Paper

Daily Overview: Today’s highlighted work focuses on the structural identification of La₃Ni₂O₇ in its pressurized superconducting state. In [1], the authors employed high-pressure, variable-temperature Raman spectroscopy combined with polarization analysis to systematically track the structural evolution of La₃Ni₂O₇ single crystals under conditions down to 3 K and up to 32.7 GPa. They discovered a first-order structural phase transition from the orthorhombic Amam phase to the orthorhombic Fmmm phase at approximately 14.5 GPa, precisely where bulk superconductivity emerges. Polarization measurements further ruled out the possibility of a tetragonal I4/mmm phase, clearly establishing that the intrinsic structure of the pressurized superconducting state is orthorhombic Fmmm. This study reveals that a Ni–O–Ni bond angle of 180° is a key structural prerequisite for achieving a high superconducting transition temperature, laying an important foundation for understanding the superconducting mechanism of bilayer nickelates. arXiv submission processing window: 2026-07-08 00:00 to 2026-07-08 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-07-08

Daily Overview: Today’s highlighted work focuses on deepening the understanding of pressure-induced structural phase transitions and oxygen-vacancy-related transport anomalies in nickelate superconductors. Synchrotron X-ray diffraction studies reveal that the bilayer nickelate La₂SmNi₂O₇ undergoes sequential monoclinic→orthorhombic→tetragonal structural transformations across the pressure range where superconductivity emerges, without the involvement of a displacive charge density wave. This provides precise constraints on bond angles and lattice parameters for the superconducting state. Transport theory work demonstrates that the sign reversal of the Hall coefficient in nickelate thin films originates from orbital-selective scattering by oxygen vacancies—in-plane oxygen vacancies strongly suppress the d_x²−y² orbital transport channel, causing the Hall coefficient to switch from negative to positive, whereas apical oxygen vacancies act in the opposite manner. This offers a microscopic picture to unify the diverse Hall responses observed experimentally as a function of oxygen stoichiometry. arXiv submission processing window: 2026-07-07 00:00 to 2026-07-07 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-07-07

Daily Overview: Today’s highlights focus on a multi-angle analysis of density waves, electronic structure characterization, and the superconducting pairing mechanism in hybrid Ruddlesden–Popper nickelates. In [1], ultrafast optical experiments reveal strong coupling between the density wave and the lattice in La₄Ni₃O₁₀ single crystals and demonstrate that ultrafast photoexcitation can non‑thermally suppress this order parameter, offering a new approach for the non‑equilibrium control of quantum states in nickelates. [2] develops a scanning tunneling microscopy/spectroscopy electronic theory for superconducting bilayer nickelate thin films, pointing out that the multi‑orbital character and the tip‑height‑dependent changes in spectral weight can distinguish the controversial γ‑band and β‑band coherence peaks, and that quasiparticle interference patterns can identify s‑wave or d‑wave pairing symmetry. [3] constructs a pairing model mediated by local d₃z²−r² spin‑triplet excitations (triplons), predicts an interband s±‑wave superconducting gap, and successfully explains the experimentally observed anomalous gap magnitude and the double‑peak structure in tunneling spectra, strongly supporting the triplon mechanism as the microscopic origin of unconventional superconductivity in nickelates. arXiv submission processing window: 2026-07-01 00:00 to 2026-07-01 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-07-01

Daily Overview: Today’s highlight work focuses on the in-depth understanding of the electronic structure of mixed Ruddlesden-Popper nickelates. Based on unrestricted Hartree-Fock calculations, researchers have established a hierarchical order of spin density waves and charge density waves in La₃Ni₂O₇, providing key clues linking the ambient-pressure ordered phase to the high-pressure superconducting phase. Meanwhile, a first-principles study of the La₃Ni₂O₅F bilayer infinite-layer system reveals an E* band composed of interstitial-region electrons and the induced self-doping effect, leading to anomalous two-dimensional fluctuation behavior of the Ni¹⁺ magnetic moment. Regarding the pairing mechanism, by combining full-gap constraints from ARPES and STM with gap features along the Brillouin zone diagonal, a Hund’s rule-driven pairing picture dominated by the d_{x²-y²} orbital in La₃Ni₂O₇ is clarified, ruling out hybridization-driven and weak-coupling random phase approximation schemes. Furthermore, by extending infinite-layer nickelates to heavy rare-earth systems via high-pressure oxygen-assisted chemical synthesis and achieving hole doping through Eu valence changes, robust magnetic-field-reentrant superconductivity arising from the competition of 4f magnetic moments is observed at the phase diagram boundary, and Tc is elevated to 40.1 K through rare-earth ion exchange. These findings reveal the key role of 4f magnetic moments in modulating pairing strength and quantum criticality, providing a synthetic platform for exploring unconventional superconductivity and quantum phase transitions. arXiv submission processing window: 2026-06-30 00:00 to 2026-06-30 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-06-30

Daily Overview: Today’s highlight focuses on revealing a ubiquitous high-temperature structural phase transition in the Ruddlesden-Popper nickelate La$_{n+1}$Ni$_n$O$_{3n+1}$ series. Through multi-technique characterization across a broad temperature range, previously overlooked lattice-parameter anomalies were discovered in the n=2 and n=3 compounds at around 560 K: the bilayer phase exhibits a sudden increase in the out-of-plane lattice constant coupled with an in-plane contraction, indicating an abrupt release of octahedral tilting; in contrast, the monolayer–trilayer polymorphs display isotropic volume shrinkage, and the monoclinic angle β of the trilayer phase shows a clear kink. Heat capacity and DSC measurements confirm the thermodynamic nature of this transition. This high-temperature transformation is distinct from the known tetragonal transition and the low-temperature density-wave transitions, and it is absent in the n=∞ perovskite LaNiO₃. The study emphasizes that such high-temperature structural instability must be seriously considered for its potential impact on the low-temperature physical properties when exploring superconductivity in nickelates. arXiv submission processing window: 2026-06-26 00:00 to 2026-06-26 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-06-26