Microscopic model for the structural transition and spin gap formation in α'NaV_{2}O_{5}
Abstract
We present a microscopic model for α'NaV_{2}O_{5}. Using an extended Hubbard model for the vanadium layers we derive an effective lowenergy model consisting of pseudospin Ising chains and Heisenberg chains coupled to each other. We find a ``spinPeierlsIsing'' 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 SlaterKoster approximation. It leads to a second instability with superexchange alternation on the chargeordered 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 lowenergy magnon dispersion and find agreement with experiment.
 Publication:

Physical Review B
 Pub Date:
 October 2002
 DOI:
 10.1103/PhysRevB.66.165108
 arXiv:
 arXiv:condmat/0108008
 Bibcode:
 2002PhRvB..66p5108B
 Keywords:

 71.30.+h;
 71.27.+a;
 75.30.Ds;
 Metalinsulator transitions and other electronic transitions;
 Strongly correlated electron systems;
 heavy fermions;
 Spin waves;
 Condensed Matter  Strongly Correlated Electrons
 EPrint:
 32 pages, 12 figures included