Atomically precise step grids for the engineering of helical states

Conventional spin-degenerate surface electrons have been effectively manipulated by means of self-organized nano-arrays. Of particular interest are one-dimensional, step superlattices at vicinal surfaces, because their fundamental behavior can be understood through simple model theory, and they can be utilized to imprint strong surface anisotropies in electron transport devices. In this work, the realization of periodic resonator arrays on the BiAg2 atom-thick surface alloy with atomic precision is presented, and their potential ability for tailoring the giant-split helical Rashba states is demonstrated. By employing curved crystals to select local vicinal planes, two sharply defined arrays of BiAg2 monoatomic steps with distinct spacing are fabricated, as experimentally determined from scanning tunneling microscopy and low-energy electron diffraction. The interaction of the Rashba helical states with the step arrays is assessed by scanning the photon beam across the BiAg2 curved surface in angle-resolved photoemission experiments and comparing these results with density functional theory. Remarkably, strong orbital-selective renormalization of bands perpendicular to the step superlattice, as well as spin mixing of Rashba bands, are induced by the coherent scattering of the periodic step potential. These results pave the way to fabricate atomically precise coupled arrays of electron resonators to engineer spin-orbital textures.