Anharmonic Decay of Coherent Optical Phonons in Antimony

The anharmonic decay of coherent optical phonons in the semimetal Sb has been investigated by a femtosecond pump-probe technique. The coherent A(1g) mode is observed in the time domain in a wide temperature range of 7-290 K. The decay rate (the inverse of the dephasing time) systematically increases as the lattice temperature increases, which is well explained by anharmonic phonon-phonon coupling, causing the decay of the optical phonon into two acoustic phonon modes. The frequency of the A(1g) mode decreases with increasing temperature, which is interpreted as the results of both thermal expansion and anharmonic phonon-phonon coupling. The temperature dependence of the amplitude of the coherent A(1g) mode exhibits a decrease with increasing lattice temperature, which is well reproduced by considering the peak intensity of spontaneous Raman scattering assuming a Lorentzian line shape with the linewidth controlled by the anharmonic decay, and this model is applicable to other metallic systems, such as Zn.