The temperature dependences of the yield stress and the strain rate sensitivity were studied for a (100)<010> slip system in monocrystals of the pure  phase at temperatures ranging from 0.5 to 4.4K. The existence of a previously observed low-temperature anomaly, which exhibited the characteristic features of a quantum process (a transition from thermally activated to thermal plastic flow at temperatures near to, and below, 1K) was confirmed. It was shown that a superconducting transition in the samples significantly extended the temperature range within which the anomaly was observed. The effect of Cd doping upon the anomaly was also investigated. It was found that a low impurity concentration increased the threshold temperature of the anomaly. On the other hand, a high Cd concentration led to the disappearance of thermal plastic flow. A detailed theoretical analysis of the experimental observations was carried out on the basis of the predominant effect of Peierls barriers upon the mobility of dislocations in the given slip system. Theoretical data on the quantum motion of dislocations in the Peierls relief were also exploited. Simple analytical expressions were obtained for the temperature dependences of the plasticity parameters in the region of the quantum anomaly. The procedure for calculating empirical values of the fundamental parameters (Peierls stress, effective mass, linear tension, electron friction coefficient) for a dislocation string in dislocation theory was applied to the slip system.

V.D.Natsik, G.I.Kirichenko, V.V.Pustovalov, V.P.Soldatov, S.E.Shumilin: Low Temperature Physics, 1996, 22[8], 740-54