J. Phys. France 51, 2465-2476 (1990)
DOI: 10.1051/jphys:0199000510210246500

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

A. Vainrub¹, E. Canadell², D. Jérome¹, P. Bernier³, T. Nunes³, M.-F. Bruniquel⁴ et P. Cassoux<sup>4

1</sup>  Laboratoire de Physique des Solides, Université de Paris-Sud, 91405 Orsay, France
²  Laboratoire de Chimie Théorique, Université de Paris-Sud, 91405 Orsay, France
³  Groupe de Dynamique des Phases Condensées, Université des Sciences et Techniques du Languedoc, 34060 Montpellier, France
⁴  Laboratoire de Chimie de Coordination du CNRS, Université Paul Sabatier, 31077 Toulouse, France

Abstract
High resolution 13C NMR results for the organic conductor TTF[Ni(dmit) 2]2 enriched by 13C 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.

PACS
7660C - Chemical and Knight shifts.
7120R - Polymers and organic compounds.
7145L - Charge-density-wave systems.

Key words
charge density waves -- conduction bands -- electronic density of states -- Fermi level -- Knight shift -- molecular orbitals calculations -- organic compounds -- synthetic metals