Photon Factory, Institute of Materials Structure Science,

1. Role of Frustration in Quasi 1D Conductor～ Charge Ordering and/or CDW in (R1,R2-DCNQI)2M (M=Ag, Li, Cu) System ～ collaboration with Kanoda Group and Kato Group Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK) Hiroshi Sawa

2. Electronic state in Q1D molecular conductor Theoretical Research:Seo & Fukuyama, Chem Rev. Charge order in ¼ filled system V ¼ filled charge ordering • various phases by strong correlation • tij: transfer integral • U : on site Coulomb • V : inter site Coulomb dimer-Mott insulator t V U t ~ 0.2eV, U ~ 1eV, V ~ 0.5eV dimer charge ordering

3. DCNQI2Ag：Ideal 1D pp-system b a Ag+ c b • Crystal system: tetragonal • Space group: I41/a • a ～ 21.5 Åc ～ 3.9 Å Ag+ DCNQI

4. LT Case of (DI-DCNQI)2Ag UV Phase Diagram Charge separation CO Metal Seo et al. RT no dimerization? Lab. X-ray Source Hiraki and Kanoda PRL 80（1998）4737 1 frame / ca. 0.5 day Y.Nogami et al. Journal de Physique IV, PR10 (1999) 201-

5. 175K 125K 100K 45K 75K 55K 25K 35K 200K 150K 250K 300K 225K 17K 350×50×50μm3 300K sample 500μm Imaging Plate X-ray Measured by BL-1A at Photon Factory 1 frame / 10 min Sample size We can determine the low-temperature electronic structure including super spots.

6. shifts of Ag cations and DCNQI molecules Ag DCNQI Shift from HT phase Large Shift / Å small Ag site No. DCNQI site No. superstructure is originated from shifts of Ag cations Ag DCNQI Ag ：ionic bonding coordination is reflected by charge modulation in the unit cell

7. D A C B Expands! A B C D A 2c c o two fold structure along c axis Charge Ordering Pattern Atomic shift in LT phase determined by Ag+ ionshifts. • Existence of charge modulation along stacking axis • → Consistent with NMR results • Existence of intermediate state Low temperature pattern

8. (DMe-DCNQI)2Li 32K 100min c* 2kF 4kF 2 3 ℓ＝1 Torizuka et al., ISSP dimer-Mott Spin Peierls insulator Case of(DMe-DCNQI)2Li Li Li+:1s2 Li 1D conducting chain weak inter-chain interaction

9. Role of frustration among the 1D chains in DCNQI2Cu System with KatoG@RIKEN Observation of Charge ordering in (DBr-DCNQI)2Cu Metal Insulator R. Kato et al. 1996 H. Kobayashi et al. PRB47 3500 (1993)

10. Insulator phase Cu+ DCNQI 3c CDWCu2+:Cu+=1:2 Cu2+ DCNQI Electronic State Metal phase Cu4/3+ c DCNQI Regular stacked DCNQI Commensurate periodicity between Cu charge ordering and CDW Theoretical hypothesis･･･ by Fukuyama，Suzumra･･･

11. X-ray diffraction image of Insulator phase by Synchrotron Radiation at 50K measured at PF BL1A Sample size 30μm× 30μm×200μm wave length :λ=0.689Å exposure time : 15 min.

12. Insulator phase a×b×3c Cu+ c’=3c Cu2+ DCNQI 3c CDWCu2+:Cu+=1:2 I Reported crystal structure model using analysis with rigid molecule method H. Kobayashi et al. PRB 47 3500 (1993) P I41/a I41 I41/a Space group is P4estimated by extinction rule C2 P43 P41 Structure Analysis at LT

13. Impossible to resolve the Physical properties by analyzed result • Result of full-refinement ; r-factor = 6% • Charge Ratio of Cu ions is inconsistent as (Cu+:Cu2+=7:5). • Incommensurate phase between Cu charge ordering and DCNQI CDWs is realized. impossible to analyze with ordinary methods New style of Structure Analysis • Separate Cu site from the whole crystal structure by energy spectroscopic analysis • Charge determination by applying the Resonant X-ray Scattering Method

14. K-Edge of Cu ℓ =5/3 k ℓ =4/3 2 Anomalous scattering factor represents large energy dependence near K-edge energy. superspot Cu signal no Cu signal k 2 h h 2 2 Energy spectroscopy for superspots Atomic Scattering Factor ： f = f0+Δf ’+ iΔf ”

15. ③ ④ ① ② zi = zi0 + dCu dCu=Asin(2zio+fj) ③ ④ ① ② 3c dCu Cu f1=0 f2=π f3=0 f4=π c b a Shift of Cu site conducted by extinction rule Cu extraction determined Cu shift pattern

16. 00 ℓ 8 7 6 5 4 Cu+ Cu2+ 3 2 1 Cu present Cu absent superspot background Identified Cu Charge ordering pattern using resonant X-ray scattering methods existence of X-ray resonant peak ⇒ determination of Cu charge ordering

17. c’=3c c’=3c I I P P Space Group in the LT phase : P P I41/a C2/c I41/a C2/c I41 I41 I41/a I41/a C2 C2 P43 P1 P21 P2 P1 P43 P21 P2 P2/c P21/c P2/c P21/c P41 P41 Reselected Space Group Inexplicable the shift pattern and charge ordering pattern at Cu site in restriction of “tetragonal” Tetragonal

18. α Cu N Cu2+ Cu+ Charge of Cu site estimation by structure analysis charge of Cu increasing with aincreasing Charge transfer consistent with the resonant x-ray scattering Cu+ : (3d)10→ Cu2+ : (3d)9 a: small→ large

19. Charge Shift c poor rich b a CDW pattern by structure analysis NOT regular intervals in a column structure forming Charge Density Wave in DCNQI column

20. Cu+ Cu+ Cu2+ Cu+ Cu+ Cu2+ Commensurate structure between Cu charge ordering and Charge Density Wave on DCNQI column Frustration point 4’ 1’ 3 6 5’ 2’ c 2 5 6’ 3’ 1 4

21. Summary • Insulator phase of (DI-DCNQI)2Ag • Coexistence of charge ordering without dimerization columns and monotonic charge dimerized columns • Insulator phase of (DBr-DCNQI)2Cu • Realizes the local commensurability of the charge valance • Frustration among charged columns is restrained by the charge ordering of the Cu ions. The decisive role of the charge ordering nature in DCNQI salts includes frustration among DCNQI chains!

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