Superconducting NbN for Strong Magnetic Field Applications: Impact of the Thin Films Intrinsic Disorder

Abstract

The research on superconducting circuits for quantum information technologies progressively extends from the academic world towards the industry. Material sciences therefore become an essential lever for the development of technologies based on such circuits as they allow finding industry-compatible routes of improvements. In this context, we propose a study on the behavior of the niobium nitride (NbN), one of the most commonly used material for these devices, when exposed to strong magnetic fields. To this aim, the properties of NbN layers with the same composition but different microstructures, tuned by changing the deposition method, are compared. This study aims to establish interdependencies between the microstructure of the material and its behavior once exposed to a magnetic field. X-ray diffraction and Hall-effect characterizations are used to assess that the microstructure is significantly modified by the choice of the deposition technique. Pushing further these investigations also allowed to quantify and compare the level of disorder in both cases by extracting the Ioffe-regel and the Ginzburg-Landau parameters from characterizations of the superconducting transition temperature for several magnetic field amplitudes. This was used to conclude that in highly disordered NbN layers, the microstructure heterogeneities are responsible for a strong electron localization allowing to significantly enhance the resilience of their superconducting state under strong magnetic fields.