6 research outputs found
Strain dependence of the acoustic properties of amorphous metals below 1K: Evidence for the interaction between tunneling states
We have conducted a thorough study of the acoustic properties between 10^-4
and 1 Kelvin for the amorphous metal Zr_x Cu_1-x (x=0.3 and x=0.4), by
measuring the relative change of sound velocity dv/v and internal friction Q^-1
as a function of temperature and also of the applied strain, in both
superconducting and normal state. 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
dv/v and Q^-1 depend on applied strain and the tunneling systems cannot be
considered as independent.Comment: 4 pages, 4 figures (submitted to PRL
Inter- and Intragranular Effects in Superconducting Compacted Platinum Powders
Compacted platinum powders exhibit a sharp onset of diamagnetic screening at
mK in zero magnetic field in all samples investigated. This
sharp onset is interpreted in terms of the intragranular transition into the
superconducting state. At lower temperatures, the magnetic ac susceptibility
strongly depends on the ac field amplitude and reflects the small intergranular
critical current density . This critical current density shows a strong
dependence on the packing fraction f of the granular samples. Surprisingly,
increases significantly with decreasing f ( A/cm for f = 0.67 and A/cm for f
= 0.50). The temperature dependence of shows strong positive curvature
over a wide temperature range for both samples. The phase diagrams of inter-
and intragranular superconductivity for different samples indicate that the
granular structure might play the key role for an understanding of the origin
of superconductivity in the platinum compacts.Comment: 11 pages including 9 figures. To appear in Phys. Rev. B in Nov. 0