  Noble metal nanoparticles exhibit localized plasmon resonance modes that span
the visible and near-infrared spectral ranges and have many applications.
Modifying the size, shape, and composition of the nanoparticles changes the
number of modes and their properties. The characteristics of these modes are
transiently affected when illuminating the nano-objects with ultrashort laser
pulses. Here, we synthesize core-shell gold-silver nanocuboids and measure
their spectral signature in the stationary and ultrafast transient regimes.
Their dipolar transverse mode vanishes with increasing Ag-shell thickness,
while higher-order modes grow in the near-ultraviolet range where no plasmon
resonance can be generated with single noble metal nanoparticles. These
higher-energy modes are associated with sharp spectral variations of the
ultrafast transient light extinction by the bimetallic nanocuboids. By carrying
out a theoretical investigation, we break down the different contributions to
this response and
