Growth, electronic structure and ultrafast electron dynamics of magnetic topological insulators

该项目的主题是磁性拓扑绝缘体的合成和表征，其中磁性原子与拓扑表面态(TSS)之间的相互作用在TSS的Dirac节点上打开了一个空隙。这种效应可能导致奇异的量子相，例如量子反常霍尔态。这项联合提案的主要目标是确定造成狄拉克点磁隙开口和大小的主要因素。通过这种方式，我们希望最终确定具有较大磁隙但真正绝缘的拓扑绝缘体(TI)。将研究不同类别的磁性拓扑绝缘体，其中磁性是通过掺杂、本征磁性化合物或通过沉积磁性原子或层来感应的。这些晶体将在新西伯利亚合成，并根据成分和温度对其结构、磁性和电传输性能进行表征。在马尔堡，费米能级的位置、能隙的大小以及费米附近占据态和未占据态的能带结构将由激光ARPES和时间分辨双光子光电子能谱(2PPE)确定。研究具有理想电子结构的样品中光激发电子的非弹性衰变动力学，将有助于探索磁缺陷散射和电声子耦合对超快电子动力学的影响。理解体态和表面态之间的相互作用是至关重要的，因为平衡布居的恢复取决于它们相互耦合的强度。直接在全二维k-空间中观测光产生的光电流的衰减将使我们能够确定微观动量散射对电流输运的影响。这些实验将在磁有序温度之上和之下进行。对于选定的样品，我们将用THz-ARPES研究磁耦合对费米能级电子输运的影响。

The topic of the project is the synthesis and characterization of magnetic topological insulators in which the interaction between magnetic atoms and the topological surface state (TSS) opens a gap at the Dirac node of the TSS. This effect may lead to exotic quantum phases, such as the quantum anomalous Hall (QAH) state. The primary goal of this joint proposal is the identification of the main factors that are responsible for the opening and the size of the magnetic gap at the Dirac point. In this way, we want to finally identify topological insulators (TIs) with large magnetic gap but which are truly insulating. Different classes of magnetic topological insulators will be investigated in which magnetism is induced either by doping, intrinsic magnetic compounds, or by deposition of magnetic atoms or layers. The crystals will be synthesized in Novosibirsk and characterized respect to their structural, magnetic and electrical transport properties in dependence on the composition and temperature. In Marburg, the position of the Fermi level, the size of the gap and the band structure of occupied and unoccupied states in the vicinity of the Fermi will be determined by laser ARPES and time-resolved two-photon photoemission (2PPE). The investigation of the inelastic decay dynamics of optically excited electrons in samples exhibiting the desired electronic structure will make it possible to explore the role of magnetic defect scattering and electron-phonon coupling on the ultrafast electron dynamics. It is essential to understand the interplay between the bulk and the surface states because the recovery of the equilibrium population depends on how strong they couple to each other. The observation of the decay of optically generated photocurrents directly in full two-dimensional k-space will allow us to determine the effects of microscopic momentum scattering on current transport. These experiments will be conducted above and below the magnetic ordering temperature. For selected samples we will investigate the impact of the magnetic coupling on the electron transport at the Fermi level by THz-ARPES.