Evidence for Supersolidity in Bulk Solid 4He
Abstract
We report low temperature measurements of bulk solid 4He in a two-frequency compound torsional oscillator with both annular and open cylinder sample geometries. The oscillators were designed to suppress period shifts arising from all known elastic effects of solid 4He. At temperatures below 0.25 K, period shift signals similar to those reported by Kim and Chan [Science 305, 1941 (2004)] were observed, albeit two orders smaller in magnitude. A sizable fraction of the observed signals are frequency-independent and consistent with the mass-decoupling expected for supersolid 4He. This result is in stark contrast with recent works on Vycor-solid-4He system and suggests that a small supersolid fraction on the order of 1 × 10-4 may indeed exist in bulk solid 4He.
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