Spectroscopic insight into current-induced spin-transfer torques in ferromagnet/topological insulator interfaces

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The goal of the planned research is to describe the electronic structure origin of the current-induced spin torque in the bilayer heterostructures containing the 3D topological insulator (3D TI) and the metallic ferromagnet (FM) or insulating ferromagnet (FMI). Further, a spectroscopic analysis of exchange splitting induced in the 3D TI by the proximity of the magnetic thin film will be carried out. It is envisioned that the planned research program will allow demonstrating current induced spin torques in the EuO/TI FMI/TI system by spin-polarized angle-resolved photoemission (spinARPES). This will allow resolving the controversy which mechanism of the current induced torque dominates in the FM/TI and FMI/TI structures: the helical locking of the Dirac cone electrons or the Rashba or spin-Hall effect torques due to the asymmetric interface. These goals will be achieved by the use of the newly developed contact stage which allows applying the current to the sample or measuring its resistance in-situ simultaneously with photoemission measurements. This experimental setup will allow combining the two typically distinct approaches: transport measurements and high-resolution photoelectron spectroscopy, with the possibility to additionally measure optically induced surface currents for example due to the photogalvanic or photon drag effects. Interface electronic structure of these heterostructures will be characterized by spinARPES and other routine surface science techniques such as XPS and LEED. Basic magnetoresistance measurements of these heterostructures will be performed in-situ simultaneously with spinARPES measurements.