Character of excitonic insulator phase in a transition metal dichalcogenide 1T-TiSe₂.

We revisit the question of the transition metal dichalcogenide 1T-TiSe₂ charge density wave (CDW) state being an excitonic insulator. The BCS-like CDW gap equation with statically screened Coulomb interaction was employed to calculate the transition temperature (T_c) as a function of the energy gap. Realistic dispersions for one hole band centered at Γ and three electron bands at M points in two-dimensional periodic hexagonal lattice were considered to model the TiSe₂. The obtained T_c (~240K) is comparable to measured one for monolayer (~232K), and T_c suppression as a function of doping concentration and pressure are reproduced by controlling chemical potential and energy gap. We discuss possibility of the 1T-TiSe₂ CDW state originating from exciton condensation through the calculated T_c, ARPES intensity and density of states.