Influence of image forces on charge-dipole interaction in two-layered systems

Interaction between a fixed point electric charge $Q$ and a freely rotatingpoint electric dipole with the magnitude $P$ pinned near a plane interfacebetween two dispersionless insulators with different dielectric permittivities$\varepsilon_{1}$ and $\varepsilon_{2}$ has been considered. It was shown thatas a result of this interaction and the interaction of the dipole with thepolarization charges induced at the interface by the charge~$Q$ and the dipoleitself, there arise regions where the dipole can possess either one or twoequilibrium orientations. The spatial distributions of the electrostaticdipole energy $W_{\mathrm{total}}$ under the combined action of the charge $Q$and the induced interface polarization charges, as well as the equibibriumdipole orientations (orientation maps), the boundaries between the regionswith different numbers of dipole orientations, and their evolution with thevariation of problem parameters (the charge and dipole magnitudes, themismatch between $\varepsilon_{1}$ and $\varepsilon_{2}$, and thecharge--interface distance) were calculated. It was shown that there canemerge local minima of $W_{\mathrm{total}}$, which may play the role of trapsfor dipoles (in particular, excitons in layered structures), and thecorresponding requirements for the problem parameters were found. Most resultswere obtained in the analytical form. The model can be applied to variousphysical systems, for instance, polar molecules, excitons, and trions in layered structures.