Field-Induced Effects of Anisotropic Magnetic Interactions in SrCu2(BO3)2

We observed a field-induced staggered magnetization in the 2D frustrated dimer-singlet spin system SrCu2(BO3)2 by 11B NMR, from which the magnitudes of the intradimer Dzyaloshinsky-Moriya interaction and the staggered g-tensor were determined. These anisotropic interactions cause singlet-triplet mixing and eliminate a quantum phase transition at the expected critical field Hc for gap closing. They also provide a quantitative account for some puzzling phenomena such as the onset of a uniform magnetization below the and the persistence of the excitation gap above Hc. The gap was accurately determined from the activation energy of the nuclear relaxation rate.Comment: 8 pages, 5 figures, published versio

Low-Lying Magnetic Excitation of the Shastry-Sutherland Model

By using perturbation calculation and numerical diagonalization, low-energy spin dynamics of the Shastry-Sutherland model is investigated paying particular attention to the two-particle coherent motion. In addition to spin-singlet- and triplet bound states, we find novel branches of coherent motion of a bound quintet pair, which are usually unstable because of repulsion. Unusual dispersion observed in neutron-scattering measurements are explained by the present theory. The importance of the effects of phonon is also pointed out.Comment: 4 pages, 6 figures combined into 1 PSfile. Final version to appear in Phys.Rev.Lett. (Jan. 2000

COHEN-MACAULAY MODULES AND HOLONOMIC MODULES OVER FILTERED RINGS

We study Gorenstein dimension and grade of a module M over a filtered ring whose associated graded ring is a commutative Noetherian ring. An equality or an inequality between these invariants of a filtered module and its associated graded module is the most valuable property for an investigation of filtered rings. We prove an inequality G-dimM <= G-dim grM and an equality grade M = grade grM, whenever Gorenstein dimension of grM is finite (Theorems 2.3 and 2.8). We would say that the use of G-dimension adds a new viewpoint for studying filtered rings and modules. We apply these results to a filtered ring with a Cohen-Macaulay or Gorenstein associated graded ring and study a Cohen-Macaulay, perfect, or holonomic module.ArticleCommunications in Algebra. 37(2):406-430 (2009)journal articl

Magnon Dispersion and Anisotropies in SrCu2_2(BO3_3)2_2

We study the dispersion of the magnons (triplet states) in SrCu$_2$(BO$_3$)$_2$ including all symmetry-allowed Dzyaloshinskii-Moriya interactions. We can reduce the complexity of the general Hamiltonian to a new simpler form by appropriate rotations of the spin operators. The resulting Hamiltonian is studied by both perturbation theory and exact numerical diagonalization on a 32-site cluster. We argue that the dispersion is dominated by Dzyaloshinskii-Moriya interactions. We point out which combinations of these anisotropies affect the dispersion to linear-order, and extract their magnitudes.Comment: 11 pages, 7 figures, 1 table, v2 conclusion shortened, figs clarifie

Two-Triplet-Dimer Excitation Spectra in the Shastry-Sutherland Model for SrCu_2(BO_3)_2

By using the perturbation expansion up to the fifth order, we study the two-triplet-dimer excitation spectra in the Shastry-Sutherland model, where the localized nature of a triplet-dimer, the propagation of a triplet-dimer pair by the correlated hopping and the long-range interactions between triplet-dimers play an essential role. It is found that the dispersion relations for first-neighbor triplet-dimer pair excitations with S=1 and p-type symmetry qualitatively explain the second-lowest branch observed in the neutron inelastic scattering experiment. It is also predicted that the second-lowest branch consists of two components, p_x- and p_y-states, with slightly different excitation energies. The origin of the singlet mode at 3.7meV observed in the Raman scattering experiment is also discussed.Comment: 5 pages, 3 figure

Magnetization plateaus of SrCu_2(BO_3)_2 from a Chern-Simons theory

The antiferromagnetic Heisenberg model on the frustrated Shastry-Sutherland lattice is studied by a mapping onto spinless fermions carrying one quantum of statistical flux. Using a mean-field approximation these fermions populate the bands of a generalized Hofstadter problem. Their filling leads to the magnetization curve. For SrCu_2(BO_3)_2 we reproduce plateaus at 1/3 and 1/4 of the saturation moment and predict a new one at 1/2. Gaussian fluctuations are shown to be massive at these plateau values.Comment: 4 pages, 5 figure

A Web-Based VOD Clipping Tool for Efficient Private Review

In this paper, we present a web-based tool for learners, to review the parts of the lecture contents that the learners have already attended. Each learner can efficiently review what they want to learn again independent of the scenario in each lecture. We assume that the contents of the lectures are stored in the internet based video streaming systems. The objects are automatically arranged on a screen of this tool, so that each object gets closer to its similar objects.ArticleKnowledge-based software engineering : proceedings of the fifth Joint Conference on Knowledge-Based Software Engineering. 313-316 (2002)conference pape