Size dependent, state-resolved studies of exciton-phonon couplings in strongly confined semiconductor quantum dots

Coherent optical and acoustic phonons are observed in strongly confined CdSe quantum dots using excitonic state-resolved femtosecond pump/probe experiments. These state-resolved time-domain experiments yield the size dependent exciton-phonon couplings for both modes as well as the excitonic state dependent couplings. The size dependences are weak in this regime, but the state dependence is large for the optical phonons via the Frohlich interaction. The state dependent coupling to optical phonons suggests that the exciton becomes less polar for higher states. The time-domain data are compared to frequency-domain resonance Raman data. The differences between the various experimental results are discussed in terms of intrinsic versus extrinsic coupling and quantified in terms of the state dependent exciton-phonon couplings.