Daily Overview: Today’s highlights focus on deepening the understanding of superconductivity in mixed Ruddlesden-Popper nickelate La₃Ni₂O₇₊δ. Experimentally, [1] successfully synthesized a series of samples containing pure bilayer phase, hybrid phase, and trilayer intergrowth phase through systematic control of oxygen content, identifying distinct superconducting transition temperatures (Tc) corresponding to different phases. A phase diagram of Tc and upper critical field as functions of oxygen content was established, revealing the key regulatory role of oxygen content in superconductivity. Theoretically, [2] provided a unified framework based on the effective d_{x²-y²} orbital bilayer t-J∥-J⊥ model to explain multiple regulatory behaviors of Tc observed in experiments, such as oxygen stoichiometry, alkaline-earth metal substitution, rare-earth element substitution, and pressure effects. This work points out the similarity between this system and hole-overdoped copper oxides and predicts that electron doping could further enhance Tc. Together, these two studies advance the understanding of nickel-based superconductivity pairing mechanisms and material design. arXiv submission processing window: 2026-05-07 00:00 to 2026-05-07 00:00 UTC.

1. Regulating oxygen content and superconductivity in La$_3$Ni$_2$O$_{7+δ}$

  • Relevance Score: 5.6419
  • Authors: Peiyue Ma, Jingyuan Li, Xing Huang, Yixing Zhao, Yifeng Han, Mengwu Huo, Deyuan Hu, Chaoxin Huang, Hengyuan Zhang, Sihao Deng, Lunhua He, Juan Rodriguez-Carvajal, Abhisek Bandyopadhyay, Alessandro Puri, Devashibhai Adroja, Xiang Chen, Tao Xie, Zhen Chen, Hualei Sun, Meng Wang
  • Affiliations: Institut Laue-Langevin, University of Chinese Academy of Sciences, Hainan University, Lalit Narayan Mithila University, CNR, Spallation Neutron Source Science Center, Sun Yat-Sen University, STFC, Alma Mater Studiorum Universita di Bologna, University of Johannesburg, Chinese Academy of Sciences
  • Link: https://arxiv.org/abs/2605.04562
  • Paper page: Regulating oxygen content and superconductivity in La₃Ni₂O₇+δ

Summary: By systematically tuning the oxygen content of La₃Ni₂O₇₊δ samples, this study synthesized materials with varying phase compositions, including pure bilayer phase, a mixed phase of bilayer and monolayer–bilayer hybrid, and a predominant bilayer phase containing trilayer intergrowths. High-pressure transport measurements revealed that these phases correspond to distinct superconducting transition temperatures (T_c), with the bilayer phase exhibiting superconductivity at approximately 80 K, while the hybrid and trilayer-intergrowth phases show lower T_c values. Oxygen content not only influences phase purity but also directly modulates the upper critical field (H_c2) of the bilayer superconductivity, with the pure bilayer phase displaying a higher H_c2. By constructing a phase diagram of T_c and H_c2 as functions of oxygen content, this study achieves precise control over oxygen stoichiometry in Ruddlesden–Popper nickelates, providing critical experimental insights for understanding the high-pressure superconducting mechanism.

2. A Unified Understanding of the Experimental Controlling of the T$_\text{c}$ of La$_3$Ni$_2$O$_7$

Summary: This study, based on an effective d_{x^2-y^2} orbital bilayer t-J∥-J⊥ model with input parameters derived from first-principles calculations, provides a unified understanding of experiments aimed at tuning the superconducting transition temperature (Tc) of La₃Ni₂O₇. As the d_{x^2-y^2} orbital is near quarter filling, the model exhibits Tc control behavior analogous to that in hole-overdoped cuprates: hole doping pushes the system further into the overdoped regime and suppresses Tc, while electron doping has the opposite effect. This explains the suppression of Tc upon hole doping via increasing oxygen stoichiometry or substituting La with alkaline-earth metals (Ca²⁺/Sr²⁺), as well as the “half-dome” behavior in oxygen stoichiometry tuning. Tc varies with the interlayer antiferromagnetic superexchange coupling J⊥, thereby accounting for the enhancement of bulk Tc under high pressure upon Sm/Nd substitution for La, the “right-triangle” shape of the bulk Tc-pressure relationship, and the increase in Tc under compressive strain in thin films. Compared to weak-coupling theories (where Tc depends primarily on the density of states) and pairing mechanisms dominated by the d_{z^2} orbital (where Tc is proportional to the hole density in the d_{z^2} orbital), this model offers a more natural and unified explanation. The authors suggest that electron doping, achieved without introducing disorder (e.g., by substituting La with higher-valent elements), holds the potential to further enhance Tc.