SPOT · Single Polaron Tracking

Polarons are quasiparticles that form in ionic lattices due to the coupling of excess electrons or holes with lattice vibrations. This leads to a spatial confinement of the charge carrier or even its complete localization, which presents a challenge for theoretical modelling. Polarons play a central role in many materials properties, such as electrical transport, optical properties, surface reactivity, or magnetoresistance, and are always investigated indirectly through such macroscopic characteristics. Here, I propose to develop a methodology for real-space experimental observation of single polarons, based on detecting their electrostatic force by noncontact Atomic Force Microscopy (nc-AFM). I will track localized polarons in the crystal lattice, observe their thermally activated hopping, interaction with light, electric and magnetic field, and coupling to lattice defects. This will provide the missing link between the atomic-scale polaron dynamics and macroscopic materials properties.The nc-AFM represents an excellent tool for watching and explaining the fundamental mechanisms involved in polaron kinetics, yet the method has a limited time resolution. I propose overcoming this limitation by combining nc-AFM with excitation by light, aiming for time resolution of 10-6 to 10-9 s, while maintaining the atomic resolution in real space through plasmonic effects at the tip apex. This will allow investigation of highly mobile polarons that stand behind complex physical phenomena, resolve their mechanisms of charge transport, the nature of their excited and transition states, as well as polaron-polaron interactions. If successful, the result of this project will provide a big leap towards understanding the physics of charge carriers in ionic lattices, open a path towards explaining unresolved polaron-based phenomena, and possibly reveal novel materials properties.