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.
Highlights
The studied energy-momentum region contains a single and pronounced electron-like band spin-split by the Rashba effect which starts to deviate from the parabolic dispersion at larger wave vectors
By means of SARPES combined with a vectorial spin analysis [33] we identify an interband SOC caused by the spin-flip term of the SOC operator
We have identified a momentum region in Pb QWS where the description of the Rashba effect breaks down due to the interband SOC
Summary
The (S)ARPES experiments were performed with the COPHEE setup at the Surface and Interface Beamline at the Swiss Light Source of the Paul–Scherrer–Institut [34]. The cleanliness of the sample was checked with ARPES, where the surface states could be identified, and by inspecting the low-energy electron diffraction (LEED) pattern which showed the√typica√l (7 × 7) surface reconstruction with intense superstructure spots. Symmetry and 1√monolayer (ML) coverage in substrate units (1 ML = 7.83 × 1014 atoms cm−2) ( Bi- 3) was prepared through the deposition of approximately 3 ML of Bi from a water-cooled Knudsen cell on√to the√clean Si(111)-(7 × 7) surface at low temperature and subsequent annealing until the ( 3 × 3)R30◦ surface reconstruction appeared in LEED [37]. The ultrathin Pb film on Cu(111) was fabricated by the deposition of Pb from a water-cooled e-beam evaporator, at a pressure below 3 × 10−10 mbar, onto a Cu(111) sample held at 80 K. The single crystal Cu(111) was cleaned before deposition by several cycles of Ar ion bombardment and annealing
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