Progress of ambient-pressure superconductivity in bilayer nickelate thin films

摘要

这篇综述总结了双层镍酸盐La₃Ni₂O₇薄膜在常压超导方面的最新进展。通过外延应变工程，利用SrLaAlO₄等衬底提供的压应变，成功在常压条件下稳定了超导相，这与块材高压超导的发现形成重要突破。实验表征方面，角分辨光电子能谱(ARPES)测量揭示了存在争议的费米面拓扑结构，不同研究组的观测结果有所差异，这可能源于薄膜生长条件的差异。在提高超导转变温度(T_c)方面，通过增大压应变和优化生长技术（如巨型氧化原子层外延），可使T_c达到约60K。理论研究聚焦于电子结构和配对对称性，弱耦合方法（如随机相位近似和泛函重整化群）预测了s±波或d波配对，而重整化平均场理论则指出节点d波配对的可能性。然而，费米面上电子袋在超导中的具体作用、晶格比与T_c的关系等关键问题尚未完全阐明。这些进展表明双层镍酸盐薄膜是一个高度可调且极具前景的高温超导研究平台。

材料

• La₃Ni₂O₇
• La₂.85Pr₀.15Ni₂O₇
• La₂PrNi₂O₇
• La_3-xSr_xNi₂O₇

方法

• PLD
• Gigantic-oxidative atomic-layer-by-layer epitaxy (GAE)
• ARPES
• STM
• X-ray absorption spectroscopy (XAS)
• STEM
• DFT
• DMFT
• Constrained random phase approximation (cRPA)
• Random phase approximation (RPA)
• Functional renormalization group (FRG)
• Renormalized mean-field theory (RMFT)
• Exact diagonalization

关键词

• ambient pressure superconductivity
• epitaxial strain engineering
• fermi surface topology
• pairing symmetry
• s± wave pairing
• d wave pairing

亮点

• The discovery of ambient-pressure superconductivity in bilayer nickelate thin films represents a major advancement following high-pressure superconductivity in bulk La₃Ni₂O₇.
• The role of the electron pocket on the Fermi surface in enabling superconductivity remains to be fully clarified.
• The relationship between lattice ratio and T_c in thin films differs from that in bulk La₃Ni₂O₇, highlighting an unresolved issue.
• Direct measurement of the superconducting gap on the Fermi surface reveals a significant gap opening on the α sheet with no signs of nodes.

结论

• Epitaxial strain engineering with compressive strain from substrates like SrLaAlO₄ enables ambient-pressure superconductivity in La₃Ni₂O₇ thin films.
• ARPES measurements reveal conflicting Fermi surface topologies on bilayer nickelate thin films, likely due to differences in growth conditions.
• Increasing compressive strain and optimizing growth techniques can raise the superconducting transition temperature T_c to approximately 60 K.
• Weak-coupling methods predict s±-wave or d-wave pairing, while renormalized mean-field theory suggests nodal d-wave pairing.

主要论断

• Compressive strain from SLAO substrate stabilizes ambient-pressure superconductivity in thin films.
  • 证据: Abstract,Summary: compressive strain from substrates like SrLaAlO₄ stabilizes superconductivity.
• ARPES measurements reveal conflicting Fermi surface topologies.
  • 证据: Abstract,Summary: ARPES measurements show conflicting Fermi surface topologies likely due to variations in growth conditions.
• Increasing compressive strain and optimizing growth techniques can raise T_c to approximately 60 K.
  • 证据: Abstract,Summary: increasing compressive strain and optimizing growth techniques enable T_c to reach approximately 60 K.

研究流程

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