Direct probe of linearly dispersing 2D interband plasmons in a free-standing graphene monolayer M. K. Kinyanjui, C. Kramberger, T. Pichler, J. C. Meyer, P. Wachsmuth, G. Benner and U. Kaiser EPL, 97 5 (2012) 57005 Published online: 02 March 2012 DOI: 10.1209/0295-5075/97/57005