Suppression of charge ordering across the spin- Peierls transition in TMTTF based Q1D material Shigeki Fujiyama Inst. for Molecular Science (Dept. of Applied Physics, UT and CREST-JST) in collaboration with T. Nakamura (Okazaki) 13 C NMR spectra and 1/T 1 of (TMTTF) 2 AsF 6

Phase diagram of TMTTF salts (Q1D electronic states are realized)

Charge ordering in 1/4 filled 1dim. system 1) para- 1/4 filled 4kF-CDW Seo, Fukuyama 4k F -BCDW Mazumdar Clay Campbell V : intersite Coulomb repuslion 2) 3)

Low T phase diagram Physical ‘ touching ’ destroys charge ordering. Coexistence of CO and sP. (Also indicated by IR/Raman) High-field spectra PF 6 (sP)

This talk 13 C NMR spectra / Nuclear spin-lattice relaxation rate 1/T 1 for (TMTTF) 2 AsF 6 1) in the paramagnetic state 2) below (in the vicinity of ) spin-Peierls transition to pursue the development of charge ordering. A1) Development of CO is demonstrated succesfully. (only one spin correlation function) A2) Reduction of CO amplitude at T SP. (CO is not a necessary condition for sP transition)

13 C NMR spectra of (TMTTF) 2 AsF 6 Charge ordering at 102 K is confirmed, and the center of gravity of the spectra is unchanged at T CO. T CO T SP

Nuclear spin-lattice relaxation rate 1/T 1 The ratio of charge densities between charge accepting and donating sites is 2:1. Only one spin correlation func. and opening of a pseudogap to differentiate charge densities. T CO

Shifts in the vicinity of spin-Peierls transition Charge ordering is suppressed at the spin-Peierls transition temperature. T SP (if charge ordering would have survived in the SP state....) T SP 

1/T 1 in the vicinity of sP transition cf) Spin-Peierls transition in this material seems to be 1 st order.

Amplitude of charge ordering T CO T sP Amplitude of CO cf) UCLA group

Charge ordering Q1d organic CTS Antiferromagnet (DI-DCNQI) 2 Ag CO (TMTTF) 2 Br ---- CO at T N (TMTTF) 2 SCN--- CO at T AO (TMTTF) 2 SbF CO spin-Peierls (DMe-DCNQI) 2 Ag----non CO (TMTTF) 2 AsF This study (TMTTF) 2 PF 6 For Q1d material, 2k F -lattice instability seems to reduce site- ordering. (2d theta-ET2RbZn shows CO and sP, but much different NMR spectra from TMTTF.)

Summary ( 13 C NMR study of (TMTTF) 2 AsF 6 ) 1)Below T CO, only one spin correlation func. and pseudogap behavior to differentiate charge densities. 2)Charge ordering (4k F -CDW) is confirmed at 102 K. 3) Charge ordering is suppressed at T SP possibly due to considerable electron-lattice coupling. This naturally leads to competitive interplay between 4k F -CDW and spin-Peierls instability. The low T electronic state is located in the vicinity of the critical point between CO and non-CO.

Souces for discrepancies between UCLA 1. Different strategies to access the sP state. 2. Different sample and amplitude of CO (2:1 in my study and 3:1 in UCLA) Inherent problem in NMR for TMTTF salts 1. Comparable spin shift and chemical shift with opposite signs in the b-c plane. 2. Alternating transfer integrals (dimerization of molecules) (This favours bond ordering.)

Charge ordering in 1/4 filled 1dim. system 1) para- 1/4 filled 4k F -CDW Seo, Fukuyama 4k F -BCDW Mazumdar Clay Campbell V : intersite Coulomb repuslion 2) 3)