A microscopic model for the structural transition and spin gap formation in alpha'-NaV2O5

Abstract

We present a microscopic model for alpha'-NaV2O5. Using an extended Hubbard model for the vanadium layers we derive an effective low-energy model consisting of pseudospin Ising chains and Heisenberg chains coupled to each other. We find a ``spin-Peierls-Ising'' phase transition which causes charge ordering on every second ladder and superexchange alternation on the other ladders. This transition can be identified with the first transition of the two closeby transitions observed in experiment. Due to charge ordering the effective coupling between the lattice and the superexchange is enhanced. This is demonstrated within a Slater-Koster approximation. It leads to a second instability with superexchange alternation on the charge-ordered ladders due to an alternating shift of the O sites on the rungs of that ladder. We can explain within our model the observed spin gap, the anomalous BCS ratio, and the anomalous shift of the critical temperature of the first transition in a magnetic field. To test the calculated superstructure we determine the low-energy magnon dispersion and find agreement with experiment.

32 pages, 12 figures included

References in corpus (3)

• The "devil's staircase" type phase transition in NaV2O5 under high pressure
• Structure determination, valence, and superexchange in the dimerized low temperature phase of alpha'-NaV2O5
• Exact diagonalisation study of charge order in the quarter-filled two-leg ladder system NaV2O5

Cited by in corpus (4)

• Creation and destruction of a spin gap in weakly coupled quarter-filled ladders
• Charge order induced by electron-lattice interaction in NaV2O5
• Dimerization-induced enhancement of the spin gap in the quarter-filled two-leg rectangular ladder
• Isospin model for suppression of charge order in hole- doped NaV_2O_5