We theoretically study the mechanical interaction between radiation and a semiconductor nanoparticle, based on a microscopic model of confined excitons. The exerted force is calculated by using the Maxwell stress tensor expressed in terms of the microscopic response field. The numerical demonstrations clarify the following: (1) The enhancement of the force by using electronic resonance is remarkable for a particle with a radius of less than 100 nm for semiconductor materials. (2) The spectral peak position of the exerted force is considerably sensitive to nanoscale-size changes which would be useful for highly accurate size-selective manipulation.

Single-molecule nanospectroscopy: Microscopic understanding and molecular-level control of individual electronic quantum states of a single molecule are a long-standing challenge in spectroscopy. Imada et al. found that a narrow-line tunable laser combined with a scanning tunneling microscope was able to generate photoluminescence spectra of the electronic and vibrational states of single molecules with micro–electron volt energy resolution and submolecular spatial resolution. The authors also discovered a way to tune the energy levels through a linear Stark effect and plasmon-exciton coupling in the tunneling junction. The proposed technique paves the way to efficient exploitation of energy conversion dynamics in electronic excited states, which constitutes the bedrock principle of such systems as LEDs, photovoltaics, and photosynthetic cells. Science , abg8790, this issue p. 95

We study the size dependence of the nonlinear response of weakly confined excitons for the size region beyond the long wavelength approximation regime. The observed degenerate-four-wave mixing signal of GaAs thin layers exhibits an anomalous size dependence, where the signal is resonantly enhanced at a particular thickness region. The theoretical analysis elucidates that this enhancement is due to the size-resonant enhancement of the internal field with a spatial structure relevant to the nondipole-type excitonic state. These results establish the formerly proposed new type of size dependence of nonlinear response due to the nonlocality induced double resonance.

Selective manipulation and spectroscopy of single nanoparticles are realized by measuring and controlling quantum resonant forces.