it Ab initio prediction of dx2-y2-wave superconductivity in infinite-layer nickelates

摘要

本文运用超导密度泛函理论对最佳掺杂无限层镍酸盐Re₀.₈Sr₀.₂NiO₂（Re=La, Pr, Nd）进行从头计算，同等处理电子-声子耦合、屏蔽库仑排斥与自旋涨落作用。研究发现这些材料为双带超导体，在不同费米面上呈现符号相反的d_(x²-y²)波配对能隙；关闭自旋涨落时，临界温度降至可忽略的~0.01 K，表明超导电性由自旋涨落驱动。在布里渊区中心的大准二维费米面上，自旋涨落强度比电子-声子耦合和库仑排斥高一个数量级，从而主导配对机制，而电子-声子耦合在布里渊区角落的小三维电子口袋上起主要作用。节线d波能隙结构源于林哈德响应函数在布里渊区角落的显著峰值。计算得到的费米面、临界温度、节线能隙和准粒子态密度与大多数实验相符，所预测的扫描隧道谱等非常规超导性质有待直接实验验证。

材料

本批次暂无数据。

方法

本批次暂无数据。

关键词

本批次暂无数据。

亮点

本批次暂无数据。

结论

本批次暂无数据。

主要论断

• Re₀.8Sr₀.2NiO₂ are two-band superconductors with sign reversal dx2-y2(±)-wave gap functions on different Fermi surface pockets.
  • 证据: We find that Re₀.8Sr₀.2NiO₂ are two-band superconductors with sign reversal dx2-y2(±)-wave gap functions on the different Fermi surface (FS) pockets.
• Superconductivity is driven by spin fluctuation interaction.
  • 证据: when the SF interaction is turned off, T_c becomes negligibly small (≈0.01 K), thus demonstrating that the superconductivity in Re₀.8Sr₀.2NiO₂ is driven by SF interaction.
• The spin fluctuation interaction is an order of magnitude stronger than electron-phonon coupling and Coulomb repulsion on the large quasi-two-dimensional Fermi surface pocket.
  • 证据: the SF interaction is an order of magnitude stronger than both EPC and Coulomb repulsion on the large quasi-two-dimensional FS pocket around the Brillouin zone (BZ) center
• The nodal d-wave gap structure originates from pronounced peaks in the Lindhard response function at the Brillouin zone corners.
  • 证据: The emergence of nodal d-wave gap structure is traced to the pronounced peaks in the Lindhard response function at the BZ corners.
• Calculated Fermi surfaces, critical temperature, nodal gap structure and quasiparticle density of states are consistent with most available experiments.
  • 证据: Our calculated FS, SC critical temperature, nodal gap structure and SC quasiparticle density of states are consistent with most available experiments.
• Predicted scanning tunneling spectra for La₀.8Sr₀.2NiO₂ and Pr₀.8Sr₀.2NiO₂ are ready for experimental verification.
  • 证据: predicted unconventional SC properties such as scanning tunneling spectra of La₀.8Sr₀.2NiO₂ and Pr₀.8Sr₀.2NiO₂ are ready for immediate experimental verifications.

研究流程

• electronic_structure_and_fermi_surface_calculation — The electronic structure of infinite-layer nickelates features a large quasi-2D Fermi surface pocket centered at Γ and small 3D pockets at the zone corners, similar to cuprates.
  • 材料: Re₀.8Sr₀.2NiO₂ (Re=La, Pr, Nd)
  • 方法: Density functional theory (DFT) with local density approximation; Optimized tetrahedron method for Brillouin zone integration; QUANTUM ESPRESSO package
  • 观察: Two bands (H and E) cross the Fermi level; Fermi surface consists of a large quasi-2D cylindrical pocket at Γ and eight small 3D electron pockets at A; Ni 3d dominates density of states near EF; FS cross-sections for LaSrNiO agree with ARPES experiments
• superconducting_properties_calculation — Re₀.8Sr₀.2NiO₂ are two-band d-wave superconductors with sign reversal dx2-y2(±) gap symmetry.
  • 材料: Re₀.8Sr₀.2NiO₂ (Re=La, Pr, Nd)
  • 方法: Superconducting density functional theory (SCDFT) gap equation solver; SCTK code; BCS-type temperature dependence fit for T_c
  • 观察: Gap function on H-band FS is d-wave with large magnitude; Gap on E-band FS pockets is d-wave with opposite sign and smaller magnitude; Calculated T_c values agree with experiments (≈18 K); Gap-to-T_c ratio 2Δ_max/kB T_c ≈ 2.3, exceeding BCS value; Quasiparticle density of states shows V-shaped gap
• pairing_mechanism_investigation — Superconductivity in infinite-layer nickelates is driven by spin fluctuations, with d-wave pairing arising from antiferromagnetic correlations due to Fermi surface nesting.
  • 材料: Re₀.8Sr₀.2NiO₂
  • 方法: Computer experiments switching off spin fluctuations and/or Coulomb repulsion; Calculation of EPC strength λ_ep, Coulomb μ*, and SF interaction V_sf on FS; Lindhard response function calculation
  • 观察: Phonon-only scenario gives T_c ≈ 1 K and s-wave gap; Adding Coulomb suppresses T_c to 0.01K; With full SF interaction, T_c ≈ 18 K and d-wave gap; V_sf is ≈10x larger than λ_ep and μ* on the H-band FS pocket; Lindhard function shows peaks at M and A points indicative of inter- and intra-pocket nesting
• experimental_comparison_and_prediction — The calculated nodal d-wave gap is consistent with most available experiments, and new STS predictions for La and Pr nickelates are ready for verification.
  • 材料: Nd₀.8Sr₀.2NiO₂ thin film STS data; Literature superfluid density and terahertz data
  • 方法: Calculation of quasiparticle density of states from SC gap function; Comparison with scanning tunneling spectroscopy (STS) spectrum
  • 观察: Calculated QPDOS of NdSrNiO matches the V-shaped STS spectrum from flat surface region; Superfluid density experiments indicate nodal gap in La and Pr nickelates, but ambiguous for Nd due to Nd magnetism; Terahertz spectroscopy on NdSrNiO suggests d-wave; Predicted STS spectra for La and Pr nickelates shown in Fig. 7(a)