[MOS] MOS October 11, 2005

[Zina Queen]

Seminar on
Modern Optics and Spectroscopy


Junichiro Kono, Rice University

Ultrafast and magneto-optical spectroscopy of carbon nanotubes

October 11, 2005
12:00 - 1:00 p.m.
Grier Room, MIT Bldg 34-401A


Abstract: This talk will describe our recent optical experiments on
single-walled carbon nanotubes (SWNTs) probing the states and dynamics of
1-D carriers and excitons [1-7].  We have carried out a series of
magneto-optical and ultrafast optical studies of micelle-suspended SWNTs in
aqueous solutions.  Through high-field magneto-optical experiments, we
investigated the influence of a tube-threading magnetic flux on the band
structure of semiconducting SWNTs for the first time [2,4].  The magnetic
flux breaks the time-reversal symmetry and thus lifts the degeneracy between
'right-handed' and 'left-handed' electrons, and the amount of state
splitting is determined by the Aharonov-Bohm phase.  We show that this
field-induced symmetry breaking overcomes the Coulomb-induced intervalley
mixing which is predicted to make the lowest exciton state optically
inactive (or "dark") [6].  Through ultrafast pump-probe experiments
[1,3,5,7], we have provided a wealth of new information on the dynamics of
carriers and excitons in semiconducting SWNTs.  Both intraband and interband
dynamics will be discussed in detail and various characteristic time scales
will be given.  In addition, the stability of 1-D excitons against a Mott
transition [5], a 1-D manifestation of the Burstein-Moss effect via pH
dependence [1,3], and the generation and detection of coherent phonons
(radial breathing modes) in the time domain [7] will be presented and
discussed.

	1. G. N. Ostojic et al., Phys. Rev. Lett. 92, 117402 (2004).
	2. S. Zaric et al., Science 304, 1129 (2004).
	3. J. Kono et al., Appl. Phys. A 78, 1093 (2004).
	4. S. Zaric et al., Nano Lett. 4, 2219 (2004).
	5. G. N. Ostojic et al., Phys. Rev. Lett. 94, 097401 (2005).
	6. S. Zaric et al., http://arxiv.org/abs/cond-mat/0509429.
	7. Y.-S. Lim et al., in preparation.
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