Charge ordering and spin- Peierls transition in alpha'-NaV2O5

TL;DR

This paper presents a theoretical model explaining the charge ordering and spin-Peierls transition in alpha'-NaV2O5, accounting for experimental observations such as the homogeneous mixed valent state and double phase transition.

Contribution

It introduces an effective Hamiltonian that describes charge order as the primary transition leading to spin chains and a secondary spin-Peierls transition, explaining experimental anomalies.

Findings

Charge order as primary transition in alpha'-NaV2O5

Linear spin chains form in the b-direction due to charge order

The model explains the anomalous BCS-ratio observed experimentally

Abstract

Recent X-ray analysis and NMR- experiments have shown that alpha'- NaV2O5 is not a conventional spin-Peierls (SP) compound because above the transition at 33K it is in a homogeneous mixed valent (MV) state and atomic spin chains do not exist. Furthermore, thermal expansion experiments have identified the existence of a double phase transition. We present a theoretical model which qualitatively explains these observations. We derive an effective Hamiltonian for the insulating state which describes the transitions as primary charge order leading to linear spin chains in b- direction and a secondary SP- transition. We show that this scenario explains in a natural way the anomalous BCS-ratio observed in alpha'- NaV2O5.