1,594 research outputs found
-Electron Ferromagnetism in Metal Free Carbon Probed by Soft X-Ray Dichroism
Elemental carbon represents a fundamental building block of matter and the
possibility of ferromagnetic order in carbon attracted widespread attention.
However, the origin of magnetic order in such a light element is only poorly
understood and has puzzled researchers. We present a spectromicroscopy study at
room temperature of proton irradiated metal free carbon using the elemental and
chemical specificity of x-ray magnetic circular dichroism (XMCD). We
demonstrate that the magnetic order in the investigated system originates only
from the carbon -electron system.Comment: 10 pages 3 color figure
Magnetic phase diagram of the Hubbard model with next-nearest-neighbour hopping
We calculate the magnetic phase diagram of the Hubbard model for a Bethe
lattice with nearest neighbour (NN) hopping and next nearest neighbour
(NNN) hopping in the limit of infinite coordination. We use the amplitude
of the NNN hopping to tune the density of states (DOS) of the
non-interacting system from a situation with particle-hole symmetry to an
asymmetric one with van-Hove singularities at the lower ()
respectively upper () band edge for large enough . For
this strongly asymmetric situation we find rather extended parameter regions
with ferromagnetic states and regions with antiferromagnetic states.Comment: 13 pages, 7 figure
Band selection and disentanglement using maximally-localized Wannier functions: the cases of Co impurities in bulk copper and the Cu (111) surface
We have adapted the maximally-localized Wannier function approach of [I.
Souza, N. Marzari and D. Vanderbilt, Phys. Rev. B 65, 035109 (2002)] to the
density functional theory based Siesta method [J. M. Soler et al., J. Phys.:
Cond. Mat. 14, 2745 (2002)] and applied it to the study of Co substitutional
impurities in bulk copper as well as to the Cu (111) surface. In the Co
impurity case, we have reduced the problem to the Co d-electrons and the Cu
sp-band, permitting us to obtain an Anderson-like Hamiltonian from well defined
density functional parameters in a fully orthonormal basis set. In order to
test the quality of the Wannier approach to surfaces, we have studied the
electronic structure of the Cu (111) surface by again transforming the density
functional problem into the Wannier representation. An excellent description of
the Shockley surface state is attained, permitting us to be confident in the
application of this method to future studies of magnetic adsorbates in the
presence of an extended surface state
Young athletes under pressure?
Regular participation in exercise has long been known to result in cardiovascular adaptation. Historically, the ‘athlete’s heart’ hypothesis has encouraged a dichotomised view of the heart’s adaptation to sport, depending on whether the physical activity was either of isotonic activity (runners and swimmers) resulting in ‘cardiomegaly’ or of isometric effort (wrestlers and shot putters, ie, ‘strength’ athletes) with clear peripheral adaptations and an ‘obvious increase in cardiac size’. Today, the classification of sports according to their physiological demands acknowledges a greater diversity of exposure, depending on the physical activity, with an emphasis on a ‘graded transition’ between the main categories: dynamic, static and impact. Still, our understanding of the determinants of structural and functional cardiovascular adaptation to exercise are limited, and the consequences for health remain a matter of debate
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