Monday, 24 February, 2014
A New Paradigm for Polaronic Behavior
Presented by Mona Berciu, Professor of Physics, University of British Columbia
Any charge carrier distorts the lattice in its neighborhood because of interactions with the ions making up the crystal (electron-phonon interactions). This results in a dressed quasiparticle, or a polaron, which is the composite object comprising the carrier and this lattice distortion that can be viewed as a cloud of phonons (quantized lattice vibrations) that are continuously absorbed and re-emitted by the carrier. This cloud may lead to a significant renormalization of the properties of the quasiparticle compared to those of the bare carrier, which is why understanding the properties of polarons and their influence on the macroscopic behavior of the host material is one of the main challenges in condensed matter physics. The widely-accepted "polaron paradigm" is that stronger electron-phonon coupling leads to bigger lattice distortions and therefore heavier polarons. In this talk I present recent work which shows that this is true only for models where the phonons modulate the potential energy of the carrier. If the phonons modulate the kinetic energy of the carrier one may find very light polarons at any coupling. The reason for this and
other surprising findings will be explained.