Scaling analysis of an apparent metal-insulator transition in a Fe3O4/Nb:SrTiO3 bilayer

Magnetite films were deposited on Nb-doped SrTiO3 substrates by pulsed laser deposition. The current-voltage characteristics were measured perpendicular to the interface. Strongly nonlinear, asymmetric current-voltage curves were observed. The resistance shows a crossover from insulating to metallic behavior for increasing voltages. The data can be neatly scaled using a scaling approach based on a quantum critical transition theory. This shows that a scaling analysis is clearly insufficient to conclude on the existence of a bulk-like metal/superconductor-insulator transition