Electrolyte gate-controlled Kondo effect in SrTiO3

We report low-temperature, high-field magnetotransport measurements of SrTiO3 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 SrTiO3 as an admixture of magnetic Ti3+ ions, i.e. localized and unpaired electrons, and delocalized electrons that partially fill the Ti 3d conduction band.