8,269 research outputs found
Double Exchange model for nanoscopic clusters
We solve the double exchange model on nanoscopic clusters exactly, and
specifically consider a six-site benzene-like nanocluster. This simple model is
an ideal testbed for studying magnetism in nanoclusters and for validating
approximations such as the dynamical mean field theory (DMFT). Non-local
correlations arise between neighboring localized spins due to the Hund's rule
coupling, favoring a short-range magnetic order of ferro- or antiferromagnetic
type. For a geometry with more neighboring sites or a sufficiently strong
hybridization between leads and the nanocluster, these non-local correlations
are less relevant, and DMFT can be applied reliably.Comment: 9 pages, 9 figures, 1 tabl
Signature of antiferromagnetic long-range order in the optical spectrum of strongly correlated electron systems
We show how the onset of a non-Slater antiferromagnetic ordering in a
correlated material can be detected by optical spectroscopy. Using dynamical
mean-field theory we identify two distinctive features: The antiferromagnetic
ordering is associated with an enhanced spectral weight above the optical gap,
and well separated spin-polaron peaks emerge in the optical spectrum. Both
features are indeed observed in LaSrMnO_4 [G\"ossling et al., Phys. Rev. B 77,
035109 (2008)]Comment: 11 pages, 9 figure
Local magnetic moments in iron and nickel at ambient and Earth's core conditions
Some Bravais lattices have a particular geometry that can slow down the
motion of Bloch electrons by pre-localization due to the band-structure
properties. Another known source of electronic localization in solids is the
Coulomb repulsion in partially filled d- or f-orbitals, which leads to the
formation of local magnetic moments. The combination of these two effects is
usually considered of little relevance to strongly correlated materials. Here
we show that it represents, instead, the underlying physical mechanism in two
of the most important ferromagnets: nickel and iron. In nickel, the van Hove
singularity has an unexpected impact on the magnetism. As a result, the
electron-electron scattering rate is linear in temperature, in violation of the
conventional Landau theory of metals. This is true even at Earth's core
pressures, at which iron is instead a good Fermi liquid. The importance of
nickel in models of geomagnetism may have therefore to be reconsidered.Comment: Supplementary Information available at
https://www.nature.com/articles/ncomms16062#supplementary-informatio
Critical properties of the half-filled Hubbard model in three dimensions
By means of the dynamical vertex approximation (DA) we include
spatial correlations on all length scales beyond the dynamical mean field
theory (DMFT) for the half-filled Hubbard model in three dimensions. The most
relevant changes due to non-local fluctuations are: (i) a deviation from the
mean-field critical behavior with the same critical exponents as for the three
dimensional Heisenberg (anti)-ferromagnet and (ii) a sizable reduction of the
N\'eel temperature () by for the onset of antiferromagnetic
order. Finally, we give a quantitative estimate of the deviation of the spectra
between DA and DMFT in different regions of the phase-diagram.Comment: 4 pages, 3 figures; accepted for publication in Phys. Rev. Let
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