Tailoring the spin-orbit interaction at surfaces and interfaces

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The spin-orbit interaction plays an important role in many different areas, such as spintronics for separating spin states without the use of magnetic fields or the intrinsic spin Hall effect. However, much of the fundamentals, especially design criteria for a strong spin separation, remain to be understood. This proposal aims at the design and study of spin-split energy bands induced by spin-orbit coupling in low-dimensional electron systems at surfaces and interfaces. During his postdoctoral studies the applicant has found a new class of materials based on the concept of surface alloying by means of high-Z element doping, where the two-dimensional band structure at the surface exhibits an extremely strong spin-splitting. Together with the design flexibility of surface alloying, this opens up excellent prospects for continuing research. Using the two very complementary techniques angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), the underlying mechanism and the design possibilities of new systems with a strongly spin-split band structure on metallic as well as semiconducting substrates will be studied. In addition, corrections to electronic interactions are expected. Furthermore, the applicant has shown for the first time that the spin-splitting can be evaluated quantitatively from differential conductance spectra by STS. This new avenue of detecting the spin-splitting on a local scale will also be explored within this proposal. In combination with the design flexibility of surface alloying, it opens up the possibility to study spin-splitting gradients. In the long term, an experiment will be devised using Kerr microscopy to probe these systems for the intrinsic spin Hall effect and test the recently proposed universality of the intrinsic spin Hall conductivity.