Imaging of current crowding effect across the metal to insulator transition in a NdNiO3 thin film with thickness gradient

The metal-insulator transition (MIT) phenomenon in materials is associated with a complex interplay of electronic correlations, magnetism, and strain effects. We image the current distribution around MIT in ${\mathrm{NdNiO}}_{3}$ thin film with a thickness gradient. Above the MIT temperature, we observe a homogeneous current distribution implying the film is uniformly metallic. Below the MIT temperature, an insulating phase forms and spreads from the thicker to thinner regions of the film, leading to a nonuniform current distribution. A thickness variation induced strain distribution causes a spread in the local MIT temperature across the film. Our analysis shows the bulk resistance represents changes in the area of the metallic phase across the MIT. Our study suggests that the MIT in the nickelate film is a first-order transition from a paramagnetic non-Fermi-liquid metallic to an antiferromagnetic insulating phase. Strain distribution across the film broadens the transition.