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的狄拉克节点上打开了一个缺口。这种效应可能导致奇异的量子相，如量子反常霍尔（QAH）态。这一联合提议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大磁隙但真正绝缘的拓扑绝缘体（TIs）。我们将研究不同种类的磁性拓扑绝缘体，其中磁性是通过掺杂、磁性化合物或磁性原子或层的沉积来诱导的。晶体将在新西伯利亚合成，并对其结构，磁和电输运性质与成分和温度的关系进行表征。在马尔堡，费米能级的位置、间隙的大小以及费米能级附近占据态和未占据态的能带结构将通过激光ARPES和时间分辨双光子光电发射（2PPE）来确定。在具有理想电子结构的样品中研究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子-声子耦合在超快电子动力学中的作用。了解体态和表面态之间的相互作用是至关重要的，因为平衡种群的恢复取决于它们彼此耦合的强度。直接在全二维k空间中观察光学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上下进行。对于选定的样品，我们将用太赫兹- 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.