title: Evidence for insulating behavior in the electric conduction of (NH(3))K(3)C(60) systems.
abstract: Microwave study using the cavity perturbation technique revealed that the conductivity of the antiferromagnet (NH(3))K(3-x)Rb(x)C(60) at 200 K is already 3-4 orders of magnitude smaller than those of superconductors, K(3)C(60) and (NH(3))(x)NaRb(2)C(60), and that the antiferromagnetic compounds are insulators below 250 K without metal-insulator transitions. The striking difference in the magnitude of the conductivity between these materials strongly suggests that the Mott-Hubbard transition in the ammoniated alkali fullerides is driven by a reduction of lattice symmetry from face-centered-cubic to face-centered-orthorhombic, rather than by the magnetic ordering.
authors.affiliation: Department of Basic Science, The University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kitano
authors.forename: R
authors.initials: R
authors.lastname: Matsuo
authors.forename: K
authors.initials: K
authors.lastname: Miwa
authors.forename: A
authors.initials: A
authors.lastname: Maeda
authors.forename: T
authors.initials: T
authors.lastname: Takenobu
authors.forename: Y
authors.initials: Y
authors.lastname: Iwasa
authors.forename: T
authors.initials: T
authors.lastname: Mitani