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Superconducting NbN and CaFe 0.88 Co 0.12 AsF studied by point-contact spectroscopy with a nanoparticle Au array

2020; American Physical Society; Volume: 101; Issue: 17 Linguagem: Inglês

10.1103/physrevb.101.174502

2469-9977

Yufeng Wu, Aobo Yu, Lei Li, Chao Zhang, T. Wang, Y. H., Zengli Huang, Lingxiu Chen, Yinshang Liu, Claus M. Schneider, Gang Mu, Hong Xiao, Tao Hu,

Superconductivity in MgB2 and Alloys

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, ${T}_{c}=16$ K) and iron superconductors ${\mathrm{CaFe}}_{0.88}{\mathrm{Co}}_{0.12}\mathrm{AsF}$ single crystals (Ca-1111, ${T}_{c}=21.3$ K) by fitting the point-contact spectroscopy with the Blonder-Tinkham-Klapwijk theory. We found that NbN's gap ($\mathrm{\ensuremath{\Delta}}$) exhibits the BCS-like temperature dependence with $\mathrm{\ensuremath{\Delta}}\ensuremath{\approx}2.88$ meV at 0 K and $2\mathrm{\ensuremath{\Delta}}/{k}_{B}{T}_{c}\ensuremath{\approx}4.22$ in agreement with previous reports. By contrast, Ca-1111 has a multigap structure with ${\mathrm{\ensuremath{\Delta}}}_{1}\ensuremath{\approx}1.99$ meV and ${\mathrm{\ensuremath{\Delta}}}_{2}\ensuremath{\approx}5.01$ meV at 0 K, and the ratio between the superconducting gap and ${T}_{c}$ is $2{\mathrm{\ensuremath{\Delta}}}_{1}/{k}_{B}{T}_{c}=2.2$ and $2{\mathrm{\ensuremath{\Delta}}}_{2}/{k}_{B}{T}_{c}=5.5$, 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.