Relaxation of two-level fluctuators in point contacts

The contributions by three different mechanisms of interactions between electrons and two-level fluctuators to the low-energy singularity present in point-contact spectra of metallic glasses have been studied by measuring rf response signals at 600 MHz and 60 GHz, and the low-frequency response at 1.85 kHz. The resulting curves indicate that a nonmagnetic Kondo-like interaction is the most important contribution, but, depending on the exact shape of the background signal due to electron-phonon and electron-electron interactions, elastic scattering on highly asymmetric two-level fluctuators may also be quite important. [S0163-1829(98)01927-4].