Superconductivity in Ruddlesden-Popper nickelates: a review of recent progress, focusing on thin films

摘要

近年来，Ruddlesden-Popper（RP）镍氧化物超导研究取得重要突破。本文系统回顾了该领域的实验与理论进展，重点聚焦薄膜体系。核心发现包括：在高压下，双层La₃Ni₂O₇（T_c~80 K）和三层La₄Ni₃O₁₀相继呈现超导电性；尤为关键的是，在提供压缩应变的衬底上制备的La₃Ni₂O₇超薄膜中实现了常压超导，这突破了高压限制，使得角分辨光电子能谱（ARPES）等此前无法在超导态使用的实验技术得以应用。理论方面，该体系需同时考虑Ni的e_g和a1g两个轨道，以及双层内强烈的层间耦合形成的“二聚体”图像，并表现出类似铜氧化物的奇特金属行为和强关联特征。本文通过对比不同RP镍氧化物的异同，为理解关联电子系统中的高温超导机制提供了新视角，并展望了未来研究方向。

材料

• La₃Ni₂O₇
• La₄Ni₃O₁₀
• NdNiO₂
• La₂.85Pr₀.15Ni₂O₇
• La_3-xSr_xNi₂O₇
• La₃Ni₂O₇ ultra-thin

方法

• ARPES
• STM
• DFT
• RPA
• DMRG
• RIXS
• PLD

关键词

• strange metal behavior
• spin density wave
• s± pairing
• compressive strain
• oxygen stoichiometry
• pseudogap
• fermi surface nesting
• superconductivity
• high tc superconductivity
• correlated electron systems

亮点

• Ambient-pressure superconductivity is achieved in ultra-thin La₃Ni₂O₇ films on compressively strained LSAO substrates, enabling ARPES studies.
• Record T_c up to 63 K in thin films at ambient pressure.
• Remarkably, ambient-pressure superconductivity was observed in La₃Ni₂O₇ ultra-thin films under compressive strain.

结论

• Superconductivity in bilayer RP nickelates requires compressive strain or high pressure to straighten Ni-O-Ni bonds and enhance interlayer coupling.
• Strange metal behavior with linear resistivity is observed in optimal-pressure bulk and optimal-strain thin films.
• The pairing symmetry is debated, with most evidence favoring s± wave, though some studies suggest d-wave.
• The discovery of superconductivity with T_c ≈ 80 K in the nickelate Ruddlesden-Popper bilayer La₃Ni₂O₇ at high pressure has opened a new platform for unconventional superconductivity.
• Ambient-pressure superconductivity was also observed recently in La₃Ni₂O₇ ultra-thin films when grown on substrates that provide compressive strain.
• This discovery significantly extends the type of experimental techniques that can be used in nickelates.

主要论断

• Superconductivity in bilayer La₃Ni₂O₇ was first discovered under high pressure with T_c ≈ 80 K.
  • 证据: Ke_y findings include the emergence of superconductivity in bilayer La₃Ni₂O₇ (T_c ≈ 80 K) and trilayer La₄Ni₃O₁₀ under high pressure
• Ambient-pressure superconductivity in ultra-thin films of La₃Ni₂O₇ was realized on compressively strained substrates, enabling ARPES and other techniques.
  • 证据: ambient-pressure superconductivity in ultra-thin films of La₃Ni₂O₇ grown on substrates providing compressive strain—a breakthrough that overcomes the high-pressure limitation and enables the use of experimental techniques previously inaccessible in the superconducting state, such as angle-resolved photoemission spectroscopy (ARPES).
• The system requires consideration of both Ni e_g and a1g orbitals and strong interlayer coupling, giving rise to a dimer picture.
  • 证据: On the theoretical side, the system requires simultaneous consideration of both the Ni e_g and a1g orbitals, as well as the strong interlayer coupling within bilayers that gives rise to a 'dimer' picture

研究流程

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