Tunable Polaronic Conduction in Anatase ${\mathrm{TiO}}_2$

Oxygen vacancies created in anatase ${\mathrm{TiO}}_2$ by UV photons (80–130 eV) provide an effective electron-doping mechanism and induce a hitherto unobserved dispersive metallic state. Angle resolved photoemission reveals that the quasiparticles are large polarons. These results indicate that anatase can be tuned from an insulator to a polaron gas to a weakly correlated metal as a function of doping and clarify the nature of conductivity in this material.