Interband spin-orbit coupling between anti-parallel spin states in Pb quantum well states

TL;DR

This study reveals how interband spin-orbit coupling in Pb quantum well states causes significant deviations from Rashba behavior, including non-linear spin splitting and sign reversal, explained by hybridization of anti-parallel spin states.

Contribution

It demonstrates the role of interband spin-orbit coupling in modifying Rashba-split bands in Pb quantum well states, independent of substrate.

Findings

Breakdown of Rashba behavior in Pb quantum well states

Spin splitting becomes non-proportional to momentum

Reversal of momentum splitting sign

Abstract

Using spin and angle-resolved photoemission spectroscopy we investigate a momentum region in Pb quantum well states on Si(111) where hybridization between Rashba-split bands alters the band structure significantly. Starting from the Rashba regime where the dispersion of the quasi-free two-dimensional electron gas is well described by two spin-polarized parabolas, we find a breakdown of the Rashba behavior which manifests itself (i) in a spin splitting that is no longer proportional to the in-plane momentum and (ii) in a reversal of the sign of the momentum splitting. Our experimental findings are well explained by including interband spin-orbit coupling that mixes Rashba-split states with anti-parallel rather than parallel spins. Similar results for Pb/Cu(111) reveal that the proposed hybridization scenario is independent on the supporting substrate.