| AVS 55th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS2-WeA |
| Session: | Electrons and Electronic Spectra at Surfaces |
| Presenter: | J. Osterwalder, University of Zurich, Switzerland |
| Authors: | J. Osterwalder, University of Zurich, Switzerland H. Dil, University of Zurich and Paul-Scherrer-Institut, Switzerland F. Meier, University of Zurich and Paul-Scherrer-Institut, Switzerland J. Lobo, University of Basel, Switzerland L. Patthey, Paul-Scherrer-Institut, Switzerland |
| Correspondent: | Click to Email |
An angle-resolved photoelectron spectrometer has been equipped with a full three-dimensional spin polarimeter by using two orthogonal Mott detectors.1 The unique capability of the instrument has made it possible to introduce a new two-step fitting routine that provides absolute spin polarization vectors for each individual band intersected in a particular ARPES spectrum or momentum distribution curve.2 This procedure is crucial when analyzing strongly overlapping peaks or weak signals sitting on a large unpolarized background. It is robust against strong intensity variations due to matrix element effects because it references the spin polarization contribution of each band to the measured peak intensity. The method is applied to two-dimensional systems where spin-orbit effects lead to complex momentum-dependent spin structures.3 Two prototypical systems, Bi/Ag(111) (√3x√3)R30° and Pb/Ag(111) (√3x√3)R30° were investigated. We confirm that the surface states experience a large spin splitting. Moreover, we find that all surface states are 100% spin polarized, and that for some states, spin polarization vectors rotate out of the surface plane. With the photoelectron spin as an additional tag in the measurement, spin-split bands with splittings far below the measured line width can be resolved. This has allowed us to see such splittings in quantum well states within ultrathin Pb layers on Si(111). Comparable to surface states, the space inversion symmetry is broken in these films, and the spin degeneracy of the valence electrons is lifted. The effect is much smaller though, and we measure energy splittings as small as 15 meV.
1 M. Hoesch et al., J. Electron Spectrosc. Relat. Phenom. 124, 263 (2002).
2 F. Meier et al., Phys. Rev. B 77, 165431 (2008).
3 S. LaShell et al., Phys. Rev. Lett. 77, 3419 (1996); M. Hoesch et al., Phys. Rev. B 69, 241401 (2004).