Regensburg 2002 – scientific programme
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HL: Halbleiterphysik
HL 11: Poster 1
HL 11.50: Poster
Monday, March 11, 2002, 17:00–19:30, Poster A
Time–resolved coherent emission of Wannier–Stark excitons — •Christian Holfeld1, Karl Leo1, and Wilfried Schäfer2 — 1Inst. f. Angewandte Photophysik, Technische Universität Dresden — 2John von Neumann-Institut f. Computing, FZ Jülich
Fano resonances are fundamental and widespread phenomena: A discrete state is coupled to a degenerate continuum of states giving rise to major changes of its absorption profile and hence its quantum dynamics. Whereas the spectral information clearly reveals broadening mechanisms, it cannot distinguish its actual origin (i. e. homogeneous or inhomogeneous broadening).
We use semiconductor superlattices which offer the unique chance to continuously tune the Fano coupling strength by sweeping an electric field across the sample. Here, the Wannier–Stark excitons are degenerate to the subband continua of lower–lying ladder states. Transient four–wave mixing (TI FWM) data reported to date proof the influence of the Fano coupling on the polarization decay [1,2]. However, there is a contrary discussion whether the polarization decay of Fano resonances can be resolved in the TI FWM or whether it disappears instantaneously due to quantum interference (corresponding to homogeneous or inhomogeneous broadening, respectively).
We present time–resolved FWM (TR FWM) data of Wannier-Stark transitions which clearly exhibit a free–induction decay. The broadening issue and the emission characteristic are discussed in detail.
[1] U. Siegner et al., PRL 78, 1363 (1997).
[2] C. P. Holfeld et al., PRL 81, 874 (1998).