Analysis of13C−NMRspectra inC60superconductors: Hyperfine coupling constants, electronic correlation effect, and magnetic penetration depth

Abstract

A C-NMR anisotropic hyperfine coupling tensor was determined as 2p(21.68, 21.68, 3.37) 310 rad/sec for C60 32 in A3C60 superconductors, where A is an alkali metal, by analyzing C-NMR spectra below 85 K. Combined with an isotropic coupling constant of (2p30.69)310 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-NMR spectra at superconducting state, the traceless chemical ~orbital! shift tensor and isotropic chemical shift were determined as ~67, 34, 2101! ppm and ;150 ppm, respectively. An estimated magnetic penetration depth is larger than 570 nm in K3C60. Furthermore, the modified Korringa relation, T1TK ;bS ~with Knight shift K, spin-lattice relaxation time T1 , and Korringa constant S!, clearly showed the existence of weak but substantial antiferromagnetic spin fluctuation in A3C60; b50.40– 0.58 with an error of 620%. 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#