Tunable band gaps and excitons in doped semiconducting carbon nanotubes made possible by acoustic plasmons

Doping of semiconductors is essential in modern electronic and photonic devices. While doping is well understood in bulk semiconductors, the advent of carbon nanotubes and nanowires for nanoelectronic and nanophotonic applications raises some key questions about the role and impact of doping at low dimensionality. Here we show that for semiconducting carbon nanotubes, band gaps and exciton binding energies can be dramatically reduced upon experimentally relevant doping, and can be tuned gradually over a broad range of energies in contrast with higher dimensional systems. The latter feature is made possible by a novel mechanism involving strong dynamical screening effects mediated by acoustic plasmons.