Observation of slow order parameter fluctuations in superconducting films using beta-detected NMR

TL;DR

This study uses beta-NMR to detect slow fluctuations in the superconducting order parameter of thin films, revealing unexpected magnetic dynamics near the critical temperature that are suppressed by small magnetic fields.

Contribution

It provides the first observation of slow order parameter fluctuations in superconducting films using beta-NMR, highlighting phenomena not detectable by conventional NMR methods.

Findings

Detected a peak in spin relaxation rate at Tc in small magnetic fields

Observed fluctuations are larger than theoretical predictions based on electron spin susceptibility

Fluctuations are rapidly suppressed by small magnetic fields

Abstract

We report beta-NMR investigations of polarized 8Li implanted in thin Pb and Ag/Nb films. At the critical superconducting temperature, we observe a singular peak in the spin relaxation rate in small longitudinal magnetic fields, which is attributed to fluctuations in the superconducting order parameter. However, the peak is more than an order of magnitude larger than the prediction based on the enhancement of the dynamic electron spin susceptibility by superconducting fluctuations and reflects the presence of unexpected slow fluctuations. Furthermore the fluctuations are rapidly suppressed in a small magnetic field, which may explain why they have not been observed previously with conventional NMR or NQR.