The role of Coulomb interaction in superconducting NbTiN thin films

We report on the superconducting properties of Nb1−xTixN thin films of thickness ∼ 10 nm, with different Ti fraction x in the range 0 ≤ x ≤ 0.5, deposited by high temperature chemical vapor deposition. In this parameter range, we observe that the superconducting critical temperature (Tc) increases with x. Our analysis, in accordance with both McMillan’s and Finkelstein’s theories, shows that disorder-enhanced Coulomb interaction decreases with x, leading to an increase of Tc.