Phys. Rev. B 65, 180201(R) (2002)

R. König, M. A. Ramos, I. Usherov-Marshak, J. Arcas-Guijarro, A. Hernando-Mañeru, and P. Esquinazi

Abstract

We have conducted a thorough study of the acoustic properties between 10^-4 and 1 K for the amorphous metal Zr_xCu_1-x (x=0.3 and x=0.4), by measuring the relative change of sound velocity Δv/v and internal friction Q^-1 as a function of temperature and also of the applied strain, in both superconducting and normal states. We have found that when plotted versus the ratio of strain energy to thermal energy, all measurements display the same behavior: a crossover from a linear regime of “independent” tunneling systems at very low strains and/or high enough temperatures to a nonlinear regime where Δv/v and Q^-1 depend on applied strain and the tunneling systems cannot be considered as independent.