Thin Films*

LaNiO₃ (LNO) is the only perovskite rare-earth nickelate without a metal-insulator transition (MIT) in its bulk form^1–3. One possible reason is the atomic radius of La, leading to a larger Ni-O-Ni bond angle^1,2. Strain control² or CaH₂ reduction⁴ has been shown to control the oxygen vacancy concentration and the Ni valence state of these materials, which can induce an insulating phase transition. Electrolyte gating can be an efficient alternative to control such properties in a reversible and controllable way³. In this study, we utilize electrolyte gating with ionic liquids to realize a MIT in LNO thin films. These gated LNO films exhibit an increase in the resistance (> 5 x 10⁵), accompanying a transition from metallic to insulating behavior. Such behavior can be reversibly controlled based on the duration and magnitude of the gate voltage. The Ni valence state and oxygen vacancy content in the gated films will be discussed based on the effect of gate voltage in LNO. These results reveal that ionic liquid gating can enhance electron-electron correlation, opening up the possibilities of realizing exotic physics in perovskite nickelates, such as MIT, infinite-layer nickelates, or superconducting phase transitions^4–6.

[1] S Catalano et al. Rep. Prog. Phys. 81 046501 (2018)

[2] M. Golalikhani et al. Nat Commun 9, 2206 (2018)

[3] S. Asanuma et al. Appl. Phys. Lett. 97, 142110 (2010)

[4] M. Kawai et al. Appl. Phys. Lett. 94, 082102 (2009)

[5] L. Qiao et al. EPL 93 57002 (2011)

[6] M. Osada et al. Adv. Mater. 33, 2104083 (2021)