Y. Aoki, X. Lin, and H. Kojima, Search for fourth sound propagation in supersolid ⁴He: Твердый гелий, Low Temp. Phys. 34, (2008) [Fiz. Nizk. Temp. 34, 414-426, (2008)] DOI: https://doi.org/10.1063/1.2911651.