In polarizable materials, electronic charge carriers interact with the surrounding ions, leading to quasiparticle behavior. The resulting polarons play a central role in many materials properties including electrical transport, interaction with light, surface reactivity, and magnetoresistance, and polarons are typically investigated indirectly through these macroscopic characteristics. Here, noncontact atomic force microscopy (nc-AFM) is used to directly image polarons in Fe2O3 at the single quasiparticle limit. A combination of Kelvin probe force microscopy (KPFM) and kinetic Monte Carlo (KMC) simulations shows that the mobility of electron polarons can be markedly increased by Ti doping. Density functional theory (DFT) calculations indicate that a transition from polaronic to metastable free-carrier states can play a key role in migration of electron polarons. In contrast, hole polarons are significantly less mobile, and their hopping is hampered further by trapping centers.

Department of Surface and Plasma Science Faculty of Mathematics and Physics Charles University 180 00 Prague Czech Republic

Dipartimento di Fisica e Astronomia Università di Bologna 40127 Bologna Italy

Institute of Applied Physics TU Wien 1040 Vienna Austria

Institute of Experimental and Applied Physics University of Regensburg 93040 Regensburg Germany

Institute of Physical Chemistry University of Innsbruck 6020 Innsbruck Austria

Institute of Physics Czech Academy of Sciences Cukrovarnická 10 162 00 Prague 6 Czech Republic

Marian Smoluchowski Institute of Physics Jagiellonian University 30 348 Krakow Poland

University of Vienna Faculty of Physics Center for Computational Materials Science Vienna Austria

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