Suppression of charge ordering across the spin-Peierls transition in TMTTF based Q1D material 13C NMR spectra and 1/T1 of (TMTTF)2AsF6 Shigeki Fujiyama Inst. for Molecular Science (Dept. of Applied Physics, UT and CREST-JST) in collaboration with T. Nakamura (Okazaki)
V : intersite Coulomb repuslion Charge ordering in 1/4 filled 1dim. system 1) para- 1/4 filled 2) 4kF-CDW Seo, Fukuyama 4kF-BCDW Mazumdar Clay Campbell 3)
Low T phase diagram Coexistence of CO and sP. (Also indicated by IR/Raman) High-field spectra PF6 (sP) Physical ‘touching’ destroys charge ordering.
This talk • 13C NMR spectra / Nuclear spin-lattice relaxation rate 1/T1 for (TMTTF)2AsF6 • 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 TSP. • (CO is not a necessary condition for sP transition)
13C NMR spectra of (TMTTF)2AsF6 TSP TCO Charge ordering at 102 K is confirmed, and the center of gravity of the spectra is unchanged at TCO.
Nuclear spin-lattice relaxation rate 1/T1 The ratio of charge densities between charge accepting and donating sites is 2:1. TCO Only one spin correlation func. and opening of a pseudogap to differentiate charge densities.
TSP TSP Dw Shifts in the vicinity of spin-Peierls transition Charge ordering is suppressed at the spin-Peierls transition temperature. (if charge ordering would have survived in the SP state....)
1/T1 in the vicinity of sP transition cf) Spin-Peierls transition in this material seems to be 1st order.
Amplitude of CO TsP TCO Amplitude of charge ordering cf) UCLA group
Summary(13C NMR study of (TMTTF)2AsF6) Below TCO, only one spin correlation func. and pseudogap behavior to differentiate charge densities. Charge ordering (4kF-CDW) is confirmed at 102 K. Charge ordering is suppressed at TSP possibly due to considerable electron-lattice coupling. This naturally leads to competitive interplay between 4kF-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 • Different strategies to access the sP state. • Different sample and amplitude of CO (2:1 in my study and 3:1 in UCLA) • Inherent problem in NMR for TMTTF salts • Comparable spin shift and chemical shift with opposite signs in the b-c plane. • Alternating transfer integrals (dimerization of molecules) (This favours bond ordering.)
V : intersite Coulomb repuslion Charge ordering in 1/4 filled 1dim. system 1) para- 1/4 filled 2) 4kF-CDW Seo, Fukuyama 3) 4kF-BCDW Mazumdar Clay Campbell