Thermal conductivity and specific heat of amorphous zirconium-nickel (Zr0.67Ni0.33) after structural relaxation.
Low-temp. measurements of the thermal cond. k (0.3 ? T ? 5 K) and of the sp. heat C (0.07 ? T ? 3.5 K) of splat-cooled amorphous superconducting Zr0.67Ni0.33 (Tc ~ 2.7 K) after different annealing stages are reported. The k increases progressively (up to 55% ) after annealing. The phonon-electron scattering remains unaltered after annealing. Hence the increase in k must be entirely attributed to structure-induced (intrinsic) scattering, i.e. by 2-level tunneling states (TLS) at low temps. (?1 K). The sp. heat shows a small decrease above Tc (by 8%), which is attributed to a small decrease of the electronic d. of states at the Fermi level and to a small increase in the Debye temp. For T << Tc where TLS dominate, the C decreases less upon annealing than expected from the increase of k in the std. tunneling model. This points to a change in the TLS relaxation time spectrum upon annealing, as obsd. previously for ZrxCu1-x glasses.
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