摘要
通过采用低温超高真空暗箱转移技术保持样品表面质量，本研究利用角分辨光电子能谱（ARPES）结合不同光子能量，系统解析了超导(La,Pr,Sm)3Ni2O7/SrLaAlO4薄膜的三维电子能带结构。实验揭示了轨道依赖的维度性：dx2-y2主导的能带呈现准二维特征，而dz2主导的γ能带则显示出明显的kz色散。在所有观测能带的高对称方向均发现有限能隙，其中γ能带的温度依赖分析表明其超导能隙约18 meV，比值2Δ/kBTc~8，远超弱耦合BCS极限。此外，费米能级附近谱权重的抑制在超导转变温度以上仍持续存在，且观测到普遍存在的瀑布状谱特征，表明电子相互作用的显著影响。这些发现强调了第三维度及dz2轨道在镍酸盐超导机制中的关键作用，对理论模型施加了重要约束。
材料
方法
关键词
- three dimensional electronic structure
- orbital dependent dimensionality
- superconducting gap
- waterfall feature
亮点
- Finite gaps are observed along high-symmetry directions for all detected bands.
- Suppression of spectral weight near the Fermi level persists above T_c, indicating a pseudogap.
- Ubiquitous waterfall-like spectral features indicate significant electron correlations.
结论
- The dx2-y2-dominated bands are quasi-two-dimensional, while the d_z2-dominated γ band exhibits finite k_z dispersion.
- A large superconducting gap of ≈18 meV and a ratio 2Δ/kBTc ≈8 are observed on the γ band, exceeding the BCS limit.
主要论断
- The dz2-dominated γ band exhibits finite kz dispersion, indicating three-dimensional electronic structure
- 证据: ARPES with multiple photon energies reveals periodic variation of γ band with kz, while dx2-y2 bands show negligible kz dispersion
- The superconducting gap on the γ band is approximately 18 meV with 2Δ/kBTc ≈8, exceeding weak-coupling BCS limit
- 证据: Temperature-dependent symmetrized EDCs fitted with BCS model yield Δ≈18 meV; Tc≈48 K gives 2Δ/kBTc≈8
研究流程
- Thin film growth and transfer — High-quality superconducting films preserved for ARPES
- 材料: (La,Pr,Sm)3Ni2O7 films on SrLaAlO4
- 方法: GAE method; Cryogenic UHV suitcase transfer
- 观察: Sharp RHEED, XRD peaks, STEM confirms structure
- ARPES measurements — 3D electronic structure with orbital-dependent dimensionality and large gap on dz2 band
- 材料: Synchrotron radiation ARPES
- 方法: Photon-energy-dependent ARPES; Fermi surface mapping
- 观察: Orbital-dependent dimensionality: dx2-y2 bands quasi-2D, dz2 band shows kz dispersion; Waterfall features; Superconducting gap on γ band ≈18 meV