Knowledge

1 linked paper

2 linked papers

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.

10 linked papers

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.

12 linked papers

2 linked papers

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 …