Density-of-states changes near the Fermi level and the lattice instability in TiSe2

We report the direct observation of the density-of-states changes near the Fermi level associated with the charge-density-wave-like lattice instability in Ti${\mathrm{Se}}_2$. Synchrotron-radiation photoemission spectra have been taken below and above the critical temperature on highly stoichiometric Ti${\mathrm{Se}}_2$. The changes in the spectra due to the phase transition have been analyzed in terms of several different models of the corresponding changes in the electronic structure. The best agreement with the experimental results is given by models in which a large gap is created upon interaction between overlapping $p$ and $d$ bands at the Fermi level.