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HL: Fachverband Halbleiterphysik

HL 38: Polaritons and Polariton Lasing

HL 38.5: Vortrag

Dienstag, 15. März 2011, 13:00–13:15, FOE Anorg

Balistic exciton polariton propagation in CdZnTe crystals — •Tillmann Godde¹, Ilya Akimov¹, Dimitri Yakovlev¹, Henri Mariette², and Manfred Bayer¹ — ¹Experimentelle Physik 2a, Technische Universität Dortmund, 44227 Dortmund, Germany — ²CEA-CNRS group Nanophysique et Semiconductors, Institute Néel, CNRS and Université Joseph Fourier, 25 Avenue des Martyrs, 38042 Grenoble, France

We study the propagation of lower branch exciton polaritons in 200 µm - 800µm thick Cd_0.88Zn_0.12Te samples using time resolved photoluminescence (PL) and time of flight techniques. The PL spectrum comprises of two peaks consistent with emission from upper and lower polariton branches with a resonance frequency of ℏ ω₀ = 1.664 eV. The lifetimes of the exciton polaritons in the upper and lower branches are 1.5 ns and 3 ns, respectivly.

In time of flight measurements we observe significant delay of 1 ps optical pulses, which increases to 350 ps at ℏ ω= 1.661 eV in a 745 µm thick sample. Femtosecond-pulses get stretched and allow to obtain the dispersion in a single streak camera measurement. We reproduce the measured delays using a single oscillator model for the lower polariton branch dispersion.

The propagation is ballistic, which follows from the observation of reflected replica pulses. Assuming that the exciton polariton scattering on optical and acoustical phonons is mainly inelastic, we conclude that the propagation is coherent. We estimate the coherence time to be about 300 ps.