Intrinsic electron injection and carrier induced breathing distortion in LaNiO₃ by ionic liquid gating

Electrolyte gating using ionic liquids is a powerful technique to induce large carrier
modulations in a material, giving rise to new phenomena not existing in the parent phase.
Here we report an investigation of electrolyte gating on LaNiO₃ (001) thin films and
determine a threshold gating voltage at 0.7 V. Hall measurements show that with gating,
electrons are injected into LaNiO₃ , which compensates the existing hole carriers. Our in-situ
X-ray diffraction measurements show that the lattice constants of LaNiO₃ respond to the
carrier modulation reversibly at gate voltages below 0.7 V, in quantitative agreement with a
model considering Ni-O bond length modulations by oxygen ligand holes. At gate voltages
above 0.7 V, both transport and in-situ X-ray measurements show a drastic change in
resistance, structure and the Ni valence state, indicating oxygen vacancies are created in the
LaNiO₃ film.