Low Temperature Physics: 26, 641 (2000); https://doi.org/10.1063/1.1312389 (8 pages)
Физика Низких Температур: Том 26, Выпуск 9-10 (Сентябрь 2000), c. 874-883    ( к оглавлению , назад )

Sound propagation in liquid He in impurity-helium solids

S. I. Kiselev, V. V. Khmelenko, and D. M. Lee

Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853-2501, USA
E-mail: khmel@ccmr.cornell.edu

Received April 6, 2000


The observed features of attenuation of ultrasound in Im-He samples created after introduction of impurity particles (D2, N2, Ne, Kr) in a volume of helium II show that a porous substance consisting of a loosely interconnected continuous network is created. It is formed by impurity particles encapsulated in solidified helium. The propagation of ordinary sound in these porous samples is similar to the fast sound mode in light aerogels. The temperature dependence of attenuation for different Im-He samples is investigated. It is established that the character of attenuation in D2-He samples is considerably different from that in heavier Im-He solids (Im = N2, Ne, Kr). Analysis of attenuation lets us conclude that Im-He samples have a wide distribution of pores from 8 nm to 800 nm. The study of ultrasound in helium in Im-He samples near the l-point shows the presence of broadening in the attenuation peak as compared with bulk liquid helium. The suppression of Tc is very small, ≤ 0.2 mK.

67.40.Yv - Impurities and other defects
67.40.Mj - First sound