Evidence for a Bose-Einstein condensate of excitons

¹ ICFO-The Institute of Photonic Sciences - Av. Carl Friedrich Gauss, num. 3, E-08860 Castelldefels, Spain
² ICREA-Institució Catalana de Recerca i Estudis Avanats - Lluis Companys 23, E-08010 Barcelona, Spain
³ IMM-Instituto de Microelectrónica de Madrid (CNM-CSIC) - C. Isaac Newton 8, PTM, E-28760 Tres Cantos, Madrid, Spain
⁴ Laboratoire de Physique Statistique, Ecole Normale Supérieure, UPMC Paris 06, Université Paris Diderot, CNRS 24 rue Lhomond, F-75005 Paris, France
⁵ Institut Universitaire de France - 103 boulevard Saint-Michel, F-75005 Paris, France
⁶ Institut des Nanosciences de Paris, UPMC Paris 06, CNRS - 2 pl. Jussieu, F-75005 Paris, France

^(a) francois.dubin@insp.jussieu.fr (corresponding author)

Received: 23 May 2014
Accepted: 19 June 2014

Abstract

We report compelling evidence for a “gray” condensate of dipolar excitons, electrically polarised in a 25 nm wide GaAs quantum well. The condensate is composed by a macroscopic population of dark excitons coherently coupled to a lower population of bright excitons. To create the exciton condensate we use an all-optical approach in order to produce microscopic traps which confine a dense exciton gas that yet exhibits an anomalously weak photoemission at sub-kelvin temperatures. This is the first fingerprint for the “gray” condensate. It is then confirmed by the macroscopic spatial coherence and the linear polarization of the weak excitonic photoluminescence emitted from the trap, as theoretically predicted.