Charge Order Driven spin-Peierls Transition in NaV2O5

TL;DR

This study reveals that in NaV2O5, a charge ordering transition initiates at 37 K, leading to a lattice distortion and spin gap formation at 34.7 K, involving a complex interplay of charge density wave and spin-Peierls order.

Contribution

It provides the first detailed NMR evidence of charge ordering preceding the spin-Peierls transition in NaV2O5, proposing a combined charge density wave and spin-Peierls model.

Findings

Charge ordering begins at 37 K.

Lattice distortion and spin gap at 34.7 K.

Observation of eight distinct Na lines below transition.

Abstract

We conclude from 23Na and 51V NMR measurements in NaxV2O5(x=0.996) a charge ordering transition starting at T=37 K and preceding the lattice distortion and the formation of a spin gap Delta=106 K at Tc=34.7 K. Above Tc, only a single Na site is observed in agreement with the Pmmn space group of this first 1/4-filled ladder system. Below Tc=34.7 K, this line evolves into eight distinct 23Na quadrupolar split lines, which evidences a lattice distortion with, at least, a doubling of the unit cell in the (a,b) plane. A model for this unique transition implying both charge density wave and spin-Peierls order is discussed.