2008/12/18

Hiroshi
Hio hi Sawa
Sa aNagoya University

Novel and exotic electronic state in molecularconductor
Salts of BEDT-TTF and their analogues
9 MMX 1D systems
9 New molecular superconductors
9Wigner Crystallization
 Precise structural analysis for Fullerene12008/12/18@KEK PF BL-1A,1B
SampleImaging Plate Weissenberg Camera

500μm

Bending magnet
Si(111) Double monochromator
Cylindrical mirror

Photon Factory
Synchrotron
Imaging
Plate

3

Metal-Insulator Transition
K. Bender, et. al., Mol. Cryst. Liq. Cryst. 108, (1984) 359

Resistivity measurement TMI = 135KTheoretical predictions

ChargeOrder

13C-NMR
Y. Takano et.al Synth. Met. 120 (2001) 1081
Y. Takano et.al J. Phys. Chem. Solids 62 (2001) 393

Raman

H. Kino and H. Fukuyama, JPSJ 64 (1995) 1877
( Hubbard model )H.Seo, JPSJ 69 (2000) 805( Extended Hubbard model )R.Wojcechowski et.al PRB 67 (2003) 224105

2

2008/12/18

Empirical Estimation of BEDT-TTF+0 5 δ+0.5-δ

Charge:C

Guionneau, et.al.

Ba

A +0.5+δ

+0.5+δ

1.00

A’ +0.5-δ

20K rich

Chargee0.75+0.5-δ
0.5 δRT0.50

Ob+0.5+δ

0.25
20K poor

0.00

A+0.5+δA’

B

Inversion Center (RT)

C+0.5-δ

+0.5-δHorizontal Stripe typeCharge Ordering

T>TMICab1CAA
b1b1’
a1b2b4Ab3bb2’B

B

b2Ab1

C0a3b2a2

T<TMIb1’

CaA

Ab2’

B

B

b2A’A’
b1bC

0A’
C

T.Kakiuchi et al., JPSJ., 76 (2007) 113702-1-4

3

2008/12/18

Novel and exotic electronic state in molecularconductor
Salts of BEDT-TTF and their analogues
9 MMX 1D systems
9 New molecular superconductors
9Wigner Crystallization
 Precise structural analysis for Fullerene
GEOMETRICAL FRUSTRATION
Well-known Frustration pattern;
the equilateral triangle is a motif

Frustration inAntiferro type
Ising spin system?
-J-J

Frustration in Kagome lattice
Frustration in tetrahedral lattice-J

Pyrochlore lattice94

2008/12/18

PHYSICAL PROPERTIES IN (R1R2-DCNQI)2AG
DMe-DCNQI C N

DI-DCNQI

N

MeC

N

R(T)//R(300K)

AgctDI

DMeH

MeNCNHICN

Spin Susceeptibility (10-3emu/mole)

NIH

H

Stacking structure of
DCNQI molecules

NDI

DMeT / K

T / K

K.Hiraki and K.Kanoda Phys.Rev.B54, 17276(1996) 12

Different Substitutions give Different Ground States

ELECTRON CORRELATION REALIZESCHARGE ORDERING GROUND STATE
NCNIH

HINC

N

DI-DCNQI

Extended Hubbard modelH=−()∑ tij ciσ c jσ + h.c. + ∑ Uni ↑ ni ↓ + ∑ Vij ni n ji
< i, j >< i, j >σtij : transfer integral
U : on site Coulomb
V : inter site Coulomb
tVU¼ filled charge ordering

Theoretical predictions :VH. Seo, et.al., JPSJ 66 (1997) 1249
135

2008/12/18～15K
Normarized Intensity

Oscillation Photograph @BL1A
10min / 1frame
l=0
l=1(0 0 4)(0 0 3/2)

1.0

R.T.

0.5

0.0
-0.2
02

-0.1
01

00
0.0

01
0.1

02
0.2

h / r.l.u

4kF

coherent length between
chains ～ 1300Å

l=24kF
l=3c*

4kF
l=44kF

225K
100K
50K
175K
200K
250K
Diffuse Scattering on c*-plane

3D-order

Structure Analysis at Low Temperature● two-fold c-axisc*● Space GroupP2/a (Monoclinic)
Data CollectionSPD @BL1A
Oscillation photographexposure time: 10min
Wave length: 0.687
Sample size: 0.35×0.05×0.05mm3
Temperature : 50K

Result of Analysis at 50K
Space Group : P2/a Twined Crystal
Obs. : 28177
Resolution : 0.45
R(all) : 0.058 R(I > 4σ) : 0.044
domain ratio : 0.52 : 0.48

156

2008/12/18

Determination of Spatial Charge Ordering
using Displacement Pattern of Ag cations• Ag mono-cation has a closed shell.
• Shift of Ag cation is proportional to the electronic
field modulated by the charge ordering on
DCNQI
Q molecules.

AgAg Æ + ion
attractive
DCNQI Æ − charged

16

Success of qualitative determination for charge ordering in DCNQI columns.

Another instance of Charge
modulation from DCNQI
displacements
Displacements of DCNQI cause
Modulation of Charge Density
One-dimensional
O dii l Chain
Ch imolecule

Charge rich area17

No shift

Small shifts

Large shifts72008/12/18

WIGNER CRYSTALLIZATION
charge rich
Charge(electron)-rich areas
form Body Centered Tetragonal↓Wigner Crystallization

Body centered cell

Coexistence of site- and bond-CDW↓
We can describe the crystal structureas “Charge Density Wave”

19T.Kakiuchi et al., PRL 98, 066402(2007)

Standard structure analysis is suitable
technique for determination of theground state in molecular crystalsystems.
 A more complex structure analysis
becomes possible by combining withResonant X-ray Scattering, too.
8