Theoretical study on ultrafast dynamics of coherent acoustic phonons in semiconductor nanocrystals

Abstract

We present a theoretical study on the ultrafast dynamics of coherent acoustic phonons in semiconductor quantum dots using continuum model calculations. The excitonic states and the coherent acoustic vibrational modes of semiconductor quantum dots are calculated using the effective mass approximation and continuum elastic medium model, respectively. By solving the Liouville–von Neumann equation and the equation of motion, we obtain the oscillation of coherent acoustic phonon amplitude excited by a pump pulse laser. Owing to the ultrafast excitation of coherent phonons, both the amplitude and the phase of the coherent phonon oscillation are constant with time. This coherent phonon oscillation results in conservation of the coherence of the exciton state, which cannot exist in a system interacting with incoherent phonons. We further study the amplitude and the period of coherent acoustic phonon oscillation as a function of pump pulse energy detuning, quantum dot size, and material.