Coherent A1g and Eg phonons of antimony

We report the ultrafast dynamics of the coherent A1g and Eg phonons of antimony as a function of temperature and optical polarization. Like in bismuth, the two phonon modes exhibit nearly π/2 difference in their initial phase, suggesting their different coupling strengths with photoexcited electrons. The dependence of the phonon amplitude on the optical polarization and temperature indicates the generation of the coherent A1g phonons through both displacive and Raman processes, rather than a purely displacive one. In contrast, the generation of the coherent Eg phonons can be understood within Raman framework alone.