Analysis of C-13-NMR spectra in C-60 superconductors: Hyperfine coupling constants, electronic correlation effect, and magnetic penetration depth

[摘要] 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) superconductors, where A is an alkali metal, by analyzing C-13-NMR spectra below 85 K. Combined with an isotropic coupling constant of (2 pi x0.69)x10(6) rad/sec, the 2s and 2p characters of the electronic wave functions at the Fermi level were deduced. The results were compatible with local-density-approximation band calculations. From a simulation of C-13-NMR spectra at superconducting state, the traceless chemical (orbital) shift tensor and isotropic chemical shift were determined as (67, 34, -101) ppm and similar to 150 ppm, respectively. An estimated magnetic penetration depth is larger than 570 nm in K3C60 Furthermore, the 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 comparison between spin susceptibility obtained from NMR and band-calculation results. [S0163-1829(98)00542-6].

[关键词] SPIN-LATTICE RELAXATION;KNIGHT-SHIFT;FULLERENE SUPERCONDUCTORS;MOLECULAR-DYNAMICS;ALKALI FULLERIDES;PHASE-TRANSITION;K3C60;NMR;RESONANCE;RB2CSC60