Résumé
The 13C NMR relaxation time T1 and Knight shift K have been measured in the organic conductor TTF-TCNQ with 13C- enriched TTF molecules. A clear anomaly in T1 and K shows that the gap in the conducting band of the TTF stack opens only below 38K. No T 1 or K anomalies have been observed either at 54 or at 49K. The authors propose a new decomposition of the total spin susceptibility into contributions coming from individual TTF and TCNQ bands, which is based on 13C NMR Knight shift data. The salient new information provided by this work is that the ratio chi Q/ chi F is larger than unity above 60K. The present results have been used to reanalyse the 1H NMR data in the literature. They have reached the conclusion that the TTF band is broader ( approximately 0.65 eV) than the TCNQ band ( approximately 0.40 eV). The observed large enhancement of the Korringa relation suggests that the Coulomb correlation energy U is of the order of the band width for both stacks.