Electron spin relaxation of N@C60 in CS2

We examine the temperature dependence of the relaxation times of the molecules N@C60 and N@C70 (which comprise atomic nitrogen trapped within a carbon cage) in liquid CS2 solution. The results are inconsistent with the fluctuating zero field splitting (ZFS) mechanism, which is commonly invoked to explain electron spin relaxation for S > 1/2 spins in liquid solution, and is the mechanism postulated in the literature for these systems. Instead, we find a clear Arrhenius temperature dependence for N@C60, indicating the spin relaxation is driven primarily by an Orbach process. For the asymmetric N@C70 molecule, which has a permanent non-zero ZFS, we resolve an additional relaxation mechanism caused by the rapid reorientation of its ZFS. We also report the longest coherence time (T2) ever observed for a molecular electron spin, being 0.25 ms at 170K.Comment: 6 pages, 6 figures V2: Updated to published versio

Topological Aspect of high-TcT_c Superconductivity, Fractional Quantum Hall Effect and Berry Phase

We have analysed here the equivalence of RVB states with $\nu=1/2$ FQH states in terms of the Berry Phase which is associated with the chiral anomaly in 3+1 dimensions. It is observed that the 3-dimensional spinons and holons are characterised by the non-Abelian Berry phase and these reduce to 1/2 fractional statistics when the motion is confined to the equatorial planes. The topological mechanism of superconductivity is analogous to the topological aspects of fractional quantum Hall effect with $\nu=1/2$.Comment: 12 pages latex fil

The viscous slowing down of supercooled liquids as a temperature-controlled superArrhenius activated process: a description in terms of frustration-limited domains

We propose that the salient feature to be explained about the glass transition of supercooled liquids is the temperature-controlled superArrhenius activated nature of the viscous slowing down, more strikingly seen in weakly-bonded, fragile systems. In the light of this observation, the relevance of simple models of spherically interacting particles and that of models based on free-volume congested dynamics are questioned. Finally, we discuss how the main aspects of the phenomenology of supercooled liquids, including the crossover from Arrhenius to superArrhenius activated behavior and the heterogeneous character of the $\alpha$ relaxation, can be described by an approach based on frustration-limited domains.Comment: 13 pages, 4 figures, accepted in J. Phys.: Condensed Matter, proceedings of the Trieste workshop on "Unifying Concepts in Glass Physics