SRC Users' Meeting - Synchrotron Radiation Center - University of ...

THE INITIAL AND FINAL STATE BANDS
IN BI ALONG T
Christian R. Ast 1,2 and Hartmut Höchst 1
1 Synchrotron Radiation Center, University of Wisconsin-Madison, Stoughton, WI 53589
2 Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
Determining the dispersion of an energy band in three dimensional momentum space
from angle resolved photoemission spectra requires knowledge of the final state band structure
since information about the momentum of the photoelectron is lost as it is refracted at the sample
surface. Commonly, a free electron final state model is assumed, however, at low final state
energies the bands can still be affected by the periodic potential such that the free electron model
breaks down. It has been shown from normal emission spectra of Bi(111) that for final state
energies below about 60 eV deviations from the free electron approximation can be observed [1].
In order to find the band dispersion in momentum space from photoemission spectra involving
low final state energies both initial and final state bands have to be extracted from the
photoemission spectra.
Fig. 1: Normal emission spectra of Bi(111) as a function of photon energy.
We report angle resolved photoemission spectra of Bi(111) measured at normal emission
as a function of photon energy. Changing the photon energy in this geometry samples the
Brillouin zone along the T line. The photon energy range extends from 8 eV to 100 eV
covering several Brillouin zones. From the data we have extracted the initial state bands within 3
eV binding energy as well as the final state bands up to a final state energy of 100 eV using a
phenomenological, modified free electron model that incorporates deviations from the freeelectron
dispersion. In Fig. 1 a close up of the photoemission spectra can be seen for one of the
bulk bands in Bi. The solid and dashed lines trace primary and secondary cone emission features
while the circles indicate peak positions in the spectra. The arrows labeled G1 to G3 indicate
final state gaps away from the Brillouin zone boundaries which are visible in the photoemission
spectra.