来源 自动抓取
作者 Xu Zhang
arXiv / 出版方 https://arxiv.org/abs/2512.09025
PDF https://arxiv.org/pdf/2512.09025
相关度评分 5.375
主分类 cond-mat.str-el
发布日期 2026-10-08
研究范式 理论研究
样品形态 未知

摘要

本文使用行列式量子蒙特卡洛研究双层镍酸盐La3Ni2O7的双轨道模型，在现实色散和特定相互作用参数下，辅助场退耦合的费米子哈密顿量具有Kramers反幺正对称性，因而无符号问题。通过调节掺杂、层间隧穿和Hund耦合，作者发现体系可形成自旋单态层三重态超导，其转变温度受掺杂和Hund耦合影响；较小掺杂有利于超导，而过大掺杂会抑制甚至消除超导。层间隧穿在超导与(π,π)层间键序的竞争中起决定作用：强相互作用极限下同一对称性还导致键序不稳定性，该键序可能与实验中的神秘密度波相关，并伴随近(π,π)的自旋密度波涨落。结论指出，增强超导可考虑强破坏粒子-空穴对称性和减弱层间/子空间隧穿，后者与顶角氧空位稳定超导的作用相符。

材料

方法

  • determinant Quantum Monte Carlo (DQMC)
  • Hubbard-Stratonovich transformation
  • stochastic analytical continuation (SAC)
  • finite-size crossing analysis
  • Kramers anti-unitary symmetry analysis
  • two-orbital bilayer model Hamiltonian

关键词

亮点

  • The authors identify a sign-problem-free limit of the two-orbital bilayer nickelate model due to Kramers anti-unitary symmetries, enabling efficient determinant QMC simulations.
  • The same anti-unitary symmetries imply that the leading superconducting instability is in the spin-singlet layer-triplet channel and that there is a competing inter-layer bond order at momentum (π,π).
  • The fluctuating inter-layer bond order is accompanied by fluctuating spin-density-wave order near (π,π), providing a promising candidate for the unknown density wave observed in experiments.
  • The results suggest that a tunneling-independent antiferromagnetic interaction, such as RKKY, could be a promising direction for finding new high-temperature superconductors.
  • Reducing inter-subspace tunneling avoids the bond-order instability and is closely related to the role of apical oxygen vacancies in stabilizing superconductivity.

结论

  • The two-orbital bilayer nickelate model supports a spin-singlet layer-triplet superconducting instability, with a transition temperature that depends on doping and Hund's coupling; lower doping favors superconductivity, while excessive doping suppresses or eliminates it.
  • Inter-layer tunneling plays a decisive role in the competition between superconductivity and (π,π) inter-layer bond order, and the bond-order instability in the strong-interaction limit may be related to the enigmatic density wave state observed experimentally.
  • When inter-layer tunneling is reduced, the hole density in the d3z2-r2 orbital increases and superconductivity emerges from both orbitals, making the superconducting transition insensitive to Hund's coupling.
  • Enhancing superconductivity can be achieved by strongly breaking particle-hole symmetry and weakening inter-layer/subspace tunneling, the latter being consistent with the role of apical oxygen vacancies in stabilizing superconductivity in bilayer nickelates.

主要论断

  • The two-orbital bilayer nickelate model has a sign-problem-free limit when the auxiliary-field-decoupled Hamiltonian preserves Kramers anti-unitary symmetries.
    • 证据: The auxiliary-field-decoupled fermion Hamiltonian has Kramers anti-unitary symmetries which guarantee the absence of a sign problem.,The trace over fermionic degrees of freedom is positive definite for any auxiliary field configuration and gives a well-defined probability weight for Monte Carlo sampling.
  • The leading superconducting instability is in the spin-singlet layer-triplet channel, with Tc affected by doping and Hund's coupling.
    • 证据: The same anti-unitary symmetries imply that the SC pairing is maximal in the appropriate channel.,Finite-size crossing of the pair correlation function is used to identify the SC transition.,Lower doping favors superconductivity, whereas large doping in an orbital suppresses or eliminates it.
  • There is a competing (π,π) inter-layer bond-order instability in the strong-interaction limit, accompanied by spin-density-wave fluctuations near (π,π).
    • 证据: The same anti-unitary symmetries show a second instability towards (π,π) inter-layer bond order in the strong interaction limit.,The BO structure factor is maximal at (π,π), and the static spin structure factor peaks near (π,π).
  • Inter-layer tunneling plays a decisive role in the competition between superconductivity and bond order.
    • 证据: When inter-layer tunneling is added, layer charge conservation is broken, introducing a direct contribution and enabling a transition from zero-momentum order to order at momentum (π,π).,Setting inter-layer tunneling to zero changes hole densities and yields a similar SC transition temperature with SC from both orbitals.
  • The (π,π) bond order is a promising candidate for the unknown density wave observed in experiment.
    • 证据: The BO instability at (π,π) found in this work is a promising candidate for the unknown density wave observed in experiment [64,13].,The fluctuating BO is accompanied by fluctuating SDW order near (π,π).
  • Superconductivity can be enhanced by strongly breaking particle-hole symmetry and weakening interlayer/subspace tunneling, consistent with the role of apical oxygen vacancies.
    • 证据: The findings suggest two avenues for enhancing superconductivity: strongly breaking particle-hole symmetry and reducing inter-subspace tunneling to avoid a BO instability.,This is closely related to the important role of apical oxygen vacancies in stabilizing superconductivity in bilayer nickelates.

研究流程

  • model_construction — A sign-problem-free limit exists for the two-orbital bilayer nickelate model under certain interaction parameters.
    • 材料: two-orbital bilayer nickelate La3Ni2O7 effective model; DFT-derived parameters [19]
    • 方法: two-orbital bilayer Hamiltonian; onsite interactions and Hund's coupling; inter-layer tunneling; Hubbard-Stratonovich transformation
    • 观察: auxiliary-field-decoupled fermion Hamiltonian has Kramers anti-unitary symmetries; trace over fermions is positive definite and sign-problem-free
  • symmetry_analysis — The anti-unitary symmetries imply a leading spin-singlet layer-triplet SC instability and a competing (π,π) inter-layer bond-order instability.
    • 材料: interacting Hamiltonian; fermion bilinear order parameters
    • 方法: Majorana basis; Kramers anti-unitary symmetry classification; bilinear correlation functions; Fierz identity
    • 观察: exchange contribution maximal for spin-singlet layer-triplet SC; competing inter-layer bond order at (π,π); layer charge conservation and direct contributions considered
  • quantum_monte_carlo_simulation — Finite-temperature determinant QMC can simulate the sign-problem-free model and reveals gapped single-particle excitations and low double occupancy.
    • 材料: two-orbital model; auxiliary fields
    • 方法: determinant Quantum Monte Carlo; Trotter decomposition; discrete Hubbard-Stratonovich transformation; finite-temperature simulations
    • 观察: single-particle gap develops and is minimal around points; low double occupancy; spectral function and imaginary-time Green's function measured
  • measurement_analysis — The model hosts superconductivity whose Tc depends on doping and Hund's coupling, with a competing (π,π) bond order and SDW fluctuations.
    • 材料: QMC correlation functions; pair correlation function; structure factors
    • 方法: finite-size crossing of order parameter with BKT exponent; stochastic analytic continuation; static structure factor calculations for SC, BO, SDW
    • 观察: SC transition temperature identified from finite-size crossing; gapless excitation branch from SAC; SC prefers small doping and is suppressed by large doping; BO structure factor maximal at (π,π); SDW fluctuations near (π,π)
  • interpretation — Inter-layer tunneling is decisive for the SC/BO competition, and the (π,π) bond order is a candidate for the experimentally observed density wave; SC may be enhanced by breaking particle-hole symmetry and weakening interlayer/subspace tunneling.
    • 材料: numerical phase diagram; experimental context
    • 方法: comparison with experiment; symmetry-based phase-diagram reasoning
    • 观察: inter-layer tunneling controls SC versus BO competition; BO at (π,π) may correspond to enigmatic density wave; reducing inter-subspace tunneling and breaking particle-hole symmetry can enhance SC