分子性導体の外場応答
強電場効果（物性研究所・新物質科学研究部門）
森 初果

強相関電子系の特徴
非ダイマー型 1/4-filled系（W ~ 0.8 eV, V ~ 0.5eV）
W (分子軌道間相互作用＝運動エネルギー)→金属vs.
V(分子間クーロン斥力)→ vs. 電荷秩序絶縁相+0.5 +0.5 +0.5 +0.5
W
0 +1.0V
0 +1.0

H.Seo, H.Fukuyama, J.Phys.Soc.Jpn., 66, 1249(1997).

外場応答
１ 圧力 電荷秩序絶縁相 →超伝導→金属相
２ 電場 巨大非線形伝導、電場誘起準安定状態、有機サイリスタ
３ 磁場 巨大磁気抵抗
４ 光 光誘起金属状態

Organic electronics
Organic EL(Electroluminescence)
CH3O

Alq3CH3N
AlN

Organic Supercon.

ON

H3CN

NSSSS

SSSSCH3O

BEDT-TTF
DiamineOrganic FET(Field-Effect Transistor)

Organic nonlinear device（Organic thyristor）

Responses by Electric Field（１）直流ー交流変換⇒振動、リズム
Organic thyristor (4K); θ-ET2CsCo(SCN)4
F. Sawano et al., Nature 437 (2005) 522.

（２）電場誘起準安定状態
Electric field induced metastable state(<70K); β-(meso-DMeET)2PF6
S. Niizeki et al., J. Phys.Soc.Jpn. 77, 073710(1-4) (2008).

（３）電荷秩序の集団励起
Voltage oscillation (88 K); α-ET2I3
K. Tamura et al., J. Appl. Phys. 107, 103716(1-5) (2010).

⇒非平衡科学（舞台：有機伝導体）

Thyristor
II
Ic1

V

J1 forward
J2 reverse

Ic2

J3 forwardII -V Characteristics of Thyristor
V electronavalanche
VBOI

I -V サイリスタの電流ー電圧特性
Characteristics of Thyristor
thyristor①、③ stable point② unstable point
pendulum③①②

Single Crystals of thetaET2CsCo(SCN)4

Competition and Co-existence of two kinds of CO
Organic thyristor θ- [ET2]+[CsCo(SCN)4](SCN)-

Cs+

アニオン
絶縁層

Co2+

100
S

S

BEDT-TTF SS

S 10 SET

有機伝導層

アニオン
絶縁層
有機伝導層

Resistivity / ohm cm

SS

1(A)+(B)

0.1(B)

0.01

アニオン
絶縁層 b

CsZn0.001
0a

H.Mori et al.,
PRB 57, 12023(1998).

100200300

Temperature / K

cV Vc VVpp ap Vc

Vp0 pV(A)Stripe 2-fold(B) 3-fold Itinerant state
Insulating state
M.Watanabe et. al: JPSJ 68 (1999) 2654.

θ- type ET Salts
cp cpppc

p=0
1D latticep=ctriangular latticec=0
2D latticetVθ-type Charge Ordered Pattern
V’=0の場合
Vc
Vp
Vp(Metal)

100K

1D<50KVc
Triangular Lattice
H. Seo: J. Phys. Soc. Jpn. 69 (2000) 805.
T. Mori: J. Phys. Soc. Jpn. 72 (2003) 1469.

2D LatticeSingle Crystals oftheta-ET2CsCo(SCN)4

1.5 mmI-V CharacteristicsResistor

V’SampleＸＸ
J2 reverse

DC V

Two stable points→Oscillation of
Current

V’

V-RIBias dependence[θ-ET2CsZn(SCN)4]
Thyristor

Silicon pnpn junction -> Organic Crystal
I

J1 順方向J2 逆方向J3 順方向Inverter DCV-ACI Conversion

Vstd=IexRstd

F. Sawano et al.: Nature 437 (2005) 522.

40 Hz

θ-ET2CsCo(SCN)4
X-ray measurement undercurrent
Disappearance of Blaggspots

0 mA

0.5 mA 1.0 mA 1.5 mA 3.0 mA

2-fold(InsulatingState)
Disappear

3-fold(Conducting)
No changeθ-ET2CsCo(SCN)4：Inhomogenous 2 and 3-folds→ Melting by Electric Field
3-fold axis
(High Conducting)Free energy

Excitation ofelectric field
ElectricField

3CO20 K2CO∆

Temp

2-fold axis(Insulating)High Conducting State

Responses by Electric Field（１）直流ー交流変換⇒振動、リズム
Organic thyristor (4K); θ-ET2CsCo(SCN)4
F. Sawano et al., Nature 437 (2005) 522.

（２）電場誘起準安定状態
Electric field induced metastable state(<70K); β-(meso-DMeET)2PF6
S. Niizeki et al., J. Phys.Soc.Jpn. 77, 073710(1-4) (2008).

（３）電荷秩序の集団励起
Voltage oscillation (88 K); α-ET2I3
K. Tamura et al., J. Appl. Phys. 107, 103716(1-5) (2010).

⇒非平衡科学（舞台：有機伝導体）

Recent research
Introduction of steric hindrance
Chemical negative pressure
ET

Chemical negativepressure∆Tc≈ −1K/kbar∆PET

Steric hindrance

ET derivatives

C5ET

C6ET

meso-DMBEDT-TTF

強相関パラメータの制御
化学修飾

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

ET

MeET

C6ET分子構造の自由度
二量化中

二量化大

二量化小

分子間相互作用+0.75

分子配列の自由度+0.255

半導体
Resistivity (ohm cm)

多彩な電子機能Resistivity (ohm cm)

104103102101100100200

Temperature (K)30010410310210110010-110-2

金属

金属ー絶縁体0100200

Temperature (K)300β-(meso-DMBEDT-TTF)2PF650~90 K:imperfect formation of CCO→Melting of CCO & nonlinear conduction

S. Kimura et al.: Chem. Commun. (2004).
S. Kimura et al.: JACS (2006).

Experiment: Nonlinear Conduction
Nonlinear conduction
Cryogenic

Liquid He cryostatElectrical transport

Source-Meter Keithley model 2611
I-driven V measurement:
V-driven I measurement:
4-probe2-probe

Pulsed source: 2 ms~20 ms
Oscilloscope…to observe the temporal change of Vsample

Result: Nonlinear Conduction
I-driven 4-probe (2ms)

V-driven 2-probe (2ms)

Fitting Function

N. Toyota et al.: Phys. Rev. B 66 (2002) 033201.

Results: Nonlinear Conductivity
ρsamples=(Rcircuit-RL) S/l

High activation voltage

NI transition material(TC=240 K)
Low activation temperature

Y. Iwasa et al.: Appl. Phys. Lett. 55 (1989) 2111.

ρ change of 3 orders@55.5 K, Vc=4 V

Giant Nonlinear Conduction
CO Material (TMI=20 K)

at high temperature and low voltage

T. Mori et al.: Phys. Rev. B 75 (2007) 235103.

Results: Time-dependent Vsample
Oscilloscope images
60.8 K

2-stepped change
Field-induced metastable state?

Flipping of the relation of magnitude⇨NDR

60.8 K, Vc sweep, RL=470 Ω

Simulation of Heating Effects
Pseudo nonlinear conduction
caused by self-heating?

Heat outflow neglected
QJoule completely converted into ΔT

Cp(T) forβ-(meso-DMBEDT-TTF)2PF6(Prof. Nishio, Toho University)

3V

Simulation of Heating Effects
Simulated behavior

2V60 K

Heat outflow neglected
QJoule completely converted into ΔT

2V

3V

60.8 K (Experimental)

Fast experimental response
Inexplicable by self-heating
Bump in the experiment⇨Field-induced metastable stateMicroscopic picture of nonlinear conduction

T. Yamaguchi et al.: PRL 96 (2006) 136602.

Nonlinear conduction at 110 μs

Experiment: Raman Scattering
Cryogenic

Thermal conduction

Raman scattering
Okamoto Lab.

Result: Raman scatteringν13M. Tanaka et al.: J. Phys. Soc. Jpn. 77 (2008) 024714.

Results: Raman scattering

ProbeMetastable

SummaryTemperature independent nonlinear conduction

・2-type NDRs below 70 K・2-stepped drop of Vsample(t)Field-induced Metastable stateResponses by Electric Field（１）直流ー交流変換⇒振動、リズム
Organic thyristor (4K); θ-ET2CsCo(SCN)4
F. Sawano et al., Nature 437 (2005) 522.

（２）電場誘起準安定状態
Electric field induced metastable state(<70K); β-(meso-DMeET)2PF6
S. Niizeki et al., J. Phys.Soc.Jpn. 77, 073710(1-4) (2008).

（３）電荷秩序の集団励起
Voltage oscillation (88 K); α-ET2I3
K. Tamura et al., J. Appl. Phys. 107, 103716(1-5) (2010).

⇒室温での動作Properties of β‐ET2PF6 : TCO = 297 K
Temperaturedependence ofresistivity

The formationof superlatticeFirst-ordertransition
TMI=297 K
H.Kobayashi et al. Chem. Lett. 581 (1983).

High temperature(T > 297 K)

G.K.Rohan Senadeera et al. J.Phys Soc. Jpn,67,4193 (1998)

Low temperature(T < 297 K)+0.5~ + 0.8~ + 0.2
Metallic state

Insulating state
Y. Nogami et al. J.Phys. France 12 Pr9-233 (2002)

The long range charge ordered (LRCO) state below Tco = 297 K

Electric field responses : I -driven mode
I -V characteristics along a axis
Pulse time : 5 ms

Nonlinear conduction below 291.4 K.
Negative differential resistance (NDR) below
273.0 K.
Sharp voltage drop in NDR region below
262.2 K.

Time dependence of V sample

Electric field responses : I -driven mode

Pulse time : 50 ms

230 K
・Voltage oscillation begins
at 1.79 A/cm2.
・Long voltage oscillation
at 1.86 A/cm2.
・Applying current , oscillation
oscillation becomes faster .
・ Suddenly oscillation
vanishes in high current
region.

Voltage oscillation in sharp voltage drop region
below 260 K.

Fourier- transform spectra from oscillation
Electric field responses : I -driven mode

f1
f2

f3
f4
f5

・Fundamental frequency f 1 : 1 － 3 kHz
・Harmonic frequencies : f 2 ~ f 5・Frequencies increase linearly to current density.

Pulse time : 50 ms

Collective excitations
Electric field responses : I-driven modeβ‐(BEDT-TTF)2PF6

1D Conductor : NbSe3

H. Fukuyama, J. Phys. Soc. Jpn., 41, 513(1976).
J. Bardeen et al., Phys. Rev. Lett. 49 (1982) 493.

Collective excitationsof LRCOν ∝ICDW
Collective excitations
CDW sliding

Collective excitations
J= Nneλ0
f1
J : current transported by aggregate
f1 : fundamental frequency
n : carrier density from composition
Nn : carrier density from experimentse : chargeof electron λ0 : lattice length
1D Conductors
NbSe3 ; 0.1 – 2 MHz at 47.6 K.

N = 1 : 1D conductor(TMTSF)2PF6 ; 15 – 240 kHz at 4.2 K.
N > 1 : LRCO
R. M. Fleming et al., Phys. Rev. Lett., 42 (1979) 1423.

a axisR. M. Fleming et al., Phys. Rev. B, 52 (1995) 2237.

(perylene)2[Pt(mnt)2] ;40 – 150 kHz at 4.2 K.

β-(BEDT-TTF)2PF6 (LRCO)
・1-3 kHz (Audible range)
・Around room temperature
・Coherence between chains

LRCO chain

E. Barthel et al., Phys. Rev. Lett., 71 (1993) 2825.

c axisLRCO chain
Nac axis:=
1 : 1D Conductors
axis: Coherence of chainsN = 2 - 5 : LRCO

Collective excitations in β-(BEDT-TTF)2PF6Electric field responses : I -driven mode

N=0

Collective excitations in β-(BEDT-TTF)2PF6
Electric field responses : I -driven mode

N=2

Collective excitations in β-(BEDT-TTF)2PF6
Collective excitations
Electric field responses : I -driven mode

N=5Singing Organic Conductor
by Mr. T. Asano非線形伝導⊂非線形科学＊準安定状態＊準安定状態＊サイリスタ(交流発振) ＊同期→正と負の フィードバック⇒有機伝導体が舞台

ジャボティンスキー反応

幾万の蛍の同期発光（アフリカ）

脳波
アルファ波 8~13 Hz
ガンマ波 20~80 Hz
脳内ニューロン（神経細胞）の同期発火

レポート（有機物性論）
講義では、分子性物質の結晶構造、バンド構造、フェルミオロジー、（超）伝導性、磁性、外場応答について言及した．講義に登場したキーワードに関係する最近の論文1編を選び，レポート用紙２～３枚程度で解説し、最後に興味深いと感じた点について簡単に述べよ．
〆切 6月17日(金)hmori@issp.u-tokyo.ac.jp
タイトル 有機物性論レポート