A Helium-Surface Interaction Potential of Bi${}_2$Te${}_3$(111) from Ultrahigh-Resolution Spin-Echo Measurements

Abstract

We have determined an atom-surface interaction potential for the He$-$Bi${}_2$Te${}_3$(111) system by analysing ultrahigh resolution measurements of selective adsorption resonances. The experimental measurements were obtained using ${}^3$He spin-echo spectrometry. Following an initial free-particle model analysis, we use elastic close-coupling calculations to obtain a three-dimensional potential. The three-dimensional potential is then further refined based on the experimental data set, giving rise to an optimised potential which fully reproduces the experimental data. Based on this analysis, the He$-$Bi${}_2$Te${}_3$(111) interaction potential can be described by a corrugated Morse potential with a well depth $D=(6.22\pm 0.05)\mathrm{meV}$, a stiffness $\kappa =(0.92\pm 0.01){\mathring{\mathrm{A}}}^{-1}$ and a surface electronic corrugation of $(9.6\pm 0.2)$% of the lattice constant. The improved uncertainties of the atom-surface interaction potential should also enable the use in inelastic close-coupled calculations in order to eventually study the temperature dependence and the line width of selective adsorption resonances.