Daily Overview: Today’s highlights focus on deepening the understanding of the electronic structure of mixed Ruddlesden–Popper nickelates. In [1], a superconducting phase diagram was constructed by synthesizing multilayer planar tetragonal nickel oxide thin films (n = 3–8). Superconducting signatures were observed for n = 4 to 8, with the highest superconducting transition temperature of approximately 12.9 K at n = 6. The superconducting anisotropy reversal is attributed to the 4f electron moments at the Nd site, and the electronic structure approaches that of cuprates. Meanwhile, persistent magnetic fluctuations overlap with the superconducting region of infinite-layer nickelates, suggesting a common physical foundation. In [2], a reanalysis of the superconducting volume fraction in pressurized Ruddlesden–Popper nickel oxide (La₄Ni₃O₁₀) was conducted. It points out that the previously reported 81–86% value was overestimated by about a factor of two due to errors in treating the demagnetization factor in the formula derivation, with the actual value being 51–59%. It emphasizes that all related reports must be corrected based on standard magnetostatic formulas. These works provide critical insights into the phase diagram regularities and measurement reliability of nickel-based superconductivity. arXiv submission processing window: 2026-02-22 08:27 to 2026-02-22 17:34 UTC.

1. Superconducting phase diagram of multi-layer square-planar nickelates

  • Relevance Score: 5.3755
  • Authors: Grace A. Pan, Dan Ferenc Segedin, Sophia F. R. TenHuisen, Lopa Bhatt, Harrison LaBollita, Abigail Y. Jiang, Qi Song, Ari B. Turkiewicz, Denitsa R. Baykusheva, Abhishek Nag, Stefano Agrestini, Ke-Jin Zhou, Jonathan Pelliciari, Valentina Bisogni, Hua Zhou, Mark P. M. Dean, Hanjong Paik, David A. Muller, Lena F. Kourkoutis, Charles M. Brooks, Matteo Mitrano, Antia S. Botana, Berit H. Goodge, Julia A. Mundy
  • Affiliations: Diamond Light Source, Argonne National Laboratory, Brookhaven National Laboratory, Cornell University, Arizona State University, Harvard University, Max Planck Institute for Chemical Physics of Solids
  • Link: http://arxiv.org/abs/2602.19093v1
  • Paper page: Superconducting phase diagram of multi-layer square-planar nickelates

Summary: This study synthesized multilayer planar tetragonal nickel oxide Nd_{n+1}Ni_nO_{2n+2} (n=3–8) thin films and constructed their superconducting phase diagram, revealing that compounds with n=4 to 8 exhibit signs of superconductivity, with a maximum superconducting transition temperature of approximately 12.9 K at n=6. As the layer number n decreases (i.e., electron dimensionality reduces), the superconducting anisotropy reverses, which is attributed to the enhanced in-plane paramagnetic decoupling effect induced by the 4f electron moments at neodymium sites, leading to anomalous anisotropic behavior in low-dimensional superconductors. The electronic structure gradually approaches that of cuprates. Magnetic fluctuations persist in both the superconducting and overdoped non-superconducting regions, and the superconducting region overlaps with that of chemically doped infinite-layer nickel oxides, indicating a common physical basis for such materials. However, unique structural features such as local lattice expansion near the fluoride layer in the multilayer structure also introduce differences. This work establishes a general template for realizing nickel-based superconductors through structural layer number modulation.

2. Nearly twofold overestimation of the superconducting volume fraction in pressurized Ruddlesden-Popper nickelates

Summary: This study reanalyzes the DC diamagnetic response data recently measured in high-pressure Ruddlesden-Popper nickel oxide (La4Ni3O10). Zhu et al. reported that the ratio of zero-field-cooled (ZFC) magnetic moment to the ideal Meissner moment, i.e., the superconducting volume fraction f, was as high as 81–86%. However, based on standard calculation procedures applied to the same raw data, the present authors recalculated this ratio and found it to be only 51–59%. Further analysis reveals a fundamental error in the equation (Eq. 3) used by Zhu et al. to compute f: the derivation of this equation fails to correctly account for the relationship between the demagnetization factor and sample geometry, leading to a systematic overestimation of the superconducting volume fraction by approximately a factor of two. By constructing virtual samples containing 50% superconducting phase (e.g., disks with halved thickness or reduced diameter), the authors demonstrate that Eq. 3 still yields f values near 100%, confirming its inability to reflect the true proportion of the superconducting phase. The authors note that this error affects all previous reports (1–4) on the superconducting volume fraction of Ruddlesden-Popper nickel oxides, and emphasize that correct calculations must be based on standard magnetostatic formulas (Eq. 7), which establish the strict relationship between magnetic moment, sample volume, demagnetization factor, and applied field in the Meissner state. Therefore, the core conclusion of this paper is that all previously reported superconducting volume fractions require revision.