Magnetically doped topological insulators: From the Ground State to Dynamics

该项目主要研究磁性掺杂对三维拓扑绝缘体(TI)系统的影响。通过自旋和角度分辨光电发射光谱(SARPES)获得了关于它们的电子结构的详细信息。相应的泵浦-探测实验允许以直接和可靠的方式表征所研究系统的动力学行为。此外，还将确定所研究系统的输运性质，除了研究纵向和横向磁输运的温度依赖关系外，还将通过改变样品厚度来研究其空间分布。伴随着实验的是在密度泛函理论和动力学平均场理论相结合的框架内所做的理论工作。完全相对论计算可靠地解释了电子结构中所有自旋轨道诱导的特征特征。这也适用于SARPES中的二色性效应，这些效应是通过光发射的一步模型的自旋密度矩阵公式来描述的。当应用Kubo的线性响应形式时，以类似的方式考虑了自旋-轨道耦合对输运性质的影响。虽然到目前为止，该项目的工作仅限于基态性质，但重点将放在有限温度的影响和动力学现象上。其中一个中心问题将是识别磁性掺杂的TI系统，对于其表面带隙开放明确地源于系统中的磁性有序。到目前为止获得的最大磁感应带隙只有10 meV宽，居里温度在10K左右。从(Bi1-xMnx)2(Se，Te)3到(Sb1-xVx)2Te3的转换将使效应提高一个数量级。表面和整体区域的相应居里温度预计会有所不同，将作为组成的函数在附加部分中确定。关于磁输运，电导率的空间分布以及它与磁掺杂和温度的依赖关系将是我们研究的重点。为了确定自旋织构及其对磁有序的依赖关系，将在磁有序TIS的居里温度上下进行SARPES测量。允许操纵自旋的泵浦-探测实验将得到模拟的支持，以确定自旋和电荷弛豫的相关通道及其特征时间尺度。静态输运测量将通过产生和观察激光感生的光电流来增强，其依赖于偏振、光子能量和随后跨越铁磁相变的激光通量。

The project investigates primarily the impact of magnetic doping on three-dimensional topological insulator (TI) systems. Detailed information on their electronic structure is obtained by means of spin and angle-resolved photo emission spectroscopy (SARPES). Corresponding pump-probe experiments allow to characterise the dynamical behaviour of the investigated systems in a direct and reliable way. In addition the transport properties of the investigated systems will be determined, studying apart from the temperature dependence of the longitudinal and transversal magneto-transport its spatial distribution by varying the sample thickness. The experiments are accompanied by theoretical work done within the framework of density functional theory combined with dynamical mean field theory. Fully relativistic calculations account reliably all spin-orbit induced characteristic features in the electronic structure. This also applies for dichroic effects in SARPES, that are described by means of the spin density matrix formulation of the one-step model of photo emission. In a analogous way the impact of spin-orbit coupling on transport properties is accounted for, when applying Kubo's linear response formalism. While the project work was restricted so far to ground state properties, emphasis will be put on the influence of finite temperatures and on dynamical phenomena. One of the central issues will be the identification of magnetically doped TI systems for which the surface band gap opening unambiguously originates from magnetic ordering in the system. The largest magnetically induced gap, obtained so far, is only 10 meV wide with a Curie temperature around 10 K. It is expected that switching from (Bi1-xMnx)2(Se,Te)3 to (Sb1-xVx)2Te3 will enhance the effect by an order of magnitude. The corresponding Curie temperatures for the surface and bulk regime, that are expected to differ, will be determined in a addition as a function of the composition. Concerning magneto-transport, the spatial distribution of the conductivity as well as its dependency on the magnetic doping and temperature will be in the focus of our investigations. To determine the spin texture and its dependency on magnetic ordering SARPES measurements will be performed above and below the Curie temperature of magnetically ordered TIs. Pump-probe experiments, that allow spin manipulation, will be supported by simulations to determine the relevant channels for spin and charge relaxation together with their characteristic time scales. The static transport measurements will be augmented by the generation and observation of laser-induced photo currents, with their dependency on the polarisation, the photon energy and laser fluence followed across the ferromagnetic phase transition.