  Ionic substitution forms an essential pathway to manipulate the carrier
density and crystalline symmetry of materials via ion-lattice-electron
coupling, leading to a rich spectrum of electronic states in strongly
correlated systems. Using the ferromagnetic metal SrRuO3 as a model system, we
demonstrate an efficient and reversible control of both carrier density and
crystalline symmetry through the ionic liquid gating induced protonation. The
insertion of protons electron-dopes SrRuO3, leading to an exotic ferromagnetic
to paramagnetic phase transition along with the increase of proton
concentration. Intriguingly, we observe an emergent topological Hall effect at
the boundary of the phase transition as the consequence of the
newly-established Dzyaloshinskii-Moriya interaction owing to the breaking of
inversion symmetry in protonated SrRuO3 with the proton compositional
film-depth gradient. We envision that electric-field controlled protonation
opens a novel strategy to design material functionalities.

Strongly Correlated Electrons;Materials Science