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

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. 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

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

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  1. 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

  2. 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

  3. The physics of ¼ filled band systems-I ta V U ta 0.1 - 0.4 eV U  1 eV V  U / 2 tc 0.1 - 1 meV ECRYS-2008, 27 August 2008

  4. The physics of ¼ filled band systems-II E V Compounds (Cation)2X or “2 :1” without dimerization - - - +0.5? Band filling = ¾ At low temperature… charge disproportionation Charge ordering (ferroelectricity) and antiferromagnetism ECRYS-2008, 27 August 2008

  5. The physics of ¼ filled band systems-III - - - E Compounds (Cation)2X or “2 :1” with dimerization Band filling = ½ At low temperature… Mott insulator and antiferromagnetism ECRYS-2008, 27 August 2008

  6. Looking for ¼ filled band systems (TMTTF)2 X k-(BEDT-TTF)2X Metal MI Temperature 40 T (K) MI Metal 22 AF 13 CO SC SC SC AF D8-Br H8-Cl H8-Br Pressure I3 Cu(NCS)2 (DI-DCNQI)2Ag CO T. Itou et al., Phys. Rev. B 72, 113109 (2005) No CO CO hardly stabilized CO extends widely ECRYS-2008, 27 August 2008

  7. Looking for ¼ filled band systems-II New families : (EDT-TTF-CONMe2)2X X = AsF6 , Br (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

  8. (o-Me2TTF)2X TCO2 TCO1 (o-Me2TTF)2X X = Cl, Br, I sc (T) e’(T) ECRYS-2008, 27 August 2008

  9. (o-Me2TTF)2X (o-Me2TTF)2X X = Cl, Br, I 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

  10. -(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

  11. -(EDT-TTF-CONMe2)2Br 1. Determination of the magnetic ground state 1H NMR Determination of 1/T1, (T, P) TN weakly increases at low P: attributed to the increase of t ECRYS-2008, 27 August 2008

  12. -(EDT-TTF-CONMe2)2Br b I c V V I V I a V I TMI = 20K 2. Resistivity measurements transverse I // b r  (T) r// (T) I // c P < 8kbar 1D regim : Mott localisation T< Tr : r=r0exp (Dr/T) P > 8kbar 1D-2D crossover r// metallic and r metallic for T<T* ECRYS-2008, 27 August 2008

  13. -(EDT-TTF-CONMe2)2Br CO 3. First phase diagram Phase diagram similar to 1D materials such as (TMTTF)2X family ECRYS-2008, 27 August 2008

  14. -(EDT-TTF-CONMe2)2Br T T CO1 CO2 1E13 1er ordre P = 2 kbar hysteresis 10K 1E12 1E11 1E10 ' e 1E9 1E8 1E7 1000000 100000 100 150 200 300 250 Temperature (K) 4. Dielectric constant measurements Curie law at the transition Low P : 2 peaks in ’ => Charge Ordering, why 2 peaks? High P : peak in ’ at the metal-insulator transition : insulating state = CO ECRYS-2008, 27 August 2008

  15. -(EDT-TTF-CONMe2)2Br d - ( EDT-TTF-CONMe ) Br 2 2 100 Metal CO1 Temperature (K) 10 CO2 AF 1 0 2 4 6 8 10 12 14 16 Pressure (kbar) 5. Second phase diagram 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

  16. -(EDT-TTF-CONMe2)2Br d - ( EDT-TTF-CONMe ) Br 2 2 100 Metal CO1 Temperature (K) 10 CO2 AF 1 0 2 4 6 8 10 12 14 16 Pressure (kbar) 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 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

  17. -(EDT-TTF-CONMe2)2Br d - ( EDT-TTF-CONMe ) Br 2 2 100 Metal CO1 Temperature (K) 10 CO2 AF 1 0 2 4 6 8 10 12 14 16 Pressure (kbar) 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)2Ag which indicates a unity in the phase diagram of weakly or non dimerized systems ECRYS-2008, 27 August 2008

  18. -(EDT-TTF-CONMe2)2Br 250 e T ( ') 1D Metal D r T , ( ) r T* ( ) CO1 r r // ^ localised 200 2D Metal 150 e T ( ') CO2 Temperature (K) 100 Charge Ordering 50 r T ( ) MI // 1 T (T H NMR) r T ( ) AF 1 CO ^ MI Antiferromagnetic 0 0 2 4 6 8 10 12 14 16 Pressure (kbar) 7. Conclusions (DI-DCNQI)2Ag (EDT-TTF-CONMe2)2Br T. Itou et al., Phys. Rev. B 72, 113109 (2005) ECRYS-2008, 27 August 2008

  19. Conclusions d - ( ) 2 100 Metal CO1 Temperature (K) 10 CO2 AF 1 0 2 4 6 8 10 12 14 16 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

  20. 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

  21. Thankyou for your attention ECRYS-2008, 27 August 2008

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