Atomically precise step grids for the engineering of helical states

TL;DR

This paper demonstrates the atomic-scale fabrication of step superlattices on BiAg2 surfaces to control and study helical Rashba states, revealing coherent scattering and tunable spin-orbit effects.

Contribution

It introduces a method to create atomically precise step arrays on BiAg2 surfaces and explores their impact on helical Rashba states for the first time.

Findings

Coherent scattering of helical Rashba states from step arrays

Rashba band shifts depend on step density

Spin-orbit splitting varies with step morphology

Abstract

Conventional spin-degenerated surface electrons have been effectively manipulated by using organic and inorganic self-assembled nanoarrays as resonators. Step superlattices naturally assembled in vicinal surfaces are a particularly interesting case since they represent simple one-dimensional (1D) models for fundamental studies, and can imprint strong anisotropies in surface electron transport in real devices. Here we present the first realization of periodic resonator arrays on the BiAg2 atom-thick surface alloy with unprecedented atomic precision, and demonstrate their potential ability for tuning helical Rashba states. By employing curved crystals to select local vicinal planes we achieve tunable arrays of monoatomic steps with different morphology and orientation. Scanning the ultraviolet light beam on the curved surface during angle-resolved photoemission experiments allows one to unveil the scattering behavior of spin-textured helical states. In this way, we find coherent scattering of helical Rashba states from the step arrays, as well as step-density-dependent Rashba band shifts and spin-orbit splitting compared to the extended BiAg2 plane.