Orbital Signatures of Density Wave Transition in La₃Ni₂O₇-delta and La₂PrNi₂O₇-delta RP-Nickelates Probed via in-situ X-ray Absorption Near-edge Spectroscopy

摘要

The report of superconductivity (SC) with T_c~80 K in bilayer Ruddlesden-Popper (RP) nickelate La₃Ni₂O₇-delta have sparked considerable investigations on its normal state properties and SC mechanism under pressure and at low temperature. It is believed that the density wave (DW) at ~150 K plays an important role in SC emergence, but its nature remains largely underexplored. Here, we utilized temperature-dependent in-situ Ni K-edge X-ray Absorption Near-edge Spectroscopy (XANES) to probe the Ni-3d/4p electronic states of La₃Ni₂O₇-delta and La₂PrNi₂O₇-delta samples down to 4.8 K, enabling us to witness the evolution of both in-plane d_(x2-y2)/px (py) and out-of-plane d_(3z2-r2)/p_z orbitals of NiO₆ octahedron across the DW transition. Main edge energy associated with Ni 4p orbital shows an anomalous decline near DW transition, signifying the occurrence of lattice distortions as a hallmark of charge density wave. Below DW transition, the enlarged crystal field splitting (CFS) indicates an enhanced NiO₆ octahedral distortion. Intriguingly, magnetic Pr substituents could activate the mutual interplay of d_(x2-y2) and d_(3z2-r2) orbitals. We discussed its relevance to the favored bulk SC in the pressurized polycrystalline La₂PrNi₂O₇-delta than pristine.

材料

• La₃Ni₂O₇-δ
• La₂PrNi₂O₇-δ

方法

• in-situ Ni K-edge X-ray Absorption Near-edge Spectroscopy (XANES)

关键词

• density wave transition
• charge density wave
• crystal field splitting
• nio6 octahedral distortion
• orbital interplay

亮点

• Orbital signatures of density wave transition probed via in-situ XANES.
• Magnetic Pr substituents activate orbital interplay relevant to favored bulk superconductivity in pressurized La₂PrNi₂O₇-delta.

结论

• Main edge energy associated with Ni 4p orbital shows an anomalous decline near DW transition, signifying lattice distortions as a hallmark of charge density wave.
• Below DW transition, the enlarged crystal field splitting indicates an enhanced NiO₆ octahedral distortion.
• Magnetic Pr substituents could activate the mutual interplay of dx2-y2 and d3z2-r2 orbitals.

主要论断

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研究流程

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