Realizing optical bistability and tristability in plasmonic coated nanoparticles with radial-anisotropy and Kerr-nonlinearity.

We theoretically study the optical bistability and tristability in plasmonic coated nanospheres containing the nonlinear plasmonic shell and the dielectric core with radial anisotropy. Based on self-consistent mean-field approximation, we establish the relationship between the local field in the shell and the applied incident field, taking into account the Lorentz local field. One or two optical bistabilities and even optical tristability can be observed. Especially, there are two critical geometric parameters between which two optical bistabilities exist. Physically, two optical bistablities result from the excitations of two surface plasmonic resonant modes in the inner and outer interfaces of coated nanospheres, which are well reflected from the spectral representation with two poles. Moreover, the involvement of the radial anisotropy is quite essential to realize the optical tristability. Further discussion on the field-induced tuning of the reflectance reveals the macroscopic properties of this nonlinear optical structure, which provides a potential candidate for designing multi-stable optical devices at the nanoscale.