  Inspired by geometrically frustrated magnetic systems, we present the optical
response of three cases of hexagonal lattices of plasmonic nanoelements. All of
them were designed using a metal-insulator-metal configuration to enhance
absorption of light, with elements in close proximity to exploit near-field
coupling, and with triangular symmetry to induce frustration of the dipolar
polarization in the gaps between neighboring structures. Both simulations and
experimental results demonstrate that these systems behave as perfect absorbers
in the visible and/or the near infrared. Besides, the numerical study of the
time evolution shows that they exhibit a relatively extended time response over
which the system fluctuates between localized and collective modes. It is of
particular interest the echoed excitation of surface lattice resonance modes,
which are still present at long times because of the geometric frustration
inherent to the triangular lattice. It is worth noting that the excitation of
collective modes is also enhanced in other types of arrays where dipolar
excitations of the nanoelements are hampered by the symmetry of the array.
However, we would like to emphasize that the enhancement in triangular arrays
can be significantly larger because of the inherent geometric incompatibility
of dipolar excitations and three-fold symmetry axes.
