Proposed strategy to sort semiconducting nanotubes by radius and   chirality
  We propose a strategy that uses a tunable laser and an alternating non-linear potential to sort a suspension of assorted semiconducting nanotubes. Since, a polarized exciton is a dipole, the excited nanotubes will experience a net force and may then diffuse towards an electrode. The calculated exciton binding energy suddenly drops to zero and the force on the nanotube increases dramatically when the exciton disassociates as the nanotube moves towards the electrode. The quantum adiabatic theorem shows that excitons will be polarized for potential frequencies typical for experiments $\approx 10$ MHz. 
V Narayan