Dr. Alex High

University of California at San Diego

Indirect Excitons: Circuits, Traps, and Spontaneous Low Temperature Physics

Abstract:
An indirect exciton is a bound state of an electron and hole in spatially separated coupled quantum wells. Due to the spatial separation, indirect excitons acquire a dipole moment that allows direct electronic control of the exciton energy. We demonstrate that through electronic control we can create excitonic circuits, i.e. optical switches that utilize excitons as an intermediate media. Also due to the spatial separation, the lifetime of an indirect exciton is orders of magnitude larger than that of a direct exciton. The long lifetime allows excitons to cool to below the temperature of quantum degeneracy. As a result, indirect excitons form a model system for studies of low temperature physics in condensed matter systems. We present measurements of a recently discovered spin texture in a cold exciton gas. The spin texture manifests itself in the exciton emission as an in-plane pattern of polarization that forms around sources of cold excitons. In regions of spin texture, we observe an extended coherence length of the exciton gas. Both the extended spontaneous coherence and spin texture emerge at temperatures below a few kelvin. We also demonstrate excitonic traps for the study of low temperature exciton physics. We explore condensation of indirect excitons in a trap, in a manner analogous to studies of atomic condensation in traps, and demonstrate a trapped condensate in which the exciton coherence length is comparable in size to the entire exciton cloud.