M.-A. Mycek

Coherent dynamics and dephasing of one-dimensional magnetoexcitons in GaAs

We study the ultrashort dynamics and the dephasing processes of one-dimensional Lorentzian and Fano magnetoexcitons in GaAs, using temporally and spectrally resolved four-wave mixing. The dephasing of the Lorentzian magnetoexcitons is determined by quasi-particle scattering, dominated by exciton – exciton scattering at low temperatures. In contrast, the dephasing time of the Fano magnetoexcitons is intrinsically limited by the Fano coupling to the continuum. Quantum interference is observed if Fano magnetoexcitons contribute to the four-wave mixing signal. This effect is absent in the case of purely Lorentzian dynamics. We show that Lorentzian and Fano magnetoexciton resonances are coupled by Coulomb correlation and discuss the consequences of this coupling.

Ultrafast spectroscopy of GaAs under a magnetic field: Coulomb correlated magnetoexcitons in the 3D to 1D transition

Abstract Using transient four-wave mixing spectroscopy, we study the ultrafast nonlinear optical response of magnetoexcitons in GaAs at 1.6 K. By spectrally and temporally resolving the coherent emission, we measure the magnetic field dependence of Coulomb interactions between magnetoexcitons. Contrary to experiments performed in quantum wells, these interactions persist for field strengths up to 10 T.

Amplitude Decay and Instantaneous Frequency Dynamics of Excitonic Polarization in Semiconductor Quantum Wells

Coherent light scattering is an ideal tool to investigate the microscopic interactions that take place in various diluted or condensed phase systems1. It is of particular interest in semiconductors where the Coulomb interaction between electrons and holes brings new features in the dynamics of the polarization established by ultrashort optical pulses2. Due to this Coulomb coupling the coherent emission observed in different wave-mixing geometries behaves in a non-trivial fashion. The usual description of the material relaxation with a simple transverse time T 2, as is done for atomic-like systems3, is no longer sufficient. Although the underlying physics is more complex, one may picture these different regimes by analogy with oscillators: the exponential T 2 behavior corresponds to a damped harmonic oscillator, while the Coulomb interacting system leads to a non-exponential damping, as with nonlinear coupled oscillators.