Excitations in quadrupolar-coupled systems
- 1 December 1974
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 10 (11), 4650-4658
- https://doi.org/10.1103/physrevb.10.4650
Abstract
The method of double-time Green's functions is used to study the excitation spectrum of an isotropic spin-one system with quadrupolar coupling. It is shown that the random-phase approximation leads to a violation of a spin-one identity and thus to equivocal results. A consistent theory free from ambiguities is developed. Also, exact upper and lower bounds on the ground-state energy of systems with dipolar as well as quadrupolar coupling are derived and studied.Keywords
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