Excitons in cuprous oxide

This work revisits the excitonic properties of Cu2O as observed with optical techniques, making use of current days experimental capabilities providing very precise measurements, with high energy and/or time resolution, using a variety of high power coherent pulsed light sources, intense magnetic fields, and cryogenic temperatures. A short overview of the theory of excitons and the excitonic Bose-Einstein condensation is presented. We discuss the ideas and results of the experiments aimed at determining the exciton gas parameters and their time evolution. It was shown that the lifetime is one of the most critical parameters determining whether a condensate state may occur. It was concluded, that the lifetime is strongly depends on amount of copper impurities and a mechanism of exciton trapping by copper impurities was proposed. The study of the optical properties of the yellow exciton series in cuprous oxide in magnetic fields is also presented. We observed the luminescence of optical inactive paraexcitons due to mixing of 1s paraexciton state with 1s orthoexciton state. The results of the magneto-absorption study suggest that the hydrogen model can be applied only for states with small value of n whereas for energies higher than the band-gap the Landau-like levels was observed. Finally, it is discussed some surprising observations in the optical properties of Cu2O in visible-pump, far infra-red (about 1 THz) probe experiments are discussed. The induced response of the Cu2O in far infra-red energy range can be well-described using the Drude + Lorentz mathematical model.