High-frequency behavior of metallic glass NixNb1-x point-contacts

Electron - two level system interaction in Ni59Nb41 metallic glass point contacts is studied by means of conventional and high-frequency point-contact spectroscopy, at frequencies of 3.6 kHz, 0.78 GHz and 64 GHz. The amplitude of the zero bias anomaly exhibits only a 25% decrease under microwave irradiation of 64 GHz. This implies that elastic electron interaction with highly-asymmetric slow two-level fluctuators explains only a small part in the anomaly, and the main contribution is due to fast nonmagnetic Kondo-like scattering. Point contacts of Ni44Nb56 in the superconducting state were also studied. The value of the energy gap was evaluated as Delta (0) similar to 0.4 meV. Under microwave irradiation with increasing power a gradual decrease of the critical current was observed. (C) 2001 Elsevier Science Ltd. All rights reserved.