Influence of microplastic deformation on the electronic absorption of ultrasound in high-purity molybdenum single crystals

The low-temperature (in the interval 100–6° K) linear absorption of ultrasound (88 kHz) in high-purity molybdenum single crystals (RRR ≈ 105) is investigated. Measurements are performed on untreated samples and on samples subjected to microplastic deformation (ε ≤ 0.45%). In the undeformed samples at T < 30° K an abrupt increase in the absorption with decreasing temperature is observed and is interpreted here as a result of electron viscosity associated with electron–phonon collisions. After deformation, this part of the absorption vanishes. The latter result leads to the conclusion that microplastic deformation produces a large number of defects in the crystal, which are capable of competing with phonons in limiting the electron mean free path. Low-temperature “dynamic annealing” of the deformed samples is observed; the nature of the absorption is almost completely restored when the samples are irradiated with sound of large amplitude ε0 ≈ 10–4 for a period of 10 min at 6° K. A previously undetected relaxation peak of the absorption at 10° K is observed in the deformed samples.

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