Neutron scattering from a coordination polymer quantum paramagnet

Inelastic neutron scattering measurements are reported for a powder sample of the spin-1/2 quantum paramagnet $\rm Cu(Quinoxaline)Br_2$. Magnetic neutron scattering is identified above an energy gap of 1.9 meV. Analysis of the sharp spectral maximum at the onset indicates that the material is magnetically quasi-one-dimensional. Consideration of the wave vector dependence of the scattering and polymeric structure further identifies the material as a two-legged spin-1/2 ladder. Detailed comparison of the data to various models of magnetism in this material based on the single mode approximation and the continuous unitary transformation are presented. The latter theory provides an excellent account of the data with leg exchange $J_{\parallel}=2.0$ meV and rung exchange $J_{\perp}=3.3$ meV.Comment: 10 pages, 11 figures, 1 tabl

Re-Entrant Quantum Phase Transitions in Antiferromagnetic Spin-1 Ladders

In response to recent chemical attempts to construct higher-spin ladder materials from organic polyradicals, we study the ground-state properties of a wide class of antiferromagnetic spin-1 ladders. Employing various numerical tools, we reveal the rich phase diagram and correct a preceding nonlinear-sigma-model prediction. A variational analysis well interprets the phase competition with particular emphasis on the {\it re-entrant phase boundary} as a function of the rung interaction.Comment: 4 pages, 5 figures embedded, J. Phys. Soc. Jpn. Vol. 71, No. 5, 1250 (2002

Efimov effect in quantum magnets

Physics is said to be universal when it emerges regardless of the underlying microscopic details. A prominent example is the Efimov effect, which predicts the emergence of an infinite tower of three-body bound states obeying discrete scale invariance when the particles interact resonantly. Because of its universality and peculiarity, the Efimov effect has been the subject of extensive research in chemical, atomic, nuclear and particle physics for decades. Here we employ an anisotropic Heisenberg model to show that collective excitations in quantum magnets (magnons) also exhibit the Efimov effect. We locate anisotropy-induced two-magnon resonances, compute binding energies of three magnons and find that they fit into the universal scaling law. We propose several approaches to experimentally realize the Efimov effect in quantum magnets, where the emergent Efimov states of magnons can be observed with commonly used spectroscopic measurements. Our study thus opens up new avenues for universal few-body physics in condensed matter systems.Comment: 7 pages, 5 figures; published versio

Reusando Modelos Conceituais : Linguagem e Compilador

TCC(graduação) - Universidade Federal de Santa Catarina. Centro Tecnológico. Ciências da Computação.Este relatório apresenta uma linguagem textual para modelagem con- ceitual (baseada em classes/associações da UML e em restrições da OCL) e um compilador que pode gerar código em qualquer linguagem ou tecnologia através de templates de texto extensíveis. A linguagem e o compilador permitem a especificação da informação gerenciada por sistemas de software cada vez mais distribuídos e em constante mu- dança. A partir de uma única fonte, a geração de código automática mantém as implementações consistentes com sua especificação atra- vés das diferentes plataformas e tecnologias. Além disso, na medida em que o horizonte tecnológico se expande, os templates textuais po- dem ser modificados para adotar novas tecnologias. Diferentemente de outras abordagens, tais como MDA e MPS, espera-se que o suporte fer- ramental acompanhando esta linguagem, juntamente com sua natureza textual, facilite a integração do desenvolvimento de software dirigido por modelos no fluxo de trabalho dos desenvolvedores de software