122 research outputs found
Doping change and distortion effect on double-exchange ferromagnetism
Doping change and distortion effect on the double-exchange ferromagnetism are
studied within a simplified double-exchange model. The presence of distortion
is modelled by introducing the Falicov-Kimball interaction between itinerant
electrons and classical variables. By employing the dynamical mean-field theory
the charge and spin susceptibility are exactly calculated. It is found that
there is a competition between the double-exchange induced ferromagnetism and
disorder-order transition. At low temperature various long-range order phases
such as charge ordered and segregated phases coexist with ferromagnetism
depending on doping and distortion. A rich phase diagram is obtained.Comment: 8 pages, 8 figure
Thermal transport in the Falicov-Kimball model
We prove the Jonson-Mahan theorem for the thermopower of the Falicov-Kimball
model by solving explicitly for the correlation functions in the large
dimensional limit. We prove a similar result for the thermal conductivity. We
separate the results for thermal transport into the pieces of the heat current
that arise from the kinetic energy and those that arise from the potential
energy. Our method of proof is specific to the Falicov-Kimball model, but
illustrates the near cancellations between the kinetic-energy and
potential-energy pieces of the heat current implied by the Jonson-Mahan
theorem.Comment: (11 pages, 7 figures, ReVTeX
Wikipedias: Collaborative web-based encyclopedias as complex networks
Wikipedia is a popular web-based encyclopedia edited freely and
collaboratively by its users. In this paper we present an analysis of
Wikipedias in several languages as complex networks. The hyperlinks pointing
from one Wikipedia article to another are treated as directed links while the
articles represent the nodes of the network. We show that many network
characteristics are common to different language versions of Wikipedia, such as
their degree distributions, growth, topology, reciprocity, clustering,
assortativity, path lengths and triad significance profiles. These
regularities, found in the ensemble of Wikipedias in different languages and of
different sizes, point to the existence of a unique growth process. We also
compare Wikipedias to other previously studied networks.Comment: v3: 9 pages, 12 figures, Change of title, few paragraphs and two
figures. Accepted for publication in Phys. Rev.
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