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Using a two-orbital bilayer model, this study systematically calculates the electronic Raman response in different Raman channels via both multiorbital and band-sum methods to distinguish the controversial pairing symmetry in the bilayer nickelate superconductor La₃Ni₂O₇. By comparing the Raman susceptibilities obtained from the multiorbital approach and the band-sum approximation, it is found that the Raman response can effectively differentiate various pairing symmetries and identify the Fermi-pocket-dependent gap sizes in fully gapped and nodal superconducting states. Specifically, nodal dₓ²⁻ᵧ²/dₓᵧ-wave pairing exhibits robust power-law behavior at low energies, distinctly different from fully gapped pairing; for s±-wave pairing, detailed gap anisotropy on the β pocket can be determined. The study also emphasizes the crucial role of multiorbital effects in shaping the Raman spectra, and points out that electronic Raman scattering, as a symmetry-resolving probe, provides a powerful means to determine the superconducting gap structure of unconventional superconductors, offering significant experimental implications for understanding the superconducting mechanism of bilayer nickelates.

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Using density functional theory, we calculate the electronic structure of the bilayer infinite-layer nickelate La₃Ni₂O₅F, revealing its ideal two-dimensional character and the coexistence of two distinct quasiparticle behaviors. After treating the oxygen/fluorine disorder with the virtual crystal approximation, band structure calculations show that the conventional Ni dpσ band forms a hole-like Fermi surface, whereas an E* band originating from interstitial density gives rise to a cylindrical electron Fermi surface, resulting in a self-doping of 0.18 electrons. This interstitial density is distributed between the La layers that lack apical oxygen, and as the Ni dₓz/dyz bands approach the M point with parallel linear dispersion, they couple with it to form a nearly non-analytic Dirac point, exhibiting an exotic interstitial-orbital band coupling effect. Concurrently, the d_z² band undergoes a symmetry-driven splitting of approximately 1 eV through interaction with the interstitial density. This dual electron–hole character is expected to govern normal-state transport and far-infrared properties, may influence the superconducting state of nickelates, and offers a fresh perspective for understanding the physics of infinite-layer nickelates.

This study investigates the dimensionality of the superconducting state in infinite-layer nickel oxides by mapping the vortex phase diagram of superconducting Pr0.8Sr0.2NiO2 thin films from multiple perspectives. Experimental results reveal that low-disorder films exhibit a quasi-two-dimensional vortex liquid-to-glass transition, while increasing disorder drives the system into a pure two-dimensional state. This finding indicates that pure two-dimensionality is not an intrinsic property but an extrinsic phenomenon caused by the decoupling of NiO2 layers due to enhanced disorder. The work establishes disorder as a key tuning parameter for superconductivity in infinite-layer nickel oxides and identifies that disorder primarily resides within the NiO2 layers, offering two fundamental insights for understanding this class of materials.