Observation of excited states in a graphene double quantum dot F. Molitor, H. Knowles, S. Dröscher, U. Gasser, T. Choi, P. Roulleau, J. Güttinger, A. Jacobsen, C. Stampfer, K. Ensslin and T. Ihn EPL, 89 6 (2010) 67005 Published online: 19 April 2010 DOI: 10.1209/0295-5075/89/67005