Spin resolved photoemission spectroscopy from InSe(0001) using circularly polarized radiation

The electronic structure of the layered semiconductor InSe along Delta is s tudied by spin resolved photoelectron spectroscopy using circularly polariz ed radiation from the BESSY 6.5 m normal incidence monochromator beamline. The experiments were performed in the highly symmetric set-up of normal inc idence and normal emission. The photon energies were varied between 7.8 eV and 18 eV. The spectra show a pair of weakly dispersing peaks arising via d irect transitions from valence-band states with symmetries Delta(9)(5), Del ta(9)(6) and Delta(7)(5), Delta(8)(6). Our data determine the spin-orbit sp litting in the valence bands to be Delta E-so = 0.3 +/- 0.1 eV. In addition the existence of a gap in the unoccupied bands along Delta above the funda mental gap is proven. Correlating measured peak positions and calculated ba nds (by a linearized augmented-plane-wave method) require an energy-depende nt correction of the valence-band positions toward higher binding energies. The changing sign of photoelectron spin polarization reveals that between 7.6 eV and 12.5 eV above the valence-band maximum unoccupied states with sy mmetries Delta(7)(5), Delta(8)(6) and Delta(9)(5), Delta(9)(6) exist.