11,930 research outputs found
Magnetism and Superconductivity in a Two-band Hubbard Model in Infinite Dimensions
We study a two-band Hubbard model using the dynamical mean-field theory
combined with the exact diagonalization method. At the electron density ,
a transition from a band-insulator to a correlated semimetal occurs when the
on-site Coulomb interaction is varied for a fixed value of the
charge-transfer energy . At low temperature, the correlated semimetal
shows ferromagnetism or superconductivity. With increasing doping , the
ferromagnetic transition temperature rapidly decreases and finally becomes zero
at a critical value of . 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 () 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
Functional organic materials for electronics industries
Topics closely related with organic, high molecular weight material synthesis are discussed. These are related to applications such as display, recording, sensors, semiconductors, and I.C. correlation. New materials are also discussed. General principles of individual application are not included. Materials discussed include color, electrochromic, thermal recording, organic photoconductors for electrophotography, and photochromic materials
First-Principles Study on Electron-Conduction Properties of C Chains
The electron-conduction properties of fullerene chains are examined by
first-principles calculations based on the density functional theory. The
conductivity of the C dimer is low owing to the constraint of the
junction of the molecules on electron conduction, whereas the C monomer
exhibits a conductance of 1 G. One of the three degenerate
states of C is relevant to conduction and the contributions of the
others are small. In addition, we found a more interesting result that the
conductance of the fullerene chain is drastically increased by encapsuling
metal atoms into cages.Comment: 10pages and 5 figure
New structural model for GeO2/Ge interface: A first-principles study
First-principles modeling of a GeO2/Ge(001) interface reveals that sixfold
GeO2, which is derived from cristobalite and is different from rutile,
dramatically reduces the lattice mismatch at the interface and is much more
stable than the conventional fourfold interface. Since the grain boundary
between fourfold and sixfold GeO2 is unstable, the sixfold GeO2 forms a large
grain at the interface. On the contrary, a comparative study with SiO2
demonstrates that SiO2 maintains a fourfold structure. The sixfold GeO2/Ge
interface is shown to be a consequence of the ground-state phase of GeO2. In
addition, the electronic structure calculation reveals that sixfold GeO2 at the
interface shifts the valence band maximum far from the interface toward the
conduction band.Comment: 18 pages, 5 figures, and 2 table
Fully spin-dependent transport of triangular graphene flakes
The magnetic moment and spin-polarized electron transport properties of
triangular graphene flakes surrounded by boron nitride sheets (BNC structures)
are studied by using first-principles calculations based on density functional
theory. Their dependence on the BNC structure is discussed, revealing that
small isolated graphene flakes have large magnetic moment. When the BNC
structure is suspended between graphene electrodes, the spin-polarized charge
density distribution accumulates at the edge of the graphene flakes and no spin
polarization is observed in the graphene electrodes. We also found that the BNC
structure demonstrates perfectly spin-polarized transport properties in the
wide energy window around the Fermi level. Our first-principles results
indicate that the BNC structure provides new possibilities to electrically
control spin
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