Crossover from itinerant to localized magnetic excitations through the metal-insulator transition in NaOsO$_{\text{3}}$

TL;DR

This study investigates how magnetic excitations in NaOsO3 evolve across its metal-insulator transition, revealing a continuous shift from localized to itinerant magnetic behavior using resonant inelastic x-ray scattering.

Contribution

It provides detailed experimental evidence of the magnetic excitation evolution through the MIT, highlighting the transition from localized to itinerant magnetic quasiparticles.

Findings

Low energy magnons weaken and dampen near the MIT

A broad continuum of excitations emerges in the metallic state

Magnetic fluctuations resemble a nearly antiferromagnetic Fermi liquid

Abstract

NaOsO$_{\text{3}}$ undergoes a metal-insulator transition (MIT) at 410 K, concomitant with the onset of antiferromagnetic order. The excitation spectra have been investigated through the MIT by resonant inelastic x-ray scattering (RIXS) at the Os L$_{\text{3}}$ edge. Low resolution ($\Delta E \sim$ 300 meV) measurements over a wide range of energies reveal that local electronic excitations do not change appreciably through the MIT. This is consistent with a picture in which structural distortions do not drive the MIT. In contrast, high resolution ($\Delta E \sim $ 56 meV) measurements show that the well-defined, low energy magnons in the insulating state weaken and dampen upon approaching the metallic state. Concomitantly, a broad continuum of excitations develops which is well described by the magnetic fluctuations of a nearly antiferromagnetic Fermi liquid. By revealing the continuous evolution of the magnetic quasiparticle spectrum as it changes its character from itinerant to localized, our results provide unprecedented insight into the nature of the MIT in \naoso. In particular, the presence of weak correlations in the paramagnetic phase implies a degree of departure from the ideal Slater limit.