11,274 research outputs found
Weakly coupled quantum spin singlets in BaCrO
Using single crystal inelastic neutron scattering with and without
application of an external magnetic field and powder neutron diffraction, we
have characterized magnetic interactions in BaCrO. Even without
field, we found that there exist three singlet-to-triplet excitation modes in
scattering plane. Our complete analysis shows that the three modes
are due to spatially anisotropic interdimer interactions that are induced by
local distortions of the tetrahedron of oxygens surrounding the Jahn-Teller
active Cr. The strong intradimer coupling of meV
and weak interdimer interactions ( meV) makes
BaCrO a good model system for weakly-coupled quantum spin
dimers
Orbital and spin chains in ZnV2O4
Our powder inelastic neutron scattering data indicate that \zvo is a system
of spin chains that are three dimensionally tangled in the cubic phase above 50
K due to randomly occupied orbitals of V () ions. Below
50 K in the tetragonal phase, the chains become straight due to
antiferro-orbital ordering. This is evidenced by the characteristic wave vector
dependence of the magnetic structure factor that changes from symmetric to
asymmetric at the cubic-to-tetragonal transition
Spin Frustration and Orbital Order in Vanadium Spinels
We present the results of our theoretical study on the effects of geometrical
frustration and the interplay between spin and orbital degrees of freedom in
vanadium spinel oxides VO ( = Zn, Mg or Cd). Introducing an
effective spin-orbital-lattice coupled model in the strong correlation limit
and performing Monte Carlo simulation for the model, we propose a reduced spin
Hamiltonian in the orbital ordered phase to capture the stabilization mechanism
of the antiferromagnetic order. Orbital order drastically reduces spin
frustration by introducing spatial anisotropy in the spin exchange
interactions, and the reduced spin model can be regarded as weakly-coupled
one-dimensional antiferromagnetic chains. The critical exponent estimated by
finite-size scaling analysis shows that the magnetic transition belongs to the
three-dimensional Heisenberg universality class. Frustration remaining in the
mean-field level is reduced by thermal fluctuations to stabilize a collinear
ordering.Comment: 4 pages, 4 figures, proceedings submitted to SPQS200
First evidence for charge ordering in NaVO from Raman spectroscopy
We argue on the basis of symmetry selection rules and Raman scattering
spectra that NaVO undergoes a charge ordering phase transition at
T=34 K. Such a transition is characterized by the redistribution of the
charges at the phase transition and corresponds to the change of the vanadium
ions, from uniform V to two different V and V states. In
the low temperature phase the V ions are forming a "zig-zag" ladder
structure along the {\bf b}-axis, consistent with the symmetry of the P2/b
space group.Comment: to be published in solid state communication
Full electroweak radiative corrections to with GRACE-Loop
We present the full electroweak radiative corrections
to the process at the International
Linear Collider (ILC). The computation is performed with the help of the
GRACE-Loop system. We present the total cross-section and the top quark
forward-backward asymmetry () as a function of the center-of-mass
energy and compare them with the process . We
find that the value of in production is larger than
in production. It is an important result for the
measurement of the top quark forward-backward asymmetry at the ILC. Applying a
structure function method, we also subtract the QED correction to gain the
genuine weak correction in both the scheme and the scheme
(). We obtain numerical values for
which are changing from 2% to -24% when we vary the center-of-mass energy from
360 GeV to 1 TeV.Comment: 13 pages, 9 figure
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