Electron-phonon and spin-phonon coupling in NaV2O5: Charge fluctuations effects

We show that the asymmetric crystal environment, of the V site in the ladde r compound NaV2O5 leads to a strong coupling of vanadium 3d electrons to ph onons. This coupling causes fluctuations of the charge on the V ions, and f avors a transition to a charge-ordered state at low temperatures. In the lo w temperature pha se the charge fluctuations modulate the spin-spin superex change interaction, resulting in a strong spin-phonon coupling.