Paper published in Communications Materials

We are excited to announce that our paper Vacancy-free cubic superconducting NbN enabled by quantum anharmonicity has been published in Communications Materials.

Niobium nitride (NbN) is known for exceptional superconducting properties, but the ideal 1:1 stoichiometric cubic phase has been considered dynamically unstable, with experimental work consistently indicating that vacancies are necessary for stabilization. In this paper, we demonstrate that quantum anharmonicity enables the stabilization of a previously unknown vacancy-free cubic structure.

Through state-of-the-art first-principles calculations accelerated by machine-learned interatomic potentials, we show that when fully relaxed under quantum anharmonic effects, NbN adopts a stable cubic phase (space group P4̄3m) that is 65 meV/atom lower in free energy than the traditional δ-NbN phase. This structure exhibits superconductivity with T_c = 20 K, matching experimental observations for near-stoichiometric samples.

Our calculations employed the stochastic self-consistent harmonic approximation and molecular dynamics spectral energy density methods to capture anharmonic vibrational properties. Electron-phonon coupling analysis based on these anharmonic phonon dispersions confirmed the superconducting behavior of this ideal stoichiometric phase.

These results open new pathways for experimental synthesis of vacancy-free NbN and could lead to enhanced superconducting performance in this technologically important material, which finds applications in quantum computing, single-photon detection, and superconducting cavities.

Read the full paper at doi.org/10.1038/s43246-025-01004-w.