Unconventional anisotropic superexchange in NaV2O5

TL;DR

This paper reveals an unconventional form of anisotropic superexchange in NaV2O5, showing it is significantly larger than traditional estimates and indicating early signs of charge ordering below 150 K.

Contribution

It introduces a new type of symmetric anisotropic exchange interaction involving spin-orbit coupling on both sites, with a much larger magnitude than conventional models.

Findings

Unusual symmetric anisotropic exchange in NaV2O5 identified

Anisotropic exchange constant nearly 100 times larger than traditional estimates

Evidence of charge ordering effects below 150 K

Abstract

The strong line broadening observed in electron spin resonance on NaV$_2$O$_5$ is found to originate from an unusual type of the symmetric anisotropic exchange interaction with simultaneous spin-orbit coupling on both sites. The microscopically derived anisotropic exchange constant is almost two orders of magnitude larger than the one obtained from conventional estimations. Based on this result we systematically evaluate the anisotropy of the ESR linewidth in terms of the symmetric anisotropic exchange, only, and we find microscopic evidence for precursor effects of the charge ordering already below 150 K.