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\bibitem{Pereira_etal2009} {\textquotedblleft}\textit{Valley polarization due to trigonal warping on tunneling electrons in graphene}{\textquotedblright}. Pereira JM, Peeters FM, Costa Filho RN, Farias GA, Journal of physics : condensed matter \textbf{21}, 045301 (2009).   http://doi.org/10.1088/0953-8984/21/4/045301

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