Special CPM Seminar

Single particle effects on the dynamics of quasi-particles:
Old ideas, new issues, performed experiments, and possible experiments

J.E. Sipe

Department of Physics
University of Toronto

Inter-particle interactions play a major role in determining the properties of quasi-particles. But for a quasi-particle in a periodic potential, aspects of the band structure -- such as its curvature and Berry curvature -- are important as well. They lead to a deviation of the effective mass from the bare mass of the particle, and to an anomalous velocity that the particle can acquire when subjected to an external force. These single-particle effects are usually thought of as non-dynamical in nature, associated simply with the location in reciprocal space of a wave packet. Nonetheless, it has been known for over half a century -- but perhaps not generally appreciated -- that the effective mass of a wave packet has a dynamics of its own, beyond the trivial changes that arise as the position of a wave packet in reciprocal space evolves. We review our work on this, mention recent experiments on cold atoms that confirm it, and consider the extension to other nominally non-dynamical quantities such as the anomalous velocity.