Heavily Sr-Doped La2SrNi2O7−δ as a Tetragonal Ruddlesden-Popper Phase at Ambient Pressure
Abstract
High-temperature superconductivity has been found in bilayer Ruddlesden-Popper (RP) nickelates in bulk samples under high pressure, or in thin films via compressive strain. In the superconducting state, a tetragonal structure with a straight Ni-O-Ni bond along c-axis has been commonly observed, together with the suppression or diminishing of the density-wave orders. Therefore, it remains an open question whether these factors are sufficient for achieving superconductivity at ambient pressure. Here we report the first successful synthesis of heavily Sr-doped La2SrNi2O7−δ under high-pressure and high-temperature (HPHT) conditions with a flux method. X-ray diffraction and scanning transmission electron microscopy (STEM) confirm that the material adopts a tetragonal (I4/mmm) structure with an 180∘ Ni-O-Ni bond angle along c-axis. Resistance measurements reveal metallic behavior with a low-temperature upturn and no density-wave features are observed. However, neither pressure nor oxygen variation induces superconductivity. Density functional theory calculations indicate that the holes introduced by Sr doping are predominantly doped into the Ni-3dz2 orbital, leading to the appearance of a very large γ pocket on the Fermi surface at ambient pressure and significantly reducing the occupation of the Ni-3dz2 orbital. Combining the experimental observations with theoretical calculations, we attribute the absence of superconductivity to the serious deviation from the half-filling state of the Ni-3dz2 band, which is crucial for the interlayer antiferromagnetic interaction and thus for pairing. Our work unravels important issues for achieving superconductivity in bilayer nickelate system.
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BibTeX
@misc{zhang2026heavily,
title = {{Heavily Sr-Doped La$_2$SrNi$_2$O$_7-δ$ as a Tetragonal Ruddlesden-Popper Phase at Ambient Pressure}},
author = {Yuhang Zhang and Xue Ming and Cui-Qun Chen and Wei Chen and Tian-Yi Li and Zhe-Ning Xiang and Qing Li and Bing-hui Ge and Dao-Xin Yao and Xiyu Zhu and Hai-Hu Wen},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.00542},
eprint = {2609.00542},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.00542},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Heavily Sr-Doped La_2SrNi_2O_7−δ as a Tetragonal Ruddlesden-Popper Phase at Ambient Pressure
AU - Yuhang Zhang
AU - Xue Ming
AU - Cui-Qun Chen
AU - Wei Chen
AU - Tian-Yi Li
AU - Zhe-Ning Xiang
AU - Qing Li
AU - Bing-hui Ge
AU - Dao-Xin Yao
AU - Xiyu Zhu
AU - Hai-Hu Wen
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.00542
UR - https://arxiv.org/abs/2609.00542
AB - High-temperature superconductivity has been found in bilayer Ruddlesden-Popper (RP) nickelates in bulk samples under high pressure, or in thin films via compressive strain. In the superconducting state, a tetragonal structure with a straight Ni-O-Ni bond along c-axis has been commonly observed, together with the suppression or diminishing of the density-wave orders. Therefore, it remains an open question whether these factors are sufficient for achieving superconductivity at ambient pressure. Here we report the first successful synthesis of heavily Sr-doped La_2SrNi_2O_7−δ under high-pressure and high-temperature (HPHT) conditions with a flux method. X-ray diffraction and scanning transmission electron microscopy (STEM) confirm that the material adopts a tetragonal (I4/mmm) structure with an 180^∘ Ni-O-Ni bond angle along c-axis. Resistance measurements reveal metallic behavior with a low-temperature upturn and no density-wave features are observed. However, neither pressure nor oxygen variation induces superconductivity. Density functional theory calculations indicate that the holes introduced by Sr doping are predominantly doped into the Ni-3d_z^2 orbital, leading to the appearance of a very large γ pocket on the Fermi surface at ambient pressure and significantly reducing the occupation of the Ni-3d_z^2 orbital. Combining the experimental observations with theoretical calculations, we attribute the absence of superconductivity to the serious deviation from the half-filling state of the Ni-3d_z^2 band, which is crucial for the interlayer antiferromagnetic interaction and thus for pairing. Our work unravels important issues for achieving superconductivity in bilayer nickelate system.
ER -