S.  Ulstrup, Johannsen, J. Christian, Cilento, F., Miwa, J. A., Crepaldi, A., Zacchigna, M., Cacho, C., Chapman, R., Springate, E., Mammadov, S., Fromm, F., Raidel, C., Seyller, T., Parmigiani, F., Grioni, M., King, P. D. C., and Hofmann, P., ?Ultrafast Dynamics of Massive Dirac Fermions in Bilayer Graphene?, Physical Review Letters, vol. 112, p. 257401, 2014.