The experimental band structure of occupied and unoccupied states of titanium dichalcogenides

The authors have studied the dispersion of the electronic states of TiTe2 by combined angle-resolved inverse photo-emission (h(cross) omega =9.8eV) and photo-emission (h(cross) omega =21.2 eV) for various high-symmetry directions. The experimental band structure E(k/sub ///) is found to be in good agreement with a simple LCAO theory in particular for the unoccupied Ti3d-like bands. At Gamma they find a large trigonal splitting of 0.9 eV within the Ti3d-derived t2g states and observe additional photon emission associated with unoccupied Te 5p states. At the Brillouin zone boundary near M(L) emission due to the lowest d states is observed below and above EF for the same kp indicating possible many-body effects in the excitation process. This is attributed to the strong localisation of the Ti3d states at the Fermi level. Unoccupied Ti 4s, p-like bands that do not overlap the d states were detected 5-8 eV above the Fermi level. In the resulting bulk band gap between the d and s, p states they observed an image potential surface state 0.7 eV below the vacuum level. From its parabolic dispersion an effective mass m*=1.5 was determined. Similar results were obtained for the unoccupied states in TiSe3. © 1987 IOP Publishing Ltd.