Superconductivity in Niobium Nitride

Tsu-Lien Hung^1*, Fan-Yun Chiu^2,1, Min-Nun Ou¹, Ting-Kuo Lee¹, Yang Yuan Chen¹

¹Institute of Physics, Academia Sinica, Taipei, Taiwan
²Department of Physics, National Taiwan University, Taipei, Taiwan

* Presenter:Tsu-Lien Hung, email:tlhung@gate.sinica.edu.tw

Niobium nitride is a hard superconductor with many excellent physical properties, such as high hardness, high shear rigidity, and high bulk modulus. There are many structure phases, such as δ-cubic (rocksalt), WC-type, ε-hexagonal, δ’- hexagonal, and tetragonal. The δ- cubic phase has been extensively studied the superconductivity with a wide range of Tc, 9 ~ 17 K due to its nitrogen concentration. In our work, the cubic phase specimens of NbN were measured by X-ray diffraction, magnetic susceptibility, resistivity, and specific heat. We observed that the Tc of cubic phase appeared 13.6 K from diamagnetic measurements and that electrical specific heat part (γ) and Debye temperature obtained 2.9 mJ mol^-1 K^-2 and 408 K, respectively. In 2015, the ε-hexagonal phase of NbN was reported the appearance of superconductivity below 10.6 K.[1] The structure of ε-hexagonal phase were determined by electron back-scattering diffraction (EBSD) technique since the size of specimens was about 20 ~ 30 μm. However, no superconductivity was found in our specimen. We inferred that the inconsistent result is according to the difference of length of c-axis. The length of c-axis of our specimen is 11.2704 Å was larger than Zou et al.’s work, 11.2497 Å.

[1]. Zou, Y., Qi, X., Zhang, C., Ma, S., Zhang, W., Li, Y., . . . Li, B. (2016). Discovery of Superconductivity in Hard Hexagonal epsilon-NbN. Sci Rep, 6, 22330.

Keywords: Niobium nitride, Superconductivity