N. Sato et al., ANALYSIS OF C-13-NMR SPECTRA IN C-60 SUPERCONDUCTORS - HYPERFINE COUPLING-CONSTANTS, ELECTRONIC CORRELATION EFFECT, AND MAGNETIC PENETRATION DEPTH, Physical review. B, Condensed matter, 58(18), 1998, pp. 12433-12440
A C-13-NMR anisotropic hyperfine coupling: tensor was determined as 2
pi(-1.68, -1.68, 3.37) x 10(6) rad/sec for C-60(3-) in A(3)C(60) super
conductors, where A is an alkali metal, by analyzing C-13-NMR spectra
below 85 K. Combined with an isotropic coupling constant of (2 pi x0.6
9)x10(6) rad/sec, the 2s and 2p characters of the electronic wave func
tions at the Fermi level were deduced. The results were compatible wit
h local-density-approximation band calculations. From a simulation of
C-13-NMR spectra at superconducting state, the traceless chemical (orb
ital) shift tensor and isotropic chemical shift were determined as (67
, 34, -101) ppm and similar to 150 ppm, respectively. An estimated mag
netic penetration depth is larger than 570 nm in K3C60 Furthermore, th
e modified Korringa relation, T(1)TK(2)similar to beta S (with Knight
shift K,: spin-lattice relaxation time T-1, and Korringa constant S),
clearly showed the existence of weak but substantial antiferromagnetic
spin fluctuation in A(3)C(60); beta=0.40-0.58 with an error of +/-20%
. The Stoner enhancement factor was also determined as 1-1.5 from a co
mparison between spin susceptibility obtained from NMR and band-calcul
ation results. [S0163-1829(98)00542-6].