Real-space investigation of polarons in hematite Fe 2 O 3

• DOI: 10.1126/sciadv.adp7833
• Publication Date: 2024-11-01T17:59:14Z
• Authors: Jesus Redondo; Michele Reticcioli; Vit Gabriel; Dominik Wrana; Florian Ellinger; Michele Riva; Giada Franceschi; Erik Rheinfrank; Igor Sokolović; Zdenek Jakub; Florian Kraushofer; Aji Alexander; Eduard Belas; Laerte L. Patera; Jascha Repp; Michael Schmid; Ulrike Diebold; Gareth S. Parkinson; Cesare Franchini; Pavel Kocan; Martin Setvin
• Keywords: Condensed Matter - Materials Science; 103015 Kondensierte Materie; 103015 Condensed matter; ddc:540; 540 Chemie; ddc:530; Materials Science (cond-mat.mtrl-sci); FOS: Physical sciences; Physical and Materials Sciences; 530 Physik

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 Fe 2 O 3 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.