Time-domain evidence for an excitonic insulator S. Hellmann, T. Rohwer, M. Kalläne, K. Hanff, A. Carr, M. M. Murnane, H. C. Kapteyn, L. Kipp, M. Bauer and K. Rossnagel EPJ Web of Conferences, 41 (2013) 03022 Published online: 13 March 2013 DOI: 10.1051/epjconf/20134103022