93Nb NMR study of the charge density wave state inNbSe2

Abstract

93Nb NMR studies were carried out for a single crystal ofNbSe2 at 73.328 MHz in the temperature range 9–300 K to investigate the normaland charge density wave (CDW) states. Detailed analysis of the NMR lineshape of the central transition using a classical incommensurate modelreveals the change in the conduction electron spin dynamics from aboveTCDW. An increase of theKnight shift below TCDW reflects modification to the uniform part of the conduction electron density of states. As suggestedtheoretically, the Knight shift distribution is found to be directly proportional to the square ofthe amplitude of the CDW. The results further indicate an incommensurate CDW state in2H-NbSe2. Analysis of the NMR spectra using the McMillan incommensuratemodel suggests a large value of the discommensuration parameter(γ) whichis almost temperature independent, in contrast to the much smaller value previously reported in the caseof 2H-TaSe2.