Daily Overview: This post sorts papers by relevance to nickelate superconductors. Summaries are AI-generated and may contain errors. arXiv submission processing window: times are unavailable (UTC).

1. Three-Dimensional Electronic Structures in Superconducting Ruddlesden-Popper Bilayer Nickelate Films

Summary: By employing a low-temperature ultrahigh-vacuum dark-box transfer technique to preserve sample surface quality, this study systematically resolves the three-dimensional electronic band structure of superconducting (La,Pr,Sm)₃Ni₂O₇/SrLaAlO₄ thin films using angle-resolved photoemission spectroscopy (ARPES) with multiple photon energies. The experiments reveal orbital-dependent dimensionality: the dx²-y²-dominated band exhibits quasi-two-dimensional character, while the dz²-dominated γ band displays clear kz dispersion. Finite gaps are observed along high-symmetry directions for all detected bands, with temperature-dependent analysis of the γ band indicating a superconducting gap of approximately 18 meV and a ratio 2Δ/kBTc ~ 8, far exceeding the weak-coupling BCS limit. Moreover, suppression of spectral weight near the Fermi level persists above the superconducting transition temperature, and ubiquitous waterfall-like spectral features are observed, indicating a significant influence of electron correlations. These findings underscore the critical role of the third dimension and the dz² orbital in the nickelate superconducting mechanism, imposing important constraints on theoretical models.

2. Granular Superconductivity in La$_{2}$PrNi$_{2}$O$_{7-δ}$ Thin Films

Summary: Research indicates that the two-step superconducting transition observed in La₂PrNi₂O₇₋δ thin films originates from their granular superconducting nature, where two superconducting phases with distinct critical temperatures coexist and couple through a Josephson junction network. For films grown via pulsed laser deposition and subsequently ozone-annealed, transport measurements reveal a pronounced secondary low-temperature transition even when the residual resistance is minimal near 30 K, resulting in a zero-resistance temperature of only about 10 K. The hysteresis in magnetoresistance and the sensitive response to weak magnetic fields align with the effective field model of granular superconductors, ruling out the possibility of a spin-glass phase. Structural characterization identifies oxygen inhomogeneity and local structural disorder, such as monolayer phase intercalation, as the primary causes of the observed phase separation. These findings elucidate the microscopic mechanisms underlying the complex superconducting behavior in bilayer nickelate films and underscore that improving oxygen uniformity is crucial for achieving bulk superconductivity with higher zero-resistance temperatures, thereby providing a foundation for subsequent spectroscopic studies.

3. Co-operating multiorbital and nonlocal correlations in bilayer nickelate

Summary: Based on the effective three-orbital model, this study systematically analyzes the interplay between multiorbital and nonlocal self-energy effects in the normal state of the high-pressure superconducting bilayer nickelate La₃Ni₂O₇ using the D-TRILEX many-body framework beyond dynamical mean-field theory. The results reveal that the low-energy physics is highly dependent on the interorbital interaction strength: when the interaction is weak, the renowned γ quasiparticle flat band lies below the Fermi level; as the interaction strengthens, this flat band crosses the Fermi level, causing electrons to scatter with ferromagnetic paramagnon excitations, thereby forming spin-polaron bound states. These bound states manifest as incoherent spectral weight shadow bands below the Fermi level. The findings unveil the existence of additional competing electronic states in bilayer nickelates, providing a theoretical basis for resolving recent controversies in angle-resolved photoemission spectroscopy experiments regarding spectral structures near the Fermi surface.

4. Orbital-Selective $d$-wave Superconductivity in the Two-Band $t$-$J$ Model: Possible Applications to La$_3$Ni$_2$O$_7$

Summary: This study employs the variational Monte Carlo method to investigate superconductivity in a two-band t-J model consisting of an itinerant orbital (orbital 0) and a quasi-localized orbital (orbital 1). The key finding is the emergence of a robust orbital-selective d-wave superconducting state, which originates entirely from the itinerant orbital 0. Analysis of the superexchange energy hierarchy reveals that the quasi-localized orbital 1 competes with superconductivity by favoring the formation of local inter-orbital bound states, which act as energy defects that disrupt phase coherence. Consequently, the superconducting order parameter decreases monotonically with increasing occupation of orbital 1. Inspired by superconductivity in the nickelate La₃Ni₂O₇, these results highlight the crucial role of multiorbital physics beyond the single-band t-J framework and identify a concrete pathway for enhancing the superconducting transition temperature: suppressing the involvement of the localized d_{z²} orbital.