Coherent acoustic phonons in a semiconductor quantum dot

Coherent acoustic phonons in PbS quantum dots are observed using femtosecond optical techniques. This is the first observation of coherent acoustic phonons in a semiconductor quantum dot; the phonons are generated through the deformation-potential coupling to the quantum-dot exciton. The acoustic modes are weakly damped, and we also find extremely weak coupling (S similar to 0.01) to the optical. modes. These conclusions have important consequences for the vibronic nature of the exciton transition in the quantum dot and its dephasing.