Electrolyte gate-controlled Kondo effect in SrTiO3.

We report low-temperature, high-field magnetotransport measurements of SrTiO(3) gated by an ionic gel electrolyte. A saturating resistance upturn and negative magnetoresistance that signal the emergence of the Kondo effect appear for higher applied gate voltages. This observation, enabled by the wide tunability of the ionic gel-applied electric field, promotes the interpretation of the electric field-effect-induced 2D electron system in SrTiO(3) as an admixture of magnetic Ti(3+) ions, i.e., localized and unpaired electrons, and delocalized electrons that partially fill the Ti 3d conduction band.