measured at two resonant mode frequencies (f1 = 493 and f2 = 1164 Hz) at temperatures (T ) between 0.02 and 1.1 K. The fractional frequency shifts of the f1 mode were much smaller than those of the f2 mode. The observed frequency shifts continued to decrease as T was increased above 0.3 K, and the conventional non-classical rotation inertia fraction was not well defined in all samples with x3 ≥ 3 ppm. Temperatures where peaks in dissipation of the f2 mode occurred were higher than those of the f1 mode in all samples. The peak dissipation magnitudes of the f1 mode was greater than those of the f2 mode in all samples. The activation energy and the characteristic time (τ0) were extracted for each sample from an Arrhenius plot between mode frequencies and inverse peak temperatures. The average activation energy among all samples was 430 mK, and τ0 ranged from 2×10 −7 s to 5×10 −5 s in samples with x3 = 0.3 to 25 ppm. The characteristic time increased with increasing x3. Observed temperature dependence of dissipation were consistent with those expected from a simple Debye relaxation model if the dissipation peak magnitude was separately adjusted for each mode. Observed frequency shifts were greater than those expected from the model. The discrepancies between the observed and the model frequency shifts increased at the higher frequency mode.

Measurements on hysteretic response of compound torsional oscillator containing annular-shaped solid 4 He samples were carried out by varying the oscillator drive amplitude starting from high to low and then back up to the initial high value. Hysteresis in the oscillator frequency and amplitudes were observed only below an onset temperature. The hysteresis onset temperature (T H ) did not depend on the oscillator frequency, width of the sample annulus, annealing and refreezing after melting. A systematic increase in T H was observed as the 3 He impurity concentration in solid 4 He samples was increased. The dependence of T H on 3 He impurity concentration followed approximately that of the dissipation peak temperatures. Possible relationships of the observed hysteresis phenomena with models of solid 4 He dynamics based on freezing of a vortex liquid and dislocation motion are discussed.

We describe the first observations on the time-dependent dissipation when the drive level of a torsional oscillator containing solid (4)He is abruptly changed. The relaxation of dissipation in solid (4)He shows rich dynamical behavior including exponential and logarithmic time-dependent decays, hysteresis, and memory effects.

Under applied magnetic field, the originally single superfluid 3 He transition near 3 mK in zero field splits into two transitions between which a new A 1 phase emerges. The two second order transitions are marked by abrupt changes in viscosity, zero sound attenuation and nuclear magnetic resonance. To date, the maximum magnetic field for producing A 1 phase is 15 T. The A 1 phase has been identified with a spin-polarized (ferromagnetic) superfluid system which breaks the relative symmetry between spin, orbit and gauge spaces. A superfluid mass current in A 1 is simultaneously a spin current resulting in the propagation of spin-entropy wave. Experiments with spin-entropy wave provide measurements of anisotropic superfluid density and strong coupling parameters, spin diffusion coefficient and texture transformations. Owing to the spin-polarized nature, superflows may be generated by applied magnetic field gradients and measured from the induced magnetic fountain pressure. The mechanical spin density detector is developed to measure the spin relaxation in A 1 phase. The observed unexpected temperature dependence of the spin relaxation time gives evidence that the A 1 phase contains a small amount of the predicted minority spin condensate from dipolar interaction energy.KEYWORDS: spin-polarized system, superfluid 3 He, magnetic fountain effect, spin pump, second sound, high magnetic field

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A systematic study was carried out to search for fourth sound propagation solid 4 He samples below 500 mK down to 40 mK between 25 and 56 bar using the techniques of heat pulse generator and titanium superconducting transition edge bolometer. If solid 4 He is endowed with superfluidity below 200 mK as indicated by recent torsional oscillator experiments, theories predict fourth sound propagation in such supersolid state. If found, fourth sound provides a convincing evidence for superfluidity and a new tool for studying the new phase. To search for a fourth sound-like mode, the response of the bolometers to heat pulses traveling through cylindrical samples of solids grown with different crystal qualities. Bolometers with increasing sensitivity were constructed. The heater generator amplitude was reduced to the sensitivity limit to search for any critical velocity effects. The fourth sound velocity is expected to vary as µ r r s / . Searches were made for signature in the bolometer response with such characteristic temperature dependence. The measured response signal has not so far revealed any signature of new propagating mode within the temperature excursion of 5 mK from the background signal shape. Possible reasons for this negative result are discussed. Prior to the fourth sound search, the temperature dependence of heat pulse propagation was studied as it transformed from «second sound» in the normal solid 4 He to the transverse ballistic phonon propagation. Our work extended the studies by Narayanamurti and Dynes [Phys. Rev. B12, 1731(1975] to higher pressures and to lower temperatures. The measured transverse ballistic phonon propagation velocity remained constant, within 0.3% scatter of data below 100 mK at all pressures and revealed no indication for an onset of supersolidity. The overall dynamic thermal response of solid to heat input was found to depend strongly on the sample preparation procedure.