Field-tuned superconductor-insulator transitions and Hall resistance in thin polycrystalline MoN films

We report on the superconductor-insulator transitions (SITs) of disordered molybdenum nitride (MoN) thin films on (1 0 0) MgO substrates as a function of the film thickness and magnetic fields. The T _c of the superconducting MoN films, which exhibit a sharp superconducting transition, monotonically decreases as the normal state R _sq increases with a decreasing film thickness. For several films with different thicknesses, we estimate the critical field H _c and the product zν  ≃  0.6 of the dynamical exponent z and the correlation length exponent ν using a finite scaling analysis. The value of this product can be explained by the (2  +  1) XY model. We found that the Hall resistance ΔR _xy (H) is maximized when the magnetic field satisfies H _HP(T) [Formula: see text] |1  -  T/T _C0| in the superconducting state and also in the normal states owning to the superconducting fluctuation corresponding to the ghost critical magnetic field. We measured the Hall conductivity δσ _xy (H)  =  σ _xy (H)  -  [Formula: see text] and fit the Gaussian approximation theory for δσ _xy (H) to the experimental data. Agreement between the data and the theory beyond H _c suggests the survival of the Cooper pair in the insulating region of the SIT.