Electromagnetic Raman Enhancement Beyond Gap Limit

Surface-enhanced Raman scattering is of great importance to trace-level detection with fingerprint information of analytes. However, there is no room for electric dipole enhancement mechanism to further improve the enhancement factor and detect macromolecules. Here, we break the limits by electric multipoles with anapole states, as well as bound states in the continuum, providing a degree of freedom to control field confinement in time and in space. The increases of gap size will benefit to both improve enhancement factor in the order of 10^{12} and take in large molecules over 100 nm. Our findings open a pathway towards promoting practical applications of surface-enhanced Raman scattering by virtue of the excitation of high-order electromagnetic multipoles in arrayed structures, and harnessing other light-matter interaction processes, such as light emission, photodetection, photocatalysis, nonlinear optics, and quantum optics.