Bongsu Kim (Potma Group) - CaSTL Seminar

Abstract:

The Optical stark effect (OSE) is a coherent light-material interaction which allows tunning of an energy gap in semiconductors. In particular, low-dimensional semiconductors form stable excitons and thus the OSE is  shown clearly. However, in the case of one-dimensional semiconductors, quantitative analysis and experiments are still lacking due to the difficulty of manipulation, despite the large applicability to nano-devices. Here we show the OSE on semiconducting single-walled carbon nanotubes observed by a transient absorption spectrum and their quantitative analysis. The many-body quantum mechanics assisted quasi-one-dimensional cylinder model was employed for comparing with the OSE measurements. The observed blue shift by the OSE was maintained until tens of picoseconds after the pump laser had disappeared. This phenomenon results from the exciton-exciton interaction which is explained by the many-body quantum mechanics model. We performed nanoscale ultrafast dynamic measurements on the carbon nanotubes using ultrafast pump-probe photo-induced force microscopy (PiFM). The PiFM results demonstrated the ensemble average results measured by a transient absorption spectrum were not significantly different from the locally analyzed carbon nanotubes.