Plastic flow of solid 4He and 3He at low temperatures (Review Article)
V.A. Maidanov, E.Ya. Rudavskii, S.N. Smirnov, and S.S. Sokolov
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
Received March 25, 2019, published online July 26, 2019
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 4He and 3He: if in solid 4He, the plastic flow rate decreases with decreasing temperature, which corresponds to a thermally activated process, then in solid 3He 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 4He 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 4He and 3He, 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.