Fig. 1: Model definition and electronic properties in the noninteracting limit.

(a) Lattice structure of the three-dimensional, four-orbital model. A Bi 6s orbital is surrounded by six O 2p_σ orbitals. Red arrows indicate the relevant hopping integrals, with the phase factor included in hole language. (b) The band structure in the noninteracting limit, α_sp = 0. The horizontal red line indicates the Fermi energy at a target filling of 1 hole per Bi atom. (c) For the target filling, the noninteracting charge susceptibility χ₀(q) is computed using the lowest energy band (black) in panel (b) for three different temperatures. As the temperature is lowered, the peak at q = (π, π, π)a⁻¹ grows. (d) At the fixed temperature β = 10 eV⁻¹, χ₀(q) for four values of the charge transfer energy ϵ_2p − ϵ_6s, the difference in the on-site energy of the O 2p_σ and Bi 6s orbitals. The peak at q = (π, π, π)a⁻¹ is approximately independent of the charge transfer energy.