We study the electronic structure of the charge density wave (CDW; T_CDW= 200 K) material 1T-TiSe₂, using core-level photoemission and valence band resonant photoemission spectroscopy (RESPES) across the Ti L-edge threshold. While 1T-TiSe₂ was extensively studied using various techniques including angle-resolved photoemission spectroscopy (ARPES)[1], time-resolved ARPES[2] and resonant inelastic X-ray scattering[3], the Ti L-edge RESPES has not been reported. The Ti 2p and Se 3d spectra show clear shifts across the CDW transition associated with band structure changes in the CDW phase. The Ti L-edge RESPES shows a clear resonance of Ti 3d character states and a Ti LVV Auger correlation satellite. Applying the Cini-Sawatzky method provides an estimate of the effective on-site Coulomb correlation energy between two holes, U_dd= -1.5 eV. The results are consistent with core level Auger spectra of 1T-TiSe₂[4], suggesting the effective attractive Coulomb correlation energy would favour a band Jahn-Teller based model for describing the CDW transition in 1T-TiSe_2.

References :
(1) T. E. Kidd et al., PRL 88, 226402 (2002).
(2) T. Rohwer et al. Nature 471, 490 (2011).
(3) C. Monney et al. PRL 109, 047401 (2012).
(4) D. deBoer, C Haas, and G.A. Sawatzky, J. Phys. F: Met. Phys. 14, 2769 (1984).