Bosonization Theory of Excitons in One-dimensional Narrow Gap Semiconductors

Excitons in one-dimensional narrow gap semiconductors of anti-crossing quantum Hall edge states are investigated using a bosonization method. The excitonic states are studied by mapping the problem into a non-integrable sine-Gordon type model. We also find that many-body interactions lead to a strong enhancement of the band gap. We have estimated when an exciton instability may occur.Comment: 4pages, 1 figure, to appear in Phys. Rev. B Brief Report

Quantum Hall Fluids

We review the effective field theory treatment of topological quantum fluids, focussing on the Hall fluids.Comment: 82 pages, TeX, Preprint ITP (This version comes with ALL the MACROS appended at the end of the file)

Isothermal Fatigue and Creep-Fatigue Interaction Behavior of Nickel-Base Directionally Solidified Superalloy

The creep-fatigue interaction in directionally solidified nickel-base superalloy was analyzed with the modified Chaboche-based unified viscoplasticity constitutive model. The model features the anisotropic material behavior, hardening/ softening, and stress relaxation. Simple low-cyclic fatigue and specified hold time experiments were conducted on a directionally solidified superalloy (DZ125) at temperatures over 760°C. The material parameters were optimized considering its tensile, cyclic and creep behavior with the Levenberg–Marquardt optimization procedure. The model was constructed in FORTRAN and integrated in FEA software UMAT/ABAQUS. The results show that experimental and simulated hysteresis loop size/shape, peak stresses, stress relaxation, and related areas are closely matched. The modified constitutive model was found to be instrumental for revealing the fatigue and creep-fatigue interaction behavior of such materials and can be used for practical applications.Взаимодействие ползучести и усталости в суперсплаве на основе никеля, полученного направленной кристаллизацией, проанализировано с помощью модифицированной унифицированной определяющей модели вязкопластичности Шабоша. Модель характеризует анизотропное поведение материала, упрочнение/разупрочнение и релаксацию напряжений. Эксперименты по определению малоцикловой усталости и времени пребывания выполнены на суперсплаве (DZ125) при температурах выше 760°С. Параметры материала оптимизированы с учетом его поведения при растяжении, циклической нагрузке и ползучести при помощи метода оптимизации Левенберга–Марквардта. Модель построена на языке ФОРТРАН и интегрирована в программу FEА UMAT/ABAQUS. Показано, что экспериментальные и модельные размеры/ форма петли гистерезиса, пиковые напряжения, релаксация напряжений и их область находятся в соответствии. Установлено, что модифицированную определяющую модель целесообразно применять при анализе усталости и взаимодействия ползучести и усталости подобных материалов, она может также найти практическое применение

Effective field theory

I give a brief review of effective field theory, disscussing the contribution of Feza G\"ursey in particular and focusing on the literature I am most familiar with.Comment: 17 pages, no figs, macros appended, plain te

Haldane's Fractional Exclusion Statistics for Multicomponent Systems

The idea of fractional exclusion statistics proposed by Haldane is applied to systems with internal degrees of freedom, and its thermodynamics is examined. In case of one dimension, various bulk quantities calculated show that the critical behavior of such systems can be described by $c=1$ conformal field theories and conformal weights are completely characterized by statistical interactions. It is also found that statistical interactions have intimate relationship with a topological order matrix in Chern-Simons theory for the fractional quantum Hall effect.Comment: 12 pages, Revtex, preprint YITP/K-107

Structural, Magnetic and Transport Properties of B-Site Substituted Perovskite La0.7Sr0.3MnO3

In this chapter, in order to understand the structural related magnetic and transport properties of B site substituted perovskites La0.7Sr0.3MnO3 (LSMO), we have systematically investigated the effects of replacing some of the Mn with nonmagnetic elements Ti, Zr, Cu, Al, Zn and magnetic elements Co, Ni, Cr, Fe. The structural, magnetic and electrical phase transitions and transport properties of these compounds were investigated by neutron diffraction, magnetization and electric resistivity measurements

Skyrmion Excitations in Quantum Hall Systems

Using finite size calculations on the surface of a sphere we study the topological (skyrmion) excitation in quantum Hall system with spin degree of freedom at filling factors around $\nu=1$. In the absence of Zeeman energy, we find, in systems with one quasi-particle or one quasi-hole, the lowest energy band consists of states with $L=S$, where $L$ and $S$ are the total orbital and spin angular momentum. These different spin states are almost degenerate in the thermodynamic limit and their symmetry-breaking ground state is the state with one skyrmion of infinite size. In the presence of Zeeman energy, the skyrmion size is determined by the interplay of the Zeeman energy and electron-electron interaction and the skyrmion shrinks to a spin texture of finite size. We have calculated the energy gap of the system at infinite wave vector limit as a function of the Zeeman energy and find there are kinks in the energy gap associated with the shrinking of the size of the skyrmion. breaking ground state is the state with one skyrmion of infinite size. In the presence of Zeeman energy, the skyrmion size is determined by the interplay of the Zeeman energy and electron-electronComment: 4 pages, 5 postscript figures available upon reques

Semi-inclusive B Decays and Direct CP Violation in QCD Factorization

We have systematically investigated the semi-inclusive B decays B->MX, which are manifestations of the quark decay b->Mq, within the framework of QCD-improved factorization. These decays are theoretically clean and have distinctive experimental signatures. We focus on a class of these that do not require any form factor information and therefore may be especially suitable for extracting information on the angles $\alpha$ and $\gamma$ of the unitarity triangle. The nonfactorizable effects, such as vertex-type and penguin-type corrections to the two-body b decay and hard spectator corrections to the 3-body decay are calculable in the heavy quark limit. QCD factorization is applicable when the emitted meson is a light meson or a charmonium. We discuss the issue of the CPT constraint on partial rate asymmetries. The strong phase coming from final-state rescattering due to hard gluon exchange between the final states can induce large rate asymmetries for tree-dominated color-suppressed modes $(\pi^0,\rho^0,\omega)X_{\bar s}$. The nonfactorizable hard spectator interactions in the 3-body decay, though phase-space suppressed, are extremely important for the tree-dominated modes $(\pi^0,\rho^0,\omega)X_{\bar s}, \phi X$, $J X_s,J X$ and the penguin-dominated mode $\omega X_{s\bar s}$. In fact, they are dominated by the hard spectator corrections. Our result for ${\cal B} (B\to J/\psi X_s)$ is in agreement with experiment. The semi-inclusive decay modes: $B^0_s\to (\pi^0,\rho^0,\omega)X_{\bar s}$, $\rho^0X_{s\bar s}$, $B^0\to(K^-X,K^{*-}X)$ and $B^-\to (K^0X_s,K^{*0}X_s)$ are the most promising ones in searching for direct CP violation. In fact, they have branching ratios of order $10^{-6}-10^{-4}$ and CP rate asymmetries of order $(10-40)$.Comment: 28 page

Final State Rescattering and Color-suppressed \bar B^0-> D^{(*)0} h^0 Decays

The color-suppressed \bar B^0-> D^{(*)0}\pi^0, D^{(*)0}\eta, D^0\omega decay modes have just been observed for the first time. The rates are all larger than expected, hinting at the presence of final state interactions. Considering \bar B^0-> D^{(*)0}\pi^0 mode alone, an elastic D^{(*)}\pi -> D^{(*)}\pi rescattering phase difference \delta \equiv \delta_{1/2} - \delta_{3/2} \sim 30^\circ would suffice, but the \bar B^0-> D^{(*)0}\eta, D^0\omega modes compel one to extend the elastic formalism to SU(3) symmetry. We find that a universal a_2/a_1=0.25 and two strong phase differences 20^\circ \sim \theta < \delta < \delta^\prime \sim 50^\circ can describe both DP and D^*P modes rather well; the large phase of order 50^\circ is needed to account for the strength of {\it both} the D^{(*)0}\pi^0 and D^{(*)0}\eta modes. For DV modes, the nonet symmetry reduces the number of physical phases to just one, giving better predictive power. Two solutions are found. We predict the rates of the \bar B^0-> D^{+}_s K^-, D^{*+}_s K^-, D^0\rho^0, D^+_s K^{*-} and D^0\phi modes, as well as \bar B^0-> D^{0}\bar K^0, D^{*0}\bar K^0, D^{0}\bar K^{*0} modes. The formalism may have implications for rates and CP asymmetries of charmless modes.Comment: REVTeX4, 18 pages, 5 figures, to appear in Phys. Rev.

Anisotropic Transport of Quantum Hall Meron-Pair Excitations

Double-layer quantum Hall systems at total filling factor $\nu_T=1$ can exhibit a commensurate-incommensurate phase transition driven by a magnetic field $B_{\parallel}$ oriented parallel to the layers. Within the commensurate phase, the lowest charge excitations are believed to be linearly-confined Meron pairs, which are energetically favored to align with $B_{\parallel}$. In order to investigate this interesting object, we propose a gated double-layer Hall bar experiment in which $B_{\parallel}$ can be rotated with respect to the direction of a constriction. We demonstrate the strong angle-dependent transport due to the anisotropic nature of linearly-confined Meron pairs and discuss how it would be manifested in experiment.Comment: 4 pages, RevTex, 3 postscript figure