Spontaneous exciton condensation in 1T-TiSe2: a BCS-like approach

Recently strong evidence has been found in favor of a BCS-like condensation of excitons in 1$\mathit{\text{T}}$-TiSe${}_2$. Theoretical photoemission intensity maps have been generated by the spectral function calculated within the excitonic condensate phase model and set against experimental angle-resolved photoemission spectroscopy data. Here, the calculations in the framework of this model are presented in detail. They represent an extension of the original excitonic insulator phase model of J'erome $\mathit{\text{et}}\mathit{\text{al.}}$ [Phys. Rev. {\bf 158}, 462 (1967)] to three dimensional and anisotropic band dispersions. A detailed analysis of its properties and further comparison with experiment are also discussed