Eur. Phys. J. B 18, 421-428 (2000)
https://doi.org/10.1007/s100510070028

Effective charge and spin Hamiltonian for the quarter-filled ladder compound a'-NaV₂O₅

Fachbereich Physik, University of the Saarland, 66041 Saarbrücken, Germany

Corresponding author: ^a gros@lusi.uni-sb.de

Received: 24 March 2000
Revised: 30 August 2000
Published online: 15 December 2000

Abstract

An effective intra- and inter-ladder charge-spin Hamiltonian for the quarter-filled ladder compound a'-NaV₂O₅ has been derived by using the standard canonical transformation method. In the derivation, it is clear that a finite inter-site Coulomb repulsion is needed to get a meaningful result otherwise the perturbation becomes ill-defined. Various limiting cases depending on the values of the model parameters have been analyzed in detail and the effective exchange couplings are estimated. We find that the effective intra-ladder exchange may become ferromagnetic for the case of zig-zag charge ordering in a purely electronic model. We estimate the magnitude of the effective inter-rung Coulomb repulsion in a ladder and find it to be about one-order of magnitude too small in order to stabilize charge-ordering.