Fig. 5: Calculated exciton properties.
From: Evidence for equilibrium exciton condensation in monolayer WTe2
a, Band structure along Γ–Λ–X in Fig. 1b, obtained from first principles (DFT-PBE0 level, Methods). The lines are guides to the eye. b, Excitation energy of the lowest exciton versus centre-of-mass momentum q = (q, 0) along the same cut, calculated by solving the Bethe–Salpeter equation. The thick curve is a guide to the eye. The excitation energy is negative over the whole range of q, implying instability of the ground state due to the spontaneous generation of excitons. Error bars are estimated by extrapolation of Brillouin zone sampling (Methods and Supplementary Fig. 7). c,d, Wavefunction of the lowest exciton with q = 0 (c) and q = kΛ (d), respectively. The plot shows the conditional probability distribution of the electron for the hole located at the red dot. The plot in d is an average over three degenerate states. e, Simulated behaviour of μ versus ng (black solid line) for an excitonic insulator within the spinful two-band model (Methods). The density of free electrons (red dashed lines) and holes (blue dashed lines) is computed self-consistently as the population of the c and v bands, respectively, which are renormalized by the presence of the condensate.
