Coherent exciton transport in semiconductors

Abstract After reviewing the physical systems that may host exciton condensation, this chapter illustrates some recent proposals concerning the detection of coherent exciton flow. It focuses on the exciton analogues of two phenomena—Andreev reflection and the Josephson effect—which are hallmarks of superconducting behavior and stress the crucial differences between excitons and Cooper pairs. It shows that the excitonic insulator is the perfect insulator in terms of both charge and heat transport, with an unusually high resistance at the interface with a semimetal—the normal phase of the condensed state. Such behavior may be explained in terms of the coherence induced into the semimetal by the proximity of the exciton condensate. The exciton superflow may be directly probed in the case that excitons are optically pumped in a double-layer semiconductor heterostructure. The chapter proposes a correlated photon counting experiment for coupled electrostatic exciton traps