Rock-salt type niobium nitride (δ-NbN) is a well-known superconductor having superconducting transition temperature (Tc) ≈ 18\,K and a large superconducting gap ≈3\,meV. The Tc of δ-NbN thin film exhibits a large scattering irrespective of the growth conditions and lattice parameter. In this work, we investigate the atomic origin of suppression of Tc in δ-NbN thin film by employing combined methods of experiments and ab-initio simulations. Sputtered δ-NbN thin films with different disorder were analyzed through electrical resistivity and x-ray absorption spectroscopy. A strong correlation between the superconductivity and the atomic distortion induced electronic reconstruction was observed. The theoretical analysis revealed that under N-rich growth conditions, atomic and molecular N-interstitial defects assisted by cation vacancies form spontaneously and are responsible for the suppression of Tc in δ-NbN by smearing its electronic densities of states around Fermi level.
@article{arxiv.2010.04509,
title = {Microscopic Origin of Structural Disorder in $\delta$-NbN: Correlation of Superconductivity and Electronic Structure},
author = {Shailesh Kalal and Sanjay Nayak and Akhil Tayal and Jens Birch and Rajeev Rawat and Mukul Gupta},
journal= {arXiv preprint arXiv:2010.04509},
year = {2020}
}