Coherent THz Phonons Driven by Light Pulses and the Sb Problem: What is the Mechanism?

G. A. Garrett,1,2 T. F. Albrecht,1,2 J. F. Whitaker,1 and R. Merlin1,2,3 1Center for Ultrafast Optical Science, The University of Michigan, Ann Arbor, Michigan 48109-2099 2The Harrison M. Randall Laboratory of Physics, The University of Michigan, Ann Arbor, Michigan 48109-1120 3Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (Received 23 July 1996)