Daily Overview: Today’s highlights focus on deepening the understanding of the electronic structure of mixed Ruddlesden-Popper nickelates. In [1], polarization-resolved electronic Raman scattering was employed to probe the density wave state of La₃Ni₂O₇ single crystals, revealing momentum-selective anisotropic electronic correlations and confirming the coexistence of spin density wave gaps with two different coupling strengths, thereby providing a microscopic foundation for understanding the emergence of nickelate superconductivity under pressure. In [2], magnetotransport measurements on compressively strained La₂SmNi₂O₇ thin films directly observed the coexistence of antiferromagnetic spin fluctuations and superconductivity at low temperatures. The unique “Mexican hat”-shaped magnetoresistance behavior reveals a novel relationship between fluctuations and superconductivity, offering key experimental evidence for elucidating the pairing mechanism of nickelate superconductivity. arXiv submission processing window: 2026-02-08 14:41 to 2026-02-08 14:47 UTC.

1. Anisotropic Electronic Correlations in the Spin Density Wave State of La$_3$Ni$_2$O$_7$

Summary: Using polarization-resolved electronic Raman scattering measurements on high-quality La₃Ni₂O₇ single crystals, we observe a pronounced, symmetry-dependent spectral weight redistribution across the density-wave transition below 150 K: the B₁g channel exhibits an asymmetric peak, while the B₂g channel shows a symmetric broad peak, corresponding to electronic excitations near the X/Y points of the Brillouin zone and along the diagonal directions, respectively. Quantitative analysis extracts two sets of SDW gap values, with the B₁g channel gap approximately 37.5–40.4 meV (2Δ/kBTc ≈ 5.5–5.9) and the B₂g channel gap about 23.0 meV (2Δ/kBTc ≈ 3.4), indicating intermediate-to-strong coupling for the former and weak coupling for the latter. This momentum-selective anisotropic coupling strength cannot be explained by simple weak-coupling nesting theory, revealing that the unconventional SDW originates from anisotropic electronic correlations. The temperature dependence of the gap is significantly weaker than mean-field expectations, and the isotropy of the B₂g channel along with the weak anisotropy of the B₁g channel further support the coexistence of two distinct coupling mechanisms. This work establishes the electronic characteristics of the SDW in La₃Ni₂O₇, providing a microscopic foundation for understanding the emergence of high-temperature superconductivity in nickelates under pressure.

2. Coexistence of Antiferromagnetic Spin Fluctuations and Superconductivity in La2SmNi2O7 Thin Films

  • Relevance Score: 5.3786
  • Authors: Minhui Xu, Yibo Wang, Jia Liu, Long Cheng, Shuyin Li, Shuaishuai Yin, Xu Zheng, Lixin Yu, Aidi Zhao, Xiaolong Li, Jiandi Zhang, Xiaofang Zhai
  • Affiliations: University of Chinese Academy of Sciences, Chinese Academy of Sciences, ShanghaiTech University
  • Link: http://arxiv.org/abs/2602.07994v1

Summary: In compressively strained La₂SmNi₂O₇ thin films, the coexistence of antiferromagnetic spin fluctuations and superconductivity is directly observed through magnetotransport measurements. The films exhibit high-quality epitaxial structures with an orthorhombic oxygen octahedral rotation pattern. Below the superconducting onset temperature, a characteristic “Mexican hat”-shaped magnetoresistance emerges under in-plane magnetic fields: a negative magnetoresistance in the low-field regime, attributed to the suppression of antiferromagnetic fluctuations and consequent reduction in scattering; and a positive magnetoresistance in the high-field regime, resulting from the Zeeman effect disrupting superconducting fluctuations. By defining a crossover field B* to quantify the strength of antiferromagnetic fluctuations, it is found that B* decreases with increasing temperature and vanishes near the superconducting onset temperature, a behavior distinctly different from that of high-temperature cuprate superconductors. These experimental results not only confirm the coexistence of antiferromagnetic fluctuations and superconductivity but also reveal a direct and novel relationship between them, providing crucial experimental evidence for understanding the pairing mechanism in nickelate superconductors.