Transport properties and point contact spectra of Ni_xNb_{1-x} metallic glasses

摘要

Bulk resistivity and point contact spectra of Ni_xNb_{1-x} metallic glasseshave been investigated as functions of temperature (0.3-300K) and magneticfield (0-12T). Metallic glasses in this family undergo a superconducting phasetransition determined by the Nb concentration. When superconductivity wassuppressed by a strong magnetic field, both the bulk sample R(T) and the pointcontact differential resistance curves of Ni_xNb_{1-x} showed logarithmicbehavior at low energies, which is explained by a strong electron - "two levelsystem" coupling. We studied the temperature, magnetic field and contactresistance dependence of Ni_{44}Nb_{56} point-contact spectra in thesuperconducting state and found telegraph-like fluctuations superimposed onsuperconducting characteristics. These R(V) characteristics are extremelysensitive detectors for slow relaxing "two level system" motion.