title: Ultranarrow optical absorption and two-phonon excitation spectroscopy of Cu2O paraexcitons in a high magnetic field.
abstract: 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.
authors.affiliation: Institut für Physik, Universität Dortmund, D-44221 Dortmund, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Brandt
authors.forename: Dietmar
authors.initials: D
authors.lastname: Fröhlich
authors.forename: Christian
authors.initials: C
authors.lastname: Sandfort
authors.forename: Manfred
authors.initials: M
authors.lastname: Bayer
authors.forename: Heinrich
authors.initials: H
authors.lastname: Stolz
authors.forename: Nobuko
authors.initials: N
authors.lastname: Naka