Non-local coherent coupling between excitons in a disordered quantum well

Yuri D Glinka,Michael N Leuenberger,Xiaoqin Li,Allan S Bracker,Chandriker K Dass,Mikhail Erementchouk

doi:10.1088/1367-2630/15/7/075026

Abstract

We investigated coherent coupling among multiple exciton resonances formed in a single disordered quantum well using the powerful electronic two-dimensional Fourier transform spectroscopy. Our experiment revealed clear signatures of non-local coherent coupling between the heavy-hole and light-hole excitons residing in regions that differ in thickness by one atomic layer. The experimental observation is qualitatively explained by spatial overlap between exciton linear response functions calculated within a single defect model.

Highlights

In QWs, quantum confinement in the growth direction lifts the degeneracy of the HH and LH valence bands, which are distinguished by their angular moments of 3/2 and 1/2, respectively
The change in exciton resonance introduced by the thickness fluctuations is most pronounced in narrow QWs where the ratio of the thickness of the single atomic layer to the QW width is appreciable
Qualitative features of the linear optical spectrum in the presence of interface disorder are determined by the relation between two characteristic length scales: the disorder correlation length rc and the confinement length ξ0

Summary

Exciton resonances in a perfect QW versus a disordered one

In QWs, quantum confinement in the growth direction lifts the degeneracy of the HH and LH valence bands, which are distinguished by their angular moments of 3/2 and 1/2, respectively. In a perfect QW, only two resonances corresponding to HH and LH excitons are spectrally resolved, both being twofold spin degenerate These resonances are plotted in the excitation picture, as shown in figure 1(b). If the typical size of islands, rc, is larger than the localization length, ξ0, the optical spectrum exhibits doublets. If the typical island size rc is much smaller than the localization length ξ0, the excitons average over the fluctuating potential and the optical spectrum exhibits a single resonance. This qualitative picture is illustrated by results of numerical simulations of the linear optical response presented. In figure 1(d), where the magnitude of the exciton linear polarization induced by an incoming plane wave is plotted as a function of energy for different cases corresponding to different relations between rc and length ξ0

Identifying relevant exciton resonances experimentally

Theoretical calculation based on the single defect model

A d R pσ

Conclusion