Fermi surface of 2H-NbSe2 and its implications on the charge-density-wave mechanism -: art. no. 235119

We report a detailed experimental and theoretical investigation of the Fermi-surface topology of the layered transition-metal dichalcogenide 2H-NbSe2, which undergoes a second-order phase transition into an incommensurate two-dimensional charge-density-wave phase at 33.5 K. High-resolution angle-resolved photoemission with synchrotron radiation yields two Nb 4d-related Fermi-surface cylinders and a Se 4p(z)-derived pocket around the center of the Brillouin zone. in good agreement with the result; of fully relativistic ab initio calculations within the local-density approximation of density-functional theory. The measurements were carried out at 50 K to identify characteristic features in the electronic structure of the normal phase that can give important clues as to the origins of the phase transition, and to achieve high resolution, at the same time. The implications of our results on the charge-density-wave mechanism in 2H-NbSe2 are discussed. Our results together with previous data from the literature seem to rule out the saddle-point mechanism, but they reveal at the same time that the driving mechanism for the transition into the charge-density-wave state is trot a simple Fermi-surface nesting, as recently suggested by Straub et al.