Excitons and many-electron effects in the optical response of carbon nanotubes and other one-dimensional nanostructures

Abstract

Owing to their reduced dimensionality, the behavior of quasi-one-dimensional systems is often strongly influenced by electron-electron interactions. We discuss some recent work on using theory and computation to understand and predict the electronic structure and the linear optical response of several one-dimensional (1D) nanostructures. The calculations are carried out employing a first-principles interacting-electron Green's function approach. It is shown that exciton states in the semiconducting carbon nanotubes have binding energies that are orders of magnitude larger than bulk semiconductors and hence they dominate the optical spectrum at all temperature, and that strongly bound excitons can exist even in <i>metallic</i> carbon nanotubes. In addition to the optically active (bright) exciton states, theory predicts a number of optically inactive or very weak oscillator strength (dark) exciton states. These findings demonstrate the importance of an exciton picture in interpreting optical experiments and in the possible applications of the carbon nanotubes. Our studies show that many-electron interaction (self-energy and excitonic) effects are equally dominant in the electronic structure and optical response of other potentially useful quasi-1D nanostructures such as the BN nanotubes, Si nanowires, and graphene nanoribbons.