Berlin 2008 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 51: Poster IV

HL 51.2: Poster

Thursday, February 28, 2008, 16:30–19:00, Poster D

Determination of exciton mass in Cu₂0 by two-phonon-spectroscopy — Jan Brandt¹, Dietmar Fröhlich¹, •Christian Sandfort¹, Manfred Bayer¹, and Heinrich Stolz² — ¹Institut für Physik, Technische Universität Dortmund, D-44221 Dortmund, Germany — ²Fachbereich Physik, Universität Rostock, D-18051 Rostock, Germany

The 1S-paraexciton in Cu₂O is a pure spin-triplet state with Γ₂⁺ symmetrie. Therefore it is optically forbidden to all orders. In a magnetic field, however, it mixes with the 1S-orthoexciton and gets quadrupole allowed. From two-phonon excitation spectroscopy involving an optical and acoustical phonon we derive by a purely kinematical analysis a very reliable value for the paraexciton mass (m_p=2.61 m₀). The resolution of this method is only limited by the linewidth of the exciting laser (<20 neV). Furthermore we show that the experimental method is suited to test the parameters of the k²-exchange interaction of the orthoexcitons and determine the sound velocity of acoustic phonons and the refractive index.