UC San Diego

Indirect excitons in coupled quantum wells form a unique system for both development of novel optoelectronic devices as well as studies of the low temperature physics of bosons in condensed matter systems. An exciton is a quasiparticle which is a bound state of an electron and hole. Excitons can be created by light, and when they recombine they can emit light. In an indirect exciton, the electron and hole are spatially separated, which results in a long exciton lifetime as well as an electronic dipole moment. The long lifetime allows excitons to travel over large distances ~ 100[mu]m. The electronic dipole moment allows direct electronic control of the exciton energy. Therefore, as an optical media that is also electronically controllable, indirect excitons offer promise for development of new, efficient optoelectronic devices. In this dissertation, we prototype two new optoelectronic devices based on indirect excitons : the exciton optoelectronic transistor, and the excitonic integrated circuit. In addition, the long radiative lifetime allows indirect excitons to cool to very low temperatures below the temperature of quantum degeneracy. Traps are of particular interest for studies of low temperature gases, as they facilitate creation of high density, cold gases as well as offer opportunities for in situ control of the gas. This dissertation presents novel, precisely engineered trapping potentials for exciton gases based on electronic control and makes a thorough examination of the physical properties of the trapped gas. Furthermore, as a bosonic quasiparticle, excitons can be expected to form a condensate under certain density and temperature conditions. A signature of condensation is the emergence of spontaneous extended coherence, where the coherence length significantly exceeds its classically expected value. We present the first evidence for extended spatial coherence in an exciton system - the system of exciton rings. A pattern of extended spontaneous coherence is correlated with a pattern of spontaneous polarization, revealing the properties of a multicomponent coherent state. We also observed phase singularities in the coherent exciton gas. Lastly, we probe the spatial coherence of excitons in an electrostatic trap and present direct evidence for Bose-Einstein condensation of excitons therein