Source capture
Authors Qingxin Dong, Fengrui Shi, Yan Zhang, Tong Shi, Yi Liu, Shaoheng Ruan, Zhongjin Wu, Jianping Sun, Zhaoming Tian, Yoshiya Uwatoko, Guanghan Cao, Xin Lu, Bosen Wang, Jin-Guang Cheng
arXiv / Publisher https://arxiv.org/abs/2607.10668
PDF https://arxiv.org/pdf/2607.10668
Relevance score 4.604
Primary category cond-mat.supr-con
Published 2026-07-14
Research paradigm Experimental
Sample form Unknown

Summary

Researchers integrated soft point-contact Andreev reflection spectroscopy into a palm-type cubic anvil high-pressure cell, employing substrate anchoring and an external wire branching strategy to stably form multiple point-contact junctions under hydrostatic pressures up to 15 GPa. Benchmark measurements on the elemental superconductor Nb verified the method’s reliability and yielded a zero-temperature superconducting energy gap ratio of 2Δ(0)/k_B T_c ≈ 3.3. Further application to the kagome metal superconductor CsCr3Sb5 and the bilayer nickelate superconductor La2PrNi2O7 revealed sharp zero-bias conductance peaks strikingly different from those of conventional BCS superconductors, and their evolution with temperature, magnetic field, and pressure was systematically investigated. Analysis indicates that these spectroscopic features are consistent with unconventional superconductivity and possible d-wave pairing symmetry, providing direct spectroscopic evidence for understanding their pairing mechanism. This work successfully establishes a high-pressure experimental platform that bridges macroscopic electrical transport and microscopic spectroscopic probes, opening a new avenue for broadly exploring the pairing symmetries of pressure-induced unconventional superconductors.

Materials

Methods

  • Soft point-contact Andreev reflection spectroscopy
  • Cubic-anvil pressure cell
  • Substrate anchoring
  • External wire-splitting
  • Resistivity measurements
  • Lock-in amplifier modulation technique

Keywords

Highlights

  • Achieves nearly 100% success rate for stable junction formation under pressure.
  • First implementation of PCARS in a cubic-anvil cell, extending the technique to 15 GPa.
  • Sharp zero-bias conductance peaks in CsCr3Sb5 and La2PrNi2O7 indicate unconventional pairing, possibly d-wave.
  • The method provides direct spectroscopic insight into pairing symmetry of pressure-induced superconductors.

Conclusions

  • Soft PCARS implemented in a cubic-anvil cell enables stable formation of multiple point-contact junctions under hydrostatic pressures up to 15 GPa.
  • Benchmark measurements on Nb reproduce known gap parameters with 2Δ(0)/k_B T_c ≈ 3.3.
  • Pronounced zero-bias conductance peaks in CsCr3Sb5 and La2PrNi2O7 provide spectroscopic evidence consistent with unconventional superconductivity.
  • The platform bridges macroscopic transport and microscopic spectroscopic probes for pressure-induced unconventional superconductors.

Main claims

  • Soft PCARS can be stably implemented in a CAC using substrate anchoring and external wire-splitting.
    • Evidence: Benchmark measurements on Nb demonstrate high reproducibility and yield a zero-temperature gap with gap ratio 3.3.,Stable formation of multiple point-contact junctions under hydrostatic pressures up to 15 GPa, with nearly 100% success rate.
  • PCARS spectra on CsCr3Sb5 show a zero-bias conductance peak, providing spectroscopic evidence consistent with unconventional superconductivity.
    • Evidence: Pronounced ZBCP observed, evolution with temperature, magnetic field and pressure investigated.,Fits using a phenomenological d-wave BTK model capture essential spectral features.
  • PCARS on La2PrNi2O7 at 13.5 GPa reveals a ZBCP, suggesting unconventional pairing.
    • Evidence: Well-defined Andreev reflection spectra displaying a sharp ZBCP.,Fits using a nodal d-wave model capture the ZBCP reasonably well; extracted gap Δ(0)≈6 meV.
  • The CAC-based PCARS platform bridges macroscopic transport and microscopic spectroscopic probes, opening new avenues for investigating pairing symmetry in pressure-induced superconductors.
    • Evidence: The method extends high-pressure studies from macroscopic transport to microscopic gap structure and pairing symmetry, demonstrated on multiple unconventional superconductors.

Workflow

  • technique_integration — Soft PCARS is successfully integrated into a CAC, enabling stable junction formation under high pressure.
    • Materials: palm-type cubic anvil pressure cell; insulating substrate (Al2O3, SiO2); gold wires; silver paste
    • Methods: substrate anchoring; external wire-splitting
    • Observations: stable multiple point-contact junctions; nearly 100% success rate
  • benchmark_measurements_on_Nb — Extracted gap Δ(0)=1.3 meV, ratio 2Δ/kTc≈3.3, consistent with known s-wave superconductivity, validating the setup.
    • Materials: elemental superconductor Nb
    • Methods: temperature-dependent PCARS; s-wave BCS model fitting
    • Observations: coherence peaks at ±1.3 meV; dip features at higher bias; spectra vanish above Tc
  • spectroscopy_of_CsCr3Sb5 — ZBCP suggests unconventional superconductivity, possibly d-wave pairing, with Δ(0)=2.3 meV and strong-coupling ratio 2Δ/kTc≈8.2.
    • Materials: kagome superconductor CsCr3Sb5
    • Methods: PCARS under pressure; temperature sweeps; d-wave BTK model fitting
    • Observations: sharp zero-bias conductance peak (ZBCP); broadening and decreasing amplitude with temperature
  • spectroscopy_of_La2PrNi2O7 — ZBCP indicates unconventional pairing; extracted gap Δ(0)≈6 meV, though possibly from filamentary superconductivity.
    • Materials: polycrystalline bilayer nickelate La2PrNi2O7
    • Methods: pressure-dependent PCARS; background normalization; d-wave model fitting
    • Observations: ZBCP at 13.5 GPa; hump persists to ≈80K