Crossover From Three‐Dimensional to Two‐Dimensional Superconducting Regime in VN Thin Films

ABSTRACT Advancing superconducting quantum technology necessitates the development of novel superconducting materials. Transition metal nitrides (TMNs) stand ou as promising superconductors due to their inherent stability, particularly against oxidation, and their relatively high superconducting critical temperatures (). While TMNs like NbN, TiN, and NbTiN have been extensively investigated for superconducting applications, vanadium nitride (VN) remains comparatively underexplored. Here, we address this knowledge gap by examining the evolution of superconductivity in VN thin films as their thickness is systematically reduced, focusing on the transition from a 3D to a 2D regime. We report the successful growth of high‐quality VN thin films with thicknesses ranging from 7.5 to 50 nm on single‐crystalline MgO (001) substrates. All VN thin films exhibited a sharp normal‐to‐superconducting transition, with critical temperatures ranging from 5.4 to 9.5 K. The monotonic decrease in and the broadening of the superconducting transition observed in thinner VN films is attributed to an increased level of disorder, as supported by structural and resistivity measurements. To investigate the superconducting behavior in detail, we performed resistivity measurements under isothermal and isomagnetic conditions with the magnetic field applied perpendicular to the film plane. Our analysis of the temperature‐dependent upper critical fields, using the Ginzburg–Landau (G–L) model and Werthamer‐Helfand‐Hohenberg (WHH) models, strongly supports the transition to quasi‐2D superconductivity in the 7.5 nm VN film. Furthermore, we conclude that orbital pair breaking is the primary factor limiting the upper critical field in VN films thicker than 7.5 nm under an out‐of‐plane magnetic field, while spin‐paramagnetic pair breaking may become significant in the 7.5 nm VN film below 1 K. Additionally, the current–voltage characteristics showed signatures of a Berezinski‐Kosterlitz‐Thouless (BKT) transition, providing further evidence for quasi‐2D superconductivity in VN thin films with thicknesses below 7.5 nm. This study provides crucial insights into the superconducting properties of VN thin films as their thickness approaches the ultrathin limit and will serve as a valuable guide for the fabrication of VN thin film‐based quantum devices.