Generation mechanism of terahertz coherent acoustic phonons in Fe

T. Henighan,1,2,* M. Trigo,1,3 S. Bonetti,3 P. Granitzka,3,4 D. Higley,3,5,6 Z. Chen,2,3 M. P. Jiang,1,2 R. Kukreja,3 A. Gray,3 A. H. Reid,3 E. Jal,3 M. C. Hoffmann,6 M. Kozina,1,6 S. Song,6 M. Chollet,6 D. Zhu,6 P. F. Xu,7,8 J. Jeong,7 K. Carva,9,10 P. Maldonado,10 P. M. Oppeneer,10 M. G. Samant,7 S. S. P. Parkin,7,8 D. A. Reis,1,3,5 and H. A. Dürr3,† 1Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA 2Physics Department, Stanford University, Stanford, California 94305, USA 3Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA 4Van der Waals-Zeeman Institute, University of Amsterdam, NL-1018 XE Amsterdam, The Netherlands 5Departments of Photon Science and Applied Physics, Stanford University, Stanford, California 94305, USA 6Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA 7IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA 8Max-Planck Institute for Microstructure Physics, D-06120 Halle (Saale), Germany 9Faculty of Mathematics and Physics, Department of Condensed Matter Physics, Charles University in Prague, Ke Karlovu 5, CZ-12116 Prague 2, Czech Republic 10Department of Physics and Astronomy, Uppsala University, P. O. Box 516, S-75120 Uppsala, Sweden (Received 1 September 2015; revised manuscript received 11 May 2016; published 10 June 2016)