The charge density wave instability in 2H-NbSe₂

Experimental and theoretical results on the charge density wave (CDW) layered compound 2H-NbSe₂ have been reviewed and discussed in relation to the nature of the CDW instability. A simple extension of the saddle point model to three dimensions has been given. The results are discussed in connection with the available band calculations. The anisotropic Knight shift, based on a [sup d]z², [sup d]xy, [sup d]x²-y² Fermi surface, has been estimated and compared with the NMR experimental value. The results indicate that the Fermi surface contains a significant mixture of the three "d" orbitals, but not enough to place the saddle point at the Fermi energy in the fitted tight binding bands. It is concluded that more work is necessary to decide whether saddle point or nesting behavior is responsible for CDW formation in 2H-NbSe₂.Science, Faculty ofPhysics and Astronomy, Department ofGraduat