Daily Overview: Today’s highlights focus on deepening the understanding of the electronic structure of hybrid Ruddlesden-Popper nickelates and clarifying experimental controversies surrounding their superconducting phase fraction. In directly related studies, [1] proposes a triplon-mediated pairing mechanism based on a model of coexisting d_{x^2-y^2} conduction bands and localized d_{3z^2-r^2} spins in bilayer nickelates, which naturally explains the larger superconducting gap in the α band and its significant gap anisotropy, providing microscopic theoretical support for superconductivity in bilayer nickelates. Meanwhile, [2] rigorously addresses methodological controversies in calculating the superconducting phase fraction of La₂SmNi₂O₇ single crystals. Through experimental confirmation of background signals, correction of demagnetization effects, and multi-point characterization, it validates the correctness of the approximately 62.1% superconducting phase fraction reported in the original Nature paper, thereby clarifying previous doubts about the uniformity and phase content of nickelate superconductor single crystals. These two works advance research in the field of nickel-based superconductivity from both theoretical mechanisms and experimental verification. arXiv submission processing window: 2026-03-02 00:00 to 2026-03-02 00:00 UTC.

1. Triplon-mediated pairing and the superconducting gap structure in bilayer nickelates

Summary: Based on a model where a conduction band of d_{x^2-y^2} symmetry coexists with localized d_{3z^2-r^2} spins in bilayer nickelates, researchers investigated the superconducting gap structure. Strong interlayer coupling drives the local magnetic moments into a spin-singlet ground state, and virtual singlet-triplet excitations (triplons) mediate pairing interactions among conduction electrons, resulting in interband s± pairing with order parameters of opposite signs on the α and β bands. This theory naturally explains key experimental features: the α band exhibits a larger superconducting gap despite its lower density of states, while nonlocal Kondo coupling leads to significant gap anisotropy. These results support triplon-mediated pairing as the microscopic origin of superconductivity in bilayer nickelates.

2. Reply to “Threefold error in the reported zero-field cooled magnetic moment of single crystal $La_2SmNi_2O_7$ (arXiv: 2602.23240)”

  • Relevance Score: 4.4726
  • Authors: Feiyu Li, Zhenfang Xing, Di Peng, Jie Dou, Ning Guo, Liang Ma, Yulin Zhang, Lingzhen Wang, Jun Luo, Jie Yang, Jian Zhang, Tieyan Chang, Yu-Sheng Chen, Weizhao Cai, Jinguang Cheng, Yuzhu Wang, Yuxin Liu, Tao Luo, Naohisa Hirao, Takahiro Matsuoka, Hirokazu Kadobayashi, Zhidan Zeng, Qiang Zheng, Rui Zhou, Qiaoshi Zeng, Xutang Tao, Junjie Zhang
  • Affiliations: Henan Academy of Sciences, National Center for Nanoscience and Technology, University of Chinese Academy of Sciences, Center for High Pressure Science and Technology Advanced Research, Chinese Academy of Sciences, Shandong University, Shanghai Advanced Research in Physical Sciences, University of Electronic Science and Technology of China, University of Chicago, Zhengzhou University, Japan Synchrotron Radiation Research Institute
  • Link: https://arxiv.org/abs/2602.23842
  • Paper page: Reply to “Threefold error in the reported zero-field cooled magnetic moment of single crystal La₂SmNi₂O₇ (arXiv: 2602.23240)”

Summary: In response to the critique by Korolev and Talantsev regarding the calculation of the superconducting phase fraction in the Nature paper by Li et al., the authors provide a point-by-point rebuttal: first, experimental confirmation shows that the weak upturn at low temperatures originates from the background, and no paramagnetic Meissner effect is observed, validating the use of field-cooled data for calculating the superconducting phase fraction; second, the demagnetization effect must be based on the actual variation of measured magnetic moment with the superconducting phase fraction f, whereas Korolev et al. erroneously treated the demagnetizing field as a constant, causing their formula to underestimate f by approximately two-thirds (by a factor close to 1/3), which explains why their calculated result is only about one-third of the reported value (approximately 62.1%); finally, multiple characterizations of the sample (energy-dispersive X-ray spectroscopy, X-ray diffraction, nuclear quadrupole resonance, scanning transmission electron microscopy, etc.) confirm it to be a homogeneous, high-quality bulk single crystal without multiple discrete superconducting regions. Therefore, the method for calculating the superconducting phase fraction in Li et al.’s Nature paper has not been invalidated by Korolev et al.’s analysis.