Superchiral-Field-Enhanced Photoinduced Force Microscopy for Nanoscale Chiral Characterization via Magnetic-Dipole Excitation

The chiral interaction between light and matter is intrinsically weak at the nanoscale, which leads to a sensitivity bottleneck in the detection of chiral samples by photoinduced force microscopy. To address this issue, we propose an enhancement strategy that combines a semiconductor tip with a superchiral optical field to improve the optical force response in nanoscale chiral detection. Compared with a conventional metallic tip, a silicon tip can generate a larger optical force difference under left- and right-handed circularly polarized illumination. This enhancement mainly arises from the more pronounced magnetic response of the silicon tip, which increases the contribution of the magnetic dipole term to the total optical force. Furthermore, when the incident field is changed from a circularly polarized field to a superchiral field, the optical force difference acting on the same tip can be further increased by more than one order of magnitude. Relative to the reference case of a gold tip excited by circularly polarized light, the combination of a superchiral field and a silicon tip enhances the optical force difference by nearly two orders of magnitude. Analysis based on the dipole approximation shows that this enhancement originates from the synergistic effect of two factors: the high-refractive-index silicon tip provides a stronger magnetic response, while the superchiral field further strengthens the coupling between the localized chiral field and the tip and effectively excites the magnetic dipole and electromagnetic coupling terms, thereby jointly amplifying the chiral optical force signal. This work provides a new route for the highly sensitive detection of chiral materials at the nanoscale and may further extend the applications of photoinduced force microscopy in the characterization of chirality and optomagnetic interactions.