Elementary Excitations in fcc Solid Ortho-Hydrogen

Abstract

An equation-of-motion formalism is used to give a nonlinear spin-wave treatment of fee solid orthohydrogen. The elementary excitations in ortho-hydrogen are librational waves and can be treated in a manner similar to spin waves in magnetism. The excitation spectrum, long-range order, and ground-state energy are calculated. It is found that the spin-wave excitations have a nonvanishing effect on both the long-range order and the ground-state energy. But, because of a large energy gap, the spin-wave-theory results deviate only slightly from their molecular-field values. ELEMENTARY EXCITATIONS IN fee. SOLID o-H 2

Orientational ordering in solid hydrogen

“…The molecular field results disagree with the experimental results by a factor of approximately two (at X ~ 1) and offer no explanation for the critical concentration Xc. Almost identical results are given by more elaborate non-linear wave (librons) treatments [25].…”

The libron spectra and conversion as a function of ortho-para concentration in solid H2 and D2

“…To compare, we have taken the density of states for the three modes calculated by Diehl and Biem (their Figs. [3][4][5] and interpolated the line shape to correspond to Cl = 0.938. We scale these density-of-states functions, which all have the same norm, by ~(1) 7., (2) the factors 1, 0.26, and 0.060 for the Eg, Ig , and -g modes, respectively.…”

Anharmonic correction to the magnetization in a ferromagnet with two sublattices

“…If we replace the spin operators in (2) For the same reason we can take effectively in accordance with (3) s; ~-(2s)l/~,,.…”

“…We note that these operators were successfully used in the libron theory. 3 c. After neglecting all the terms in these equations which give exponentially small corrections at low temperatures, the effective equations are written in the momentum space.…”