Observation of suppressed viscosity in the normal state of $^3$He due to superfluid fluctuations

TL;DR

This study reports the detection of reduced viscosity in normal-state $^3$He caused by superfluid fluctuations near the transition temperature, providing insights into Fermi liquid behavior and superfluid properties.

Contribution

It presents the first experimental observation of fluctuation-driven viscosity suppression in bulk $^3$He near $T_c$, with detailed characterization of temperature and pressure dependence.

Findings

Viscosity reduction occurs within 100 μK of $T_c$

Data collapse matches theoretical predictions

Fluctuations encode Fermi liquid and pairing information

Abstract

By monitoring the quality factor of a quartz tuning fork oscillator we have observed a fluctuation-driven reduction in the viscosity of bulk $^3$He in the normal state near the superfluid transition temperature, $T_c$. These fluctuations, which are only found within $100 \mu$K of $T_c$, play a vital role in the theoretical modeling of ordering; they encode details about the Fermi liquid parameters, pairing symmetry, and scattering phase shifts. They will be of crucial importance for transport probes of the topologically nontrivial features of superfluid $^3$He under strong confinement. Here we characterize the temperature and pressure dependence of the fluctuation signature, finding data collapse consistent with the predicted theoretical behavior.