93Nb NMR study of NbSe3

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Abstract
We present a NMR study of the anisotropic metal NbSe3. 93Nb NMR lines have been recorded by conventional pulsed NMR techniques and field sweeping around 65 and ,140 kG. Measurements were made at room temperature, 77 and 4.2 K on a powder sample and on a sample made of crystals aligned along the b axis (chain axis). At room temperature, spectra with the magnetic field along b allow us to distinguish three inequivalent sites with different Knight shifts and quadrupolar frequencies. At low temperature, one site remains unaffected by the occurrence of the charge density waves at 144 and 59 K. For the two others, the quadrupolar structures disappear as a consequence of the modulation of the local electric field by the charge density waves, and the Knight shifts are changed because of the partial destruction of the Fermi surface. An interpretation is proposed in terms of band structure : the site which is not affected by the charge density waves would belong to an insulating chain with filled d subband, while the two other sites would correspond to the metallic chains with nearly one-quarter-filled bands, which are involved in the two successive charge density wave transitions. A decomposition of the paramagnetic susceptibility in orbital and spin contributions is given

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