Coherent phonon generation mechanism in solids - art. no. 180301

We investigate the driving force for coherent phonons by employing a nonlin ear two-pump/probe technique. In accordance with the displacive excitation mechanism we demonstrate that the electronic excitation is the driving forc e for the coherent phonons in semimetals. This is accomplished by analyzing the relation between the nonlinearities in the electronic and phononic con tributions. On the other hand, no dependence of the coherent phonon dynamic s on the electronic excitation was observed in high temperature superconduc tors (HTSC), although displacive excitation has been invoked for these mate rials. We discuss the possible implications of this observation on the micr oscopic nature of the coherent phonons in the HTSC.