Events

Superfluid Phase Transition of Long-lifetime Polaritons

November 15, 2011 at 3pm/34-401A

David Snoke
Department of Physics and Astronomy, University of Pittsburgh

Abstract:
Polaritons are quasiparticles of electronic excitation in semiconductor structures with extremely light mass, about four orders of magnitude less than a free electron. Because of this very light mass, polaritons show Bose quantum effects even at moderate densities and temperatures from tens of Kelvin up to room temperature. In the past five years, multiple experiments have shown effects of polaritons analogous to Bose condensation of cold atoms, such as a bimodal momentum distribution, quantized vortices, Bogoliubov excitation spectrum, and spatial condensation in a trap. In these experiments, though, the lifetime of the polaritons has been just a little longer than their thermalization time, which means that nonequilibrium effects play an important role; in particular, the transition to superfluidity has been smeared out rather than a sharp transition. In this talk I report new results with polaritons that have very long lifetime compared to their thermalization time. We see a discontinuous jump in the properties of the polariton gas indicative of a true phase transition, and we see ballistic transport over hundreds of microns. We also now have a way to use a laser to create a potential barrier for the polaritons.

Bio:
Snoke received his PhD in physics from the University of Illinois at Urbana-Champaign. He has worked for The Aerospace Corporation and was a visiting scientist and Fellow at the Max Planck Institute. In 2006, he was elected a Fellow of the American Physical Socieity with the citation, “For his pioneering work on the experimental and theoretical understanding of dynamical optical processes in semiconductor systems.” His research has focused on basic processes and phase transitions of electrons, holes, including non equilibrium dynamics of electron plasma and excitons, the Mott transition from exciton gas to electron-hole plasma and Bose-Einstein condensation of excitons and polaritons. His research group at the University of Pittsburgh uses stress to trap excitons in confined regions, similar to the way atoms are confined in traps for Bose-Einstein condensation experiments.