Interlayer interaction in the conduction bands of layered transition-metal dichalcogenides studied by inverse photoemission

We have studied the dispersion of the unoccupied Ti 3d–derived conduction bands in 1T-${\mathrm{TiSe}}_2$ along the ΓA direction normal to the basal plane by measuring the photon spectra excited by normal-incidence electrons with kinetic energies between 10 and 20 eV. A triplet structure associated with two low-lying $t_{2g}$-like d bands and a higher $e_g$-like d band is clearly resolved within 3 eV above the Fermi level. The $t_{2g}$ bands show noticeable dispersion up to 0.4 eV from point Γ to point A resulting from interlayer interaction. No emission is observed related to empty Se 4p states at point Γ near the Fermi level. The results are critically compared with theoretical predictions and optical spectra.