Symmetry-tailored dielectric environments for metal nanoplasmonics

The manipulation of nanoplasmonic optical fields depends critically on both the intrinsic plasmonic resonance of metal nanoparticles and the properties of their surrounding dielectric environment. Key governing factors include the dielectric's relative permittivity, nanoparticle-dielectric separation distance, and the structural configuration of the dielectric medium. Despite their importance, systematic studies examining how dielectric architectures influence plasmonic excitation modes in metal nanoparticles remain scarce. In this work, we employ a quantum hydrodynamic approach incorporating nonlocal quantum effects to investigate optical field distributions in nanoplasmonic systems coupled to N symmetric dielectric nanoparticles or a dielectric ring structure. Our group-theoretical analysis demonstrates that symmetry reduction in the dielectric environment alters the spatial distribution of two orthogonal eigenmodes, leading to enhanced asymmetric broadening in the plasmonic resonance spectrum. Most significantly, we establish that when the dielectric configuration preserves complete rotational symmetry about the metal nanoparticle, substantial localized field enhancement can be maintained even at extreme sub-nanometer (∼0.1 nm) separations—a finding that contrasts sharply with conventional symmetry-breaking scenarios. These insights provide fundamental design principles for advanced nanoplasmonic systems.