Low temperature ellipsometry of NaV2O5

TL;DR

This study uses low-temperature ellipsometry to investigate the dielectric properties of NaV2O5, revealing charge ordering phenomena and temperature-dependent electronic state changes near 34K.

Contribution

First measurement of NaV2O5's dielectric function at low temperatures and detailed analysis of charge ordering related to the phase transition.

Findings

Decrease in 1 eV peak intensity with temperature

Charge ordering associated with the 34K phase transition

No significant shift in valence state peaks

Abstract

The dielectric function of alpha'NaV2O5 was measured with electric field along the a and b axes in the photon energy range 0.8-4.5 eV for temperatures down to 4K. We observe a pronounced decrease of the intensity of the 1 eV peak upon increasing temperature with an activation energy of about 25meV, indicating that a finite fraction of the rungs becomes occupied with two electrons while others are emptied as temperature increases. No appreciable shifts of peaks were found s in the valence state of individual V atoms at the phase transition is very small. A remarkable inflection of this temperature dependence at the phase transition at 34 K indicates that charge ordering is associated with the low temperature phase.