  The hydrodynamic Drude model known from metal plasmonics also applies to
semiconductor structures of sizes in between single-particle quantum
confinement and bulk. But contrary to metals, for semiconductors two or more
types of plasma may have to be taken into account in order to properly describe
their plasmonic properties. In this combined analytical and computational
study, we explore predictions of the recently proposed two-fluid hydrodynamic
Drude model for the optical properties of plasmonic semiconductor nanowires, in
particular for thermally excited InSb nanowires. We focus on the low-frequency
acoustic surface and bulk plasmon resonances that are unique fingerprints for
this model and are yet to be observed. We identify these resonances in spectra
for single nanowires based on analytical calculations, and they are in complete
agreement with our numerical implementation of the model. For dimers of
nanowires we predict substantial increase of the extinction cross section and
field enhancement of the acoustic localized surface plasmon resonance, which
makes its observation in dimers more likely.
