CPM Seminar

One hundred years of polarons

Feliciano Giustino

University of Texas at Austin

In 1933, Lev Landau wrote a 500-word article analyzing what might happen when an electron travels through a crystal lattice. That deceivingly simple paper marked the birthdate of the concept of polarons. Almost a hundred years later, new experiments and new high-performance computing methods are helping us to shed light on these ubiquitous yet elusive entities. Polarons are emergent quasiparticles that arise from the interaction between fermions and bosons. In crystals, polarons form when an electron becomes dressed by a cloud of virtual phonons in the form of a distortion of the atomic lattice. In the presence of weak electron-phonon interactions, polarons behave like conventional Bloch waves, only with slightly heavier masses. In the presence of strong interactions, on the other hand, polarons become localized wavepackets and profoundly alter the transport, electrical, and optical properties of the host material. In applications, polarons are important in solar photovoltaics, photocatalysis, touchscreens, organic displays, and even neuromorphic computing. In this talk I will introduce the notion of polarons starting from elementary models that capture their essential features. Then I will describe recent explorations of polaron physics from the point of view of first-principles atomic-scale calculations, ranging from density-functional theory to many-body field-theoretic methods. These and many other recent theoretical and experimental advances in the field raise the hope that it will soon be possible to engineer advanced materials with tailored polaronic properties.