Search for supersolidity in 4He in low-frequency sound experiments

TL;DR

This study investigates the potential supersolid phase of 4He through low-frequency sound experiments, revealing anomalous non-linear resonances below 0.8 K that depend on sample history, but no such features are observed in 3He.

Contribution

First experimental search for supersolidity in 4He using low-frequency sound, identifying temperature-dependent non-linear resonances absent in 3He.

Findings

Non-linear resonances observed below 0.8 K in 4He

Resonance features depend on sample history

No similar features found in 3He

Abstract

We present results of the search for supersolid 4He using low-frequency, low-level mechanical excitation of a solid sample grown and cooled at fixed volume. We have observed low frequency non-linear resonances that constitute anomalous features. These features, which appear below about 0.8 K, are absent in 3He. The frequency, the amplitude at which the nonlinearity sets in, and the upper temperature limit of existence of these resonances depend markedly on the sample history.