1,276 research outputs found
Disentangling density and temperature effects in the viscous slowing down of glassforming liquids
We present a consistent picture of the respective role of density and
temperature in the viscous slowing down of glassforming liquids and polymers.
Specifically, based in part upon a new analysis of simulation and experimental
data on liquid ortho-terphenyl, we conclude that a zeroth-order description of
the approach to the glass transition should be formulated in terms of a
temperature-driven super-Arrhenius activated behavior rather than a
density-driven congestion or jamming phenomenon. The density plays a role at a
quantitative level, but its effect on the viscosity and the structural
relaxation time can be simply described via a single parameter, an effective
interaction energy that is characteristic of the high temperature liquid
regime; as a result, density does not affect the ``fragility'' of the
glassforming system.Comment: RevTeX4, 8 pages, 8 eps figure
Antiferromagnetism and phase separation in the t-J model at low doping: a variational study
Using Gutzwiller-projected wave functions, I estimate the ground-state energy
of the t-J model for several variational states relevant for high-temperature
cuprate superconductors. The results indicate antiferromagnetism and phase
separation at low doping both in the superconducting state and in the
staggered-flux normal state proposed for the vortex cores. While phase
separation in the underdoped superconducting state may be relevant for the
stripe formation mechanism, the results for the normal state suggest that
similar charge inhomogeneities may also appear in vortex cores up to relatively
high doping values.Comment: 4 pages, 3 figures, reference adde
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- Superconductivity, Fractional Quantum Hall Effect and Berry Phase
We have analysed here the equivalence of RVB states with 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 .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 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
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