Analysis of 13C−NMR spectra in C60 superconductors: Hyperfine coupling constants, electronic correlation effect, and magnetic penetration depth

Abstract

A 13C−NMR anisotropic hyperfine coupling tensor was determined as 2π(−1.68,−1.68,3.37)×106rad/sec for C603− in A3C60 superconductors, where A is an alkali metal, by analyzing 13C−NMR spectra below 85 K. Combined with an isotropic coupling constant of (2π×0.69)×106rad/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 13C−NMR spectra at superconducting state, the traceless chemical (orbital) shift tensor and isotropic chemical shift were determined as (67, 34, -101) ppm and ∼150 ppm, respectively. An estimated magnetic penetration depth is larger than 570 nm in K3C60. Furthermore, the modified Korringa relation, T1TK2∼βS (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; β=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.

Source-reported materials — not catalogue approval

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