Magnetic excitation spectra in pyrochlore iridates

TL;DR

This paper investigates the magnetic excitation spectra in pyrochlore iridates, revealing how charge fluctuations influence spin-waves and proposing experimental signatures to identify magnetic order, aiding understanding of metal-insulator transitions.

Contribution

It provides a detailed analysis of magnetic excitations in pyrochlore iridates, highlighting the impact of charge fluctuations on spin-wave spectra and suggesting experimental markers for magnetic order.

Findings

Charge fluctuations cause significant deviations from simple spin-wave models.

Characteristic spectral features can identify magnetic order in experiments.

Insights into magnetic order help understand metal-insulator transitions.

Abstract

Metal-insulator transitions in pyrochlore iridates (A2Ir2O7) are believed to occur due to subtle interplay of spin-orbit coupling, geometric frustration, and electron interactions. In particular, the nature of magnetic ordering of iridium ions in the insulating phase is crucial for understanding of several exotic phases recently proposed for these materials. We study the spectrum of magnetic excitations in the intermediate-coupling regime for the so-called all-in/all-out magnetic state in pyrochlore iridates with non-magnetic A-site ions (A=Eu,Y), which is found to be preferred in previous theoretical studies. We find that the effect of charge fluctuations on the spin-waves in this regime leads to strong departure from the lowest-order spin-wave calculations based on models obtained in strong-coupling calculations. We discuss the characteristic features of the magnetic excitation spectrum that can lead to conclusive identification of the magnetic order in future resonant inelastic x-ray (or neutron) scattering experiments. Knowledge of the nature of magnetic order and its low-energy features may also provide useful information on the accompanying metal-insulator transition.