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Surface recoil force on dielectric nano--particles enhancement via graphene acoustic surface plasmons excitation: non--local effects consideration

Controlling opto--mechanical interactions at sub--wavelength levels is of great importance in academic science and nano--particle manipulation technologies. This letter focuses on the improvement of the recoil force on nano--particles placed close to a graphene--dielectric--metal structure. The momentum conservation involving the non--symmetric excitation of acoustic surface plasmons (ASPs), via near field circularly polarized dipolar scattering, % induced by the circular dipole moment on the nano--particle, implies the occurrence of a huge momentum kick on the nano--particle. Owing to the high wave--vector values entailed in the near field scattering process, it has been necessary to consider %apply the non--locality of the graphene electrical conductivity to explore the influence of the scattering loss on this large--wave--vector region, which is neglected by the semi--classical model. Surprisingly, %our results show that %, \textcolor{red}{depending on the particle position and the dielectric thickness layer}, the contribution of ASPs to the recoil force %can be is negligibly modified when the non--local effects are incorporated through the graphene conductivity. On the contrary, our results show that the contribution of the non--local scattering loss to this force becomes dominant when the particle is placed very close to the graphene sheet and that it is mostly independent of the dielectric thickness layer. Our work can be helpful for designing new and better performing large--plasmon momentum opto--mechanical structures using scattering highly dependent of the polarization for moving dielectric nano--particles.