Transport properties and point-contact spectra of Ni x Nb 1-x metallic glasses

Bulk resistivity and point contact spectra of ${\mathrm{Ni}}_{x}{\mathrm{Nb}}_{1\ensuremath{-}x}$ metallic glasses have been investigated as functions of temperature (0.3--300 K) and magnetic field (0--12 T). Metallic glasses in this family undergo a superconducting phase transition determined by the Nb concentration. When superconductivity was suppressed by a strong magnetic field, both the bulk sample $R(T)$ and the point contact differential resistance curves of ${\mathrm{Ni}}_{x}{\mathrm{Nb}}_{1\ensuremath{-}x}$ showed logarithmic behavior at low energies, which is explained by a strong electron-``two level system'' coupling. We studied the temperature, magnetic field, and contact resistance dependence of ${\mathrm{Ni}}_{44}{\mathrm{Nb}}_{56}$ point-contact spectra in the superconducting state and found telegraphlike fluctuations superimposed on superconducting characteristics. These $R(V)$ characteristics are extremely sensitive detectors for slow relaxing ``two level system'' motion.