2002/04/12 by V. Brouet, H. Alloul, L. Forró +1 · 2 citations
Chemistry · Materials Science · Physics and Astronomy · #Boron and Carbon Nanomaterials Research #Diamond and Carbon-based Materials Research #Fullerene Chemistry and Applications #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.66.155123
9 pages, 10 figures
arxiv created 2002/04/12 · openalex publication_date 2002/10/31 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We present a detailed nuclear magnetic resonance (NMR) study of simple cubic CsC60, the only metallic cubic fulleride known so far besides A3C60, obtained by quenching from high temperature. 133Cs NMR signals the presence of about 12--15 % of ``anomalous'' C60 balls, characterized by a 15-meV gap. We present different experimental observations supporting the idea that a spin singlet (i.e., a C60^2\ensuremath-) is localized on these latter balls and stabilized by a Jahn-Teller distortion. A splitting of the 133Cs spectrum into three different lines, with distinct electronic environments, is observed, which emerges naturally from such a situation. Quadrupole effects on 133Cs confirm an inhomogeneous distribution of the charge between C60 molecules. Analysis of the relative intensities of the 133Cs lines show that the spin singlets do not form clusters at the local scale, but are diluted within the lattice. This is probably to avoid the occurrence of neighboring C60^2\ensuremath- and minimize electrostatic repulsion between these balls. Through spin-lattice relaxation measurements, we detect chemical exchange between the Cs sites above 100 K. From this, we deduce that the lifetime of a spin singlet on a given ball decreases exponentially with increasing temperature (from 15 s at 100 K to 3 ms at 130 K) with an activation energy of 320 meV. The implications of the presence of such spin singlets for the nature of the metallic state is discussed, in relation with a decrease of 1/T1T for 13C at low temperatures, which indicates a deviation from a simple metallic model.