NMR measurements of phenomena related to charge density waves in NbSe₂

Abstract

NMR techniques have been used to investigate the charge density wave (CDW) state in NbSe2. Above the transition temperature T0, the Knight shift and electric field gradient (EFG) tensors have been measured. Broadening of quadrupolar transitions above T0 has been attributed to fluctuations in the EFG which are a precursor to the formation of CDW's. Below T0, a Knight shift distribution is observed whose width can be correlated with the amplitude of an incommensurate CDW which shows a temperature dependence characteristic of BCS type order parameter. The width of the distribution extrapolated to T=0 is shown to be proportional to T0, a fact which supports the hypothesis of a BCS model for the CDW state.