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\bibitem{Riva_etal2001} {\textquotedblleft}\textit{Positive and negative charged excitons in a semiconductor quantum well}{\textquotedblright}. Riva C, Peeters FM, Varga K, Physica status solidi: B: basic research \textbf{227}, 397 (2001).   http://doi.org/10.1002/1521-3951(200110)227:2<397::AID-PSSB397>3.0.CO;2-X

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