2,293 research outputs found
Half-magnetization plateau stabilized by structural distortion in the antiferromagnetic Heisenberg model on a pyrochlore lattice
Magnetization plateaus, visible as anomalies in magnetic susceptibility at
low temperatures, are one of the hallmarks of frustrated magnetism. We show how
an extremely robust half-magnetization plateau can arise from coupling between
spin and lattice degrees of freedom in a pyrochlore antiferromagnet, and
develop a detailed symmetry of analysis of the simplest possible scenario for
such a plateau state. The application of this theory to the spinel oxides
CdCr2O4 and HgCr2O4, where a robust half magnetization plateau has been
observed, is discussed.Comment: 4 pages, 4 figure
Magnetic Excitations in the Quasi-1D Ising-like Antiferromagnet TlCoCl
Neutron inelastic scattering measurements have been performed in order to
investigate the magnetic excitations in the quasi-1D Ising-like antiferromagnet
TlCoCl. We observed the magnetic excitation, which corresponds to the
spin-wave excitation continuum corresponding to the domain-wall pair excitation
in the 1D Ising-like antiferromagnet. According to the Ishimura-Shiba theory,
we analyzed the observed spin-wave excitation, and the exchange constant
and the anistropy were estimated as 14.7 meV and 0.14 in TlCoCl,
respectively.Comment: 2 pages, 3 figures, jpsj2.cls, to be published in J. Phys. Soc. Jpn.
Vol.75 (2006) No.
Structural and dynamical heterogeneities in two-dimensional melting
Using molecular dynamics simulation, we study structural and dynamical
heterogeneities at melting in two-dimensional one-component systems with 36000
particles. Between crystal and liquid we find intermediate hexatic states,
where the density fluctuations are enhanced at small wave number k as well as
those of the six-fold orientational order parameter. Their structure factors
both grow up to the smallest wave number equal to the inverse system length.
The intermediate scattering function of the density S(k,t) is found to relax
exponentially with decay rate Gamma_k ~ k^z with z~2.6 at small k in the
hexatic phase.Comment: 6 pages, 8 figure
Quantum Corrals, Eigenmodes and Quantum Mirages in s-wave Superconductors
We study the electronic structure of magnetic and non-magnetic quantum
corrals embedded in s-wave superconductors. We demonstrate that a quantum
mirage of an impurity bound state peak can be projected from the occupied into
the empty focus of a non-magnetic quantum corral via the excitation of the
corral's eigenmodes. We observe an enhanced coupling between magnetic
impurities inside the corral, which can be varied through oscillations in the
corral's impurity potential. Finally, we discuss the form of eigenmodes in
magnetic quantum corrals.Comment: 4 pages, 4 figure
Susceptibility of the one-dimensional, dimerized Hubbard model
We show that the zero temperature susceptibility of the one-dimensional,
dimerized Hubbard model at quarter-filling can be accurately determined on the
basis of exact diagonalization of small clusters. The best procedure is to
perform a finite-size scaling of the spin velocity , and to calculate
the susceptibility from the Luttinger liquid relation . We
show that these results are reliable by comparing them with the analytical
results that can be obtained in the weak and strong coupling limits. We have
also used quantum Monte Carlo simulations to calculate the temperature
dependence of the susceptibility for parameters that should be relevant to the
Bechgaard salts. This shows that, used together, these numerical techniques are
able to give precise estimates of the low temperature susceptibility of
realistic one-dimensional models of correlated electrons.Comment: 10 pages, latex, figures available from the authors. To appear in
Phys. Rev. B, Rapid Comm
Binding of holons and spinons in the one-dimensional anisotropic t-J model
We study the binding of a holon and a spinon in the one-dimensional
anisotropic t-J model using a Bethe-Salpeter equation approach, exact
diagonalization, and density matrix renormalization group methods on chains of
up to 128 sites. We find that holon-spinon binding changes dramatically as a
function of anisotropy parameter \alpha=J_\perp/J_z: it evolves from an exactly
deducible impurity-like result in the Ising limit to an exponentially shallow
bound state near the isotropic case. A remarkable agreement between the theory
and numerical results suggests that such a change is controlled by the
corresponding evolution of the spinon energy spectrum.Comment: 4 pages, 5 figures, published versio
Distribution of Microscopic Energy Flux in Equilibrium State
The distribution function P(j) of the microscopic energy flux, j, in
equilibrium state is studied. It is observed that P(j) has a broad peak in
small j regime and a stretched-exponential decay for large j. The peak
structure originates in a potential advection term and energy transfer term
between the particles. The stretched exponential tail comes from the momentum
energy advection term.Comment: 5 pages, 2 figure
Effect of Inter-Site Repulsions on Magnetic Susceptibility of One-Dimensional Electron Systems at Quarter-Filling
The temperature dependence of the magnetic susceptibility, \chi (T), is
investigated for one-dimensional interacting electron systems at
quarter-filling within the Kadanoff-Wilson renormalization-group method.
The forward scattering on the same branch (the g_4-process) is examined
together with the backward (g_1) and forward (g_2) scattering amplitudes on
opposite branches.
In connection with lattice models, we show that \chi (T) is strongly enhanced
by the nearest-neighbor interaction, an enhancement that surpasses one of the
next-nearest-neighbor interaction.
A connection between our predictions for \chi (T) and experimental results
for \chi (T) in quasi-one-dimensional organic conductors is presented.Comment: 4 pages, 4 figures, to be published in Journal of the Physical
Society of Japan, vol. 74, No. 1
Theoretical study of a localized quantum spin reversal by the sequential injection of spins in a spin quantum dot
This is a theoretical study of the reversal of a localized quantum spin
induced by sequential injection of spins for a spin quantum dot that has a
quantum spin. The system consists of ``electrode/quantum
well(QW)/dot/QW/electrode" junctions, in which the left QW has an energy level
of conduction electrons with only up-spin. We consider a situation in which
up-spin electrons are sequentially injected from the left electrode into the
dot through the QW and an exchange interaction acts between the electrons and
the localized spin. To describe the sequentially injected electrons, we propose
a simple method based on approximate solutions from the time-dependent
Schrdinger equation. Using this method, it is shown that the spin
reversal occurs when the right QW has energy levels of conduction electrons
with only down-spin. In particular, the expression of the reversal time of a
localized spin is derived and the upper and lower limits of the time are
clearly expressed. This expression is expected to be useful for a rough
estimation of the minimum relaxation time of the localized spin to achieve the
reversal. We also obtain analytic expressions for the expectation value of the
localized spin and the electrical current as a function of time. In addition,
we found that a system with the non-magnetic right QW exhibits spin reversal or
non-reversal depending on the exchange interaction.Comment: 12 pages, 12 figures, to be published in Phys. Rev. B, typos
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