Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 20: Symposium Bose-Einstein Kondensation in Halbleitern

HL 20.2: Invited Talk

Tuesday, March 27, 2007, 11:15–11:45, H15

On the way to an excitonic Bose-Einstein condensate: New experiments in Cuprous Oxide. — •Heinrich Stolz¹ and Dietmar Fröhlich² — ¹Institut für Physik, Universität Rostock, Universitätsplatz 3, 18055 Rostock — ²Institut für Physik, Universität Dortmund, Otto-Hahn-Straße 4, 44227 Dortmund

The lowest exciton transitions in Cu₂O are considered to be an ideal system to observe Bose-Einstein condensation (BEC). Despite the large experimental efforts, (for a review see Ref. [1]), a clear evidence for an excitonic BEC was not given up to now. In this contribution we present temperature and excitation power dependent absorption measurements of the paraexciton, which is the lowest exciton state of the yellow series, via the polariton effect using a tunable single frequency laser. At 10 Tesla we get in high quality samples an absorption coefficient of about 80 cm-1 and a line width of 80 neV at T=1.2K and µW laser power. The absorption line shows a blue-shift and a broadening with increasing intensity. Both effects can be explained quantitatively by taking acoustic phonon scattering and a density dependent exciton-exciton interaction into account. Under these excitation conditions we observe in phonon sidebands of the paraexciton emission a sharp peak at the low energy side. The possibility that it reflects resonant Raman scattering or a transition from k = 0 excitons and thus a BEC is discussed, based on its characteristic density and temperature dependence. [1] D. W. Snoke, Science 298, 1368 (2002).