Orbital-dependent band renormalization in BaNi₂(As_1−xP_x)₂ (x = 0.00 and 0.092)

We have studied the multi-band electronic structure of BaNi₂(As₁−_xP_x)₂ (x = 0.00 and 0.092) in which the P substitution suppresses unusual Ni–Ni zigzag bond order and induces strong coupling superconductivity. At x = 0.092, all the Fermi surfaces predicted by the ab-initio band calculations are successfully identified including the small electron pocket around the Z point. Interestingly, whereas the Ni 3d xy and x² − y² bands crossing E_F agree with the band calculations, the Ni 3d yz=zx bands around 1 eV below the Fermi level (E_F) are moderately renormalized similar to those in the Fe-based superconductors. The orbital-dependent band renormalization in BaNi₂(As₁−_xP_x)₂ indicates that the less correlated xy and x² − y² bands play important roles in the strong coupling superconductivity. Across the Ni–Ni bond order at x = 0.00, the less correlated Ni 3d xy and x² − y² bands near E_F are selectively reconstructed across the Ni–Ni bond order. The band reconstruction is consistent with the orbital-selective Peierls instability proposed by Streltsov and Khomskii [Phys. Rev. B 89, 161112(R) (2014)], in which the itinerant orbital sector governs the structural instability and fluctuations.