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.

1. Density waves in low-pressure bilayer nickelates

Summary: Using the unrestricted Hartree-Fock method based on a multiorbital Hubbard-Hund model, we investigate the density-wave phase diagram of the low-pressure bilayer nickelate La₃Ni₂O₇. Our calculations reveal that in the orthorhombic phase, the electron system first develops a double-stripe spin-density-wave order with wave vector Q_Y = (0, π) at about 150 K; subsequently, at about 130 K, the pure double-stripe spin state becomes unstable against a commensurate charge density wave, resulting in a spin-modulated double-stripe ordered state where the magnetic moments and charge densities on the in-plane Ni1 and Ni2 sites are modulated, forming low-spin sites. This charge order parameter is an order of magnitude smaller than the magnetic order parameter and induces additional band gaps and folded Fermi surfaces in the electronic structure. The study establishes the hierarchical relationship between spin-density-wave and charge-density-wave orders in La₃Ni₂O₇, provides important clues for understanding the connection between the ambient-pressure ordered phases and the high-pressure superconducting phase, and proposes suggestions for further experimental verification.

2. Anomalous Behavior of the Ni$^{1+}$ moment and interstitial band in bi-infinite-layered La$_3$Ni$_2$O$_5$F

Summary: This study employs first-principles density functional theory (GGA and GGA+U) to investigate the electronic and magnetic properties of La3Ni2O5F, which features a bilayer NiO2 infinite-layer structure where La(O/F)La blocking layers achieve strict isolation of the NiO2 bilayers, forming a purely two-dimensional electronic and magnetic system. Calculations reveal an E* single band composed of electron density in the interstitial region, which is not associated with any atomic orbital, dips below the Fermi level along the M-A direction, and provides a self-doping of 0.09 holes per Ni, resulting in an actual Ni valence of +1.09; the Fermi surface of this E* band is cylindrical, occupying 9% of the Brillouin zone area. The dpσ band is nearly half-filled but is shifted near a Van Hove singularity due to the self-doping, and the magnetic response exhibits anomalous characteristics distinct from previous nickelates, with the magnetic susceptibility tending to vanish under a large magnetic field. The absence of a magnetic phase transition can be attributed to strong two-dimensional spin fluctuations and the self-doping effect away from half-filling, revealing the unique behavior of Ni¹⁺ ions in this system and the critical influence of the interfacial blocking layer on the interstitial band morphology.

3. What Does the Single-Particle Spectrum Imply on the Pairing Nature and Pairing Mechanism in La$_3$Ni$_2$O$_7$?

Summary: Addressing the controversy over the pairing mechanism in the bilayer nickelate La₃Ni₂O₇, this work exploits the low-anisotropy nodeless full gap revealed by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) as a constraint, and proposes the pairing gap along the Brillouin zone diagonal as a decisive probe. Symmetry analysis shows that the hybridization between the d_(x²−y²) and d_(z²) orbitals vanishes along this diagonal, so that the gaps on the γ pocket and on the α/β pockets separately encode the intrinsic pairing strength of the two orbitals. A d_(z²)-orbital-dominated hybridization-driven pairing mechanism would force gap nodes on the α/β pockets along the diagonal direction, directly contradicting the observed U-shaped dI/dV spectrum, whereas a d_(x²−y²)-orbital-dominated Hund’s-rule-driven pairing mechanism yields a uniform full gap over the entire Fermi surface, consistent with the ARPES and STM results. Weak-coupling random-phase approximation calculations, owing to the density-of-states advantage of the d_(z²) orbital, also produce nodal or near-nodal behavior near the diagonal, in conflict with experiment. This work therefore clarifies the dominant role of the d_(x²−y²) orbital in pairing and establishes the Hund’s-rule-driven pairing mechanism as the most relevant superconducting picture for La₃Ni₂O₇.

4. A chemical avenue to manipulate field-reentrant superconducting rivalries in infinite layer nickelates

  • Relevance Score: 4.8646
  • Authors: Haowen Han, Yusong Zhao, Yi Bian, Tong Ma, Wenlong Yang, Shaohua Yang, Binghui Ge, Hongliang Dong, Chuanying Xi, Ze Wang, Nuofu Chen, Tian Shang, Toni Shiroka, Zaher Salman, Jia-Cai Nie, Ho-Kwang Mao, Jikun Chen
  • Affiliations: Institute for Shanghai Advanced Research in Physical Sciences (SHARPS), Beijing Normal University, Center for High Pressure Science and Technology Advanced Research, Anhui University, East China Normal University, Paul Scherrer Institute, University of Science and Technology Beijing, North China Electric Power University, Chinese Academy of Sciences
  • Link: https://arxiv.org/abs/2511.22026
  • Paper page: A chemical avenue to manipulate field-reentrant superconducting rivalries in infinite layer nickelates

Summary: This study developed a megapascal-level high-pressure oxygen-assisted chemical synthesis route that successfully enabled the effective growth of infinite-layer nickelates extending to heavier rare earth elements, with composition (RE₁₋ᵧRE’ᵧ)₁₋ₓEuₓNiO₂ (RE/RE’: Pr, Nd, Sm, Gd, Dy). Hole doping was realized through Eu²⁺/Eu³⁺ valence variation. At the superconducting dome boundaries of Nd₁₋ₓEuₓNiO₂ and Pr₁₋ₓEuₓNiO₂ systems, robust uniaxial anisotropic magnetic-field reentrant superconductivity was observed, arising from the competition between Eu²⁺ 4f⁷ magnetic moments and magnetic fluctuations, while the optimally doped regions exhibited conventional high-temperature superconductivity with a critical current density reaching ~266 kA/cm² at 2 K, surpassing that of traditional Sr/Ca-doped systems. Further introduction of different RE′ magnetic ions allowed tuning of the exchange field strength and thereby modulation of quantum criticality, both enhancing the reentrant behavior and elevating T_c to 40.1 K. This work reveals the critical role of rare-earth 4f magnetic moments in modulating pairing strength and quantum criticality, establishing a synthetic foundation for utilizing the infinite-layer nickelate platform to investigate 4f-related unconventional superconductivity and quantum phase transitions.