Helium-Surface Interaction and Electronic Corrugation of Bi₂Se₃(111)

We present a study of the atom-surface interaction potential for the He-Bi₂Se₃(111) system. Using selective adsorption resonances, we are able to obtain the complete experimental band structure of atoms in the corrugated surface potential of the topological insulator Bi₂Se₃. He atom scattering spectra show several selective adsorption resonance features that are analyzed, starting with the free-atom approximation and a laterally averaged atom-surface interaction potential. Based on quantum mechanical calculations of the He-surface scattering intensities and resonance processes, we are then considering the three-dimensional atom-surface interaction potential, which is further refined to reproduce the experimental data. Following this analysis, the He-Bi₂Se₃(111) interaction potential is best represented by a corrugated Morse potential with a well depth of D = (6.54 ± 0.05) meV, a stiffness of κ = (0.58 ± 0.02) Å^-1, and a surface electronic corrugation of (5.8 ± 0.2)% of the lattice constant. The experimental data may also be used as a challenging benchmark system to analyze the suitability of several van der Waals approaches: the He-Bi₂Se₃(111) interaction captures the fundamentals of weak adsorption systems where the binding is governed by long-range electronic correlations.