来源 自动抓取
作者 Jiangfan Wang, Yi-feng Yang
arXiv / 出版方 https://arxiv.org/abs/2606.04821
PDF https://arxiv.org/pdf/2606.04821
相关度评分 5.464
主分类 cond-mat.supr-con
发布日期 2026-06-04
研究范式 理论研究
样品形态 薄膜

摘要

该研究基于两分量模型提出了一个统一理论，用以解释双层镍酸盐超导体在加压块材与薄膜中的一系列核心实验现象。理论以轨道镍原子的强关联局域电子与巡游电子间的层间超交换耦合和杂化为核心，预言超导转变温度随掺杂变化呈现两类行为：当层间超交换耦合较强时，电子或空穴掺杂分别形成两个超导穹顶，半填充附近出现非超导的层间价键态；当耦合较弱或适中时，两个穹顶合并为一个跨越半填充的单一穹顶，但最高温度较低。掺杂增加会使正常态从费米液体转变为非费米液体或弱绝缘态，并在最优掺杂附近出现准线性电阻散射率。氧空位或化学替代可破坏层间价键，同时抑制超导并诱发巡游电子的局域近藤散射，解释了非超导样品中观测到的电阻对数温度依赖及负磁阻。该框架统一说明了块材和薄膜中超导转变与正常态的差异、孔穴掺杂及氧计量对穹顶状的影响，以及超导与近藤效应的竞争关系。基于理论，作者提出通过掺杂或降低层间磁耦合可在常压下实现块材超导，并预言电子掺杂将获得更高的转变温度。

材料

方法

关键词

亮点

  • A unified framework reconciles disparate superconducting and normal-state behaviors in pressurized bulk and thin-film bilayer nickelates.
  • The valence bond state at dz2 half-filling acts as a non-superconducting phase that separates or connects the superconducting domes depending on interlayer coupling strength.
  • Breaking of interlayer valence bonds simultaneously destroys superconductivity and produces Kondo scattering, explaining Kondo effect in non-superconducting samples.
  • Ambient-pressure superconductivity is predicted through tuning of interlayer distance or doping.
  • The universal linear relation between Tc and the c-axis lattice constant highlights the crucial role of interlayer superexchange.

结论

  • The two-component scenario with strongly correlated dz2 electrons and itinerant dx2-y2 electrons explains key experimental observations in bilayer nickelates.
  • For strong interlayer superexchange coupling (bulk), two superconducting domes upon electron and hole doping are separated by a valence bond state near half filling; for weak coupling (thin films), a single dome spans half filling with lower Tc.
  • Increasing doping drives the normal state from Fermi liquid to non-Fermi liquid to weakly insulating, with quasi-linear-in-T scattering near optimal Tc.
  • Oxygen vacancies or nonmagnetic substitution break interlayer valence bonds, suppressing superconductivity and inducing local Kondo scattering.
  • Ambient pressure bulk superconductivity is predicted via doping or reducing interlayer magnetic coupling, with higher Tc possible upon electron doping.

主要论断

  • The two-component model with interlayer superexchange coupling and hybridization can unify the key experimental observations of bilayer nickelates.
    • 证据: Abstract: 'We provide a unified explanation based on the two-component scenario for a number of key experimental observations reported recently.',Full text: 'This work provides a unified theory that can satisfactorily address all above observations.'
  • For strong interlayer coupling (bulk), electron and hole doping produce two separate superconducting domes with a non-superconducting valence bond state near half filling.
    • 证据: Full text: 'For large J with strong pairing strength, we obtain two separate superconducting domes on electron and hole doping regions… The suppression of Tc… Close to half filling… Tc rapidly drops to zero, suggesting… non-superconducting valence bond state (VBS).'
  • In thin films with weaker interlayer coupling, the two domes merge into a single dome with lower maximum Tc, explaining the experimental observations.
    • 证据: Full text: 'For smaller or moderate J, the VBS is also weakened… and can now couple with electrons to form superconductivity. This leads to a finite Tc around half filling that merges the two superconducting domes into a single one.'
  • Oxygen vacancies break interlayer valence bonds, suppress superconductivity, and induce Kondo scattering, explaining the observed Kondo effect in non-superconducting samples.
    • 证据: Full text: 'When there exist inner apical oxygen vacancies… the VBS is destroyed to produce one or two decoupled Ni-dz2 spins, whose hybridization with surrounding electrons can induce effective Kondo scattering… Numerically, one can simulate this by setting the local J to zero…. We see a sharp peak in ImSigma and a dip in the DOS at zero frequency, a clear indication of Kondo resonance.'
  • Doping drives the normal state from Fermi liquid to non-Fermi liquid with linear-in-T scattering near optimal Tc, and further to weakly insulating, consistent with transport experiments.
    • 证据: Full text: 'Close to half filling, it vanishes at low temperatures… indicating a Fermi liquid normal state. Increasing hole (electron) doping quickly suppresses the VBS gap and enhances the inter-orbital scattering, causing a NFL normal state with quasi-linear-in-T behavior… A WI region emerges where ImSigma increases logarithmically with decreasing temperature.'
  • The theory predicts that bulk superconductivity at ambient pressure can be achieved by doping or reducing interlayer magnetic coupling, and electron doping will yield even higher Tc.
    • 证据: Abstract: 'We propose bulk superconductivity at ambient pressure by doping or reducing the interlayer magnetic coupling and predict even higher Tc upon electron doping.',Full text: 'Our theory has two immediate predictions: 1) ambient pressure superconductivity by doping or reducing the interlayer magnetic coupling…; 2) a second superconducting dome upon electron doping with an even higher maximal Tc.'

研究流程

  • model_formulation — The two-component model captures the essential physics of bilayer nickelates, with interlayer superexchange coupling as a key parameter.
    • 材料: two-orbital t-t_perp-J model; slave particle representation
    • 方法: definition of Hamiltonian with interlayer superexchange J, hybridization V, and Coulomb repulsion U; slave particle decomposition with spinon, holon, doublon operators
    • 观察: effective interlayer pairing of dz2 electrons; hybridization between localized dz2 and itinerant dx2-y2 electrons
  • superconductivity_and_VBS_calculations — Interlayer superexchange strength controls the number of superconducting domes and the appearance of an intermediate valence bond state.
    • 材料: Bethe-Salpeter equation; normal state Green's functions
    • 方法: solving pairing vertex divergence to determine Tc; analyzing momentum dependence of pairing gap
    • 观察: two separate superconducting domes for strong J, separated by non-superconducting valence bond state near half filling; single superconducting dome for moderate J; anisotropic s+–wave pairing on bonding/antibonding bands, isotropic s-wave on dz2 pocket; maximum Tc at optimal doping
  • normal_state_and_kondo_analysis — Doping and oxygen vacancies control the normal state from FL to NFL/WI and induce Kondo scattering in non-superconducting samples.
    • 材料: self-energy of dx2-y2 electrons; density of states
    • 方法: calculation of imaginary part of self-energy to obtain scattering rate; simulation of broken VBS by setting local J=0 to mimic oxygen vacancies
    • 观察: Fermi liquid behavior near half filling with VBS gap; non-Fermi liquid with quasi-linear-in-T resistivity near optimal doping; weakly insulating state at higher doping with log-T resistivity; Kondo resonance peak in self-energy and dip in DOS when VBS broken
  • unified_phase_diagram_and_predictions — The theory predicts ambient pressure bulk superconductivity by doping or reducing interlayer coupling, and a second superconducting dome under electron doping with potentially higher Tc.
    • 材料: combined computational results
    • 方法: synthesis of Tc, normal state, and VBS/Kondo results into a global phase diagram
    • 观察: phase diagram showing superconducting domes, VBS, FL, NFL, WI, Kondo, and magnetic regions; unified explanation for differences between bulk and thin films