Static and dynamic magnetism of topologically non-trivial magnetic materials

电子能带的拓扑结构在凝聚态物理领域显示出其重要性，为发现诸如拓扑绝缘体（TI）等物质的新状态铺平了道路。这类材料中存在的强自旋-轨道耦合导致体带拓扑的非平凡性，这反过来又产生无质量的狄拉克色散，在表面具有自旋动量锁定。磁性拓扑绝缘体（MTI）的发现为探索量子反常霍尔效应、拓扑磁电效应和手性马约拉纳费米子等奇异现象开辟了新的途径，这些奇异现象可以从拓扑电子态和磁性自由度之间的相互作用中产生，无论是有序的还是强烈波动的。研究后者的一个非常有用的方法是高场高频电子自旋共振（ESR）光谱与静态磁强计技术相结合。在我们的项目中，我们建议使用ESR光谱来获得mti中磁性的基本起源和细节的新的全面见解，并建立磁性各向异性，相互作用和有序与观察到的非平凡带拓扑特征的关系。我们将利用德累斯顿IFW的高场高频ESR仪器的优势，在0.01至1太赫兹的非常宽的频率范围内，在高达16 T的场中，在0.3 - 300 K的温度范围内，对ESR信号进行高灵敏度检测。系统地研究单晶样品中ESR模式的频率、磁场和角度依赖关系，可以准确地确定其磁各向异性、基态下的自旋结构和自旋动力学参数。对ESR响应的温度依赖性的准确评估可以获得磁矩的动力学，从而允许研究顺磁状态下电子结构与波动磁矩之间的相互作用。我们将把所有这些参数与所研究的mti的化学成分、晶体结构和观察到的非平凡带拓扑特征联系起来。该项目的一个重要方面将是对剥离样品的研究，这将使研究表面主导磁性的厚度依赖演化成为可能。所获得的信息对于全面理解磁性拓扑绝缘体在有序和无序状态下的静态和动态磁性的性质至关重要，这对于进一步评估磁性和非平凡带拓扑之间的相互作用是必要的。

The topology of the electronic bands has shown its importance in the field of condensed matter physics by paving a way to a discovery of new states of matter such as topological insulators (TI). Strong spin-orbit coupling present in this class of materials causes a non-triviality of the bulk band topology, which, in turn, yields a massless Dirac dispersion with spin-momentum locking at the surface. The recent discovery of magnetic topological insulators (MTI) has opened new avenues to explore exotic phenomena, such as the quantum anomalous Hall effect, the topological magnetoelectric effect and chiral Majorana fermions, which can emerge from the interplay between topological electronic states and magnetic degrees of freedom, be they ordered or strongly fluctuating. A very informative method to study the latter is high-field high-frequency electron spin resonance (ESR) spectroscopy complemented with static magnetometry technique. In our project, we propose to use ESR spectroscopy to obtain new comprehensive insights into the fundamental origin and the details of the magnetism in MTIs, and to establish a relation of the magnetic properties such as magnetic anisotropy, interactions and ordering with observed signatures of the non-trivial band topology. We will use the advantages of the high-field high-frequency ESR instrumentation at the IFW Dresden enabling a high-sensitivity detection of ESR signals in a very broad frequency range from 0.01 to 1 THz, in fields up to 16 T, and in a temperature range 0.3 - 300 K. Systematic studies of frequency, magnetic field, and angular dependences of the ESR modes in single-crystalline samples will allow an accurate determination of the magnetic anisotropies, the spin structures in the ground state, and parameters of the spin dynamics. The accurate evaluation of the temperature dependences of the ESR response grants access to the dynamics of the magnetic moments, thereby allowing the investigation of the interplay between electronic structure and fluctuating magnetic moments in the paramagnetic state. We will relate all these parameters with the chemical composition, crystallographic structure, and with the observed features of the non-trivial band topology in the studied MTIs. An important aspect of the project will be studies of exfoliated samples, which will enable the investigation of the thickness dependent evolution of the surface dominated magnetism. The obtained information should be of a paramount importance for a comprehensive understanding of the nature of the static and dynamic magnetism in both, ordered and not ordered, states of magnetic topological insulators, which is necessary for further assessment of the interplay between magnetism and non-trivial band topology.