Mona Berciu, Department of Physics & Astronomy, 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 is a dressed quasiparticle, -- the 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 will discuss 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 discussed.

The web site of Professor Berciu.

Cette conférence est présentée par le RQMP Versant Nord du Département de physique de l'Université de Montréal et le Département de génie physique de Polytechnique Montréal.