Fig. 4: Optical Hall conductivity in a tight-binding model of d_xz + id_yz-wave superconductors.

a Lattice structure. B₁ and B₂ atoms are displaced oppositely along the out-of-plane direction. The square box represents the unit cell, and a is the in-plane lattice constant. We take hopping parameters that are relevant for the electron-doped FeSe. b Fermi surfaces. There are two almost overlapping Fermi surfaces near M, each with twofold spin degeneracy. c Energy bands of the Bogoliubov-de Gennes Hamiltonian with a d_xz + id_yz-wave pairing amplitude Δ₀. Line colors indicate the electron \(\hat{c}\) (red) vs hole \({\hat{c}}^{{\dagger} }\) (blue) characters. The inset shows the angular dependence of the superconducting gap on the Fermi surfaces. d Optical Hall conductivity. We take a Lorentzian broadening Γ = 0.1 meV. Unlike in Fig. 3, the optical excitation gap E_exc coincides with the spectral gap E_g. e Pairing dependence of the Hall conductivity in the zero-frequency limit. f Evolution of the Bogoliubov Fermi surface with varying Δ₀ below Δ_c.