The interplay between structural, magnetic and electronic states in the pyrochlore iridate Eu2Ir2O7

TL;DR

This study investigates the metal-insulator transition and magnetic ordering in Eu2Ir2O7, revealing that bond angle anomalies and potential topological phases are linked to electron correlations and can be influenced by external pressure.

Contribution

It combines experimental and theoretical methods to elucidate the interplay of structural, magnetic, and electronic states in Eu2Ir2O7, highlighting the role of bond angles and potential topological phases.

Findings

No change in lattice symmetry across MIT

Anomaly in Ir-O-Ir bond angle at MIT

Potential for topological phase under pressure

Abstract

We address the concomitant metal-insulator transition (MIT) and antiferromagnetic ordering in the novel pyrochlore iridate Eu2Ir2O7 by combining x-ray absorption spectroscopy, x-ray and neutron diffractions and density functional theory (DFT) based calculations. The temperature dependent powder x-ray diffraction clearly rules out any change in the lattice symmetry below the MIT, nevertheless a clear anomaly in the Ir-O-Ir bond angle and Ir-O bond length is evident at the onset of MIT. From the x-ray absorption near edge structure (XANES) spectroscopic study of Ir-L3 and L2 edges, the effective spin-orbit coupling is found to be intermediate, at least quite far from the strong atomic spin-orbit coupling limit. Powder neutron diffraction measurement is in line with an all-in-all-out magnetic structure of the Ir-tetrahedra in this compound, which is quite common among rare-earth pyrochlore iridates. The sharp change in the Ir-O-Ir bond angle around the MIT possibly arises from the exchange striction mechanism, which favors an enhanced electron correlation via weakening of Ir-Ir orbital overlap and an insulating phase below TMI . The theoretical calculations indicate an insulating state for shorter bond angle validating the experimental observation. Our DFT calculations show a possibility of intriguing topological phase below a critical value of the Ir-O distance, which is shorter than the experimentally observed bond length. Therefore, a topological state may be realized in bulk Eu2Ir2O7 sample if the Ir-O bond length can be reduced by the application of sufficient external pressure.