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Abstract

Resonant secondary emission at the disorder-broadened exciton transition is a fundamental process studied by ultra-fast spectroscopy on high-quality quantum wells. A quantitative interpretation is provided by the speckle analysis pioneered by Langbein, Zimmermann, and collaborators. The background panels show emission intensities versus time and scattering angle; from Langbein [1]. A theoretical understanding can be obtained via the steps symbolized by the front panels and systematically pursued by Roland Zimmermann's group during the last decade: (i) The interface disorder (characterized by the island size , a few atoms) can be mapped onto (ii) an Anderson disorder model for the center-of-mass motion with energy fluctuations V(R) correlated over distances of the order of the exciton radius aB. Numerical simulations of the disorder-localized eigenstates yield, e. g., (iii) distributions of radiative life times r - and, thus, predict secondary emission properties; details and calculation parameters in Savona and Runge [2] and Refs. [6, 10, 20, 23] therein. In this way, the figure covers many aspects of the work of Roland Zimmermann, Professor of Theoretical Physics at the Humboldt-Universität zu Berlin, to whom this special issue of physica status solidi (b) is dedicated on the occasion of his 60th birthday.