Suppression of charge ordering across the spin peierls transition in tmttf based q1d material
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Suppression of charge ordering across the spin-Peierls transition in TMTTF based Q1D material 13 C NMR spectra and 1/T 1 of (TMTTF) 2 AsF 6 Shigeki Fujiyama Inst. for Molecular Science (Dept. of Applied Physics, UT and CREST-JST) in collaboration with T. Nakamura (Okazaki)

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Suppression of charge ordering across the spin-Peierls transition in TMTTF based Q1D material

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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)


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


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


Charge ordering Q1d organic CTS


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


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