Superconductivity and band topology of double-layer honeycomb structure M₂N₂ (M = Nb, Ta)

Two-dimensional double-layer honeycomb (DLHC) materials are known for their diverse physical properties, but superconductivity has been a notably absent characteristic in this structure. We address this gap by investigating M₂N₂ (M = Nb, Ta) with DLHC structure using first-principles calculations. Our results show that M₂N₂ are stable and metallic, exhibiting superconducting behavior. Specifically, Nb₂N₂ and Ta₂N₂ display superconducting transition temperatures of 6.8 K and 8.8 K, respectively. Their electron–phonon coupling is predominantly driven by the coupling between metal d-orbitals and low-frequency metal-dominated vibration modes. Interestingly, two compounds also exhibit non-trivial band topology. Thus, M₂N₂ are promising platforms for studying the interplay between topology and superconductivity and fill the gap in superconductivity research for DLHC materials.