Spin waves in the spin-flop phase of a one-dimensional Heisenberg antiferromagnet

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Abstract
The energies of the spin waves are first calculated numerically for short chains. The results indicate a periodicity in the spin-wave spectrum with period Delta k=2 pi r/Na where r is the number of deviations from the aligned (ferromagnetic) state. The method of des Cloiseaux and Pearson (1962) and of Griffiths (1964) is then used to obtain the corresponding energies in the limit as N to infinity . The amplitude of the periodic spectrum decreases as the applied field is increased. The authors' results agree with the 'hole-like' excitations given recently by Ishimura and Shiba (1977) but only for one period of the spectrum. The periodic spectrum consists of 'hole-like' excitations over the whole range of wavenumbers with lower energies than the 'particle-like' states.