Large radius excitons in single-walled carbon nanotubes

The spectrum of large-radius excitons in an individual semiconducting single-walled carbon nanotube (SWCNT) is described within the framework of an elementary potential model, in which an exciton is modelled as a bound state of two oppositely charged quasi-particles confined on the tube surface. Due to the parity of the interaction potential the exciton states split into the odd and even series. It is shown that for the bare and screened Coulomb electron-hole (e-h) potentials the binding energy of even excitons in the ground state well exceeds the energy gap. The factors preventing the collapse of single-electron states in isolated semiconducting SWCNTs are discussed.