431 research outputs found
Spatially Anisotropic Heisenberg Kagome Antiferromagnet
We study the quasi-one-dimensional limit of the spin-1/2 quantum Heisenberg
antiferromagnet on the kagome lattice. The lattice is divided into
antiferromagnetic spin-chains (exchange J) that are weakly coupled via
intermediate "dangling" spins (exchange J'). Using one-dimensional
bosonization, renormalization group methods, and current algebra techniques the
ground state is determined in the limit J'<<J. We find that the dangling spins
and chain spins form a spiral with O(1) and O(J'/J) static moments,
respectively, atop of which the chain spins exhibit a smaller O[(J'/J)^2]
antiferromagnetically ordered component along the axis perpendicular to the
spiral plane.Comment: 17 pages, 3 figures, corrected sign error, corrected typos, updated
reference
The square-lattice spiral magnet Ba_2CuGe_2O_7 in an in-plane magnetic field
The magnetic structure of Ba_2CuGe_2O_7 is investigated by neutron
diffraction in magnetic fields applied along several directions in the
plane of the crystal. In relatively weak fields, ~T, the
propagation vector of the spin-spiral rotates to form a finite angle with the
field direction. This angle depends on the orientation of itself. The
rotation of the propagation vector is accompanied by a re-orientation of the
plane of spin rotation in the spiral. The observed behaviour is well described
by a continuous-limit form of a free energy functional that includes exchange
and Dzyaloshinskii-Moriya interactions, as well as the Zeeman energy and an
empirical anisotropy term.Comment: 7 pages, 6 figure
An Initial Step of GAS-Containing Autophagosome-Like Vacuoles Formation Requires Rab7
Group A streptococcus (GAS; Streptococcus pyogenes) is a common pathogen that invades non-phagocytic human cells via endocytosis. Once taken up by cells, it escapes from the endocytic pathway to the cytoplasm, but here it is contained within a membrane-bound structure termed GAS-containing autophagosome-like vacuoles (GcAVs). The autophagosome marker GFP-LC3 associates with GcAVs, and other components of the autophagosomal pathway are involved in GcAV formation. However, the mechanistic relationship between GcAV and canonical autophagy is largely unknown. Here, we morphologically analyzed GcAV formation in detail. Initially, a small, GFP-LC3-positive GcAV sequesters each streptococcal chain, and these then coalesce into a single, large GcAV. Expression of a dominant-negative form of Rab7 or RNAi-mediated knockdown of Rab7 prevented the initial formation of small GcAV structures. Our results demonstrate that mechanisms of GcAV formation includes not only the common machinery of autophagy, but also Rab7 as an additional component, which is dispensable in canonical autophagosome formation
Vertex Corrections and the Korringa Ratio in Strongly Correlated Electron Materials
We show that the Korringa ratio, associated with nuclear magnetic resonance
in metals, is unity if vertex corrections for the dynamic spin susceptibility
are negligible and the hyperfine coupling is momentum independent. In the
absence of vertex corrections we also find a Korringa behaviour for , the
nuclear spin relaxation rate, i.e., , and a temperature
independent Knight shift. These results are independent of the form and
magnitude of the self-energy (so far as is consistent with neglecting vertex
corrections) and of the dimensionality of the system.Comment: 5 pages. accepted for publication in J. Phys.: Condens. Matte
Fermi liquid theory for the Anderson model out of equilibrium
We study low-energy properties of the Anderson impurity under a finite bias
voltage using the perturbation theory in of Yamada and Yosida in the
nonequilibrium Keldysh diagrammatic formalism, and obtain the Ward identities
for the derivative of the self-energy with respect to . The self-energy is
calculated exactly up to terms of order , and , and the
coefficients are defined with respect to the equilibrium ground state. From
these results, the nonlinear response of the current through the impurity has
been deduced up to order .Comment: 8 pages, 1 figur
Construction of the free energy landscape by the density functional theory
On the basis of the density functional theory, we give a clear definition of
the free energy landscape. To show the usefulness of the definition, we
construct the free energy landscape for rearrangement of atoms in an FCC
crystal of hard spheres. In this description, the cooperatively rearranging
region (CRR) is clealy related to the hard spheres involved in the saddle
between two adjacent basins. A new concept of the simultaneously rearranging
region (SRR) emerges naturally as spheres defined by the difference between two
adjacent basins. We show that the SRR and the CRR can be determined explicitly
from the free energylandscape.Comment: 11 pages, 3 figures, submitted to J. Chem. Phy
Effect of Disorder on Fermi surface in Heavy Electron Systems
The Kondo lattice model with substitutional disorder is studied with
attention to the size of the Fermi surface and the associated Dingle
temperature. The model serves for understanding heavy-fermion Ce compounds
alloyed with La according to substitution Ce{x}La{1-x}. The Fermi surface is
identified from the steepest change of the momentum distribution of conduction
electrons, and is derived at low enough temperature by the dynamical mean-field
theory (DMFT) combined with the coherent potential approximation (CPA). The
Fermi surface without magnetic field increases in size with decreasing x from
x=1 (Ce end), and disappears at such x that gives the same number of localized
spins as that of conduction electrons. From the opposite limit of x=0 (La end),
the Fermi surface broadens quickly as x increases, but stays at the same
position as that of the La end. With increasing magnetic field, a metamagnetic
transition occurs, and the Fermi surface above the critical field changes
continuously across the whole range of x. The Dingle temperature takes a
maximum around x=0.5. Implication of the results to experimental observation is
discussed.Comment: 5 pages, 5 figure
Magnetic anisotropy and low-energy spin waves in the Dzyaloshinskii-Moriya spiral magnet Ba_2 Cu Ge_2 O_7
New neutron diffraction and inelastic scattering experiments are used to
investigate in detail the field dependence of the magnetic structure and
low-energy spin wave spectrum of the Dzyaloshinskii-Moriya helimagnet Ba_2 Cu
Ge_2 O_7. The results suggest that the previously proposed model for the
magnetism of this compound (an ideal sinusoidal spin spiral, stabilized by
isotropic exchange and Dzyaloshinskii-Moriya interactions) needs to be refined.
Both new and previously published data can be quantitatively explained by
taking into account the Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) term, a
special magnetic anisotropy term that was predicted to always accompany
Dzyaloshinskii-Moriya interactions in insulators.Comment: 30 pages, 10 figures, submitted to PR
Fermi-liquid theory for a conductance through an interacting region attached to noninteracting leads
We study the relation between the dc conductance and the transmission through
an interacting region based on the Kubo formalism using the perturbation
analysis in the Coulomb interaction developed by Yamada-Yosida and Shiba. We
find that the contributions of the vertex correction to the dc conductance
disappear at T=0 if the currents are measured in the noninteracting leads.
Consequently, the dc conductance is written in a Landauer-type form using the
transmission coefficient for single-particle-like excitation at the Fermi
energy. The results are generalized to a system with a number of scattering
channels, and may be regarded as an extension of the relation derived by
Fisher-Lee.Comment: text is not changed, 6 PS figures were replaced by 6 EPS figures in
order to prevent the control-D problem of the PS file
Orbital ferromagnetism and anomalous Hall effect in antiferromagnets on distorted fcc lattice
The Berry phase due to the spin wavefunction gives rise to the orbital
ferromagnetism and anomalous Hall effect in the non-coplanar antiferromagnetic
ordered state on face centered cubic (fcc) lattice once the crystal is
distorted perpendicular to (1,1,1) or (1,1,0)- plane. The relevance to the real
systems -FeMn and NiS is also discussed.Comment: 4 pages, 3 figure
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