Strain tuning of the photocurrent spectrum in single-wall carbon nanotubes.

The effect of uniaxial strain on the photocurrent spectrum of semiconducting single-wall carbon nanotubes is measured. The energy of the lowest-lying free electron transition is observed to shift with strain as predicted by a simple noninteracting model. The higher-order transitions also shift with strain, but being excitonic, their strain dependence differs from the predictions for the free carrier states. An anomalous photocurrent increase is also observed near the ground-state transition and is attributed to the formation of optically active defect states within the nanotube band gap.