Elementary Excitations in fcc Solid Ortho-Hydrogen

Abstract

An equation-of-motion formalism is used to give a nonlinear spin-wave treatment of fcc solid ortho-hydrogen. 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.