Dresden 2011 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 89: Optical Properties II
HL 89.11: Talk
Friday, March 18, 2011, 13:00–13:15, POT 251
Exciton dynamics in potential traps and the possibility of Bose-Einstein condensation — •Rico Schwartz1, Nobuko Naka2,3, Jan Brandt4, Christian Sandfort4, and Heinrich Stolz1 — 1Institut für Physik, Universität Rostock, D-18051 Rostock, Germany — 2Department of Physics, Kyoto University, Kyoto 606-8502, Japan — 3PRESTO, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan — 4Fakultät Physik, Technische Universität Dortmund, D-44221 Dortmund, Germany
Experiments on excitons in Cu2O confined in a stress-induced potential trap [1] at subkelvin temperatures are reported. The paraexcitons were created by resonant excitation of orthoexcitons followed by ortho-para conversion. We excited with a pulsed laser (linewidth 1 GHz, repetition rate 1 kHz, pulse length 50 ns). With a gated CCD time dependent spatially resolved luminescence spectra were observed. A fit of the data with a simple rate equation model leads to bimolecular decay rates of the para- and orthoexcitons which are at least 5 orders of magnitude lower than those from literature [2]. Concomitant, we reached exciton numbers in the order of 109 in the trap. The effective temperature of the excitons was determined by fitting the high energy flank in the spectra with a Bose distribution. This temperature decreases after the excitation pulse to the bath temperature (0.15 K), which is well below the critical temperature of BEC at these exciton numbers. We also discuss whether the shape of the spectra points to an excitonic BEC.
[1] N. Naka and N. Nagasawa, Phys. Rev. B 65, 075209 (2002)
[2] K. Yoshioka et al., Phys. Rev. B 82, 041201(R) (2010)