Probing the exciton condensate phase in 1T-TiSe2with photoemission

We present recent results obtained using angle-resolved photoemission spectroscopy performed on 1 T -TiSe 2 . Emphasis is put on the peculiarity of the bandstructure of TiSe 2 compared to other transition metal dichalcogenides, which suggests that this system is an excellent candidate for the realization of the excitonic insulator phase. This exotic phase is discussed in relation to the BCS theory, and its spectroscopic signature is computed via a model adapted to the particular bandstructure of 1 T -TiSe 2 . A comparison between photoemission intensity maps calculated with the spectral function derived for this model and experimental results is shown, giving strong support for the exciton condensate phase as the origin of the charge density wave transition observed in 1 T -TiSe 2 . The temperature-dependent order parameter characterizing the exciton condensate phase is discussed, both on a theoretical and an experimental basis, as well as the chemical potential shift occurring in this system. Finally, the transport properties of 1 T -TiSe 2 are analyzed in the light of the photoemission results.