Pseudogap Effects in Disordered Niobium Nitride Superconducting Thin Films

The pseudogap region in the disordered Niobium Nitride (NbN) superconductors has been a subject of contemporary interest and its existence for higher disorder films have been established. Niobium Nitride (NbN) thin films have been deposited by reactive direct current magnetron sputtering at 0.266 Pa total pressure in a mixture of argon and nitrogen. The Glancing Incidence X-ray Diffraction (GIXRD) analysis indicates the formation of NbN cubic fcc B1 structure. All the films were found to be superconducting with a maximum superconducting transition temperature (Tc) of 12 K. At higher temperatures, all the films exhibited a negative temperature coefficient of resistance indicating the presence of disorder in the films. The downturn of resistance due to the appearance of superconducting state is observable in the resistance versus temperature plot at a temperature above Tc defined as T*. It has been observed the downturn in resistance versus temperature plot of NbN thin film happens at a temperature around 20 K (T*) for a sample which is superconducting at 11.5 K (Tc).