MULTIPLE QUANTUM RESONANCE SPECTROSCOPY THROUGH WEAKLY CONNECTED SUPERCONDUCTORS

Abstract

Voltage-biased superconducting weak contacts have been used as oscillating detectors to observe radio-frequency absorption spectra including the Co59 nuclear magnetic resonance in ferromagnetic cobalt. The detection is attributed to multiple quantum processes and differentiation of the dynamic I-V characteristics. Used as a spectrometer, the point contact is shown to be a continusously tunable ultra-low power oscillator-detector from 0 to 3 × 108 Hz. It is likely that the frequency limit could be extended to the superconducting gap frequency.