Paper

Daily Overview: Today’s highlighted work focuses on an in-depth understanding of the electronic structure of mixed Ruddlesden–Popper nickelates. Addressing the controversy over the crystal structure of the pressurized superconducting state of La3Ni2O7, [1] used high-pressure Raman spectroscopy and polarization analysis at temperatures as low as 3 K and pressures up to 32.7 GPa to track its pressure-driven structural evolution. It found that at about 14.5 GPa a transition from the orthorhombic Amam phase to the orthorhombic Fmmm phase occurs, accompanied by pronounced phonon reconstruction, while D2h symmetry persists before and after the transition, thereby ruling out the tetragonal I4/mmm phase as a possible structure of the superconducting state. The onset of bulk superconductivity precisely coincides with this structural transition, indicating that below 19.45 GPa the intrinsic superconducting main phase of La3Ni2O7 is the orthorhombic Fmmm structure. These results settle the long-standing structural controversy and provide a key foundation for understanding the superconductivity mechanism of bilayer nickelates and their structure–electronic-state correlation. arXiv submission processing window: 2026-09-29 00:00 to 2026-09-29 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-09-29

Daily Overview: Today’s highlighted work focuses on a deeper understanding of the electronic structure of mixed-type Ruddlesden-Popper nickelates. Motivated by pressure- or compressive-strain-induced high-temperature superconductivity in the bilayer nickelate La3Ni2O7, a study based on an effective four-orbital model, building on the fact that the normal-state electronic structure can give rise to bonding-antibonding s±-wave or d-wave pairing, further examined the orbital-antiphase sign structure of the superconducting gap. The authors first generalized the gap-node conditions of the single-layer two-orbital model to the bilayer system and, using the bonding/antibonding basis, related the nodal features to the signs and relative magnitudes of the intra- and interlayer pairing components. The results show that when the gaps on the pairing orbitals have opposite signs, additional node pairs appear on the α and/or β Fermi surface sheets in addition to the symmetry-enforced nodes; these nodes are not required by the symmetry of the gap function and can be detected by ARPES. Meanwhile, the orbital-antiphase gap also alters the temperature dependence of the low-temperature superfluid stiffness, providing concrete experimental criteria for testing this superconducting state in bilayer nickelates and related multiorbital systems. arXiv submission processing window: 2026-09-25 00:00 to 2026-09-25 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-09-25

Daily Overview: Today’s highlighted work focuses on a deeper understanding of the electronic structure of mixed-type Ruddlesden–Popper nickelates. Using a first-principles six-band three-layer multiorbital model, Yamakawa and Kontani treat electron correlations within the FLEX approximation and combine vertex-corrected density-wave equations with the Bethe–Salpeter method to systematically study charge-density-wave instability and superconducting pairing in La4Ni3O10. Their central conclusion is that short-range spin-density-wave fluctuations near Q_SDW on the outer NiO2 planes can, through quantum interference, generate an inter-outer-layer bond order with Q_CDW ≈ 2Q_SDW and further induce an inner-layer-centered orbital density wave, causing out-of-phase modulation of the Ni d_{3z^2−r^2} and d_{x^2−y^2} orbital occupations, thereby yielding strong orbital polarization but only weak total charge modulation. This intertwined bond-order–orbital-order state not only explains the layer-selective electronic reconstruction inferred from NMR/NQR but is also consistent with Raman spectroscopy and scanning tunneling microscopy results. Moreover, because the CDW has even mirror parity while the SDW has odd mirror parity, their fluctuations can synergistically stabilize s±-wave superconductivity via the M_z mirror-parity selection rule. This work provides a unified microscopic framework for intertwined density-wave order and high-temperature superconductivity in multilayer nickelates. arXiv submission processing window: 2026-09-23 00:00 to 2026-09-23 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-09-23

Daily Overview: Today’s highlighted work focuses on gaining a deeper understanding of the electronic structure of infinite-layer nickelates, particularly the orbital origin of the A-pocket and the controversy surrounding its identification in photoemission spectra. [1] By combining DFT+DMFT to study bulk NdNiO2 and employing a plane-wave final-state approximation to simulate polarization-dependent ARPES, the study shows that the A-pocket is not of single-orbital character but is formed through strong hybridization among interstitial s, Nd-dxy, and Ni-dxz/yz orbitals, with all three contributing significantly near the DMFT Fermi level. The simulations reproduce the main polarization-dependent Fermi surface features observed experimentally and reveal that removing the interstitial s matrix element leads to pronounced disagreement with experiment, whereas suppressing the Nd-dxy or Ni-dxz/yz matrix elements has only a minor effect. This work emphasizes that, when assigning the microscopic orbital origins of low-energy spectral features in such nickelates, both orbital hybridization and photoemission matrix elements must be treated simultaneously, providing important constraints for understanding the electronic structure relevant to infinite-layer nickel-based superconductivity. arXiv submission processing window: 2026-09-21 00:00 to 2026-09-21 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-09-21

Daily Overview: Today’s highlighted work focuses on progress in nickel-based superconductivity across three areas: ambient-pressure bulk phase boundaries, the bilayer interlayer pairing mechanism, and infinite-layer spin/orbital excitations. In ambient-pressure bulk nickelates, [1] observed signatures of superconductivity in (La1-xPrx)4Ni3O8 and (La1-xYx)4Ni3O8 single crystals, where superconductivity appears within a narrow window near the insulator-metal transition and coexists with a charge stripe phase; the low superconducting volume fraction and nonpercolative character suggest that superconductivity may nucleate in filamentary form at phase boundaries, while the presence of intergrowth defects leaves its origin unresolved. This study further establishes spacer-layer engineering as an important means of tuning the electronic structure of nickel-oxide sandwich layers and exploring this competing regime. On the theoretical side, [2] systematically reviewed interlayer pairing mechanisms in bilayer nickelates, emphasizing Ni-3d_{x^2-y^2} and 3d_{z^2} hybridization, orbital-dependent correlations, Hund coupling, and strong interlayer magnetic coupling. They pointed out that half-filled d_{z^2} local singlet pairs provide pairing energy, and that their hybridization with itinerant d_{x^2-y^2} promotes phase coherence, with interlayer pairing regarded as central to understanding this class of superconductors. Spectroscopically, [3] used RIXS to compare nominally undoped yet superconducting infinite-layer PrNiO2 with insulating CaCuO2. They found that PrNiO2 has a smaller in-plane magnetic exchange integral but similar out-of-plane exchange; spin excitations remain relatively sharp and exhibit single-magnon dispersion, while orbital excitations show that the Ni-dxy peak has lower energy and a dispersion direction opposite to that of Cu-dxy. This indicates that infinite-layer nickelates and cuprates share most spin and orbital properties, but the larger charge-transfer energy and smaller hopping integrals in nickelates lead to lower-energy spin fluctuations and more localized doped charge. Overall, today’s work—from ambient-pressure phase-boundary superconductivity and interlayer pairing theory to infinite-layer magnetism and orbital excitations—collectively deepens the understanding of pairing mechanisms, phase competition, and materials-design boundaries in nickel-based superconductors. arXiv submission processing window: 2026-09-18 00:00 to 2026-09-18 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-09-18