Theory of the decay luminescence spectrum of a Bose-condensed interacting exciton gas

Bose-Einstein condensation of excitons in Cu2O: progress over 30 years

Experiments on Bose-Einstein condensation (BEC) of excitons in the semiconductor Cu2O started over 30 years ago, as one of the first serious attempts at exciton BEC. Early claims were based on spectroscopic signatures and transport data which have since been reinterpreted, in large part because the Auger recombination process for excitons was not well understood. Understanding of the Auger process has advanced, and recent experiments have made significant progress toward exciton BEC. We review the history of experiments on exciton BEC in Cu2O, the Auger recombination process, and the prospects for observing exciton BEC in this system in the near future.

Ultranarrow optical absorption and two-phonon excitation spectroscopy of Cu2O paraexcitons in a high magnetic field

We show that in a magnetic field B the otherwise forbidden lowest exciton in Cu2O (paraexciton of Gamma(2)(+) symmetry) gives rise to a narrow absorption line of 80 neV at a temperature of 1.2 K. The B2 dependence of the field-induced oscillator strength and the low energy shift DeltaE with increasing field strength are measured. From two-phonon excitation spectroscopy measurements we derive by a merely kinematical analysis a very reliable value for the paraexciton mass. A blueshift and a broadening of the absorption line are observed for increasing excitation intensity. These observations are discussed in connection with a Bose-Einstein condensation of paraexcitons in Cu2O.

Spontaneous Bose coherence of excitons and polaritons

In the past decade, there has been an increasing number of experiments on spontaneous Bose coherence of excitons and polaritons. Four major areas of research are reviewed here: three-dimensional excitons in the bulk semiconductor Cu2O, two-dimensional excitons in coupled quantum wells, Coulomb drag experiments in coupled two-dimensional electron gases, and polaritons in semiconductor microcavities. The unifying theory of all these experiments is the effect of spontaneous symmetry breaking in the Bose-Einstein condensation phase transition.