Paper

Daily Overview: Today’s highlights focus on the experimental verification of the superconducting pairing symmetry in Ruddlesden–Popper nickelates and the theoretical elucidation of the correlation-enhanced mechanism. A team from the University of Science and Technology of China, using angle-resolved photoemission spectroscopy, directly observed for the first time a nodeless superconducting gap opening at the transition temperature in pseudogap-free La₂PrNi₂O₇ thin films. The order parameter is approximately 16 meV, and the corresponding specific-heat jump was extracted, providing the previously missing thermodynamic evidence for the superconducting phase transition in nickelates. They also found no one-to-one correspondence between the γ pocket on the Fermi surface and superconductivity, but that Fermi surface topology and strain effects profoundly influence the emergence of superconductivity. The experiment unambiguously supports s-wave pairing. On the theoretical side, for La₃Ni₂O₇ under high pressure, studies combining dynamical mean-field theory with self-energy renormalized random phase approximation reveal that only when the selective correlation renormalization of the d₃z²−r² orbital is included does the dominant pairing instability reverse from a d-wave channel to a sign-changing s± state. This resolves the ambiguity in the pairing symmetry that plagued bare weak-coupling calculations and highlights the decisive role of strong correlation effects in determining the superconducting pairing symmetry in nickelates. arXiv submission processing window: 2026-08-05 00:00 to 2026-08-05 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-08-05

Daily Overview: Today’s highlights focus on deepening the understanding of the electronic structure of hybrid Ruddlesden-Popper nickelates. A series of experimental and theoretical studies, spanning strain engineering, high-pressure phase diagrams, pairing symmetry, and multi-orbital density waves, reveal the unique roles of orbital selectivity and unconventional pairing mechanisms in nickel-based superconductors. In La₂PrNi₂O₇ thin films, an extreme compressive strain of up to –2.14% achieves an onset superconducting transition at 60 K, and the Hall effect exhibits electron-like carrier character, in stark contrast to the hole-like behavior observed in the bulk under high pressure, highlighting the potential of strain tuning to transcend limits imposed by Fermi surface topology. Pressure-evolution calculations for La₃Ni₂O₇ indicate that enhanced interlayer hopping and Kondo screening jointly suppress the effective magnetic exchange coupling, providing a self-consistent picture for the dome-shaped pressure dependence of the superconducting transition temperature. Concurrently, theory based on a bilayer t-J model reproduces the s± pairing-dominated nodeless gap structure and a critical temperature of about 60 K in films, and points out that d-wave pairing components among multiple orbitals can further enhance superconductivity. Ab initio calculations on infinite-layer nickelates establish spin-fluctuation-driven d_(x²−y²)-wave pairing and predict nodal-line gap features awaiting experimental verification. Polarization-resolved Raman scattering on the trilayer nickelate La₄Ni₃O₁₀ directly observes the incoherent opening of a density-wave gap and confirms that this instability intrinsically originates from the mixed contributions of the Ni-3d_(x²−y²) and 3d_(z²) orbitals. Moreover, free-standing La₀.₈Sr₀.₂NiO₂ films exhibit a dome-shaped superconducting phase diagram under ultra-high pressure up to 210 GPa, with the onset temperature rising to 74.5 K at 146 GPa, indicating that the NiO₂ plane can sustain anomalously robust pairing strength under extreme compression and is almost unaffected by rare-earth magnetic moments. Collectively, these results enrich the multi-orbital physical picture of nickelate superconductivity and provide crucial experimental and theoretical foundations for exploring new dimensions of high-temperature superconductivity. arXiv submission processing window: 2026-08-04 00:00 to 2026-08-04 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-08-04

Daily Overview: Today’s highlight work focuses on the in-depth understanding of the electronic structure of hybrid Ruddlesden–Popper nickelates. In Ref. [1], the researchers employed single-crystal synchrotron X-ray diffraction with helium as the pressure-transmitting medium to map for the first time the intrinsic pressure–temperature structural phase diagram of the stoichiometric bilayer nickelate La₃Ni₂O₇ under hydrostatic pressure. The experiment reveals a clear phase-transition pathway: the charge ordering and octahedral tilting in the ambient-pressure polar orthorhombic Am2m phase gradually weaken upon compression, and the structure transforms directly into the tetragonal I4mm structure at about 10 GPa without passing through the previously disputed intermediate Amam phase. In this tetragonal phase, the interlayer Ni–O–Ni bonds become completely straightened and the orthorhombic twinning disappears; moreover, its stable temperature–pressure region coincides exactly with the region where superconductivity at approximately 68 K emerges in resistance measurements, thus establishing the precise structural framework that hosts the superconducting state. This discovery provides crucial experimental evidence for understanding the structural basis and microscopic origin of superconductivity in this nickelate system. arXiv submission processing window: 2026-07-31 00:00 to 2026-07-31 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-07-31

Daily Overview: Today’s highlights focus on gaining deeper, multi-faceted insight into the electronic structure and superconducting mechanism of hybrid Ruddlesden-Popper nickelates. Precise transport measurements on La₃Ni₂O₇ single crystals reveal how pressure reshapes anisotropic charge dynamics by suppressing the density-wave order and triggering a structural phase transition, giving rise at the density-wave phase boundary to zero-resistance superconductivity with an onset temperature reaching 68 K and a strange metal state exhibiting Planckian dissipation over a wide temperature range. In parallel, theoretical studies on La₅Ni₃O₁₁ show that its intercalated La₂NiO₄ layers, driven by correlation effects, order into antiferromagnetic or band-insulating states and are electronically inert, so that the low-energy physics is entirely dominated by the La₃Ni₂O₇ blocks, providing a unified picture for the minimal effective model of such mixed-layer nickelates. Furthermore, first-principles molecular dynamics that incorporate nuclear quantum effects identify a lattice quantum disordered phase in La₃Ni₂O₇ and related systems, and point out that this phase boundary aligns precisely with the transition temperature on the left side of the superconducting dome, revealing the crucial role of lattice quantum many-body effects in unconventional superconductivity. arXiv submission processing window: 2026-07-30 00:00 to 2026-07-30 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-07-30

Daily Overview: Today’s highlight centers on a theoretical study of the superconducting mechanism in the 1313 phase La₃Ni₂O₇. Through combined DFT+DMFT and RPA analysis, it is revealed that the single-layer NiO₂ plane is nearly insulating and the d_{z²} orbital exhibits Mott physics, while superconductivity is predominantly confined to the metallic trilayer subsystem and forms s^±-wave pairing symmetry. The study points out that hole doping in the trilayer weakens Fermi surface nesting, and together with the extremely weak S–N–S Josephson junction formed by the nearly insulating monolayer, leads to its superconducting transition temperature being far lower than that of the bulk material. It further clarifies that the high-temperature superconductivity in this Ruddlesden-Popper series should be attributed to the 2222 phase rather than the 1313 phase. arXiv submission processing window: 2026-07-28 00:00 to 2026-07-28 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-07-28