Simultaneous Measurements of the Torsional Oscillator Anomaly and Thermal Conductivity in Solid 4He

TL;DR

This study simultaneously measured torsional oscillator anomalies and thermal conductivity in solid helium-4, revealing no correlation between defect-related frequency shifts and thermal properties, with notable excess conductivity in natural helium samples at very low temperatures.

Contribution

It provides the first simultaneous measurements of torsional oscillator anomalies and thermal conductivity in solid helium-4, exploring their relationship and defect effects.

Findings

No correlation between oscillator frequency shifts and crystalline defects.

Excess thermal conductivity observed below 120 mK in natural helium samples.

Thermal conductivity follows a T^3 dependence with notable deviations in some samples.

Abstract

In these torsional oscillator experiments the samples of solid $^4$He were characterized by measuring their thermal conducitvity. Polycrystalline samples of helium of either high isotopic purity or natural concentration of $^3$He were grown in an annular container by the blocked-capillary method and investigated before and after annealing. No correlation has been found between the magnitude of the low-temperature shift of the torsional oscillator frequency and the amount of crystalline defects as measured by the thermal conductivity. In samples with the natural $^3$He concentration a substantial excess thermal conductivity over the usual $T^3$ dependence was observed below 120 mK.