Infrared Nano-Imaging of Electronic Phase across the Metal–Insulator Transition of NdNiO_3 Films

NdNiO_3 is a typical correlated material with temperature-driven metal–insulator transition. Resolving the local electronic phase is crucial in understanding the driving mechanism behind the phase transition. Here we present a nano-infrared study of the metal–insulator transition in NdNiO_3 films by a cryogenic scanning near-field optical microscope. The NdNiO_3 films undergo a continuous transition without phase coexistence. The nano-infrared signal shows significant temperature dependence and a hysteresis loop. Stripe-like modulation of the optical conductivity is formed in the films and can be attributed to the epitaxial strain. These results provide valuable evidence to understand the coupled electronic and structural transformations in NdNiO_3 films at the nano-scale.