Source capture
Authors Shuxiang Xu, Guangdi Zhou, Hao Wang, Tianyi Wu, Wei Wang, Liyu Shi, Dong Wu, Haoliang Huang, Xinbo Wang, Jinfeng Jia, Qi-Kun Xue, Zhuoyu Chen, Tao Dong, Nanlin Wang
arXiv / Publisher http://arxiv.org/abs/2604.04421v1
PDF https://arxiv.org/pdf/2604.04421v1
Relevance score 5.129
Primary category Not available in this batch.
Published Not available in this batch.
Research paradigm Experimental
Sample form Thin Film

Summary

By combining linear terahertz time-domain spectroscopy with third-harmonic generation, this study systematically probes the superconducting pairing symmetry and normal-state pseudogap in compressively strained (La,Pr)3Ni2O7 thin films. Linear terahertz spectroscopy reveals a significant suppression of low-frequency spectral weight below the superconducting transition temperature, accompanied by a weak coherence peak and a large residual conductivity persisting down to near-zero temperature, consistent with a disordered s±-wave pairing scenario. The nonlinear third-harmonic signal sharply enhances upon entering the superconducting state, but its response persists above the superconducting transition temperature, exhibiting a kink at approximately 100 K, which is attributed to the normal-state pseudogap based on similar temperature scales observed in angle-resolved photoemission spectroscopy on analogous films. This study establishes (La,Pr)3Ni2O7 as a bulk superconductor with s±-wave-like pairing, where superconductivity coexists and likely competes with another ordered state, providing a new platform for exploring unconventional superconducting mechanisms beyond cuprates and iron-based superconductors.

Materials

Methods

  • terahertz time-domain spectroscopy
  • third-harmonic generation

Keywords

Highlights

  • The superconducting gap scale is above the measurement window, with about 65% of carriers remaining uncondensed at 2 K.
  • The London penetration depth is approximately 620 nm, implying a strongly reduced superfluid density.

Conclusions

  • Linear THz spectroscopy reveals a bulk superconducting response with a weak coherence peak and large residual conductivity, consistent with disordered s±-wave pairing.
  • The nonlinear third-harmonic signal persists above Tc, attributed to a normal-state pseudogap.

Main claims

  • (La,Pr)3Ni2O7 thin films exhibit bulk superconductivity with disordered s±-wave pairing
    • Evidence: Linear THz shows suppression of spectral weight, weak coherence peak, large residual conductivity, large penetration depth ≈620 nm
  • An anomalous normal-state pseudogap emerges above Tc, evidenced by persistent third-harmonic signal with kink at ≈100K
    • Evidence: THG signal persists above Tc and shows reproducible kink near 100 K, matching ARPES pseudogap temperature

Workflow

  • Sample growth and characterization
    • Materials: (La,Pr)3Ni2O7 thin films on SrLaAlO4 substrates
    • Methods: Gigantic-Oxidative Atomic-Layer-by-Layer Epitaxy (GAE)
  • Linear terahertz spectroscopy — Bulk superconducting response with s±-wave pairing in disordered limit
    • Materials: THz time-domain spectroscopy setup
    • Methods: Fresnel analysis; Temperature-dependent conductivity extraction
    • Observations: Suppression of low-frequency spectral weight below Tc; Weak coherence peak near Tc; Large residual conductivity at 2K; London penetration depth ≈620 nm
  • Nonlinear THz third-harmonic generation — Pseudogap phase above Tc suggested by nonlinear response
    • Materials: Narrowband multicycle THz pulses; Band-pass filters
    • Methods: Third-harmonic generation; Electro-optic sampling
    • Observations: THG enhancement below Tc; THG persists above Tc with kink at ≈100K