Nuclear Spin Relaxation of Very Dilute 3He impurities in Solid 4He

TL;DR

This study measures nuclear spin relaxation times of dilute 3He in solid 4He at very low temperatures, revealing anomalies linked to elastic properties and impurity tunneling, which may explain observed elastic dissipation phenomena.

Contribution

It provides new NMR measurements of 3He relaxation times at ultra-low temperatures, highlighting deviations from classical theory and connecting microscopic tunneling to macroscopic elastic anomalies.

Findings

Sharp increase in relaxation times near elastic anomalies

Tunneling of 3He impurities influenced by elastic distortions

Results suggest a link between microscopic tunneling and macroscopic dissipation

Abstract

We report measurements of the nuclear spin-lattice and spin-spin relaxation times of very dilute 3He in solid 4He in the temperature range 0.01 \leq T \leq 0.5 K for densities where anomalies have been observed in torsional oscillator and shear modulus measurements. We compare the results with the values of the relaxation times reported by other observers for higher concentrations and the theory of Landesman that takes into account the elastic properties of the 4He lattice. A sharp increase in the magnitude of the nuclear spin-lattice relaxation times compared to the the classical Landesman theory is observed close to the temperatures where the torsional and shear modulus anomalies are observed. The NMR results suggest that the tunneling of 3He impurities in the atomic-scale elastic distortion is affected by the same processes that give rise to the macroscopic elastic dissipation anomalies.