Daily Overview: The highlighted work today centers on gaining deeper insight into the electronic structure of mixed Ruddlesden–Popper nickelates. Specifically, Song et al. take the bilayer Ni(^{1+}) nickelate La(_3)Ni(_2)O(5)F (i.e., La(3)(NiO(2))(2)OF, with O/F disorder treated within the O({0.5})F({0.5}) virtual-crystal approximation) as their subject and, using density functional calculations, reveal that interstitial electron density extending through the three open “apical” layers forms a partially occupied E* band, gives a single cylindrical electron Fermi surface, and produces self-doping of about 0.18 electrons, bringing the Ni valence close to +1.09; the conventional Ni (dp\sigma) hole Fermi surface coexists with the E* electron cylinder, forming a two-fluid dichotomous structure of hole and electron quasiparticles. The calculations further indicate that coupling between the otherwise rather inert Ni (d{xz}/d{yz}) orbitals and E* can generate critical non-analytic Dirac points, a degeneracy protected by crystal symmetry and reachable via pressure or further F insertion (F fraction about 0.700); on this basis, the authors propose a two-band transport picture in which the two carrier species have markedly different scattering times and argue that normal-state transport should test this dichotomous feature. arXiv submission processing window: 2026-10-28 00:00 to 2026-10-28 00:00 UTC.

1. Dichotomous electronic system in a bilayer Ni$^{1+}$ nickelate

Summary: The paper focuses on the bilayer Ni1+ nickelate La3Ni2O5F (i.e., La3(NiO2)2OF, with O/F disorder treated in the virtual-crystal approximation as O0.5F0.5) and studies its electronic structure using density functional calculations. The authors find that interstitial electron density extending through three open “apical” layers forms a partially occupied E* band, yielding a single cylindrical electron Fermi surface and producing self-doping (about 0.18 electrons, bringing the Ni valence close to +1.09); the conventional Ni dpσ hole Fermi surface coexists with the E* electron cylinder, constituting a two-fluid dichotomous structure of hole and electron quasiparticles. The otherwise relatively inert Ni dxz/dyz orbitals couple to E*, generating a critical nonanalytic Dirac point; this degeneracy is protected by crystal symmetry and can be reached via pressure or further F insertion (F fraction about 0.700). On this basis, the authors propose a two-band transport picture in which the two carrier types have markedly different scattering times, and argue that normal-state transport should test this dichotomous feature.