Electron spin resonance spectroscopy on complex iridium oxides

我们建议用高频强磁场电子自旋共振波谱(HF-ESR)系统地研究近年来出现的一种称为自旋轨道Mott绝缘体的新型量子磁体复合Ir氧化物的静态和动态磁性。这类材料目前在全世界凝聚态物理学界引起了非常强烈的关注。与三维铜酸盐和锰酸盐相比，由于自旋-轨道耦合(SOC)的强烈增强，新的量子磁现象有望在5DIrriate中出现，因为SOC很小，只起到很小的作用。由SOC驱动的自旋和轨道动量的纠缠被预测在虹彩新的奇异磁相互作用和基态中产生，范围从反铁磁(AFM)Néel序到条状和锯齿状的AFM自旋结构和自旋液体。由于ESR谱对可直接测量的与SOC相关的磁各向异性非常敏感，例如ESR激发的g因子张量和能隙，这种方法成为研究氧化Ir中磁性相的一种有指导意义的工具。我们将利用德累斯顿IFW的HF-ESR仪器的优势，在0.01到1 THz的非常宽的频率范围内，在高达16 T的磁场中，在低至300MK的温度下，实现对ESR信号的高灵敏度检测。系统地研究具有不同晶体结构和不同Ir有效自旋网络拓扑结构的Ir氧化物多晶和单晶样品中ESR模的频率、磁场和取向关系，将有助于准确确定磁各向异性、基态自旋结构和低能自旋动力学参数。所获得的信息应该能够根据理论上提出的磁相对所研究的材料进行分类，并且应该有助于验证自旋轨道Mott绝缘体的理论模型。

We propose to apply high-frequency high-magnetic field electron spin resonance spectroscopy (HF-ESR) for a systematic study of static and dynamic magnetic properties of complex iridium oxides which have recently emerged as a novel kind of quantum magnets called spin orbital Mott insulators. This class of materials attracts currently very strong attention in the condensed matter physics community worldwide. New quantum magnetic phenomena are expected to occur in the 5d iridates due to a strongly enhanced spin-orbit coupling (SOC) as compared to the 3d cuprates and manganites where the SOC is small and plays only a minor role. The SOC driven entanglement of the spin and orbital momenta is predicted to yield in the iridates new exotic magnetic interactions and ground states, ranging from the antiferromagnetic (AFM) Néel order, to stripy and zigzag AFM spin structures and to a spin liquid state. Since ESR spectroscopy is very sensitive to the SOC related magnetic anisotropies which inter in directly measurable quantities, such as the g-factor tensors and energy gaps for the ESR excitations, this method emerges as an instructive tool to investigate magnetic phases in iridium oxides. We will use the advantages of the HF-ESR instrumentation at the IFW Dresden which enables a high sensitive detection of ESR signals in a very broad frequency range from 0.01 to 1 THz, in fields up to 16 T and at temperatures down to 300 mK. Systematic studies of frequency, magnetic field and orientation dependences of the ESR modes in the poly- and single crystalline samples of iridium oxides with different crystallographic structures and different topologies of the networks of Ir effective spins will allow an accurate determination of the magnetic anisotropies, the spin structures in the ground state and parameters of the low energy spin dynamics. The obtained information should enable to classify the studied materials with respect to the theoretically proposed magnetic phases and should help to verify theoretical models of spin orbital Mott insulators.