Temperature-dependent N-type negative differential resistance in planar LaNiO₃/SmNiO₃/LaNiO₃ heterojunctions

Dimensional reduction represents a powerful approach for investigating emergent phenomena in strongly correlated oxide materials. Although vertical confinement effects have been extensively examined, the intrinsic properties associated with lateral confinement frequently remain obscured due to artifacts introduced during fabrication processes. In this study, we examine the intrinsic in-plane transport characteristics of pristine LaNiO₃/SmNiO₃/LaNiO₃ heterojunctions, fabricated using a damage-free epitaxial liftoff technique that produces single-crystalline SmNiO₃ microribbons. These devices demonstrate a pronounced, temperature-dependent N-type negative differential resistance (NDR), with a peak-to-valley current ratio adjustable from 5.9 at 450 K to 1.1 at 550 K. Unlike the abrupt switching behavior typical of conventional memristors, the observed NDR manifests as a smooth and reproducible phenomenon. We ascribe this behavior to a trap-mediated electrothermal mechanism, which is enhanced by the quasi-one-dimensional geometry of the system. At a critical applied voltage, the interplay between localized Joule heating and the strong electric field generated by trapped charges induces a localized insulator-to-metal transition. The subsequent reduction in current is governed by a dual mechanism involving self-heating of the emergent conductive channel and Coulombic repulsion from adjacent trapped charges. This work highlights lateral confinement as an effective strategy to activate and control charge-induced phase transitions in correlated oxides, thereby providing a platform for the development of tunable planar electronic devices.