Tracking polarons in real space by STM/AFM

Abstract

While the concept of polaron was formulated almost a century ago, this topic has been gradually emerging in many fields in physics, chemistry, and materials science. Polarons, i.e., charge carriers that are spatially confined by electron–phonon coupling, affect various properties of materials and devices. While we mostly deduce their properties indirectly from macroscopic characteristics of materials, it is appealing to observe these localized charge carriers in real space. Such experimental inputs could directly answer fundamental questions, as well as provide precise quantitative information about the polaron physics. In this perspective, we discuss seminal works focused on real-space imaging of polarons by scanning tunneling microscopy and atomic force microscopy, summarize the opportunities emerging from such experiments, highlight both the technical and fundamental challenges that remain, and provide an outlook on future directions and open questions in the field.