ECRYS-2008, 27 August 2008 Charge ordering in (EDT-TTFCONMe 2 )Br and o-(Me 2 TTF)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-TTFCONMe 2 )X and o-(Me 2 -TTF) 2 X Study of o-(Me 2 -TTF) 2 Br and o-(Me 2 -TTF) 2 I Study of (EDT-TTF-CONMe 2 )Br Conclusions

ECRYS-2008, 27 August 2008 The physics of ¼ filled band systems-I U  1 eVV  U / 2t a  eV t c  meV V U tata

ECRYS-2008, 27 August 2008 The physics of ¼ filled band systems-II Compounds (Cation) 2 X or “2 :1” without dimerization ? 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) 2 X 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 SCSC T (K) Metal (TMTTF) 2 X MI CO  -(BEDT-TTF) 2 X 40 Temperature Pressure AF SC MI Metal SC D 8 -Br H 8 -Br Cu(NCS) 2 I3I3 H 8 -Cl No COCO hardly stabilizedCO extends widely (DI-DCNQI) 2 Ag CO AFAF T. Itou et al., Phys. Rev. B 72, (2005)

ECRYS-2008, 27 August 2008 Looking for ¼ filled band systems-II New families : (EDT-TTF-CONMe 2 ) 2 X X = AsF 6, Br (o-Me 2 TTF) 2 X X = Cl, Br, I X = AsF 6 : K. Heuzé, et al., Adv. Mat. 15 (2003) P. Batail et al., CIMA AngersM. Fourmigué et al., ISC Rennes Very weak dimerization ?

ECRYS-2008, 27 August 2008 (o-Me 2 TTF) 2 X (o-Me 2 TTF) 2 X X = Cl, Br, I  c (T) T CO1 T CO2  ’(T)

ECRYS-2008, 27 August 2008 (o-Me 2 TTF) 2 X (o-Me 2 TTF) 2 X X = Cl, Br, I Metallic in a large range of temperature (better coupling along the chain than in the TMTTF 2 X) Signatures of CO are observable : 2 anomalies, why? AF state? NMR has to be done

ECRYS-2008, 27 August 2008  -(EDT-TTF-CONMe 2 ) 2 Br (EDT-TTF-CONMe 2 ) 2 Br Complete set of data: NMR Resistivity Dielectric constant Thermopower all under hydrostatic pressure

ECRYS-2008, 27 August 2008  -(EDT-TTF-CONMe 2 ) 2 Br 1 H NMR Determination of 1/T 1, (T, P) 1. Determination of the magnetic ground state T N weakly increases at low P: attributed to the increase of t

ECRYS-2008, 27 August 2008  -(EDT-TTF-CONMe 2 ) 2 Br 2. Resistivity measurements V V I I c a b transverse I // b P < 8kbar 1D regim : Mott localisation    =  0 exp (   /T ) I // c I I V V P > 8kbar 1D-2D crossover  // metallic and   metallic for T<T* T MI = 20K  // (T)   (T)

ECRYS-2008, 27 August 2008  -(EDT-TTF-CONMe 2 ) 2 Br 3. First phase diagram CO Phase diagram similar to 1D materials such as (TMTTF) 2 X family

ECRYS-2008, 27 August 2008  -(EDT-TTF-CONMe 2 ) 2 Br 4. Dielectric constant measurements Low P : 2 peaks in  ’ => Charge Ordering, why 2 peaks? High P : peak in  ’ at the metal-insulator transition : insulating state = CO Curie law at the transition

ECRYS-2008, 27 August 2008  -(EDT-TTF-CONMe 2 ) 2 Br 5. Second phase diagram H.Seo, C.Hotta, H.Fukuyama, Chemical Reviews (2004) H.Seo, J.Merino, H.Yoshioka, M.Ogata,JPSJ 75 (2006),

ECRYS-2008, 27 August 2008  -(EDT-TTF-CONMe 2 ) 2 Br 6. Thermopower (TEP) 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 2 nd peak in dielectric constant. High P : anomaly in TEP exactly at the metal-insulator transition. No change of the sign of the TEP. T>T MI: linear in T

ECRYS-2008, 27 August 2008  -(EDT-TTF-CONMe 2 ) 2 Br 7. Conclusions 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) 2 Ag which indicates a unity in the phase diagram of weakly or non dimerized systems

ECRYS-2008, 27 August 2008  -(EDT-TTF-CONMe 2 ) 2 Br 7. Conclusions (DI-DCNQI) 2 Ag T. Itou et al., Phys. Rev. B 72, (2005) (EDT-TTF-CONMe 2 ) 2 Br

ECRYS-2008, 27 August 2008 Conclusions 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-CONMe 2 ) 2 Br close to (DI-DCNQ) 2 Ag 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. JéromeLPS Orsay P. Foury-Leylekian, J.-P. Pouget C. Mézière, P. BatailCIMA Angers M. FourmiguéISC Rennes €€€ :

ECRYS-2008, 27 August 2008