Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 49: Ultrafast Phenomena

HL 49.9: Talk

Wednesday, March 28, 2012, 11:30–11:45, EW 202

Spectrally resolved photon echo measurements in CdTe QWs — •L. Langer¹, S. Poltavtsev², I. A. Yugova^1,2, G. Karczewski³, T. Wojtowicz³, J. Kossut³, D. R. Yakovlev^1,4, I. A. Akimov^1,4, and M. Bayer¹ — ¹Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany — ²Physical Faculty of St. Petersburg State university, 198504 St. Petersburg, Russia — ³Institute of Physics, Polish Academy of Sciences, 02668 Warsaw, Poland — ⁴A.F. Ioffe Physical-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia

We report on trion and exciton decoherence in epitaxially grown, 20 nm thick CdTe/CdMgTe quantum wells using degenerate transient four wave mixing (TFWM) technique with heterodyne detection.Use of spectrally narrow picosecond pulses allows measuring the FWM signal for exciton and trion resonances separately. Time-resolving the FWM signal provides direct information on reversible and irreversible dephasing in the system under study. The measured photon-echo behavior for both inhomogeneously broadened exciton- and trion resonances reveals decoherence times of τ_X = 5 ps and τ_T = 24 ps at temperature T = 2 K. Depending on the polarization configuration of two beams, different light induced gratings can be generated. For colinearly polarized beams, a population grating is induced while for crossed-linearly polarized beams a spin grating is formed. While a magnetic field of up to 0.7 T applied in Voigt geometry does not alter the population grating, the spin grating’s FWM signal is modulated at the Larmor frequency.