13aWF-7
単層カーボンナノチューブにおける
光誘起キャリア緩和ダイナミクスおよびその偏光特性
Relaxation and polarization dynamics of photo-induced carriers in individuallysuspended single-walled carbon nanotubes
Y. HashimotoA. B, A. SrivastavaB , J. KonoB, J. ShaverC, V.C. MooreC,
R.H. HaugeC, R.E. SmalleyC
Graduate School of Chiba Univ.A, ECE Dept., Rice Univ.B, Chemistry Dept., Rice Univ.C
Out line
•Introduction & Purpose
•Sample and Experimental setup
•Results and discussion
•Photo-induced carrier dynamics
•Polarization memory
•Summary
Supported by TATP and Welch Foundation
1
Single-Walled Carbon Nanotubes
photo-induced carrier lifetimes
< 1 ps Bundled SWNT
5 - 120 ps Isolated SWNT
~ ns Isolated SWNT
~ 20 ns Theoretical
Hertel and Moos, Phys. Rev. Lett. 84, 5002 (2000)
Chen et al., Appl. Phys. Lett. 81, 975 (2002)
Han et al., Appl. Phys. Lett. 82, 1458 (2003)
Lauret et al., Phys. Rev. Lett. 90, 057404 (2003)
Korovyanko et al. Phys. Rev. Lett. 92, 017403 (2004)
G. N. Ostojic et al., Phys. Rev. Lett. 92, 117402 (2004)
Y.-Z. Ma et al., J. Chem. Phys. 120, 3368 (2004)
A. Hagen et al., Appl. Phys. A 78, 1137 (2004)
F. Wang et al., Phys. Rev. Lett. 92, 177401 (2004)
L. Huang et al., Phys. Rev. Lett. 93, 017403 (2004)
This work
C. D. Spataru et al., cond-mat/0301220 v1 (2003)
2
Relaxation Dynamics of
Photo-excited Carriers in SWNTs
Radiative Non-radiative
1


1
 rad
~ ns
~ ps

1
 non rad
 non rad   rad
   nonrad
What kind of the Non-radiative relaxation is taking place ?
~1 mJ/cm2
PRL 92, 011742 (2004)
~640 e-h pairs
in
1 mm SWNT
rs  1.5nm  aB  2.5nm
PRL 92, 077402 (2004)
Exciton-exciton interaction ?
Purpose
Photo-induced carrier relaxation dynamics
in the low excitation limit
1 e-h pair per 1 mm SWNT
3
Single-Walled Carbon Nanotube Samples
Absorption spectrum
-1
Absorption [cm ]
SDS miscelled SWNT
SWNT
2.2
2.0
1.8
1.6
1.4
1.2
1.2
1.4
1.6
Photon energy [eV]
1.8
Absorption shows sharp peaks
SDS micelle
Science VOL 297 593 (2002)
SWNT is well isolated
4
Experimental Setup
-1
Absorption [cm ]
Pulse picker
80 MHz  800kHz
Laser wavelength: 1.550 eV (E2H2)
Ti:S laser
80MHz
2.4
2.0
1.6
1.2
1.4 1.5 1.6 1.7 1.8
Photon Energy [eV]
Si detector
Delay stage (2 ns)
l/2
Excitation fluence: 100 nJ/cm2
Pump : Probe = 10 : 1
SWNT
Aperture
Lock in
5
Checking the Experimental Setup
GaAs
T/T
Polarization of the
pump and probe pulse
-2
-1
0
1
Time delay [ps]
No difference
2
3
6
Photo-Induced Carrier Dynamics in SWNT
in Low Excitation Limit
Room temperature
4
10
2
-3
Repetition rate: 8 MHz
T/T
4
10
Polarization of the
pump and probe:
2
-4
4
10
2
-5
0
500
Time delay [ps]
1000
Previous reports
in high excitation
 < 120 ps
Pump-probe signal exists even at 1 nano-second !!!
7
Decay Dynamics
1.0x10
-3
1:  < 1 ps
T/T
0.8
0.6
2:  ~ 1 ns
0.4
0.2
0.0
0
500
Time delay [ps]
1000
8
Decay Dynamics
E2H2  E1H1 intraband transition
E
5x10
-3
4
T/T
3
2
1
< 1 ps
E2
0
-1
E1
~ ns
DOS
E1H1 carrier recombination
H1
1.0x10
-3
0.8
T/T
H2
0
1
Time delay [ps]
0.6
0.4
0.2
0.0
0
500
1000
Time delay [ps]
9
10
10
10
10
1.0
Parallel
Perpendiculer
-3
Tll  T
P
Tll  T
0.8
-4
0.6
P
T/T
Polarization Memory
0.4
-5
0.2
-6
0.0
0
500
Time delay [ps]
1000
0
500
Time delay [ps]
1000
Polarization memory exists even at 1 ns !!!
In bundled SWNT, the polarization decay time ~ 10 ps
O. J. Korovyanko et al., Phys. Rev. Lett. 92 017403 (2004)
10
Polarization Memory
Pump
Absorption is reduced
Pump
No change
n  I pump cos2q
 /2
q
Tll  I pump 
cos4 qdq
 / 2
 /2
T  I pump 
cos2 q sin 2 qdq
 / 2
Pump pulse polarization
Tll  T
P
 0.5  0.45
Tll  T
11
Summary
T/T
10
10
10
10
-3
-4
-5
-6
0
400
Time delay [ps]
800
•The transient absorption of the
isolated SWNTs in low excitation
regime shows very fast (< 1 ps)
E2H2  E1H1 intraband transition
and very long (~ 1ns) E1H1 carrier
recombination
1.0
0.6
P
•The polarization memory in
isolated SWNTs shows no
decay even at 1 ns.
0.8
0.4
0.2
0.0
0
200 400 600 800
Time delay [ps]
1000
Future work
Two color pump-probe in the isolated SWNT
in the low excitation limit
12

Nanotube Structure

Iron-based superconductors

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