Bose Condensation, Superfluidity, and the Quantum Hall Effect Jim Eisenstein, Frank J. Roshek Professor of Physics, California Institute of Technology

Composite particles consisting of an even number of fermions (e.g. 4He atoms) can pretend to be bosons. Bosons, of course, can Bose condense and do remarkable things. Superconductivity, which is certainly remarkable when you stop to think about it, results (sort of) from the Bose condensation of electron pairs. With this in mind, theorists have speculated since the early 1960’s that excitons (electron-hole pairs in a semiconductor) might be able to do the same thing. Bose condensation of excitons has traditionally been sought by first optically exciting electron-hole pairs and then hoping that they bind, cool down, and do something wonderful before they recombine back into photons. Substantial progress has been made over the years in this direction, but clear-cut observations of superfluidity and long-range quantum coherence has remained elusive. In this talk I will describe experiments done here at Caltech on a special collection of excitons that exists in equilibrium and does indeed show many (but not all) of the expected signs of excitonic superfluidity. Surprisingly, the system in question is a double layer two dimensional electron gas. With no valence band holes in sight, where do the excitons come from?