12,196 research outputs found

    Critical Behaviour near the Mott Metal-Insulator Transition in a Two-band Hubbard Model

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    The Mott metal-insulator transition in the two-band Hubbard model in infinite dimensions is studied by using the linearized dynamical mean-field theory. The discontinuity in the chemical potential for the change from hole to electron doping is calculated analytically as a function of the on-site Coulomb interaction UU at the dd-orbital and the charge-transfer energy Δ\Delta between the dd- and pp-orbitals. Critical behaviour of the quasiparticle weight is also obtained analytically as a function of UU and Δ\Delta. The analytic results are in good agreement with the numerical results of the exact diagonalization method.Comment: 10 pages, 8 figure

    Growth or Stagnation: Economic Consequences of Status Preference.

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    Using a dynamic optimization model with status preference this paper shows that depending on the object of people's status preference an economy exhibits a completely opposite performance; permanent growth or persistent stagnation. If the object is a producible asset (viz. real capital), new employment is created and extra production is invested in capital, which generates permanent growth even under decreasing returns to capital. If it is an unproducible asset (viz. money), commodity demand is not created and deflation occurs. Full employment is never reached under nominal wage sluggishness although prices and wages continue to adjust.UNEMPLOYMENT ; INVESTMENTS ; CAPITAL

    International Spillover of Economic Fluctuations:A Dynamic Optimization Approach.

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    After the 1990 Japanese stock market crash the Japanese economy began to stagnate whereas the U.S. economy began to expand, yet the yen tended to appreciate against the dollar. Such a phenomenon is difficult to explain in conventional models. This paper examines its mechanism using a two-country dynamic model that accommodates a liquidity trap and unemployment. If the marginal utility of consumption relative to that of liquidity declines in a country, its current account improves, which appreciates the home currency against the foreign currency. Consequently, home products lose competitiveness, causing home employment to decrease and foreign employment to increase.UNEMPLOYMNENT ; EXCHANGE RATE ; STOCK MARKET

    Magnetism and Superconductivity in a Two-band Hubbard Model in Infinite Dimensions

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    We study a two-band Hubbard model using the dynamical mean-field theory combined with the exact diagonalization method. At the electron density n=2n=2, a transition from a band-insulator to a correlated semimetal occurs when the on-site Coulomb interaction UU is varied for a fixed value of the charge-transfer energy Δ\Delta. At low temperature, the correlated semimetal shows ferromagnetism or superconductivity. With increasing doping n2|n-2|, the ferromagnetic transition temperature rapidly decreases and finally becomes zero at a critical value of nn. The second-order phase transition occurs at high temperature, while a phase separation of ferromagnetic and paramagnetic states takes place at low temperature. The superconducting transition temperature gradually decreases and finally becomes zero near n=1n=1 (n=3n=3) where the system is Mott insulator which shows antiferromagnetism at low temperature.Comment: 3 pages, 5 figures, proceedings of the International Conference on Strongly Correlated Electrons with Orbital Degrees of Freedom (ORBITAL2001

    Degeneracy of Ground State in Two-dimensional Electron-Lattice System

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    We discuss the ground state of a two dimensional electron-lattice system described by a Su-Schrieffer-Heeger type Hamiltonian with a half-filled electronic band, for which it has been pointed out in the previous paper [J. Phys. Soc. Jpn. 69 (2000) 1769-1776] that the ground state distortion pattern is not unique in spite of a unique electronic energy spectrum and the same total energy. The necessary and sufficient conditions to be satisfied by the distortion patterns in the ground state are derived numerically. As a result the degrees of degeneracy in the ground state is estimated to be about NN/4N^{N/4} for N1N \gg 1 with NN the linear dimension of the system.Comment: 2pages, 2figure

    Antisymmetrized molecular dynamics with quantum branching processes for collisions of heavy nuclei

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    Antisymmetrized molecular dynamics (AMD) with quantum branching processes is reformulated so that it can be applicable to the collisions of heavy nuclei such as Au + Au multifragmentation reactions. The quantum branching process due to the wave packet diffusion effect is treated as a random term in a Langevin-type equation of motion, whose numerical treatment is much easier than the method of the previous papers. Furthermore a new approximation formula, called the triple-loop approximation, is introduced in order to evaluate the Hamiltonian in the equation of motion with much less computation time than the exact calculation. A calculation is performed for the Au + Au central collisions at 150 MeV/nucleon. The result shows that AMD almost reproduces the copious fragment formation in this reaction.Comment: 24 pages, 5 figures embedde

    Valley Polarization in Si(100) at Zero Magnetic Field

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    The valley splitting, which lifts the degeneracy of the lowest two valley states in a SiO2_2/(100)Si/SiO2_2 quantum well is examined through transport measurements. We demonstrate that the valley splitting can be observed directly as a step in the conductance defining a boundary between valley-unpolarized and polarized regions. This persists to well above liquid helium temperature and shows no dependence on magnetic field, indicating that single-particle valley splitting and valley-polarization exist in (100) silicon even at zero magnetic field.Comment: Accpeted for publication in Phys. Rev. Let

    Current-feedback-stabilized laser system for quantum simulation experiments using Yb clock transition at 578 nm

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    We developed a laser system for the spectroscopy of the clock transition in ytterbium (Yb) atoms at 578 nm based on an interference-filter stabilized external-cavity diode laser (IFDL) emitting at 1156 nm. Owing to the improved frequency-to-current response of the laser-diode chip and the less sensitivity of the IFDL to mechanical perturbations, we succeeded in stabilizing the frequency to a high-finesse ultra-low-expansion glass cavity with a simple current feedback system. Using this laser system, we performed high-resolution clock spectroscopy of Yb and found that the linewidth of the stabilized laser was less than 320 Hz.Comment: 5 pages, 7 figure
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