Charge ordering in (EDT-TTFCONMe 2 )Br and o-(Me 2 TTF)Br

ECRYS-2008, 27 August 2008

Charge ordering in (EDT-TTFCONMe2)Br and o-(Me2TTF)Br

P. Auban-Senzier, C.PasquierLaboratoire de Physique des Solides, ORSAY, France


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


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

VU

ta


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


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

- - -


Looking for ¼ filled band systems

SC

T

(K)

Metal

(TMTTF)2 X

MI

CO13

22

-(BEDT-TTF)2X

40

Tem

pera

ture

Pressure

AF

SC

MI Metal

SCD8-Br

H8-BrCu(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)


Looking for ¼ filled band systems-IINew 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 ?


(o-Me2TTF)2X

S

S S

S

H3C

H3C H

H

o-Me2TTF


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)


(o-Me2TTF)2X

S

S S

S

H3C

H3C H

H

o-Me2TTF


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


-(EDT-TTF-CONMe2)2Br

(EDT-TTF-CONMe2)2Br

Complete set of data:

• NMR• Resistivity• Dielectric constant• Thermopower

all under hydrostatic pressure



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



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

Res

istiv

ity (m

.cm

)

Temperature (K)

TMI = 20K

// (T) (T)



3. First phase diagram

0 10 20 30 40 50 60 70 80

1

10

100

1000

2D3D

1D T*

T ()

Br

ClO

4

PF6X = B

F 4

PF6

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



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



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

pera

ture

(K)

Pressure (kbar)H.Seo, C.Hotta, H.Fukuyama, Chemical Reviews (2004)

H.Seo, J.Merino, H.Yoshioka, M.Ogata,JPSJ 75 (2006), 051009



6. Thermopower (TEP)

CO2

CO1

AF

0 2 4 6 8 10 12 14 161

10

100

Metal

-(EDT-TTF-CONMe2)

2 Br

Tem

pera

ture

(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



7. Conclusions

CO2

CO1

AF

0 2 4 6 8 10 12 14 161

10

100

Metal

-( EDT-TTF-CONMe2) 2 Br

Tem

pera

ture

(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



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


Conclusions

CO2

CO1

AF

0 2 4 6 8 10 12 14 161

10

100

Metal

-( 2)

Tem

pera

ture

(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 ?


Acknowledgments

• D. Jérome LPS Orsay

• P. Foury-Leylekian, J.-P. Pouget

• C. Mézière, P. Batail CIMA Angers

• M. Fourmigué ISC Rennes

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Charge ordering in (EDT-TTFCONMe 2 )Br and o-(Me 2 TTF)Br