A reinvestigation of the giant Rashba-split states on Bi-covered Si(111)

TL;DR

This study uses spin-ARPES and calculations to clarify the spin and electronic structures of giant Rashba-split states on Bi/Si(111), confirming the standard Rashba vortex model and resolving previous ambiguities around the K-point.

Contribution

It provides a detailed analysis of the spin structure on Bi/Si(111), demonstrating that the complex dispersion still conforms to the standard Rashba model, correcting earlier misconceptions.

Findings

Spin experiences a vortex around the Γ-point, consistent with the Rashba model.

No evidence of a spin vortex around the K-point, contrary to previous suggestions.

The complex spin structure can be explained by symmetry and zone intersection effects.

Abstract

We study the electronic and spin structures of the giant Rashba-split surface states of the Bi/Si(111)-($\sqrt{3} \times \sqrt{3}$)R30 trimer phase by means of spin- and angle-resolved photoelectron spectroscopy (spin-ARPES). Supported by tight-binding calculations of the surface state dispersion and spin orientation, our findings show that the spin experiences a vortex-like structure around the $\bar{\Gamma}$-point of the surface Brillouin zone - in accordance with the standard Rashba model. Moreover, we find no evidence of a spin vortex around the $\bar{\mathrm{K}}$-point in the hexagonal Brillouin zone, and thus no peculiar Rashba split around this point, something that has been suggested by previous works. Rather the opposite, our results show that the spin structure around $\bar{\mathrm{K}}$ can be fully understood by taking into account the symmetry of the Brillouin zone and the intersection of spin vortices centered around the $\bar{\Gamma}$-points in neighboring Brillouin zones. As a result, the spin structure is consistently explained within the standard framework of the Rashba model although the spin-polarized surface states experience a more complex dispersion compared to free-electron like parabolic states.