11,499 research outputs found

    Ferromagnetic transition in a double-exchange system containing impurities in the Dynamical Mean Field Approximation

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    We formulate the Dynamical Mean Field Approximation equations for the double-exchange system with quenched disorder for arbitrary relation between Hund exchange coupling and electron band width. Close to the ferromagnetic-paramagnetic transition point the DMFA equations can be reduced to the ordinary mean field equation of Curie-Weiss type. We solve the equation to find the transition temperature and present the magnetic phase diagram of the system.Comment: 5 pages, latex, 2 eps figures. We explicitely present the magnetic phase diagram of the syste

    The Development of Global Science.

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    How do we build research capacity throughout the world and capture the great human potential? To us, the answer is rather straightforward: the time-honored tradition of scientific mentoring must be practiced on a wider scale across borders. Herein, we detail the necessity for expanding mentorship to a global scale and provide several important principles to be considered when designing, planning, and implementing programs and centers of research around the world

    Carrier States and Ferromagnetism in Diluted Magnetic Semiconductors

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    Applying the dynamical coherent potential approximation to a simple model, we have systematically studied the carrier states in A1xA_{1-x}MnxB_xB-type diluted magnetic semiconductors (DMS's). The model calculation was performed for three typical cases of DMS's: The cases with strong and moderate exchange interactions in the absence of nonmagnetic potentials, and the case with strong attractive nonmagnetic potentials in addition to moderate exchange interaction. When the exchange interaction is sufficiently strong, magnetic impurity bands split from the host band. Carriers in the magnetic impurity band mainly stay at magnetic sites, and coupling between the carrier spin and the localized spin is very strong. The hopping of the carriers among the magnetic sites causes ferromagnetism through a {\it double-exchange (DE)-like} mechanism. We have investigated the condition for the DE-like mechanism to operate in DMS's. The result reveals that the nonmagnetic attractive potential at the magnetic site assists the formation of the magnetic impurity band and makes the DE-like mechanism operative by substantially enhancing the effect of the exchange interaction. Using conventional parameters we have studied the carrier states in Ga1x_{1-x}Mnx_xAs. The result shows that the ferromagnetism is caused through the DE-like mechanism by the carriers in the bandtail originating from the impurity states.Comment: 20 pages, 14 figure

    Critical Exponents of the Metal-Insulator Transition in the Two-Dimensional Hubbard Model

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    We study the filling-controlled metal-insulator transition in the two-dimensional Hubbard model near half-filling with the use of zero temperature quantum Monte Carlo methods. In the metallic phase, the compressibility behaves as κμμc0.58±0.08\kappa \propto |\mu - \mu_c|^{-0.58\pm0.08} where μc\mu_c is the critical chemical potential. In the insulating phase, the localization length follows ξlμμcνl\xi_l \propto |\mu - \mu_c|^{-\nu_l} with νl=0.26±0.05\nu_l = 0.26 \pm 0.05. Under the assumption of hyperscaling, the compressibility data leads to a correlation length exponent νκ=0.21±0.04\nu_\kappa = 0.21 \pm 0.04. Our results show that the exponents νκ\nu_\kappa and νl\nu_l agree within statistical uncertainty. This confirms the assumption of hyperscaling with correlation length exponent ν=1/4\nu = 1/4 and dynamical exponent z=4z = 4. In contrast the metal-insulator transition in the generic band insulators in all dimensions as well as in the one-dimensional Hubbard model satisfy the hyperscaling assumption with exponents ν=1/2\nu = 1/2 and z=2z = 2.Comment: Two references added. The DVI file and PS figure files are also available at http://www.issp.u-tokyo.ac.jp/labs/riron/imada/furukawa/; to appear in J. Phys. Soc. Jpn 65 (1996) No.

    A survey of thermodynamic properties of the compounds of the element CHNOPS Progress report, 1 Mar. - 30 Jun. 1968

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    Thermodynamic property data tables for CHNOPS compounds and heats of combustion and formation for organic compounds of biological interes

    Survey of thermodynamic properties of the compounds of the elements CHNOPS Sixth preliminary report, 1 Oct. - 31 Dec. 1965

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    Heat capacity data on polyhydroxy compounds, water, carbon dioxide, and ammonia and vapor pressure data on methane, ammonia, and amino acid

    A survey of thermodynamic properties of the compounds of the elements CHNOPS Fifth preliminary report, 1 Jul. - 30 Sep. 1965

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    Literature survey of heat capacity, enthalpy, and entropy properties of ammonia, carbon dioxide, and wate
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