843 research outputs found
Low-lying excitations of the three-leg spin tube using the density-matrix renormalization group method
Using the (dynamical) density-matrix renormalization group method, we study
the low-energy physics of three-leg antiferromagnetic Heisenberg model where
the periodic boundary conditions are applied in the rung direction. We confirm
that the spin excitations are always gapped as long as the intra-ring couplings
form a regular triangle. From precise finite-size-scaling analyses of the spin
gap and dimerization order parameter, we also find that the spin gap is
collapsed by very small asymmetric modulation of the intra-ring couplings.
Moreover, the dynamical spin structure factors on the intra- and inter-leg
correlations are calculated. It is demonstrated that the low-lying structure of
the inter-leg spectra is particularly affected by the asymmetric modulation.Comment: 10 pages, 8 figure
Dynamics in two-leg spin ladder with a four-spin cyclic interaction
We study two-leg Heisenberg ladder with four-spin cyclic interaction using
the (dynamical) density-matrix renormalization group method. We demonstrate the
dependence of the low-lying excitations in the spin wave, staggered dimer
order, and scalar-chirality order structure factors on the four-spin cyclic
interaction. We find that the cyclic interaction enhances spin-spin
correlations with wave vector around momentum .
Also, the presence of long-range order in the staggered dimer and
scalar-chirality phases is confirmed by a -function peak contribution
of the structure factors at energy .Comment: 4 pages, 4 figure
Anisotropic Thermal Conduction in Supernova Remnants: Relevance to Hot Gas Filling Factors in the Magnetized ISM
We explore the importance of anisotropic thermal conduction in the evolution
of supernova remnants via numerical simulations. The mean temperature of the
bubble of hot gas is decreased by a factor of ~3 compared to simulations
without thermal conduction, together with an increase in the mean density of
hot gas by a similar factor. Thus, thermal conduction greatly reduces the
volume of hot gas produced over the life of the remnant. This underscores the
importance of thermal conduction in estimating the hot gas filling fraction and
emissivities in high-stage ions in Galactic and proto-galactic ISMs.Comment: Submitted to Astrophysical Journal Letters. 4 pages, 3 figure
Thermal OH (1667/65 MHz) Absorption and Nonthermal OH (1720 MHz) Emission Towards the W28 Supernova Remnant
The W28 supernova remnant is an excellent prototype for observing shocked gas
resulting from the interaction of supernova remnants (SNRs) and adjacent
molecular clouds (MCs). We present two new signatures of shocked molecular gas
in this remnant. One is the detection of main-line extended OH (1667 MHz)
absorption with broad linewidths. The column density of OH estimated from the
optical depth profiles is consistent with a theoretical model in which
OH is formed behind a C-type shock front. The second is the detection of
extended, weak OH (1720 MHz) line emission with narrow linewidth distributed
throughout the shocked region of W28. These give observational support to the
idea that compact maser sources delineate the brightest component of a much
larger region of main line OH absorption and nonthermal OH (1720 MHz) emission
tracing the global structure of shocked molecular gas. Main line OH (1665/67)
absorption and extended OH (1720 MHz) emission line studies can serve as
powerful tools to detect SNR-MC interaction even when bright OH (1720 MHz)
masers are absent.Comment: 14 pages, 3 figures, one table, to appear in ApJ (Jan 10, 2003
Topological quantum phase transition in the BEC-BCS crossover phenomena
A crossover between the Bose Einstein condensation (BEC) and BCS
superconducting state is described topologically in the chiral symmetric
fermion system with attractive interaction. Using a local Z_2 Berry phase, we
found a quantum phase transition between the BEC and BCS phases without
accompanying the bulk gap closing.Comment: 4 pages, 5 figure
Exact spin dynamics of the 1/r^2 supersymmetric t-J model in a magnetic field
The dynamical spin structure factor S^{zz}(Q,omega) in the small momentum
region is derived analytically for the one-dimensional supersymmetric t-J model
with 1/r^2 interaction. Strong spin-charge separation is found in the spin
dynamics. The structure factor S^{zz}(Q,omega) with a given spin polarization
does not depend on the electron density in the small momentum region. In the
thermodynamic limit, only two spinons and one antispinon (magnon) contribute to
S^{zz}(Q,omega). These results are derived via solution of the SU(2,1)
Sutherland model in the strong coupling limit.Comment: 20 pages, 8 figures. Accepted for publication in J.Phys.
Derivation of Green's Function of Spin Calogero-Sutherland Model by Uglov's Method
Hole propagator of spin 1/2 Calogero-Sutherland model is derived using
Uglov's method, which maps the exact eigenfunctions of the model, called
Yangian Gelfand-Zetlin basis, to a limit of Macdonald polynomials (gl_2-Jack
polynomials). To apply this mapping method to the calculation of 1-particle
Green's function, we confirm that the sum of the field annihilation operator on
Yangian Gelfand-Zetlin basis is transformed to the field annihilation operator
on gl_2-Jack polynomials by the mapping. The resultant expression for hole
propagator for finite-size system is written in terms of renormalized momenta
and spin of quasi-holes and the expression in the thermodynamic limit coincides
with the earlier result derived by another method. We also discuss the
singularity of the spectral function for a specific coupling parameter where
the hole propagator of spin Calogero-Sutherland model becomes equivalent to
dynamical colour correlation function of SU(3) Haldane-Shastry model.Comment: 36 pages, 8 figure
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