学术文献库

Rock-salt type niobium nitride ($δ$-NbN) is a well-known superconductor having superconducting transition temperature (Tc) $\approx$ 18\,K and a large superconducting gap $\approx$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.