12,363 research outputs found
On the Behavior of F2 and its Logarithmic Slopes
It is shown that the CKMT model for the nucleon structure function F2, taken
as the initial condition for the NLO evolution equations in perturbative QCD,
provides a good description of the HERA data when presented in the form of the
logarithmic slopes of F2 vs x and Q2 (Caldwell-plot), in the whole available
kinematic ranges. Also the results obtained for the behavior of the gluon
component of a nucleon are presented.Comment: 16 pages, 10 figure
Effects of anisotropy in spin molecular-orbital coupling on effective spin models of trinuclear organometallic complexes
We consider layered decorated honeycomb lattices at two-thirds filling, as
realized in some trinuclear organometallic complexes. Localized moments
with a single-spin anisotropy emerge from the interplay of Coulomb repulsion
and spin molecular-orbit coupling (SMOC). Magnetic anisotropies with bond
dependent exchange couplings occur in the honeycomb layers when the direct
intracluster exchange and the spin molecular-orbital coupling are both present.
We find that the effective spin exchange model within the layers is an XXZ +
120 honeycomb quantum compass model. The intrinsic non-spherical
symmetry of the multinuclear complexes leads to very different transverse and
longitudinal spin molecular-orbital couplings, which greatly enhances the
single-spin and exchange coupling anisotropies. The interlayer coupling is
described by a XXZ model with anisotropic biquadratic terms. As the correlation
strength increases the systems becomes increasingly one-dimensional. Thus, if
the ratio of SMOC to the interlayer hopping is small this stabilizes the
Haldane phase. However, as the ratio increases there is a quantum phase
transition to the topologically trivial `-phase'. We also predict a quantum
phase transition from a Haldane phase to a magnetically ordered phase at
sufficiently strong external magnetic fields.Comment: 22 pages, 11 figures. Final version of paper to be published in PRB.
Important corrections to appendix
Heisenberg and Dzyaloshinskii-Moriya interactions controlled by molecular packing in tri-nuclear organometallic clusters
Motivated by recent synthetic and theoretical progress we consider magnetism
in crystals of multi-nuclear organometallic complexes. We calculate the
Heisenberg symmetric exchange and the Dzyaloshinskii-Moriya antisymmetric
exchange. We show how, in the absence of spin-orbit coupling, the interplay of
electronic correlations and quantum interference leads to a quasi-one
dimensional effective spin model in a typical tri-nuclear complex,
MoS(dmit), despite its underlying three dimensional band structure.
We show that both intra- and inter-molecular spin-orbit coupling can cause an
effective Dzyaloshinskii-Moriya interaction. Furthermore, we show that, even
for an isolated pair of molecules the relative orientation of the molecules
controls the nature of the Dzyaloshinskii-Moriya coupling. We show that
interference effects also play a crucial role in determining the
Dzyaloshinskii-Moriya interaction. Thus, we argue, that multi-nuclear
organometallic complexes represent an ideal platform to investigate the effects
of Dzyaloshinskii-Moriya interactions on quantum magnets.Comment: This update incorporates the corrections described in a recently
submitted erratum. Changes are confined to sections IV.A and B. The
conclusions of the paper are unchanged. 12 + 4 pages, 9 figure
Spin-orbit coupling in {MoS(dmit)}
Spin-orbit coupling in crystals is known to lead to unusual direction
dependent exchange interactions, however understanding of the consequeces of
such effects in molecular crystals is incomplete. Here we perform four
component relativistic density functional theory computations on the
multi-nuclear molecular crystal {MoS(dmit)} and show that both
intra- and inter-molecular spin-orbit coupling are significant. We determine a
long-range relativistic single electron Hamiltonian from first principles by
constructing Wannier spin-orbitals. We analyse the various contributions
through the lens of group theory. Intermolecular spin-orbit couplings like
those found here are known to lead to quantum spin-Hall and topological
insulator phases on the 2D lattice formed by the tight-binding model predicted
for a single layer of {MoS(dmit)}
Mott transition in two-dimensional frustrated compounds
The phase diagrams of isotropic and anisotropic triangular lattices with
local Coulomb interactions are evaluated within cluster dynamical mean field
theory. As a result of partial geometric frustration in the anisotropic
lattice, short range correlations are shown to give rise to reentrant behavior
which is absent in the fully frustrated isotropic limit. The qualitative
features of the phase diagrams including the critical temperatures are in good
agreement with experimental data for the layered organic charge transfer salts
kappa-(BEDT-TTF)_2Cu[N(CN)_2]Cl and kappa-(BEDT-TTF)_2Cu_2(CN)_3.Comment: 4 pages, 4 figure
Unconventional metallic conduction in two-dimensional Hubbard-Wigner lattices
The interplay between long-range and local Coulomb repulsion in strongly
interacting electron systems is explored through a two-dimensional
Hubbard-Wigner model. An unconventional metallic state is found in which
collective low-energy excitations characteristic of the Wigner crystal induce a
flow of electrical current despite the absence of one-electron spectral weight
at the Fermi surface. Photoemission experiments on certain quarter-filled
layered molecular crystals should observe a gap in the excitation spectrum
whereas optical spectroscopy should find a finite Drude weight indicating
metallic behavior.Comment: 10 pages, accepted for publication in PR
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