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グラフェンエッジの物理とスピン素子応用
春山純志
青山学院大学大学院理工学研究科機能物質創成コース
-ナノリボンとアンチドット格子-
スコッチテープ方式の開発
マンチェスター大学 Geim,Novoselov
Graphene World
2004年
絶句 激怒
頑張ろう
2010 ノーベル物理学賞
イグノーベル賞2000 分子・バイオ磁性体の浮遊
With Michael Berry
frog.mpg
「グラフェン物性の新展開」 座長:押山・青木先生
(1) 安藤 恒也 (東工大院理工物性) はじめに(2) 榎 敏明 (東工大院理工化学)
ナノグラフェンとそのエッジの幾何学構造に依存した電子状態・磁性(3) 春山 純志 (青学大理工)
グラフェンナノリボンとナノ細孔グラフェン:エッジと電子物性(4) 福山 寛 (東大院理)
走査トンネル分光法で探るグラフェンとグラファイト表面の電子状態(5) 若林 克法 (物材機構MANA)
グラフェンナノリボン・エッジ電子物性の理論
(6) 樽茶 清悟 (東大工) 3層グラフェンの電気伝導とバンド構造
(7) 長田 俊人 (東大物性研) グラフェン接合系における量子ホール端伝導
(8) 越野 幹人 (東北大理) グラフェンの量子物性-ディラック点における特異な物理
来春物理学会シンポジウム 領域7 @新潟
3月27日午後
グラフェンの電子状態
グラフェンシート
sp2混成軌道 σバンド
グラフェンバンド構造
ディラック点
VG
半金属 Gap less半導体
ディラックコーン
リニア
空π
占有π
pz πバンド
巨大平均自由行程、高移動度、強スピン位相コヒーレンス
le > ~ 10μm Lφ > ∼50μm
電子:Mass less Dirac Fermion
Kkk’ 結合反結合
二個のスピノル
K点での線形エネルギー分散
相対論的ディラック方程式で質量0としたニュートリノの方程式で記述
ベリー位相CNTs後方散乱 前方散乱
μ>200,000 cm2V-1s-1
時間反転対称性同位相 アンダーソン局在
逆位相 反局在位相差 π
ベリー位相による後方散乱の消滅東工大・安藤
炭素:スピン・軌道相互作用は無いスピン反転
散乱源
干渉
入口
出口
UCF, AB(AAS)効果
Ns = ∼1012 cm-2
Grapheneの特異な量子物性異常整数量子ホール効果
Rxy-1=±4(N+1/2)e2/h
Y. Zhang, H. Stormer, P. Kim, Narture 438, 201 (2005)
室温量子ホール効果
K. S. Novoselov, P. Kim, et al., Science 315, 1379 (2007)
Suspended Graphene
分数量子ホール効果
Ns <∼3.5 ×1011 cm-2
μ∼100,000 cm2V-1s-1
K. Bolotin, H.L. Stormer, P. Kim, Narture 462, 196 (2005)
LG=150nm
超高電子移動度
IBM
fT=100GHz(LG=260um)
Samsung
Touch Panel for i-Pod
Contents
1.背景
2.カーボンナノチューブの酸化開口+熱処理で形成した低欠陥グラフェンナノリボン
欠陥ナノリボンの約7倍のエネルギーバンドギャップ
3.多孔質アルミナ膜マスクで形成した低欠陥アンチドット(ナノ細孔)格子グラフェン
細孔エッジに起因した室温強磁性の発現異常磁気抵抗振動
Non-lithographic
4.今後 素子応用 電場によるエッジ偏極スピンの制御
PRL
温故知新
Nature Nanotech & Latest Highlights, News & Views
Nature Nanotech In-depth Review
Arm Chair
zigzag
zigzag
Edge atomic structures of Graphene (Graphite)
Arm chair
Graphene nanoribbon
Flat band
Arm chair Zigzag
Tight-binding
Band gap
K.Nakata et al., Phys. Rev. B 54, 17954 (1996)
Strong Electron localizationHigh EDOSSpin polarization
Edge states of Graphene (Graphite)
Spin polarization and ferromagnetism at zigzag edges with hydrogen termination
Kusakabe and Maruyama, Phys. Rev. B 67, 092406 (2003)
Up spin Down spin
Hydrogen
local-spin-density approximation
Why graphene edges are important and interesting??
1. Band gap engineering
3. All carbon magnetism (magnets)
4. Spin Current & (Quantum) Spin Hall Effect
2. Electron correlation with localized edge electrons
So many theoretical reports, but no experimental reports
Large damages by lithographic methods
Non-lithographic methods
Contents
1.背景
Non-lithographic 温故知新
2.カーボンナノチューブの酸化開口+熱処理で形成した低欠陥グラフェンナノリボン
欠陥ナノリボンの約7倍のエネルギーバンドギャップ
Nature Nanotech & Latest Highlights, News & Views
Arm Chair
Advance online publication 19th Dec.NanoelectronicsArticle by Shimizu et al.Graphene nanoribbons manufactured by annealing unzipped carbon nanotubes have been measured to have a large energy bandgap.
Latest highlights
Nature Nanotechnology | News and ViewsNanoelectronics: Graphene gets a better gapStephan RocheJournal name: Nature Nanotechnology Volume: 6, Pages: 8–9 Year published: (2011)
DOI:doi:10.1038/nnano.2011.262 Published online 23 December 2010
Nature Nanotechnology 6, 45-50 (2011)
Introduction of energy band gaps
Absence of energy band gaps
Destruction of symmetry in bilayer graphenesVoltages, Carrier doping, Substrate
Carrier confinement into 1D space GNRs
Semi metal, Zero- gap semiconductor
Han, Kim et al., Phys. Rev. Lett., 104, 056801 (2010)
Disordered Graphene Nano-ribbon(Lithographic)
Hopping conductance
Stochastic Coulomb diamond
Large difference between Δ & EaLarge transport gaps Δ
Ec=e2/2C
J.Tour et al., Nature 458, 872 (2009)
Rice University, Smalley Institute for Nanoscale Science and Technology
①Formation of GNRs on substrate by air blow②3stepped annealing(high vacuum, H2)
Our originality
Low-defect GNR formed by unzipping of MWCNTs
1μm
200nm
As-depo
Our originality①Formation of GNRs on substrate by air blow
②by air blowing to droplet①by brushing
AFM
Brush Air blowIsolated 47 58Rectangle 14 26Monolayer 5 15
Formation of GNRs on Si-substrate by air blow
Number of GNRs within 5mm2-substrate
②3-stepped annealing during FET formation process
Our originality for deoxidization and carrier doping
Right after formation of GNRs on substrate High vacuum・ 800 °C
Right before formation of EB mark H2 atmosphere・800 °C
Right before formation of FET electrode High vacuum ・300 °C
For deoxidization & Recovery of defects
For carrier doping
For cleaning
for long time
HRTEM
Raman
AFM
As-grown nanoribbon
FET
Quality of GNRs: low defects
Before annealing
After annealing
AISTSuenaga
Nature Nanotech. 6, 45-50 (2011)
Electronic transport for 4 different-type GNRs
W Width (nm)N Layer number
Nature Nanotech. 6, 45-50 (2011)
Correlation of ambipolar feature with annealing time at high vacuum
Deoxidization:p-type Ambipolar
t = 0
t = 24h
Electronic transport:Zero-bias anomaly & Transport gap
ΔVBG = 1V
Small transport gap
Low defects
W=75nmN=1
Nature Nanotech. 6, 45-50 (2011)
Single-electron Spectroscopy
No stochastic diamonds
Disordered GNRsLow-defects GNRCoulomb diamonds
Stochastic diamonds due to defects (Q-dots connected in
series)Low defects
W=75nmN=1
Nature Nanotech. 6, 45-50 (2011)
Energy band gap in thermal-activation relationships
7-times larger EaNo hopping conductance
Transport gap close to Ea values
55meV
Nature Nanotech. 6, 45-50 (2011)
Louie et al., UC BerkeleyTheory for energy band gaps of GNRs with arm chair edge
GWA
LDA
3 eV for W=1nm
Ea∼30 meVfor W∼100nm
Q1: The large band gaps are relevant for large-width GNRs?
le ∼300nm
W < 300nm
Remaining 1D
Mean free path ∼300nm
GNR Width < 300nm
One dimensionality
GNR length (nm)
Res
istiv
ity (h
/4e2
)
100 300200 400 500
1
2
3
4
00
Measurement of mean free path
W ∼100nm
Remained 1D in large width GNRs
Ballistic transport regime
Dai Stanford
Contents1.背景
2.カーボンナノチューブの酸化開口+熱処理で形成した低欠陥グラフェンナノリボン
欠陥ナノリボンの約7倍のエネルギーバンドギャップ
Non-lithographic 温故知新
Arm Chair
3.多孔質アルミナ膜マスクで形成した低欠陥アンチドット(ナノ細孔)格子グラフェン
細孔エッジに起因した室温強磁性の発現 (単層)
Nature Nanotech In-depth Review zigzag
Flat bandZigzag
Tight-binding
K.Nakata et al., Phys. Rev. B 54, 17954 (1996)
Strong Electron localizationHigh EDOS
Electron localization and spin polarization in zigzag-edge Graphene Y.Son, S.G.Louie et al.,
Spin polarization and magnetism in zigzag-edge nanoribbon
On one edge On both edges
Hunt’s rule
H. Lee et al.,. Phys. Rev. B 72, 174431 (2005)
first-principles density-functional calculations
Ferro Anti-Ferro
Maximizing exchange energy gain
Spin interaction
Spin polarization and ferromagnetism at zigzag edges with hydrogen termination
Kusakabe and Maruyama, Phys. Rev. B 67, 092406 (2003)
Up spin Down spin
Hydrogen
Local-spin-density approximation
Mono-H
Di-H
Under magnetic field
EF
Zigzag edges
Group-theoretical consideration
Why graphene edges are important and interesting??
1. Band gap engineering
3. All carbon magnetism (magnets)
4. Control of edge spin by electric field : (Quantum) Spin Hall Effect
2. Electron correlation with localized edge electrons
So many theoretical reports, but few experimental reports
Large damages by lithographic methods
Non-lithographic methods
Example of defect-spin related Ferromagnetism
Cervenka et al., Nature Physics 5, 840 (2009)
ZIGZAG?Arm chair Uncontrollable and
unclear
T. Enoki et al., Sol. Stat. Comm. 149, 1144 (2009)
Zigzag-edge related Ferromagnetism in Activated carbon Fibers
Mechanically exfoliated Graphene
Hexagonal nano pores
Zigzag edge
Formation of low-defect graphene nano-pore arrays by porous alumina templates
GNR
Careful Ar etchingHigh vacuum and Hydrogen annealing at 800℃
SEM images of Porous alumina templates
φ ∼ 50nmPore spacing ∼ 40nm
φ ∼ 80nmPore spacing ∼ 20nm
φ ∼ 15nmPore spacing ∼ 20nm
Advantage of porous alumina template for formation of low-defect GNPAs
zigzag
Non-lithographicHexagonal-shaped nano-pores
①Low defect GNPAs
②Alignment of edge structures of all boundaries to hexagonal carbon lattice of graphene ∼50%Six boundaries/one AD
③Large ensemble of GNRs
GNRs
a b c
AFM STMSEM
Images of graphene nano-pore arrays
After annealing
High EDOS at pore edges
Possible zigzag edge
Tokyo Univ.Matsui and Fukuyama
Raman spectroscopy on annealingBefore After
②Reduced defects
①Alignment of edge chirality to
hexagonal carbon lattice of graphene
Sample Number1 2 3 4 5 6 7 8
I(D)/I
(G)
0.5
0.25
0.75
Ferro No Ferro
Before
After
∼50%Zigzag Arm
chair?
Kraus, V.Klitzing et al., Nano Lett. 10, 4544 (2010)
Raman spectroscopy of aligned hexagonal pores on graphene Round
Round Hexagonal
Hexagonal
D peak maps
②Reduced defects
①Alignment of edge chirality to
hexagonal carbon lattice of graphene
1000-1000 -500 5000-1000 -500 0 500 1000-6.0e-5
-4.0e-5
-2.0e-5
0.0
2.0e-5
4.0e-5
6.0e-5
0.4
0.2
-0.4
0
-0.2
1000-500 5000-1000
0
-400
-800
400
800
1000-1000 -500 5000
Mag
netic
mom
ent
(×μ B
/edg
e on
e π-
orbi
tal)
a b c
T = 2K T = 2KT = 2K
0
30
20
-10
-20
10
-301000500-1000 -500 0
T = 300K
10000-500 500-1000
Magnetic Field (gauss)
T = 300K0.2
0
0.1
-0.1
-0.2
-500-1000 10005000
T = 300KHydrogen
Hydrogen Oxygen
Oxygen
No antidots
No antidots
d e f
0.3
-0.3
Magnetization (μem
u/100μm2)M
agne
tic m
omen
t (a.
u.)
Hydrogen OxygenNo nano-pores
Magnetization measurement
5/11 samples
Reconfirmation of no contribution of parasitic factors
Si
Bulk Graphene
Si
Porous alumina template
No Ferromagnetism
Magnetic Field (gauss)
0.2
-0.2
0
1000-1000 500-500 0
Hydrogen
Mag
netic
mom
ent
(×μ B
/edg
e on
e π
orbi
tal)
Hydrogen
W=∼40nmW=∼10nm
10005000-500-1000
T = 300KT = 300K
Pore spacing (W:GNR-width) and Ferromagnetism
0.34
W=20nm
0.2Farromagnetismderived from nano-pore edges
GNR
zigzag edges
Nano-pores
W
Spin polarization and magnetism of zigzag-edge nanoribbon
On one edge On both edgesHunt’s rule
H. Lee et al.,. Phys. Rev. B 72, 174431 (2005)
first-principles density-functional calculations
Ferro Anti-Ferro
Mono-Hydrogenation
Hydrogen atom
Localized π orbital
Localized π orbital
1.42Å2.46Å
No Hydrogenation
Localized π orbital
Localized π orbital
Dangling bond
Edge spin configuration
Beforehydrogen annealing
After hydrogen annealing
①Total area of bulk-graphenes used for formation of nano-pore array: ∼4 cm2
②Area of one hexagonal unit cell: S = 6(3-1/2/2)(a/2)2 = ∼4300 nm2; a = [80 nm(pore diameter) + 20nm (pore spacing)]
③Total number of nano-pores: ①/② = 4 cm2 /4300 nm2 = ∼1011
④Total number of dangling bond per one hexagonal pore:40 nm/(0.142 nm×31/2)×6 = 166×6 = ∼1000
⑤Total number of edge dangling bonds of the nano-pore graphene used for SQUID: ③×④=1014
⑥Saturation magnetization value per one edge dangling bond: 1.2×10-6 (emu)×10-3/(⑤=1014) = 1.2×10-23 (J/T)
⑦Magnetic moment per one edge dangling bond:(⑥=1.2×10-23)/(μB=9.3×10-24)= ∼1.3μB
Estimation of edge-carbon magnetic moment
Correlation of Flat band and Spin polarization with Hydrogen termination
H. Lee et al.,. Phys. Rev. B 72, 174431 (2005)
FerroMajority Spin Minority Spin
Up Spin Down Spin
Antiferro
Mono-H Di-H Di+Mono
Mono-Hydrogenation
Hydrogen atom
Localized π orbital
Localized π orbital
Possible mono-H termination of edge dangling bonds
After hydrogen annealing
GNR
zigzag edges
Nano-pores
Number of H atoms should be equal on both edges of a GNR (neighboring two nano-pore edges)
Di-H termination results in sp3 and σ orbital
Suppression of ferromagnetism
Mono-H
①Total area of bulk-graphenes used for formation of nano-pore array: ∼4 cm2
②Area of one hexagonal unit cell: S = 6(3-1/2/2)(a/2)2 = ∼4300 nm2; a = [80 nm(pore diameter) + 20nm (pore spacing)]
③Total number of nano-pores: ①/② = 4 cm2 /4300 nm2 = ∼1011
④Total number of dangling bond per one hexagonal pore:40 nm/(0.142 nm×31/2)×6 = 166×6 = ∼1000
⑤Total number of edge dangling bonds of the nano-pore graphene used for SQUID: ③×④=1014
⑥Saturation magnetization value per one edge dangling bond: 1.2×10-6 (emu)×10-3/(⑤=1014) = 1.2×10-23 (J/T)
⑦Magnetic moment per one edge dangling bond:(⑥=1.2×10-23)/(μB=9.3×10-24)= ∼1.3μB
⑧Magnetic moment per one edge π-orbital after mono-hydrogenation of dangling bond: (⑦=1.3μB)/3 = ∼0.43μB
Estimation of edge-carbon magnetic moment
Elimination of Magnetic moment at zigzag edges with Oxygen termination
R.G.A. Veiga, et al., J. Chem. Phys. 128, 201101 (2008)
No oxygenOxygen
Edge
Spin paired C-O
Suppression of Ferromagnetism in Graphitenano-pore arrays with Hydrogen-terminated
edges
HydrogenT = 2K
Mag
netiz
atio
n (μ
emu/
100μ
m2 ) 4
-2
0
2
-4
HydrogenT = 300K
-1
-0.5
0
0.5
1
Magnetic Field (gauss)10005000500-1000 5000-500
Elimination of Magnetic moment by Interlayer coupling in Zigzag-edge graphite with Hydrogen termination
No termination
Lee, H. et al. Chem.Phys.Lett. 398 207 (2004)
Contents1.背景
2.カーボンナノチューブの酸化開口+熱処理で形成した低欠陥グラフェンナノリボン
欠陥ナノリボンの約7倍のエネルギーバンドギャップ
3.多孔質アルミナ膜マスクで形成した低欠陥アンチドット(ナノ細孔)格子グラフェン
細孔エッジに起因した室温強磁性の発現
Non-lithographic
異常磁気抵抗振動 (約10層)
PRL
温故知新
Nature Nanotech & Latest Highlights, News & Views
Arm Chair
zigzag
Antidot Lattice on Semiconductor 2DEG (∼1990)
M. Kato,S. Katsumoto, Y. Iye, PRB 77, 155318 (2008).
D. Weiss, K. von Klitzing et al., PRL 70, 4118 (1993)
Rc = (πnS)1/2 (h/2π)/eB∆BABT = (h/e)/S
Commensurability peak
Aharonov-Bohm-type Oscillation
Antidots
-
Antidot
Cyclotron orbit
High B
Low B
Under enough antidot spacing
Anomalous FQHEsφ∼200nm/Ls∼600nm = ∼1/3
Anomalous filling factor
Antidots
No antidots
Composite Fermion
Kang, Stormer, PRL71, 3850 (1993)
In Graphenes: How edge-localized electrons are interacted with cyclotron-moton electrons?
Antidot Lattice as a scattering center for electrons on 2DEG
Antidot Lattice Graphene
T. Shen et al., APL 93, 122102 (2008).
S.Russo et al., PRB 77, 085413 (2008).
J. Bai et al., Nature Nanotech. 5, 190 (2010).
Only a few publications No reports for edges
FESEM images of ADLGs
100
0
-100
50
-50
1000-1000 -500 5000-1000 -500 0 500 1000-6.0e-5
-4.0e-5
-2.0e-5
0.0
2.0e-5
4.0e-5
6.0e-560
20
40
-60
0
-40
-20
1000-500 5000-1000
0
-400
-800
400
800
1000-1000 -500 5000Mag
netiz
atio
n (e
mu/
100μ
m2 )
Magnetic field (gauss)
(a) (b) (c)
T = 2K T = 2KT = 2K
Hydrogen Oxygen No antidots
All-carbon Ferromagnetism in ADLG with Hydrogen-terminated edges
Mono-layer graphene
Evidence for zigzag at antidot edgeCorrelation of localized electrons
with MR oscillations??
Aharonov-Bohm-type Oscillations in H2-terminated ADLGs
Commensurability peak φ= ∼80 nmAD Space ∼80 nm
2Rc = (πnS)1/2 (h/2π)/eB= a
nS ∼ 4 × 1011 cm-2
le = 2D/vF ∼ 800 nm > 2π(a/2) = ∼ 540 nm
ΔB = ∼ 200 mT
∆BABT = (h/e)/(S)
Sample B
Fourier Spectrum
AB-type oscillation
Low B
High B
Low B ΔB∼200 mT
Electron trajectories on honey-comb ADL and magnetoresistance oscillations
∆BABT=(h/e)/S S = 6(3-1/2/2)(a/2)2
Quantized electron orbitals around antidotsin an unit cell
a = ∼160 nm
En = h2/2mL2(n - Φ/φ0)
AB-type oscillation
2Rc = (πnS)1/2 (h/2π)/eB= a
nS ∼ 4 × 1011 cm-2
le = 2D/vF ∼ 800 nm > 2π(a/2) = ∼ 540 nm
En = h2/2mL2(n - Φ/φ0)
Aharonov-Bohm-type effect
∆BABT=(h/e)/S
Anomalous MR Oscillations in ADL- multi-layered Graphenes
Commensurability peak φ= ∼80 nm
Sample B
Fourier Spectrum
2Rc = (πnS)1/2 (h/2π)/eB= a
nS ∼ 4 × 1011 cm-2
le = 2D/vF ∼ 800 nm > 2π(a/2) = ∼ 540 nm
ΔB∼260 mT High B
High B
S: r for pore radius
ΔB∼260 mT
Electron trajectories on honey-comb ADL and magnetoresistance oscillations
∆B=(h/e)/(πr2) with r = ∼ 40 nm
Antidot radius
Absent AB effect
Bohr–Sommerfeld quantization condition Φ=Bπr2=m(h/e) m: integer
Like flux quanta in superconductor
Edge-Localized electrons
Quantization of magnetic flux
-
∆BAB = (h/e)/(πr2)
Aharonov-Bohm effect
2Rc = (πnS)1/2 (h/2π)/eB= a
nS ∼ 4 × 1011 cm-2
le = 2D/vF ∼ 800 nm > 2π(a/2) = ∼ 540 nm
En = h2/2mL2(n - Φ/φ0)
Aharonov-Bohm-type effect
Vector potential A
Ensemble average Disappearance
∆BABT=(h/e)/S
Fourier Spectrum
△B2 = ∼70 mT ∆BABT =(h/e)/S = ∼50 mT
Contribution of larger unit cell (2nd unit cell)
Contents1.背景
2.カーボンナノチューブの酸化開口+熱処理で形成した低欠陥グラフェンナノリボン
欠陥ナノリボンの約7倍のエネルギーバンドギャップ
3.多孔質アルミナ膜マスクで形成した低欠陥アンチドット(ナノ細孔)格子グラフェン
細孔エッジに起因した異常磁気抵抗振動
室温強磁性の発現
Non-lithographic
(約10層)
(単層)
4.今後 電場によるエッジ偏極スピンの制御
温故知新
Nature Nanotech & Latest Highlights, News & Views
Arm Chair
zigzag
Y-W. Son, S.Louie et al., Nature 444, 347–349 (2006)
0.0
Eext = 0.0 0.05 0.1 VA -1
Spin Current & Filter
Eext
0.05
0.1
Jsy = (h/2e)(J↑y − J↓y )
E
S. Murakami, N. Nagaosa, and S. C. Zhang, Science 301,1348 (2003).
J. Sinova, et al., Phys. Rev. Lett. 92 126603 (2004)
Spin Current & Spin Hall EffectLuttinger模型
Rashba型スピン軌道相互作用
半導体
遷移金属
Pt/Ni-Fe 接合
Sr2RuO4
強磁性/非磁性複合構造
異常ホール効果
スピンホール効果
東北大 高梨
強磁性体
多バンド現象 h/∆Eに比例 τに独立
Kane, C. L. and Mele, E. J.,. Phys.Rev. Lett. 95, 226801 (2005)
(Quantum) Spin Hall Effect in Graphene
QSHE regime Insulating regime
Modulation of flat band
M.Schmidt & D.Loss, Phys. Rev. B 81, 165439 (2010)
Spin Hall Effect in graphen/graphen junction with hydrogen termination
No SO Interaction
H-CH-C
sp3 SOI
M.Schmidt & D.Loss, Phys. Rev. B 81, 165439 (2010)
SO Interaction
Spin Hall Effect in graphen/graphen junction with hydrogen termination
Edge Bulk
Conclusion
1.カーボンナノチューブの酸化開口・熱処理で形成した低欠陥グラフェンナノリボン
欠陥ナノリボンの約7倍のエネルギーバンドギャップ
2.多孔質アルミナ膜マスクで形成した低欠陥アンチドット格子グラフェン
細孔エッジに起因した異常磁気抵抗振動
室温強磁性の発現
Non-lithographic
今後: 細いGNRの電子輸送特性磁性の起源解明&制御電場によるエッジスピン制御
グラフェンのエッジと電子・磁気物性
炭素磁石
Arm Chair
zigzag
MIT: Millie Dresselhaus
Colombia University: Philip Kim
Rice University: James Tour
Tokyo Institute of Technology: T.Ando, T.Enoki
Tokyo University: S.Tarucha, M.Yamamoto, H.Fukuyama, T.Matsui, H. Aoki
Tokyo University, ISSP: Y.Iye, S.Katsumoto, T.Otsuka
AIST: K. Suenaga
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