Effects ofHe3impurity on solidHe4studied by compo

Abstract

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.

Aging of solid 4He under torsional oscillation at low temperatures

“…Day and Beamish [5] discovered that the shear modulus of solid 4 He showed strikingly similar behaviors as those found in torsional oscillator experiments in temperature dependence, nonlinearity and hysteresis [6] in drive dependence, and dependence on 3 He impurity [7][8][9]. These similarities pointed to the shear modulus of solid 4 He contributing, at least in part, to the observed decoupling effects in TO experiments.…”

“…The sample container attached to the TO is a thin annulus (10.0 mm outer diameter, 9.6 inner diameter, 8.0 mm height). The cell design is essentially identical to that described in detail by Gumann et al [9] except for the thickness of the annular sample chamber. The sample chamber is filled through a hole (0.8 mm diameter) drilled into the BeCu torsion rod (2.0 mm diameter) of the TO.…”

NMR investigation of the low-temperature dynamics of solid4He doped with3He impurities

“…This is because the NCRIFs could be the signature of a supersolid state as outlined by Leggett 4 and predicted by Andreev and Lifshitz several years ago. 5 A large number of independent experiments [6][7][8][9][10] have shown that the NCRIF magnitude and temperature dependence are strongly dependent on defects such as 3 He impurities 11,12 and the quality of the crystals, and can be made very small by very careful annealing. 3 The observation of…”

Excitations of amorphous solid helium

“…The NCRI has now been widely reproduced in other laboratories in a variety of sample cells. [3][4][5][6][7][8][9] However, the magnitude of the NCRI observed varies between zero and 1.5 %, depending on how the sample is prepared, quenched or annealed, on the 3 He concentration and on other factors. This suggests that the NCRI is associated with defects in the solid, dislocations, grain boundaries, amorphous regions or other defects.…”

“…This suggests that the NCRI is associated with defects in the solid, dislocations, grain boundaries, amorphous regions or other defects. [10][11][12][13] The magnitude and character of the NCRI depends on the oscillator frequency 7,8,14 and shows effects 15,16 not usually associated with superflow. For example, the NCRI is associated with substantial elastic energy dissipation in the solid described by the Q of the oscillator.…”