Argonne National Laboratory

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Coherent Light-Matter Coupling and Nonequilibrium Carrier Dynamics in Single-Chirality Carbon Nanotubes

XSD/TRR Special Presentation
Kankan Cong, Rice University
February 14, 2018 11:00AM to 12:00PM
Building 431

Abstract: Single-wall carbon nanotubes (SWCNTs) are unique one-dimensional condensed matter systems in which strongly enhanced Coulomb interactions are combined with unusual band structure. There are metallic and semiconducting SWCNTs, in both of which electron-electron interactions have significant impact on their electronic and optical properties.

In this talk, I will demonstrate how ultrafast optical pump-probe spectroscopy can be used to investigate nonequilibrium dynamics of photogenerated electron-hole pairs, or excitons, in a sample in which a particular species, or chirality, of semiconducting SWCNTs was enriched. Depending on the pump photon energy, intensity, and polarization, different physical processes ensue after ultrafast pumping, including coherent light-matter interactions and incoherent relaxation of carriers/excitons.

For example, under below-gap pumping, a transient blueshift of the exciton peak occurred, only during the pump pulse duration, a hallmark of the optical Stark effect. Under resonant pumping, transient splitting of the exciton peak was observed within the pulse duration, which is a manifestation of the Rabi doublet due to coherent light-matter interaction in the strong coupling regime. In the case of above-gap excitation, incoherent relaxation processes dominated the dynamics of excitons. Analysis of these ultrafast, nonequilibrium, and strongly driven phenomena provided considerable new insight into the states and dynamics of electrons in the presence of extreme quantum confinement and strong many-body interactions.