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<div><font face="Arial" size="+4" color="#000000">Seminar
on</font></div>
<div><font face="Arial" size="+5" color="#000000"><b>Modern Optics and
Spectroscopy<br>
<br>
<br>
Junichiro Kono</b>, Rice University<br>
<br>
<i><b>Ultrafast and magneto-optical spectroscopy of carbon
nanotubes<br>
<br>
</b></i>October 11, 2005</font></div>
<div><font face="Arial" size="+5" color="#000000">12:00 - 1:00
p.m.</font><br>
<font face="Arial" size="+5" color="#000000"></font></div>
<div><br>
Abstract: This talk will describe our recent optical experiments
on<br>
single-walled carbon nanotubes (SWNTs) probing the states and dynamics
of<br>
1-D carriers and excitons [1-7]. We have carried out a series
of<br>
magneto-optical and ultrafast optical studies of micelle-suspended
SWNTs in<br>
aqueous solutions. Through high-field magneto-optical
experiments, we<br>
investigated the influence of a tube-threading magnetic flux on the
band<br>
structure of semiconducting SWNTs for the first time [2,4]. The
magnetic<br>
flux breaks the time-reversal symmetry and thus lifts the degeneracy
between<br>
'right-handed' and 'left-handed' electrons, and the amount of
state<br>
splitting is determined by the Aharonov-Bohm phase. We show that
this<br>
field-induced symmetry breaking overcomes the Coulomb-induced
intervalley<br>
mixing which is predicted to make the lowest exciton state
optically<br>
inactive (or "dark") [6]. Through ultrafast pump-probe
experiments<br>
[1,3,5,7], we have provided a wealth of new information on the
dynamics of<br>
carriers and excitons in semiconducting SWNTs. Both intraband
and interband<br>
dynamics will be discussed in detail and various characteristic time
scales<br>
will be given. In addition, the stability of 1-D excitons
against a Mott<br>
transition [5], a 1-D manifestation of the Burstein-Moss effect via
pH<br>
dependence [1,3], and the generation and detection of coherent
phonons<br>
(radial breathing modes) in the time domain [7] will be presented
and<br>
discussed.<br>
<br>
<x-tab> </x-tab>1. G. N. Ostojic
et al., Phys. Rev. Lett. 92, 117402 (2004).<br>
<x-tab> </x-tab>2. S. Zaric et al., Science 304,
1129 (2004).<br>
<x-tab> </x-tab>3. J. Kono et al., Appl. Phys. A 78, 1093
(2004).<br>
<x-tab> </x-tab>4. S. Zaric et
al., Nano Lett. 4, 2219 (2004).<br>
<x-tab> </x-tab>5. G. N. Ostojic et al., Phys. Rev. Lett. 94,
097401 (2005).<br>
<x-tab> </x-tab>6. S. Zaric et al.,
http://arxiv.org/abs/cond-mat/0509429.</div>
<div><x-tab> </x-tab>7.
Y.-S. Lim et al., in preparation.</div>
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