Ionic-liquid-gating study of the incipient ferroelectrics SrTiO₃ and KTaO₃

Strontium titanate (SrTiO₃, STO) and potassium tantalate (KTaO₃, KTO) are band insulators and incipient ferroelectrics with cubic perovskite structure at room temperature [1,2]. Charge-carrier doping is usually achieved via heterovalent substitution or the introduction of oxygen vacancies. In this study, we use ionic-liquid gating as an alternative method to control the carrier density, i.e., we introduce an electric double-layer between the sample surface and an ionic liquid or gel via an applied gate voltage [3]. Ionic-liquid gating may introduce electrochemical effects involving ionic motion within the sample and across the gated surface. We report a systematic study of the gating-induced insulator-metal transitions and temperature-dependent resistivity in STO and KTO. Notably, the resistance exhibits canonical Fermi-liquid behavior, R = R₀ + aT², yet with a linear relationship between the coefficient a and the residual resistance R₀. We discuss our experimental data and explore possible explanations for this unusual linear relationship.



[1] C. Collignon et al., Annual Review of Condensed Matter Physics 10, 25 (2019)

[2] S. H. Wemple, Phys. Rev. 137, A1575 (1965)

[3] C. Leighton, Nat. Mater. 18, 13 (2019)