Source capture
Authors Yueying Li, Lizhi Xu, Wei Lv, Zihao Nie, Zechao Wang, Yu Miao, Jianchang Shen, Guangdi Zhou, Wenhua Song, Heng Wang, Haoliang Huang, Junfeng He, Jin-Feng Jia, Peng Li, Qi-Kun Xue, Zhuoyu Chen
arXiv / Publisher http://arxiv.org/abs/2604.08430v2
PDF https://arxiv.org/pdf/2604.08430v2
Relevance score 5.525
Primary category Not available in this batch.
Published Not available in this batch.
Research paradigm Experimental
Sample form Thin Film

Summary

By employing a low-temperature ultrahigh-vacuum dark-box transfer technique to preserve sample surface quality, this study systematically resolves the three-dimensional electronic band structure of superconducting (La,Pr,Sm)3Ni2O7/SrLaAlO4 thin films using angle-resolved photoemission spectroscopy (ARPES) with multiple photon energies. The experiments reveal orbital-dependent dimensionality: the dx2-y2-dominated band exhibits quasi-two-dimensional character, while the dz2-dominated γ band displays clear kz dispersion. Finite gaps are observed along high-symmetry directions for all detected bands, with temperature-dependent analysis of the γ band indicating a superconducting gap of approximately 18 meV and a ratio 2Δ/kBTc ~ 8, far exceeding the weak-coupling BCS limit. Moreover, suppression of spectral weight near the Fermi level persists above the superconducting transition temperature, and ubiquitous waterfall-like spectral features are observed, indicating a significant influence of electron correlations. These findings underscore the critical role of the third dimension and the dz2 orbital in the nickelate superconducting mechanism, imposing important constraints on theoretical models.

Materials

Methods

Keywords

  • three dimensional electronic structure
  • orbital dependent dimensionality
  • superconducting gap
  • waterfall feature

Highlights

  • 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.

Conclusions

  • 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.

Main claims

  • The dz2-dominated γ band exhibits finite kz dispersion, indicating three-dimensional electronic structure
    • Evidence: 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
    • Evidence: Temperature-dependent symmetrized EDCs fitted with BCS model yield Δ≈18 meV; Tc≈48 K gives 2Δ/kBTc≈8

Workflow

  • Thin film growth and transfer — High-quality superconducting films preserved for ARPES
    • Materials: (La,Pr,Sm)3Ni2O7 films on SrLaAlO4
    • Methods: GAE method; Cryogenic UHV suitcase transfer
    • Observations: Sharp RHEED, XRD peaks, STEM confirms structure
  • ARPES measurements — 3D electronic structure with orbital-dependent dimensionality and large gap on dz2 band
    • Materials: Synchrotron radiation ARPES
    • Methods: Photon-energy-dependent ARPES; Fermi surface mapping
    • Observations: Orbital-dependent dimensionality: dx2-y2 bands quasi-2D, dz2 band shows kz dispersion; Waterfall features; Superconducting gap on γ band ≈18 meV