Nonlinear optical properties in semiconductor double quantum wires coupled to a quantum-sized metal nanoparticle

We theoretically investigate linear and nonlinear optical absorption coefficients (OACs) and refractive index changes (RICs) of two quantum wires (QWs) separated by a quantum-sized metal nanoparticle (MNP) using a density matrix method and dielectric quantum theory. The exciton-plasmon coupling and the dipole-dipole interaction (DDI) between the two QWs are taken into account. We find that the magnitudes of the linear and nonlinear OACs (RICs) from the QWs are enhanced by one order of magnitude, in contrast to the case without a MNP, due to the exciton-plasmon coupling and the DDI between the two QWs. The quantum size effect in a MNP induces a pronounced enhancement in the magnitudes of the linear and nonlinear OACs (RICs) with the increase of the MNP radius. Furthermore, the optical responses can be further strengthened via increasing the MNP radius or decreasing the radius and gap of the QWs, owing to the enhanced exciton-plasmon coupling and the DDI between the two QWs. Moreover, the magnitudes of the total OACs (RICs) are reduced by increasing the optical intensity, along with a splitting effect of the OACs under strong optical intensity. Our results provide the possibility of designing the hybrid nanostructures with large nonlinearity for applications in nano-devices such as optical switches and amplifiers.