Dirac plasmons in bipartite lattices of metallic nanoparticles

Abstract

We study theoretically "graphene-like" plasmonic metamaterials constituted by two-dimensional arrays of metallic nanoparticles, including perfect honeycomb structures with and without inversion symmetry, as well as generic bipartite lattices. The dipolar interactions between localised surface plasmons in different nanoparticles gives rise to collective plasmons that extend over the whole lattice. We study the band structure of collective plasmons and unveil its tunability with the orientation of the dipole moments associated with the localised surface plasmons. Depending on the dipole orientation, we identify a phase diagram of gapless or gapped phases in the collective plasmon dispersion. We show that the gapless phases in the phase diagram are characterised by collective plasmons behaving as massless chiral Dirac particles, in analogy with electrons in graphene. When the inversion symmetry of the honeycomb structure is broken, collective plasmons are described as gapped chiral Dirac modes with an energy-dependent Berry phase. We further relax the geometric symmetry of the honeycomb structure by analysing generic bipartite hexagonal lattices. In this case we study the evolution of the phase diagram and unveil the emergence of a sequence of topological phase transitions when one hexagonal sublattice is progressively shifted with respect to the other.

Topological collective plasmons in bipartite chains of metallic nanoparticles

“…V). The present realization of 1D Dirac-like bosons encapsulated in the Hamiltonian (19) complements the recent discovery of their counterparts in 2D honeycomb metasurfaces [52,53,69].…”

“…Therefore, we suggest bipartite chains of plasmonic nanoparticles as an ideal testbed to experimentally probe 1D Dirac-like bosons, which undergo exotic phenomena such as Klein tunneling. While our proposal complements the hosting of 2D Dirac-like bosons in honeycomb lattices [52,53], it also has the notable advantage that the bipartite linear lattice may be easier to realize experimentally.…”

Nonradiative limitations to plasmon propagation in chains of metallic nanoparticles

“…The latter gives rise to the second term on the right-hand side of Eq. (2) [21,[29][30][31][32] with the coupling constant…”

Plasmon polaritons in cubic lattices of spherical metallic nanoparticles

“…where H pl and H ph denote the plasmonic and photonic Hamiltonians, respectively, and where H pl-ph is the interaction Hamiltonian between both subsystems. In the Coulomb gauge [42,43], the purely plasmonic Hamiltonian reads [33,34,36,37,39]…”

“…Three-dimensional metastructures were also investigated using more approximate approaches such as the Maxwell-Garnett effective medium theory [7] or Bruggeman effective medium theory [31]. In addition to the classical, typically fully numerical treatments, an analytically tractable approach based on a Hamiltonian formalism was recently applied to 1D [32][33][34][35], 2D [36][37][38] and 3D systems [39].…”