Insights into the Spin–Orbital Entanglement in Complex Iridium Oxides from High-Field ESR Spectroscopy

Abstract

Complex iridium oxides have attracted recently a substantial interdisciplinary attention due to an intimate entanglement of spin and orbital degrees of freedom which may give rise to a novel spin–orbital Mott insulating behavior and exotic quantum spin liquid phases. Electron spin resonance (ESR) spectroscopy is known to be an instructive tool for studying the spin–orbital coupling (SOC) effects as it can directly access the relevant parameters sensitive to SOC, such as the g factor tensor, magnetic anisotropy gaps and spin dynamics. In this article, a systematic study at the Leibniz IFW Dresden of the static and dynamic properties of selected Ir-based materials with multi-frequency high-field ESR spectroscopy will be reviewed. Specifically, evidence for a surprisingly isotropic antiferromagnetic spin dynamics and the inversion of the orbital states in the prototypical spin–orbital Mott insulator Sr 2IrO 4, observation of the collective resonance modes in the family of double perovskites La 2BIrO 6 (B = Cu, Co) and the origin of the unexpected magnetism in the double perovskite Ba 2YIrO 6 will be highlighted.