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\bibitem{Helm_etal1999} {\textquotedblleft}\textit{Minibands and Wannier-Strak ladders in semiconductor superlattices studied by infrared spectroscopy}{\textquotedblright}. Helm M, Hilber W, Strasser G, de Meester R, Peeters FM, Brazilian journal of physics \textbf{29}, 652 (1999)

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