ECRYS-2008, 27 August 2008 Charge ordering in (EDT-TTFCONMe 2 )Br and o-(Me 2 TTF)Br P....
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Transcript of ECRYS-2008, 27 August 2008 Charge ordering in (EDT-TTFCONMe 2 )Br and o-(Me 2 TTF)Br P....
ECRYS-2008, 27 August 2008
Charge ordering in (EDT-TTFCONMe2)Br and o-(Me2TTF)Br
P. Auban-Senzier, C.Pasquier
Laboratoire de Physique des Solides, ORSAY, France
ECRYS-2008, 27 August 2008
Outline
• Interest in ¼ band filled systems
• The new families (EDT-TTFCONMe2)X and o-(Me2-TTF)2X
• Study of o-(Me2-TTF)2Br and o-(Me2-TTF)2I
• Study of (EDT-TTF-CONMe2)Br
• Conclusions
ECRYS-2008, 27 August 2008
The physics of ¼ filled band systems-I
jijiijiijiij nnVnnUcctH
,
U 1 eV V U / 2ta 0.1 - 0.4 eV
tc 0.1 - 1 meV
V
U
ta
ECRYS-2008, 27 August 2008
The physics of ¼ filled band systems-II
Compounds (Cation)2X or “2 :1” without dimerization
- - -
+0.5?
Band filling = ¾
E
V
At low temperature… charge disproportionation
Charge ordering (ferroelectricity) and antiferromagnetism
ECRYS-2008, 27 August 2008
The physics of ¼ filled band systems-III
Compounds (Cation)2X or “2 :1” with dimerization
Band filling = ½
E
At low temperature…
Mott insulator and antiferromagnetism
- - -
ECRYS-2008, 27 August 2008
Looking for ¼ filled band systems
SC
T
(K
)Metal
(TMTTF)2 X
MI
CO13
22
-(BEDT-TTF)2X
40
Tem
per
atu
re
Pressure
AF
SC
MI Metal
SC
D8-BrH8-Br
Cu(NCS)2
I3H8-Cl
No CO CO hardly stabilized
CO extends widely
(DI-DCNQI)2Ag
CO
AF
T. Itou et al., Phys. Rev. B 72, 113109 (2005)
ECRYS-2008, 27 August 2008
Looking for ¼ filled band systems-II
New families :
(EDT-TTF-CONMe2)2X X = AsF6 , Br
S
S S
S
H3C
H3C H
H
o-Me2TTF
(o-Me2TTF)2X X = Cl, Br, I
X = AsF6: K. Heuzé, et al., Adv. Mat. 15 (2003) 1251.
P. Batail et al. , CIMA Angers M. Fourmigué et al. , ISC Rennes
Very weak dimerization ?
ECRYS-2008, 27 August 2008
(o-Me2TTF)2X
S
S S
S
H3C
H3C H
H
o-Me2TTF
(o-Me2TTF)2X X = Cl, Br, I
0 20 40 60 80 100 1200.1
1
10
100
1000
10000
1E5
1E6
1E7
11.5 kbar
Idc
=0.1-100 A
o-(DMTTF)2 I #22.5 kbar8.8 kbar
7.5 kbar
Res
istiv
ity (
m.
cm)
Température (K)
c (T)
TCO1TCO2
’(T)
ECRYS-2008, 27 August 2008
(o-Me2TTF)2X
S
S S
S
H3C
H3C H
H
o-Me2TTF
(o-Me2TTF)2X X = Cl, Br, I
0 2 4 6 8 10 12 14
10
100
TCO2
(')T
CO1 (')
TMI
(dc
)
ChargeOrdering
insulator?
Metal
O-(DMTTF)2 I
Tem
pera
ture
(K
)
Pressure (kbar)
Metallic in a large range of temperature
(better coupling along the chain than in the TMTTF2X)
Signatures of CO are observable : 2 anomalies, why?
AF state? NMR has to be done
ECRYS-2008, 27 August 2008
-(EDT-TTF-CONMe2)2Br
(EDT-TTF-CONMe2)2Br
Complete set of data:
• NMR• Resistivity• Dielectric constant• Thermopower
all under hydrostatic pressure
ECRYS-2008, 27 August 2008
-(EDT-TTF-CONMe2)2Br
1H NMRDetermination of 1/T1, (T, P)
0 5 10 150
5
10
15
20
AF
-(EDT-TTF-CONMe2)
2 Br
T A
F (
K)
Pressure (kbar)
1. Determination of the magnetic ground state
TN weakly increases at low P: attributed to the increase of t
ECRYS-2008, 27 August 2008
-(EDT-TTF-CONMe2)2Br
2. Resistivity measurements
V
V
I
Ic
a
btransverse
I // b
P < 8kbar 1D regim : Mott localisation = 0 exp (/T)
I // cI IVV
P > 8kbar 1D-2D crossover// metallic and metallic for T<T*
0 50 100 150 200 250 3000
10
20
30
40
T = 230 K
11.5 kbar #6
(EDT-TTF-CONMe2)
2Br
// I // c
7.6 kbar #3
6 kbar #2
Re
sist
ivity
(m.
cm)
Temperature (K)
TMI = 20K
// (T) (T)
ECRYS-2008, 27 August 2008
-(EDT-TTF-CONMe2)2Br
3. First phase diagram
0 10 20 30 40 50 60 70 80
1
10
100
1000
2D3D
1D T*
T ()
Br
ClO
4
PF 6
X = BF 4
PF 6
Tem
pera
ture
(K
)
(TMTTF)2 X
Mottinsulator
Pressure (kbar)
SC
METAL
AF SDWSP
(TMTSF)2 X
CO
Phase diagram similar to 1D materials such as (TMTTF)2X family
ECRYS-2008, 27 August 2008
-(EDT-TTF-CONMe2)2Br
4. Dielectric constant measurements
100 150 200 250 300100000
1000000
1E7
1E8
1E9
1E10
1E11
1E12
1E13TCO21er ordre
hysteresis 10K
TCO1
P = 2 kbar
'
Temperature (K)
0 10 20 30 40 50 600.0
0.2
0.4
0.6
0.8
1.0
TCO2
= 7 K
42 Hz
5 kHz
TCO1
= 30.5 K
P = 8.1 kbarI // c
1010
/ '
Temperature (K)
0 10 20 30 40 50 6010000
1E6
1E8
1E10
1E12
1E14T
CO1
42 Hz
5 kHz
TCO2
P = 8.1 kbarI // c
'
Temperature (K)
0 10 20 30 40 50 600.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
TCO2
= 7 K42 Hz
5 kHz
TCO1
= 30.5 K
P = 8.1 kbarI // c
1010
/ '
Temperature (K)
Low P : 2 peaks in ’ => Charge Ordering, why 2 peaks?
High P : peak in ’ at the metal-insulator transition : insulating state = CO
0,)('
FEFE
TTT
AT
Curie law at the transition
ECRYS-2008, 27 August 2008
-(EDT-TTF-CONMe2)2Br
5. Second phase diagram
CO2
CO1
AF
0 2 4 6 8 10 12 14 161
10
100
Metal
-(EDT-TTF-CONMe2)
2 Br
Tem
per
atu
re (
K)
Pressure (kbar)H.Seo, C.Hotta, H.Fukuyama, Chemical Reviews (2004)
H.Seo, J.Merino, H.Yoshioka, M.Ogata,JPSJ 75 (2006), 051009
ECRYS-2008, 27 August 2008
-(EDT-TTF-CONMe2)2Br
6. Thermopower (TEP)
CO2
CO1
AF
0 2 4 6 8 10 12 14 161
10
100
Metal
-(EDT-TTF-CONMe2)
2 Br
Tem
per
atu
re (
K)
Pressure (kbar)
Low P : anomaly in TEP more or less related to 1st peak in dielectric constant. Change of sign of TEP more or less related to 2nd peak in dielectric constant.
High P : anomaly in TEP exactly at the metal-insulator transition . No change of the sign of the TEP. T>TMI: linear in T
ECRYS-2008, 27 August 2008
-(EDT-TTF-CONMe2)2Br
7. Conclusions
CO2
CO1
AF
0 2 4 6 8 10 12 14 161
10
100
Metal
-( EDT-TTF-CONMe2)
2 Br
Tem
per
atu
re (
K)
Pressure (kbar)
• CO extends widely : expected for a weakly dimerized system (or non dimerized at all)
• CO manifests in dielectric constant and thermopower measurements
• No signatures of superconductivity
• Phase diagram close to (DI-DCNQ)2Ag which indicates a unity in the phase diagram of weakly or non dimerized systems
ECRYS-2008, 27 August 2008
-(EDT-TTF-CONMe2)2Br
7. Conclusions
(DI-DCNQI)2Ag
T. Itou et al., Phys. Rev. B 72, 113109 (2005)
0 2 4 6 8 10 12 14 160
50
100
150
200
2501D Metal
CO
ChargeOrdering
TMI
()
T* ()T, (//
)
TCO2
(')
TCO1
(')
TAF
(T1 1H NMR)
TMI
(//)
Antiferromagnetic
localised
2D Metal
Tem
pera
ture
(K
)
Pressure (kbar)
(EDT-TTF-CONMe2)2Br
ECRYS-2008, 27 August 2008
Conclusions
CO2
CO1
AF
0 2 4 6 8 10 12 14 161
10
100
Metal
-( 2)
Tem
per
atu
re (
K)
Pressure (kbar)
• Study of new families of ¼ filled (or very weakly dimerized) systems with NMR, resistivity, dielectric constant and thermopower.
• CO extends widely which is expected for a weakly dimerized system (or non dimerized at all)
• No signatures of superconductivity : is it intrinsic or related to disorder (CO fluctuations)?
• Phase diagram of -(EDT-TTF-CONMe2)2Br close to (DI-DCNQ)2Ag which indicates a unity in the phase diagram of weakly or non dimerized systems
• Open questions : why a phase repulsion between the 2 CO states?
why 2 peaks in dielectric constant ?
ECRYS-2008, 27 August 2008
Acknowledgments
• D. Jérome LPS Orsay
• P. Foury-Leylekian, J.-P. Pouget
• C. Mézière, P. Batail CIMA Angers
• M. Fourmigué ISC Rennes
€€€ :
ECRYS-2008, 27 August 2008