Optical properties of semiconductor-metal nanocrystal molecules: Exciton-plasmon interactions

Motivated by recent experiments on bio-conjugated semiconductor-metal hybrid nanocrystal superstructures, we develop a theory to describe a system composed of a semiconductor quantum dot (QD) and a metal nanoparticle (NP) in the presence of external electric fields. The interaction between exciton (in QD) and plasmon (in NP) leads to interesting optical properties. We explore both the linear regime (for weak external field) and the non-linear regime (for strong external field). The interference between the external field and the induced internal field results in strong enhancement of energy absorption (compared with the energy absorption of QD in the absence of a metal NP) and also leads to an asymmetric peak and valley in the total energy absorption (Fano-like shape). We also consider Rayleigh scattering which also reveals this type of behavior. Our theory is useful for understanding present experimental results and can give guidance for future experiments, which may have important applications.