Orientational ordering in monolayers of ortho–para hydrogen

• Published in: Физика низких температур
• Date: 2003
• Main Authors: Kokshenev, V.B., Sullivan, N.S.
• Format: Article
• Language: English
• Published: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2003
• Subjects: Physics in Quantum Crystals
• Online Access: https://nasplib.isofts.kiev.ua/handle/123456789/128913
• Journal Title: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Cite this: Orientational ordering in monolayers of ortho–para hydrogen / V.B. Kokshenev, N.S. Sullivan // Физика низких температур. — 2003. — Т. 29, № 9-10. — С. 980-984. — Бібліогр.: 23 назв. — англ.

We discuss orientational ordering in monolayers of solid hydrogen in view of recent experimental findings in NMR studies of (ortho)c–(para)₁–c-hydrogen mixtures on boron nitride substrate. Analysis of the temperature-concentration behavior for the observed NMR frequency splitting is given on the basis of a two-dimensional (J = 1)c–(J = 0)₁–c-rotor model with the quadrupolar coupling constant Г₀ = (0.50 ± 0.03) K and the crystalline field amplitude V₀ = (0.70 ± 0.10) K derived from experiment. The two distinct para-rotational short-range ordered structures are described in terms of the local alignment and orientation of the polar principal axis, and are shown to be due to the interplay between the positive and negative crystalline fields. It is shown that the local structures observed below the 2D site-percolation threshold cp = 0.72 are rather different from the ferromagnetic-type para-rotational ordering suggested earlier by Harris and Berlinsky.