Optical bistability of metal-coated semiconductor nanocrystals

We study intrinsic optical bistability in nonlinear composites of coated spheres, motivated by a recent experiment on small-particle heterogeneous systems. A self-consistent theory is applied to calculate the local fields in composites of coated spheres with a nonlinear dielectric core and a metallic shell, embedded in a linear host. To study the resonance response, we use the spectral representation and find that the local field in the core generally consists of two resonant terms, each of which has a form similar to that in the case of spherical inclusions but with a pole whose location and residue depend strongly on the dielectric constant of the core material as well as on the thickness of the shell. Thus by tuning the relevant microstructure parameters, it may be possible to reduce the threshold applied field and enhance the bistable response. Model calculations on various physical quantities are performed in accord with the experimental conditions.