Cooperative phenomena in (TMTSF)2ClO4 : an NMR evidence

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Abstract
We present 1H and 77Se NMR relaxation data on oriented (TMTSF)2ClO4 single crystals in the relaxed state. The data show the existence of three distinct regimes for the nuclear relaxation rate T-11. In the high temperature part (T > 25 K) the Korringa law seems to be well satisfied whereas in the lower temperature part we have strong deviations down to 8 K or so. At T ≲ 6 K, a different and enhanced Korringa regime appears to be restored. Preliminary results on (TMTSF)2FSO3 under pressure also show similar features. We propose an interpretation of the T-11 behaviour based on the existence of one-dimensional 2 k F spin correlations for repulsive short range intrachain electron-electron interactions. The coherent interchain hopping acts as the main mechanism for the restored but renormalized Korringa behaviour. Moreover, from the low-field data, the proposed scheme of interpretation is not incompatible with the presence of superconducting precursor effects

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