Temperature effects on the 13C high resolution NMR in (TMTSF)2X salts

Abstract We report the results of the 13 C NMR experiments performed on TMTSF molecules of the organic conductors (TMTSF) 2 ClO 4 and (TMTSF) 2 ReO 4 . This investigation has allowed to resolve all individual sites of the organic molecule. Strong and widely distributed enhanced nuclear relaxation rates on different sites of the molecule suggest a picture where Coulomb correlations play a major role for the sites at the corners of the molecule. On the system (TMTSF) 2 ReO 4 , continuous variations of the resonance positions are observed when the temperature is decreased down to 182 K, temperature at which the system exhibits a structural transition, leading to a semiconducting state at lower temperature. This experiment constitutes the first observation in direct space of the collapse of the conduction electron density at a metal-semiconductor transition.