  Transient absorption in plasmonic materials has recently attracted attention
of the chemistry and optics communities as a technique to understand dynamic
processes and hot carriers generation on ultrafast timescales. In this context,
hybrid Au/CuS nanostructures were recently investigated via ultrafast
pump-probe transient absorption spectroscopy revealing an exotic dual-plasmonic
behavior. Namely, the excitation of a localized surface plasmon resonance
(LSPR) in Au (pump at 551 nm) or CuS (pump at 1051 nm), leads to a transient
response in the counterpart. This phenomenon was attributed to Landau damping,
which stems from hot carrier generation and injection mechanisms at the
interface between the two materials. Here, we employ numerical modeling to
further clarify the origin of such response in hybrid Au/CuS nanostructures.
The geometry of the hybrid nanostructures is first investigated via
steady-state simulations (only probe), confirming an UFO-shaped configuration.
We provide clarification on the role of the size ratio between Au and CuS.
Finally, we present the simulation of transient absorption in the pump-probe
regime, which qualitatively replicates our experimental observations, thus
identifying the plasmonic response modified via Landau damping as the main
governing mechanism. Our numerical approach provides an important tool for the
modeling of transient absorption spectroscopy and can support experimental
research on dual-plasmonic materials for applications in spectroscopy,
photocatalysis, thermoplasmonics, sensing, and energy harvesting.
