Creep at low temperatures: unzipping of dislocations, inertia, and criticality processes

We consider creep processes in plastically deformed materials as a critical process such as proposed by Zaitsev (Physica A 189 (1992) 411). We give arguments that the low-temperature creep rate necessarily has two different modes. During the first (fast) stage of stress relaxation, dislocations surmount many barriers simultaneously due to their inertia and a low viscosity of the electron liquid. In the second (slow) stage the depinning of dislocations is mostly due to thermal activation. Our experiments on the mechanical relaxation process in lead alloys and zinc are consistent with the proposed mechanism of depinning of dislocations.