Optical Spectroscopy of Carbon Nanotubes: Chiral-Index Assignment and Excitonic Effects
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Date: 11-10-2005
Start Time:
11:00am
End Time: 12:00pm
Speaker: Dr. Janina Maultzsch
From:
Technical University of Berlin, Germany
Location: 414 Schapiro/CEPSR
Hosted by:
Center for Integrated Science
Abstract:
Carbon nanotubes are cylinders from graphene with fascinating physical
properties. Many of them depend critically on the arrangement of carbon
atoms on the cylinder surface, as defined by the chiral index (n,m). In
this talk, I will first show how to determine (n,m) by resonant Raman
scattering. Simultaneous measurement of optical transition energies and
vibrational frequencies directly reveals the chiral index, without
using any empirical parameters. The assignment allows to analyze and
understand the properties of carbon nanotubes, such as electron-phonon
coupling, as a function of their chiral index. The measured transition
energies deviate from any calculations performed within a
single-particle picture. As I will discuss in the second part of my
talk, this is caused by strong Coulomb interaction between excited
electron and hole. The excitonic nature of the optical excitations in
carbon nanotubes is demonstrated by two-photon absorption spectroscopy,
indicating binding energies on the order of 400 meV.