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Complex iridium oxides have attracted recently a lot of 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-orbit 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 talk, two of our recent results on multi-frequency sub-THz ESR spectroscopy on iridium oxides in strong magnetic fields will be discussed: (1) surprising inversion of the orbital states in the prototypical spin-orbital Mott insulator Sr2IrO4 with Ir4+ (5d5, J = 1/2) due to the long-range crystal field effects; (2) evidence that the unexpected magnetism in the “non-magnetic” Ir5+ (5d4, J = 0) double perovskite Ba2YIrO6 may not be due to the “failed dominance of SOC” as proposed in recent literature.

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Vladislav Kataev, IFW Dresden
Seminar Room of the Institute of Physics II
Contact: T. Lorenz