Evidence for Supersolidity in Bulk Solid ${}^4$He

Abstract

We report low temperature measurements of bulk solid ${}^4$He 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 ${}^4$He. At temperatures below 0.25 K, period shift signals similar to those reported by Kim and Chan [Science {\bf 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 ${}^4$He. This result is in stark contrast with recent works on Vycor-solid-${}^4$He system and suggests that a small supersolid fraction on the order of $1\times 10^{-4}$ may indeed exist in bulk solid ${}^4$He.

5 pages, 5 figures, Supplement 4 pages, 2 figures