Bose-Einstein condensation of excitons

Bose-Einstein condensation is an intriguing phenomenon predicted by Einstein in 1925. When the temperature of a gas of bosons (particles with integer spin) decreases below a certain critical temperature (depending on the mass and density), a large fraction of these particles collapses into a single state, showing quantum behavior on a macroscopic scale. Bose-Einstein condensation explains the amazing properties of superfluid helium and of superconductors at low temperatures. In 1995 Cornell and Wieman managed to create Bose-Einstein condensation in a dilute gas of atoms confined in a trap. The goal of our project is to create a Bose-Einstein condensate of excitons. An exciton is a bound state of an electron and a hole in a semiconductor. We optically create long-lived excitons in a Cu2O single crystal and we cool these excitons below the critical temperature in a dilution refrigerator with optical windows (see picture), which can reach the extremely low temperature of 10 mK (= 0.01 K). We study the optical and superfluid properties of the condensate.

Students interested in this project are welcome to contact Dr. Marijn Versteegh. E-mail: verst@kth.se. Possible student projects involve working with advanced equipment, such as a dilution refrigerator, pulsed lasers, spectrometers and single-photon detectors. We also have opportunities for students interested in theory of excitonic Bose-Einstein condensation.

Top page top