Microscopic Origin of Structural Disorder in $\delta$-NbN: Correlation of Superconductivity and Electronic Structure

Shailesh Kalal; Sanjay Nayak; Akhil Tayal; Jens Birch; Rajeev Rawat; Mukul Gupta

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arXiv · 2010.04509

Microscopic Origin of Structural Disorder in $\delta$-NbN: Correlation of Superconductivity and Electronic Structure

Shailesh Kalal·Sanjay Nayak·Akhil Tayal·Jens Birch·Rajeev Rawat·Mukul Gupta

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Abstract

Rock-salt type niobium nitride ($\delta$-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 $\delta$-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 $\delta$-NbN thin film by employing combined methods of experiments and ab-initio simulations. Sputtered $\delta$-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 $\delta$-NbN by smearing its electronic densities of states around Fermi level.

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Shailesh Kalal, Sanjay Nayak, Akhil Tayal, Jens Birch, Rajeev Rawat, Mukul Gupta. 2020-10-09. Microscopic Origin of Structural Disorder in $\delta$-NbN: Correlation of Superconductivity and Electronic Structure. https://arxiv.org/abs/2010.04509

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