Yuan, YifanKotiuga, MichelePark, Tae JoonPatel, Ranjan KumarNi, YuanyuanSaha, ArnobZhou, HuaSadowski, Jerzy T.Al-Mahboob, AbdullahYu, HaomingDu, KaiZhu, MinningDeng, SunbinBisht, Ravindra S.Lyu, XiaoWu, Chung-Tse MichaelYe, Peide D.Sengupta, AbhronilCheong, Sang-WookXu, XiaoshanRabe, Karin M.Ramanathan, Shriram2024-06-192024-06-192024-06-192024-06-0310.1038/s41467-024-49213-0https://infoscience.epfl.ch/handle/20.500.14299/208736WOS:001238270100034Materials with field-tunable polarization are of broad interest to condensed matter sciences and solid-state device technologies. Here, using hydrogen (H) donor doping, we modify the room temperature metallic phase of a perovskite nickelate NdNiO3 into an insulating phase with both metastable dipolar polarization and space-charge polarization. We then demonstrate transient negative differential capacitance in thin film capacitors. The space-charge polarization caused by long-range movement and trapping of protons dominates when the electric field exceeds the threshold value. First-principles calculations suggest the polarization originates from the polar structure created by H doping. We find that polarization decays within similar to 1 second which is an interesting temporal regime for neuromorphic computing hardware design, and we implement the transient characteristics in a neural network to demonstrate unsupervised learning. These discoveries open new avenues for designing ferroelectric materials and electrets using light-ion doping.Metal-Insulator-TransitionFilmstext::journal::journal article::research article