Coherent Dynamics of Magneto-excitons in Quantum Wells and Dots

Cavendish Laboratory, University of Cambridge, UK

3.30pm, Friday 17 December 2004, AR103 Seminar Room, Graduate Research Centre

Time-resolved Four-Wave mixing experiments using a heterodyne detection system has allowed the coherent dynamics of magneto-excitons in a single quantum well to be studied with greater sensitivity than previously possible. Transitions between Free polarisation decay and photon echo behaviour, are observed, along with beating due to monolayer fluctuations and some interesting effects at negative delay times. This has enabled the clarification of the type of coupling across monolayer fluctuations.

The temperature and magnetic field dependence of spin coherence of excitons in InGaAs quantum dots was obtained from quantum beats observed in polarisation resolved pump-probe differential reflection spectroscopy. The average Lande g-factor for the excitons was found to be 1.213 ± 0.009. It is apparent however, that the range of g-factors in the different dots is large, which leads to increased inhomogeneous broadening with increasing magnetic field, and hence the masking of the spin coherence time.

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