Redox gating-induced modulation of charge carrier density and lattice expansion in LaNiO₃ thin films

Redox gating involves the use of reversible redox functionalities combined with ionic electrolytes to substantially alter the charge carrier density in functional condensed materials. This modification leads to the emergence of physical properties not observed in the original material. In our study, we focus on redox gating applied to a LaNiO₃ (001) film within a field-effect device and identify a critical gate voltage of 0.7 V. Hall measurements indicate that redox gating markedly increases the charge carrier density in LaNiO₃, reaching over 10¹⁴ cm⁻². This increase is primarily due to the injection of electrons into LaNiO₃, which offsets the existing hole carriers. These adjustments in the carrier concentration result in reversible lattice expansion in LaNiO₃ when gate voltages are below 0.7 V. This expansion correlates well with theoretical models that consider adjustments to the Ni-O bond length, influenced by oxygen ligand holes. Conversely, at gate voltages above 0.7 V, there are significant changes in resistivity, lattice structure, and Ni valence, stemming from the formation of oxygen vacancies in the LaNiO₃ film.