Not yet reviewed by Pith; the record is open.

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.