Phase coexistence and dynamical behavior in NdNiO3 ultrathin films

Rare-earth nickelates exhibit several temperature-driven phase transitions that are tunable by the size of the rare-earth ions, pressure, epitaxial strain in ultrathin films, etc. We investigate the metal-insulator and Neel transitions in a series of NdNiO3 thin films with varying degrees of lattice mismatch using ultralow frequency electrical noise measurements. The noise magnitude follows a 1/f behavior and is Gaussian in the high temperature paramagnetic metallic phase of the films, however deviations are seen in the low temperature paramagnetic and antiferromagnetic insulating phases. The noise magnitude increases by orders of magnitude at temperatures below the metal-insulator transition and is indicative of inhomogeneous electrical conduction arising from phase separation. The inhomogeneous nature of conduction is corroborated by the presence of a large non-Gaussian noise signature in the low temperature phases. Well below the Neel temperature, the noise behavior evolves between Gaussian and non-Gaussian over several hours pointing to dynamically competing ground states with subtle variations within the antiferromagnetic insulating phase.