New preprint announcement

Vacancy-Free Cubic Superconducting Niobium Nitride (NbN)

Niobium nitride (NbN) is known for exceptional superconducting properties, but synthesizing its ideal cubic structure without vacancies has long seemed impossible—until now. In our latest preprint arXiv:2507.03417, we report the discovery of a previously unknown stable cubic phase of NbN, entirely vacancy-free and stabilized by quantum anharmonicity.

Using advanced first-principles calculations coupled with machine-learned interatomic potentials, we demonstrate that fully relaxed NbN, incorporating quantum anharmonic effects, stabilizes into a novel cubic structure (space group P4̄3m). This new structure is thermodynamically favorable — 65 meV/atom lower in free energy compared to the traditional δ-NbN phase.

This newly identified phase retains metallic characteristics and exhibits superconductivity, with a predicted transition temperature (Tc) of 20 K, closely matching experimental observations. Our findings challenge the long-held assumption that vacancies are necessary for cubic NbN stability, emphasizing instead the essential role of quantum anharmonicity in superconductivity.

This work results from extensive collaboration among theorists and computational scientists across several institutions. We believe our results offer exciting new possibilities for experimental synthesis and could significantly enhance superconducting performance.

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