Ultrafast Coulomb-induced dynamics of 2D magnetoexcitons

Details Ultrafast Coulomb-induced dynamics of 2D magnetoexcitons Ultrafast Coulomb-induced dynamics of 2D magnetoexcitons

2000-08-29

arxiv.org/abs/cond-mat/0008417v1

Phys. Rev. B 62, 15925 (2000)

Physics

Condensed Matter

41 pages with 11 figs

Scientific paper

10.1103/PhysRevB.62.15925

We study theoretically the ultrafast nonlinear optical response of quantum well excitons in a perpendicular magnetic field. We show that for magnetoexcitons confined to the lowest Landau levels, the third-order four-wave-mixing (FWM) polarization is dominated by the exciton-exciton interaction effects. For repulsive interactions, we identify two regimes in the time-evolution of the optical polarization characterized by exponential and {\em power law} decay of the FWM signal. We describe these regimes by deriving an analytical solution for the memory kernel of the two-exciton wave-function in strong magnetic field. For strong exciton-exciton interactions, the decay of the FWM signal is governed by an antibound resonance with an interaction-dependent decay rate. For weak interactions, the continuum of exciton-exciton scattering states leads to a long tail of the time-integrated FWM signal for negative time delays, which is described by the product of a power law and a logarithmic factor. By combining this analytic solution with numerical calculations, we study the crossover between the exponential and non-exponential regimes as a function of magnetic field. For attractive exciton-exciton interaction, we show that the time-evolution of the FWM signal is dominated by the biexcitonic effects.

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