Electron–hole instability in 1T-TiSe2 (original) (raw)

In this paper, we address the question of the origin of the charge density wave instability in 1T-TiSe 2. We develop a model considering the direct Coulomb interaction between electrons and holes in the valence and conduction bands near the Fermi energy. Using the Bethe-Salpeter equation, we calculate the electron-hole correlator, which reveals an instability at low temperature leading to a transition toward a commensurate superstructure mediated by the electron-phonon coupling, in agreement with experiments. On the basis of this correlator, the electron self-energies are then calculated and the corresponding photoemission spectra are compared with the experimental ones, revealing good agreement. The signature of electron-hole fluctuations in photoemission is emphasized. Furthermore, we calculate the spectral function of the phonon mode, whose softening is experimentally observed at the transition.