Paper

This paper points out that Li et al. made three errors in calculating the superconducting volume fraction from zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements on single crystals of the high-pressure nickelate superconductor La₂SmNi₂O₇. First, due to the paramagnetic Meissner effect (Wohlleben effect), the magnetic moment in FC mode can be either positive or negative, and thus cannot be used to calculate the superconducting volume fraction. Second, reanalysis of Li et al.’s ZFC data reveals that, according to their own calculation method, the superconducting volume fraction should be 22.8%, not the reported 62.1%—a discrepancy of about a factor of three, primarily arising from differences in the demagnetization factor (Li et al. used 0.849, while the authors calculated 0.81548 using Brandt’s formula). Third, even if the ZFC magnetic moment value is correctly calculated, it cannot be directly used to determine the superconducting volume fraction, because there are infinitely many shapes and distributions of superconducting regions smaller than the actual sample size that can produce the same measured magnetic moment. The authors emphasize that they agree with Li et al.’s experimental confirmation of bulk superconductivity in pressurized nickelates, but argue that these calculation errors need to be corrected to avoid misleading future research.

The research team conducted electrical transport measurements on (La, Pr, Sm)₃Ni₂O₇ double-layer nickelate thin films and discovered a time-reversal symmetry breaking superconducting state accompanied by electronic glass behavior. This superconducting state emerges in the low-temperature regime near zero resistance, exhibiting three prominent features: first, an unconventional magnetoresistance hysteresis that directly evidences time-reversal symmetry breaking and remains robust under different magnetic field orientations, fundamentally distinct from vortex pinning or long-range magnetic order; continuous oxygen reduction simultaneously weakens both superconductivity and the hysteresis, revealing their connection to specific Ni 3d electronic orbitals. Second, the current–voltage response demonstrates magnetic history dependence and non-reciprocity under zero field, further confirming spontaneous intrinsic time-reversal symmetry breaking. Third, the resistance exhibits slow logarithmic relaxation after removing the magnetic field, a hallmark of glassy dynamics. These phenomena reveal for the first time in nickel-based superconductors a superconducting state that simultaneously possesses spontaneous time-reversal symmetry breaking and intrinsic glassy characteristics, providing significant phenomenological and conceptual breakthroughs for understanding the mechanism of high-temperature superconductivity.

Layered perovskites─including the Dion–Jacobson, Ruddlesden–Popper, and Aurivillius families─exhibit a wide range of correlated electron phenomena, from high-temperature superconductivity to multiferroicity. Here, we report a new family of layered perovskites realized through topochemical oxidation of Lan+1NinO3n+1+δ (n = 1–4) Ruddlesden–Popper nickelate thin films. Postgrowth ozone annealing induces a substantial c-axis expansion─17.8% for La2NiO4+δ (n = 1)─that monotonically decreases with increasing n. Surface synchrotron X-ray diffraction and coherent Bragg rod analysis (COBRA) reveal that this structural expansion arises from the intercalation of approximately δ ≈ 0.7–1.0 oxygen atoms into interstitial sites within the rock salt spacer layers, far exceeding the previous record of δ ≈ 0.3 for any Ruddlesden–Popper oxide. These oxygen-intercalated phases form a new class of layered perovskites with a spacer layer composition intermediate between the Ruddlesden–Popper and Aurivillius phases. Furthermore, oxygen intercalation induces metallicity, enhances nickel–oxygen hybridization, and suppresses oxygen octahedral rotations, a feature associated with high-temperature superconductivity in Ruddlesden–Popper nickelates. Our work establishes topochemical oxidation as a powerful approach to accessing highly oxidized, metastable phases across a broad range of layered oxide systems, offering new platforms to engineer electronic properties via intercalation chemistry.

Topotactical Hydrogen Induced Single-Band d -Wave Superconductivity in La₂ NiO 4

This study employs pressure-temperature single-crystal X-ray diffraction and ab initio density functional theory calculations to reveal that the transition from the tetragonal phase (I4/mmm) to the monoclinic phase (P2₁/c) in flux-grown trilayer nickelate La₄Ni₃O₁₀ does not involve an intermediate orthorhombic Bmab phase; instead, it is a direct structural phase transition accompanied by the formation of a two-fold superstructure, manifested by the appearance of commensurate superlattice reflections. The transition temperature can be continuously suppressed from approximately 1030 K to 20 K under a pressure of 14 GPa, indicating that pressure effectively stabilizes the tetragonal phase. Furthermore, weak satellite reflections associated with incommensurate density wave ordering are detected for the first time in X-ray diffraction from flux-grown crystals, complementing previous results observed only in float-zone crystals, and Raman spectroscopy reveals additional phonon modes below 130 K, further corroborating this ordered state. The ab initio calculations are in good agreement with the experimental observations. This work clarifies the long-standing dispute over the structural symmetry of La₄Ni₃O₁₀, supports the emergence of superconductivity after the restoration of tetragonal symmetry under high pressure, and provides a critical crystallographic foundation for subsequent studies of electronic structure and superconducting mechanisms.

The metal-insulator transition of La 3 Ni 2 O 7-δ with 2-dimensional electrons has been studied. Various physical properties can be understood by introducing a model of charge orderings in the NiO …

This study constructs a microscopic theoretical model for the superconducting gap structure of bilayer nickel oxides, where a conduction band with dx²-y² symmetry coexists with localized d3z²-r² spins. Strong interlayer coupling leads to a singlet ground state of local magnetic moments, whose virtual singlet-triplet excitations (i.e., “triplons”) mediate pairing interactions between conduction electrons, thereby generating interband s±-wave pairing with opposite signs of the order parameters on the two bands (α and β). The theoretical results naturally explain key experimental observations: despite the smaller density of states of the α band, its superconducting gap is larger, and the gap exhibits significant momentum-space anisotropy arising from nonlocal Kondo coupling. These findings strongly support the triplon-mediated pairing mechanism as the microscopic origin of superconductivity in bilayer nickel oxides.

Using first-principles calculations and the singular-mode functional renormalization group method, we systematically investigate the effect of interlayer nickel-nickel distance on the ground state in La₃Ni₂O₇/LaAlO₃ thin films. The results show that a smaller interlayer distance leads to a C-type spin density wave (interlayer ferromagnetic coupling), while a larger interlayer distance yields a G-type spin density wave (interlayer antiferromagnetic coupling). Between these two phases, an s±-wave superconducting state emerges, dominated by pairing in the Ni 3d₃z²⁻ᵣ² orbital. This finding explains the origin of superconductivity observed in the thin films under ambient pressure and predicts that applying pressure will suppress the superconducting transition temperature until the system enters the C-type spin density wave. If confirmed experimentally, this prediction will provide deep insight into the nature of electronic correlations in this system, as the C-type spin density wave naturally emerges within the itinerant electron picture, whereas it is difficult to realize within the local magnetic moment picture (where interlayer spins remain antiferromagnetically coupled).

By combining density functional theory and random phase approximation, the effects of compressive and tensile strain on the superconductivity of 1313-La3Ni2O7 thin films are systematically investigated. A self-doping effect is found between the monolayer and trilayer blocks regardless of compressive or tensile strain, and it is most pronounced under tensile strain. Under compressive strain imposed by an LSAO substrate, even considering hole doping from strontium ion migration in the substrate, superconductivity is difficult to appear, consistent with experiments. However, under tensile strain from a KTO substrate, a band in the trilayer subsystem that originally did not cross the Fermi level shifts downward, giving rise to a small hole-type γ pocket at the M point, which is connected to a small electron-type σ pocket at the Γ point by a near-(π,π) wavevector. Random phase approximation calculations reveal that the trilayer subsystem can then form a stable s±-wave pairing state, with the order parameter reversing sign between these two pockets. Further analysis indicates that the size of the γ pocket is crucial for pairing, and an excessively large γ pocket suppresses superconductivity. This work predicts a strain-driven electronic structure reconstruction and proposes a design principle to realize superconductivity in 1313-La3Ni2O7 under ambient pressure through tensile strain engineering.

This study developed an ultrafast magneto-pressure optical spectroscopy platform capable of operating simultaneously at pressures up to 40 GPa, magnetic fields up to 7 T, and temperatures as low as 5 K, and applied it to investigate the evolution of quasiparticle dynamics under magnetic pressure in the trilayer nickelate Pr₄Ni₃O₁₀. The experiments revealed a pronounced critical slowing down of quasiparticle relaxation near the charge density wave (CDW) transition, which disappears upon the application of pressure. At higher pressures, the low-temperature relaxation time instead becomes longer, consistent with initial superconducting correlation signatures. However, a magnetic field as high as 7 T hardly alters the relaxation behavior, and no vortex-induced pre-bottleneck dynamics—robustly observed in bulk superconducting control samples—was detected, suggesting that any superconducting state under the present pressure conditions is not bulk-like but rather filamentary or strongly inhomogeneous. This magneto-pressure ultrafast capability opens a new pathway for addressing unresolved issues of pressure-induced superconductivity and intertwined orders in correlated quantum materials.