Effect of microplastic deformation on the electron ultrasonic absorption in high-purity molybdenum monocrystals

The low temperature (100-6 K) linear absorption of ultrasound (88 kHz) by high purity molybdenum single crystals have been studied. Both unstrained samples and samples sub ected to microplastic deformation (epsilon<=0.45%) were used. Unstrained samples displayed at T<30 K a rapid increase in the absorption with lowering temperature which is interpreted as an indication of electron viscosity due to electron-phonon collisions. After deformation this part of absorption disappeared. This seems to suggest that microplastic deformation brings about in the crystal a sufficiently large number of defects that can compete with phonons in restricting the electron mean free path. A low temperature ''dynamic annealing'' has been revealed in strained samples, that is almost complete recovery of the absorption nature under irradiation with high amplitUde sound, epsilon0 approximately 10-4, during 10 min, at 6 K. A new relaxation peak of absorption at 10 K has been found in strained samples