NMR study on a 2H-NbSe₂single crystal: A microscopic investigation of the charge density waves state

Presents a pulsed NMR study on a single crystal of 2H-NbSe 2 at atmospheric pressure and under hydrostatic pressure of 21 kbar in the temperature range 4.2-273K. Analysis of Knight shift (KS) and nuclear spin-lattice relaxation (NSLR) time data in the normal state are consistent with N(E F )=2.4 states/eV spin and an admixture of 40% of d xy and d x2-y2 wavefunctions in the d z2 band. The product T 1 T=500+or-100 ms K was found constant in the temperature range 4.2-77K and pressure independent; measurements at the 'magic angle' indicate an orbital contribution (T 1 T) -1 approximately=0.9+or-0.9 (sK) -1 . The results are consistent with the onset of incommensurate charge density waves (ICDW) at T 0 =33K at P=1 bar and T 0 =26K at 21 kbar. Below T 0 , the lineshapes of the m to m-1 transitions agree with a local distribution of KS and EFG respecting the symmetry of a triple ICDW with a maximum value of 9% for the redistribution of conduction electrons within an atomic cell. Above T 0 , nuclear spin-spin relaxation measurements demonstrate that the observed pretransitional broadening of the lines is due to static CDW fluctuations, induced by impurities.