6,604 research outputs found
Analytical study of tunneling times in flat histogram Monte Carlo
We present a model for the dynamics in energy space of multicanonical
simulation methods that lends itself to a rather complete analytic
characterization. The dynamics is completely determined by the density of
states. In the \pm J 2D spin glass the transitions between the ground state
level and the first excited one control the long time dynamics. We are able to
calculate the distribution of tunneling times and relate it to the
equilibration time of a starting probability distribution. In this model, and
possibly in any model in which entering and exiting regions with low density of
states are the slowest processes in the simulations, tunneling time can be much
larger (by a factor of O(N)) than the equilibration time of the probability
distribution. We find that these features also hold for the energy projection
of single spin flip dynamics.Comment: 7 pages, 4 figures, published in Europhysics Letters (2005
Phenomenological study of the electronic transport coefficients of graphene
Using a semi-classical approach and input from experiments on the
conductivity of graphene, we determine the electronic density dependence of the
electronic transport coefficients -- conductivity, thermal conductivity and
thermopower -- of doped graphene. Also the electronic density dependence of the
optical conductivity is obtained. Finally we show that the classical Hall
effect (low field) in graphene has the same form as for the independent
electron case, characterized by a parabolic dispersion, as long as the
relaxation time is proportional to the momentum.Comment: 4 pages, 1 figur
Exact Solution of Ising Model on a Small-World Network
We present an exact solution of a one-dimensional Ising chain with both
nearest neighbor and random long-range interactions. Not surprisingly, the
solution confirms the mean field character of the transition. This solution
also predicts the finite-size scaling that we observe in numerical simulations.Comment: 9 pages, 7 figures, submitted to pr
Disorder Induced Localized States in Graphene
We consider the electronic structure near vacancies in the half-filled
honeycomb lattice. It is shown that vacancies induce the formation of localized
states. When particle-hole symmetry is broken, localized states become
resonances close to the Fermi level. We also study the problem of a finite
density of vacancies, obtaining the electronic density of states, and
discussing the issue of electronic localization in these systems. Our results
also have relevance for the problem of disorder in d-wave superconductors.Comment: Replaced with published version. 4 pages, 4 figures. Fig. 1 was
revise
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