Low-frequency broadband NMR on UPt3 using DC SQUIDs

Abstract An NMR spectrometer has been constructed based on a DC SQUID with additional positive feedback, operating in flux locked loop mode. The system has an overall bandwidth of 3MHz and a coupled energy sensitivity of 800 h . The spectrometer is being used to study high-quality single-crystal samples of UPt 3 , in order to investigate the superconducting order parameter. NMR signals have been observed in the superconducting mixed state at significantly lower frequencies than hitherto, down to 100 kHz.