A. Pashkin, M. Porer, M. Beyer, K. W. Kim, A. Dubroka, C. Bernhard, X. Yao, Y. Dagan, R. Hackl, A. Erb, J. Demsar, R. Huber, A. Leitenstorfer: Femtosecond Response of Quasiparticles and Phonons in Superconducting YBa2Cu3O7-delta Studied by Wideband Terahertz Spectroscopy. 2010Physical Review Letters: 105. ISBN 0031-9007 http://dx.doi.org/10.1103/PhysRevLett.105.067001