There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.

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The electronic properties of graphene

J. Appl. Cryst.の発刊に際して

We review the dynamical mean-field theory of strongly correlated electron systems which is based on a mapping of lattice models onto quantum impurity models subject to a self-consistency condition. This mapping is exact for models of correlated electrons in the limit of large lattice coordination (or infinite spatial dimensions). It extends the standard mean-field construction from classical statistical mechanics to quantum problems. We discuss the physical ideas underlying this theory and its mathematical derivation. Various analytic and numerical techniques that have been developed recently in order to analyze and solve the dynamical mean-field equations are reviewed and compared to each other. The method can be used for the determination of phase diagrams (by comparing the stability of various types of long-range order), and the calculation of thermodynamic properties, one-particle Green's functions, and response functions. We review in detail the recent progress in understanding the Hubbard model and the Mott metal-insulator transition within this approach, including some comparison to experiments on three-dimensional transition-metal oxides. We present an overview of the rapidly developing field of applications of this method to other systems. The present limitations of the approach, and possible extensions of the formalism are finally discussed. Computer programs for the numerical implementation of this method are also provided with this article.

Dynamical mean-field theory of strongly correlated fermion systems and the limit of infinite dimensions

Magnetization measurements on polycrystalline samples with nominal composition ${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{Ba}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{La}}_{\mathit{x}}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (x=0.0, 0.05, 0.10, 0.50, and 1.0) show that only samples with x=1.0 or 0.0 contain a single superconducting phase. Gas evolution experiments on (Ca,Ba,La)${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (x=1.0, \ensuremath{\delta}\ensuremath{\sim}0.07) reveal the presence of an oxygen phase that is indistinguishable from the oxygen chain structure of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (x=0.0, \ensuremath{\delta}\ensuremath{\sim}0.05); however, the total amount of evolved oxygen is very different between the two phases. These studies suggest that two phases coexist in (Ca,Ba,La)${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$: a superconducting phase in which ${\mathrm{La}}^{3+}$ ions occupy the ${\mathrm{Y}}^{3+}$ sites, and a second nonsuperconducting phase where ${\mathrm{Ca}}^{2+}$ ions occupy the ${\mathrm{Y}}^{3+}$ sites.

Superconductivity and oxygen ordering in (Ca,Ba,La) Cu 3 O 7 − δ

Experimental evidence is presented for the intercalation of carbon nanotubes (CNs) in polycrystalline Bi2Sr2CaCu2O8 (BSCCO) samples at the 12 wt.%-CN doping level, based on high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction measurements. Magnetization measurements performed on BSCCO samples with various CN doping levels do not indicate a change in the critical current density Jc within experimental error. The embedding process did not have any detrimental effects on the superconducting critical temperature of any of the samples. In contrast to previous work, the temperatures and widths of the superconducting transition of all the samples were similar.

Nondestructive interactions of carbon nanotubes with Bi2Sr2CaCu2O8

We have measured the resistivity and Hall coefficient of ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ (NCCO) thin films sequentially damaged by ion irradiation. The ${T}_{c}$ of the NCCO decreases linearly with residual resistivity and extrapolates to zero at ${R}_{\ensuremath{\square}}/(\mathrm{unit}\mathrm{}\mathrm{cell})\ensuremath{\approx}5\ensuremath{-}10 \mathrm{k}\ensuremath{\Omega},$ results similar to Y-Ba-Cu-O. We suggest that the physical basis for this behavior in NCCO may be disorder effects in a homogeneous two-dimensional superconductor. Unusual behavior of the Hall coefficient gives further evidence that NCCO may be a two-carrier conductor.

M. B. Maple

Papers

Superconductivity and oxygen ordering in (Ca,Ba,La) Cu 3 O 7 − δ

Nondestructive interactions of carbon nanotubes with Bi2Sr2CaCu2O8

Destruction of superconductivity in Nd 2 − x Ce x CuO 4 − δ thin films by ion irradiation

Magnetic ordering in (La, Gd) Al2 alloys

Non-Fermi-liquid behavior and magnetic order in the U 1-x Y x Pd 2 Al 3 system