Near degeneracy and pseudo Jahn-Teller effects in mixed-valence ladders: the phase transition in NaV$_2$O$_5$

TL;DR

This paper investigates the electronic structure of NaV$_2$O$_5$, revealing that charge localization and pseudo Jahn-Teller effects driven by electron-lattice interactions are key to understanding its phase transition.

Contribution

It introduces a detailed analysis of how structural anisotropy and electron correlations induce charge localization and Jahn-Teller effects in mixed-valence ladder systems.

Findings

Charge localization occurs on the ladder rungs due to anisotropy and correlations.

Pseudo Jahn-Teller effects are significant in the phase transition mechanism.

The phase transition is driven by electron-lattice interactions related to charge fluctuations.

Abstract

We analyze the electronic structure of a mixed-valence ladder system. We find that structural anisotropy and complex electron correlations lead to on-rung charge localization and insulating character. Charge fluctuations within the rung of the ladder interact strongly to the lattice degrees of freedom, which gives rise to large pseudo Jahn--Teller effects. The phase transition in NaV$_2$O$_5$ should be driven by this kind of mechanism.