Time-dependent density functional theory (TDDFT) simulations are
conducted on a series of chiral gold nanowires to explore whether an enhancement of
circular dichroism at the plasmon resonance is possible and identify its quantummechanical
origin. We find that in linear two-dimensional chiral nanowires the
dichroic response is suppressed by destructive interference of nearly degenerate
components with opposite signs, pointing to this phenomenon as a common and
likely origin of the difficulty encountered so far in achieving a plasmonic CD response
in experiment and suggesting nevertheless that these opposite components could be
“decoupled” by using multiwall arrangements. In contrast, we predict a giant dichroic
response for nanowires with three-dimensional helical coiling. We rationalize this
finding via an electronic structure analysis of longitudinal and transversal plasmonic
excitations and their coupling into chiral components, and we propose a simple
formula for the chiral response as a function of structural parameters (nanowire
length and coiling number).
