Cluster mean-field analysis of the finite-temperature properties of the one-dimensional extended Falicov-Kimball model*

Motivated by a recent finding that Ta2NiSe5 is in a strong-coupling excitonic insulator state [1], we study finite-temperature properties of the one-dimensional extended Falicov-Kimball model (EFKM), the simplest lattice model for the excitonic insulator state. Here, we use the cluster mean-field method with a sine-square deformation and calculate the finite-temperature phase diagrams of the model, which are compared with the results of a previous study at zero temperature [2]. Moreover, we calculate the optical conductivity spectra of the model at finite temperatures and find that the temperature dependence of the spectral features observed in experiment [3] are well reproduced by our calculations.
[1] K. Sugimoto et al, Phys. Rev. Lett. 120, 247602 (2018).
[2] S. Ejima et al., Phys. Rev. Lett. 112, 026401 (2014).
[3] T. I. Larkin et al., Phys. Rev. B 95, 195144 (2017).