Hexagonal Close-Packed 4He as Crystalline Multilayered Polytype: An Alternative for ‘Supersolid’ or ‘Glassy-Like’ Phase

• Published in: Journal of low temperature physics 2017, Vol.187 (5-6), p.468-474
• Main Authors: Chishko, K. A., Antsygina, T. N., Poltavskaya, M. I.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Magnetic Materials; Magnetism; Physics; Physics and Astronomy
• ISSN: 0022-2291; 1573-7357
• DOI: 10.1007/s10909-016-1726-2

We apply the model of a crystalline polytype built of close-packed 2D monoatomic basal planes with triangular lattice to interpret the anomalous thermodynamical and mechanical properties of solid hexagonal close-packed (HCP) 4 He . The polytype is a 3D stack of the basal planes, and its structure can be built from the simplest periodic packing (HCP, FCC, 4H, 5H, 6R, … etc.) up to random stacking fault system (RSFS) totally aperiodic in only c -direction perpendicular to the basal planes. RSFS is a crystal without microscopic translation symmetry along c -axis, i.e., entirely disordered in only one spatial direction. Despite of packing disorder, c -direction remains the crystallographic axis of third order at arbitrary sequence of the 2D plates in the whole stack. In a long-wave limit the HCP polytype can be treated as 3D anisotropic continuum, as a result its phonon spectrum and Helmholtz free energy have been calculated. The temperature dependence of the phonon pressure is calculated theoretically and compared with experimental data. A quantitative agreement between the theory and the experiment is achieved. Mechanical properties of 4 He crystals in the framework of the polytype model are briefly discussed.