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

Sato N.

Tou Hideki

Maniwa Y.

Kikuchi K.

Suzuki S.

Achiba Y.

Kosaka M.

Tanigaki K.

Physical review. B

A 13C-NMR anisotropic hyperfine coupling tensor was determined as 2π(-1.68, -1.68, 3.37)×106 rad/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)×106 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 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%.0 The Stoner enhancement factor was also determined as 1–1.5 from a comparison between spin susceptibility obtained from NMR and band-calculation results.

Physics [ 420 ]

eng

American Physical Society

Copyright (c) 1998 The American Physical Society

[ISSN] 1098-0121

[DOI] 10.1103/PhysRevB.58.12433

[NCID] AA11187113

[DOI] http://dx.doi.org/10.1103/PhysRevB.58.12433