Thermal conductivity and torsional oscillations of solid ⁴He

• Опубліковано в: Физика низких температур
• Дата: 2012
• ISSN: 0132-6414
• Автори: Brazhnikov, M.Yu., Zmeev, D.E., Golov, A.I.
• Формат: Стаття
• Мова: Англійська
• Опубліковано: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2012
• Теми: К 75-летию Л.П. Межова-Деглина
• Онлайн доступ: https://nasplib.isofts.kiev.ua/handle/123456789/117966
• Назва журналу: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Цитувати: Thermal conductivity and torsional oscillations
 of solid ⁴He/ M.Yu. Brazhnikov, D.E. Zmeev, A.I. Golov // Физика низких температур. — 2012. — Т. 38, № 11. — С. 1329–1335. — Бібліогр.: 29 назв. — англ.

Polycrystalline samples of hcp ⁴He of molar volume Vm = 19.5 cm³ with small amount of ³He impurities
 were grown in an annular container by the blocked-capillary method. Three concentrations of ³He, x₃, were studied:
 isotopically purified ⁴He with the estimated x₃ < 10⁻¹⁰, commercial ‘well-grade’ helium with x₃ ~ 3⋅10⁻⁷ and
 a mixture with x₃ = 2.5⋅10⁻⁶. Torsional oscillations at two frequencies, 132.5 and 853.6 Hz, and thermal conductivity
 were investigated before and after annealing. The solid helium under investigation was located not only in
 the annular container but also in the axial fill line inside two torsion rods and dummy bob of the doublefrequency
 torsional oscillator. The analysis of the frequency shifts upon loading with helium and changing temperatures
 of different parts of the oscillator suggests that the three techniques probe the properties of solid helium
 in three different locations: the two different torsion modes respond to the changes of the shear modulus of solid
 helium in either of the two torsion rods while the thermal conductivity probes the phonon mean free path in solid
 helium inside the annular container. The temperature and width of the torsional anomaly increase with increasing
 frequency and x₃. The phonon mean free path increases with increasing x3. Annealing typically resulted in an increased
 phonon mean free path but often in little change in the torsional oscillator response. While the magnitude
 of the torsional anomaly and phonon mean free path can be very different in different samples, no correlation
 was found between them.