Dominant Kitaev interactions on the fcc lattice in iridate double perovskites La2BIrO6 (B=Mg, Zn)

TL;DR

This study reveals that dominant Kitaev interactions govern magnetic excitations in fcc iridate double perovskites La2ZnIrO6 and La2MgIrO6, suggesting unconventional exchange mechanisms influence magnetic order in frustrated systems.

Contribution

It demonstrates the presence of dominant Kitaev interactions in fcc iridate double perovskites, expanding understanding beyond honeycomb materials.

Findings

Gapped spin wave excitations observed with weak dispersion

Theoretical modeling confirms dominant Kitaev interactions

Conventional magnetic orders may arise from Kitaev exchange

Abstract

We have performed inelastic neutron scattering experiments to investigate the magnetic excitations in the quasi-face-centered-cubic (fcc) iridate double perovskites La2ZnIrO6 and La2MgIrO6, which are characterized by A-type antiferromagnetic ground states. The neutron scattering data, which reveal gapped spin wave excitations with a very weak dispersion, are shown to be well-described by theoretical calculations on a model Hamiltonian with dominant Kitaev interactions. Our surprising finding shows that in contrast to honeycomb materials, where the Kitaev interaction manifests itself via complex magnetic order, even conventional magnetic orders in certain geometrically frustrated systems might owe their existence to unconventional Kitaev exchange.