Magnetic excitations in charge- ordered NaV2O5
release_ckraco34xbaydm6423piovjdya
by
P. Thalmeier, A.N. Yaresko
1999
Abstract
An investigation of the spin excitation spectrum of charge ordered (CO)
NaV2O5 is presented. We discuss several different exchange models which may be
relevant for this compound, namely in- line and zig-zag chain models with weak
as well as strong inter- chain coupling and also a ladder model and a CO/MV
(mixed valent) model. We put special emphasis on the importance of large
additional exchange across the diagonals of V- ladders and the presence of
exchange anisotropies on the excitation spectrum. It is shown that the observed
splitting of transverse dispersion branches may both be interpreted as
anisotropy effect as well as acoustic- optic mode splitting in the weakly
coupled chain models. In addition we calculate the field dependence of
excitation modes in these models. Furthermore we show that for strong inter-
chain coupling, as suggested by recent LDA+U results, an additional high energy
optical excitation appears and the spin gap is determined by anisotropies. The
most promising CO/MV model predicts a spin wave dispersion perpendicular to the
chains which agrees very well with recent results obtained by inelastic neutron
scattering.
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