Disorder Tuned Superconductor Insulator Transition in La2−x(Sr/Ce)xCuO4 & NbN Superconducting Thin Films

In studying the magneto-resistivity ρ(B) in high pulsed magnetic fields up to 55 T, it is often observed that the ρ(B) curves for different temperatures in the vicinity of the critical temperature cross at the same field value, B=BCP. We show how the crossing field changes as a function of the hole (or electron) doping x in La2−x(Sr/Ce)xCuO4. The resistivity ρ and the magnetic field B at different temperatures may be scaled as R/RCP and |B−BCP|/Tγ, respectively. This kind of scaling resulted in a conventional critical exponent γ=1/νz=1.35 (νz∼0.74) in our La2−x(Sr/Ce)xCuO4 thin films, and a much higher value of γ=4.35 (νz∼0.23) in the case of our disordered NbN films.