One-dimensional all-metal nanowires with strong excitonic effect

Excitons form in semiconductors and govern light-matter interaction, while for metals, the Coulomb interaction is strongly screened and the dominant excitations are plasmons. Here we assemble all-metal nanowires using icosahedral $M@{X}_{12}$ ($M$ = group VB and VIB elements; $X$ = Au, Ag, Cu) superatomic clusters, which are accessible in the laboratory. They exhibit strong excitonic effects featuring large binding energies and high energy-momentum dispersions of excitons, along with strong optical responses in the mid- and far-infrared regions. Moreover, the nanowires assembled by $\mathrm{Nb}@\mathrm{A}{\mathrm{u}}_{12}$ and $\mathrm{Ta}@\mathrm{A}{\mathrm{u}}_{12}$ clusters have quasiparticle gaps below 1 eV, exhibiting excitonic instability to the formation of an excitonic insulator. These one-dimensional superatomic crystals present a paradigm for exploring new exciton physics toward practical device implementations.