886 research outputs found
Note on Spin Structure of the Classical Vector Spin Heisenberg Model
A comment on Yoshimori's helical spin structure theory.Comment: 2 pages, short note. Accepted by J. Phys. Soc. Jp
Spinons and helimagnons in the frustrated Heisenberg chain
We investigate the dynamical spin structure factor S(q,w) for the Heisenberg
chain with ferromagnetic nearest (J1<0) and antiferromagnetic next-nearest
(J2>0) neighbor exchange using bosonization and a time-dependent density-matrix
renormalization group algorithm. For |J1|<< J2 and low energies we analytically
find and numerically confirm two spinon branches with different velocities and
different spectral weights. Following the evolution of S(q,w) with decreasing
J1/J2 we find that helimagnons develop at high energies just before entering
the ferromagnetic phase. Furthermore, we show that a recent interpretation of
neutron scattering data for LiCuVO4 in terms of two weakly coupled
antiferromagnetic chains (|J_1|<< J2) is not viable. We demonstrate that the
data are instead fully consistent with a dominant ferromagnetic coupling, J1/J2
~ -2.Comment: 5 pages, 3 figure
Ground states of dipolar gases in quasi-1D ring traps
We compute the ground state of dipoles in a quasi-one-dimensional ring trap
using few-body techniques combined with analytic arguments. The effective
interaction between two dipoles depends on their center-of-mass coordinate and
can be tuned by varying the angle between dipoles and the plane of the ring.
For weak enough interactions, the state resembles a weakly interacting Fermi
gas or an (inhomogeneous) Lieb-Liniger gas. A mapping between the Lieb-Liniger
and the dipolar-gas parameters in and beyond the Born approximation is
established, and we discuss the effect of inhomogeneities based on a
local-density approximation. For strongly repulsive interactions, the system
exhibits crystal-like localization of the particles. Their inhomogeneous
distribution may be understood in terms of a simple few-body model as well as a
local-density approximation. In the case of partially attractive interactions,
clustered states form for strong enough coupling, and the dependence of the
state on particle number and orientation angle of the dipoles is discussed
analytically.Comment: 15 pages, 10 figure
A Start-Timing Detector for the Collider Experiment PHENIX at RHIC-BNL
We describe a start-timing detector for the PHENIX experiment at the
relativistic heavy-ion collider RHIC. The role of the detector is to detect a
nuclear collision, provide precise time information with an accuracy of 50ps,
and determine the collision point along the beam direction with a resolution of
a few cm. Technical challenges are that the detector must be operational in a
wide particle-multiplicity range in a high radiation environment and a strong
magnetic field. We present the performance of the prototype and discuss the
final design of the detector.Comment: 12 pages, LaTeX, 9 gif and 4 ps figures. Submitted to NIM
Ground-State Properties of a One-Dimensional System of Hard Rods
A quantum Monte Carlo simulation of a system of hard rods in one dimension is
presented and discussed. The calculation is exact since the analytical form of
the wavefunction is known, and is in excellent agreement with predictions
obtained from asymptotic expansions valid at large distances. The analysis of
the static structure factor and the pair distribution function indicates that a
solid-like and a gas-like phases exist at high and low densities, respectively.
The one-body density matrix decays following a power-law at large distances and
produces a divergence in the low density momentum distribution at k=0 which can
be identified as a quasi-condensate.Comment: 4 pages, 4 figure
Beyond Tonks-Girardeau: strongly correlated regime in quasi-one-dimensional Bose gases
We consider a homogeneous 1D Bose gas with contact interactions and large
attractive coupling constant. This system can be realized in tight waveguides
by exploiting a confinement induced resonance of the effective 1D scattering
amplitude. By using a variational {\it ansatz} for the many-body wavefunction,
we show that for small densities the gas-like state is stable and the
corresponding equation of state is well described by a gas of hard rods. By
calculating the compressibility of the system, we provide an estimate of the
critical density at which the gas-like state becomes unstable against cluster
formation. Within the hard-rod model we calculate the one-body density matrix
and the static structure factor of the gas. The results show that in this
regime the system is more strongly correlated than a Tonks-Girardeau gas. The
frequency of the lowest breathing mode for harmonically trapped systems is also
discussed as a function of the interaction strength.Comment: 4 pages, 4 figure
Symmetry Analysis of Multiferroic Co_3TeO_6
A phenomenological explanation of the magnetoelectric behavior of Co_3TeO_6
is developed. We explain the second harmonic generation data and the magnetic
field induced spontaneous polarization in the magnetically ordered phase below
20K.Comment: Phys rev B Rapids, to appea
Dilute-Bose-Gas Approach to ground state phases of 3D quantum helimagnets under high magnetic field
We study high-field phase diagram and low-energy excitations of
three-dimensional quantum helimagnets. Slightly below the saturation field, the
emergence of magnetic order may be mathematically viewed as Bose-Einstein
condensation (BEC) of magnons. The method of dilute Bose gas enables an
unbiased quantitative analysis of quantum effects in three-dimensional
helimagnets and thereby three phases are found: cone, coplanar fan and an
attraction-dominant one. To investigate the last phase, we extend the usual BEC
approach so that we can handle 2-magnon bound states. In the case of 2-magnon
BEC, the transverse magnetization vanishes and long-range order occurs in the
quadrupolar channel (spin-nematic phase). As an application, we map out the
phase diagram of a 3D helimagnet which consists of frustrated J1-J2 chains
coupled by an interchain interaction J3.Comment: 4pages, 3figures, International Conference on Magnetism (ICM) 2009
(Karlsruhe, Germany, July 26-31, 2009)
Spiral Magnets as Gapless Mott Insulators
In the large limit, the ground state of the half-filled, nearest-neighbor
Hubbard model on the triangular lattice is the three-sublattice
antiferromagnet. In sharp contrast with the square-lattice case, where
transverse spin-waves and charge excitations remain decoupled to all orders in
, it is shown that beyond leading order in the three Goldstone modes
on the triangular lattice are a linear combination of spin and charge. This
leads to non-vanishing conductivity at any finite frequency, even though the
magnet remains insulating at zero frequency. More generally, non-collinear spin
order should lead to such gapless insulating behavior.Comment: 10 pages, REVTEX 3.0, 3 uuencoded postscript figures, CRPS-94-0
Cupric chloride CuCl2 as an S=1/2 chain multiferroic
Magnetoelectric properties were investigated for an S=1/2 chain
antiferromagnet CuCl2, which turns out to be the first example of non-chalcogen
based spiral-spin induced multiferroics. Upon the onset of helimagnetic order
propagating along the b-axis under zero magnetic field (H), we found emergence
of ferroelectric polarization along the c-axis. Application of H along the
b-axis leads to spin-flop transition coupled with drastic suppression of
ferroelectricity, and rotation of H around the b-axis induces the rotation of
spin-spiral plane and associated polarization direction. These behaviors are
explained well within the framework of the inverse Dzyaloshinskii-Moriya model,
suggesting the robustness of this magnetoelectric coupling mechanism even under
the strong quantum fluctuation.Comment: 5 pages, 5 figure
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