Heat capacity and magnetic properties of NbTiN films in the bulk limit

Abstract

Heat capacity and magnetic measurements were used to extract superconducting parameters for deposited NbTiN films in the bulk limit, including the critical temperature, the ratio of the superconducting gap to the critical temperature, the phase coherence length, and the upper critical field. We found that the film is a strong coupling superconductor, with a small phase coherence length, consistent with trends reported in the literature. Due to the large thickness, these materials correspond to 3D analogues of bulk NbTiN. The upper critical fields determined from heat capacity and magnetic field measurements are different, emphasizing the sensitivity of magnetic field measurements to defects. The Ginzburg number is much smaller compared to high-T_c superconductors, while magnetic relaxation measurements point towards a Kim-Anderson vortex creep regime.