Fig. 2: T_c-suppression as a function of impurity concentrations for different superconducting gap structures in a two-orbital bilayer model of La-327.

a The superconducting transition temperature T_c is calculated for different impurity concentrations n_imp for La-327²⁸ for the interlayer s_±-wave gap structure determined by the bonding/antibonding superconducting order parameters Δ_b/a = ± Δ_⊥ and intralayer d-wave gap structure (\({\Delta }_{{{{\rm{b/a}}}}}={\Delta }_{{{{\rm{d}}}}}(\cos ({k}_{x})-\cos ({k}_{y}))/2\)). The temperature is normalized to the transition temperature in the clean system T_c0. The impurity concentrations are normalized using also the impurity strength W and density of states at the Fermi level N(0). The intralayer interaction J and interlayer interaction J_⊥ are chosen such that T_c ≈ 80 K. In (b) the on-site orbital energies are chosen such that the γ pocket is shifted 50 meV below the Fermi surface as it is the case for the La-327 at ambient pressure^43,44, keeping the band filling unchanged. The insets show the corresponding Fermi surface where the solid blue and dashed red lines refer to bonding and antibonding Fermi surface sheets, respectively.