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 $(q_x,q_y)=(\frac{\pi}{2},0)$. Also, the presence of long-range order in the staggered dimer and scalar-chirality phases is confirmed by a $\delta$-function peak contribution of the structure factors at energy $\omega=0$.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