Temperature dependent locally resolved 13C knight shifts in the organic conductor TTF[Ni(dmit)2]2

Abstract

High resolution 13 C NMR results for the organic conductor TTF[Ni(dmit) 2 ] 2 enriched by 13 C isotope in Ni(dmit) 2 molecules are reported. Variable temperature magic angle spinning experiments were performed between 160 and 295 K. Paramagnetic Knight shifts in the range 41-106.5 ppm at room temperature are observed for all Ni(dmit) 2 carbon sites. These shifts are slightly temperature dependent for inner carbons. However, for outer carbons, the shifts strongly decrease towards low temperature due to precursor effects of the charge density wave (CDW) transition. The results confirm the occurrence of both HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) conduction bands and are compared with calculated partial contributions of individual carbon atoms to the density of states at the Fermi level. We suggest that CDW effects above 160 K are associated with the LUMO bands