Superconducting NbN and CaFe0.88Co0.12AsF studied by point-contact spectroscopy with a nanoparticle Au array
Y. F. Wu, A. B. Yu, L. B. Lei, C. Zhang, T. Wang, Y. H. Ma, Z. Huang, L. X. Chen, Y. S. Liu, C. M. Schneider, G. Mu, H. Xiao, T. Hu
DOI 10.1103/PhysRevB.101.174502 · Physical Review B
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Abstract
The point-contact-spectroscopy measurement is a powerful method to detect the superconducting gap and the spin polarization of materials. However, it is difficult to get a stable and clean point contact by conventional techniques. In this work, we fabricate multiple point contacts by depositing Au nanoparticle arrays on the surface of a superconductor through an anodic aluminum oxide patterned shadow mask. We obtained the superconducting gaps of niobium nitride thin film (NbN, Tc=16 K) and iron superconductors CaFe0.88Co0.12AsF single crystals (Ca-1111, Tc=21.3 K) by fitting the point-contact spectroscopy with the Blonder-Tinkham-Klapwijk theory. We found that NbN's gap (Δ) exhibits the BCS-like temperature dependence with Δ≈2.88 meV at 0 K and 2Δ/kBTc≈4.22 in agreement with previous reports. By contrast, Ca-1111 has a multigap structure with Δ1≈1.99 meV and Δ2≈5.01 meV at 0 K, and the ratio between the superconducting gap and Tc is 2Δ1/kBTc=2.2 and 2Δ2/kBTc=5.5, suggesting an unconventional paring mechanism of Ca-1111 also in agreement with previous reports on other Fe-based superconductors. Our multiple point-contacts method thus provides an alternative way to perform measurements of the superconducting gap.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| NbN Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 16 | Pressure not reported | onset |
| CaFe0.88Co0.12AsF Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 21.3 | Pressure not reported | unknown |
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