Fermi surface chirality induced in a TaSe$_2$ monosheet formed by a Ta/Bi$_2$Se$_3$ interface reaction

A. Polyakov, K. Mohseni, R. Felici, C. Tusche, Y. Chen, V. Feyer, J. Geck, T. Ritschel, A. Ernst, J. Rubio-Zuazo, G. R. Castro, H. L. Meyerheim, and S. S. P. Parkin


Spin-momentum locking in topological insulators and materials with Rashba-type interactions is an extremely attractive feature for novel spintronic devices and is therefore under intense investigation. Significant efforts are underway to identify new material systems with spin-momentum locking, but also to create heterostructures with new spintronic functionalities. In the present study we address both subjects and investigate a van der Waals-type heterostructure consisting of the topological insulator Bi$_2$Se$_3$ and a single Se-Ta-Se triple-layer (TL) of H-type TaSe$_2$ grown by a method which exploits an interface reaction between the adsorbed metal and selenium. We then show, using surface x-ray diffraction, that the symmetry of the TaSe$_2$-like TL is reduced from D$_{3h}$ to C$_{3v}$ resulting from a vertical atomic shift of the tantalum atom. Spin- and momentum-resolved photoemission indicates that, owing to the symmetry lowering, the states at the Fermi surface acquire an in-plane spin component forming a surface contour with a helical Rashba-like spin texture, which is coupled to the Dirac cone of the substrate. Our approach provides a route to realize chiral two-dimensional electron systems via interface engineering in van der Waals epitaxy that do not exist in the corresponding bulk materials.

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