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.

/pdf/the-electronic-properties-of-graphene-2siyzsnf5w.pdf

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

Electrical resistance R(T) measurements on UAsSe and ThAsSe single crystals were performed under hydrostatic conditions at pressures up to 1.88 GPa (2 K ≤ T ≤ 300 K). For ferromagnetic UAsSe, a reduction of a low-T upturn in R(T) accompanied by an increase of T c was observed. However, this effect is smaller than that introduced by chemical substitution. For diamagnetic ThAsSe, a hump-like anomaly (T = 65 K, p = 0) vanishes at p = 1.88 GPa. However, the ratio R(4.2 K)/R(300 K) was only slightly reduced by pressure. Below 20 K, a pressure-independent logarithmic increase of R(T) over one decade in temperature has been found. The results reported here fit well with the theoretical predictions of the non-magnetic TLS Kondo model.

Interaction between TLS and the conduction electrons in actinide arsenoselenides: a high-pressure study

We present electrical transport, magnetization, and specific heat measurements on bulk MgB2 samples (T_{c} = 38.5 K) synthesized under 200 MPa pressure using a process based on hot isostatic pressing with cooling under pressure. The samples are fully dense and display excellent superconducting properties, including a narrow superconducting transition width (\Delta T_{c} = 0.75 K), a high upper critical field H_{c2} (H_{c2}(0) ~ 155 kOe), and a critical current density J_{c} that is the largest yet measured for bulk samples of MgB2 (J_{c}(0) ~ 1.4 MA/cm^{2}). Specific heat measurements yielded a jump \Delta C at T_{c} of 92 mJ/mol K. These superconducting properties are comparable to those obtained with techniques that are not so well suited to industrial scale fabrication.

Improved superconducting properties of MgB2

In this article, we describe an ultrahigh vacuum (UHV) compatible superconducting quantum interference device (SQUID) magnetometer system for investigations of surface, interface, and thin film magnetism. This system provides a new capability for a commercial SQUID magnetometer to characterize freshly deposited thin film samples transported from a separate molecular‐beam epitaxy deposition facility without breaking vacuum. Magnetic measurements can be performed over a wide range of temperatures down to 4.2 K in applied magnetic fields as high as 1 T, and under a variable vacuum environment in which pressures as low as 10−10 Torr can be achieved. The combination of the extremely high sensitivity of the SQUID for magnetic measurements with UHV analysis techniques offers the unique capability for films to be prepared, processed, and characterized repeatedly without substantial contamination. The capabilities of the UHV‐SQUID magnetometer system are demonstrated by in situ measurements of the magnetic propert...

Ultrahigh vacuum compatible superconducting quantum interference device magnetometer system for studies of magnetic thin films

We have performed measurements of acmagnetic susceptibility χac as a function of temperature and magnetic field on polycrystalline specimens of Sm2−x Ce x CuO4−y (0.15≤x≤0.18) prepared from a sol‐gel precursor. All the samples studied show a striking double resistive superconducting transition. One of the resistive transitions occurs at a higher temperatureT ci and the other one at a lower Josephson‐coupling temperatureT cj . Magnetic measurements reveal the appearance of superconductivity below T cj which is evident from the resistive component χ″ which peaks only at T cj . Measurements made on pellets and crushed samples with average grain size ∼1 μm show essentially the same features. This suggests that Josephson coupling occurs inside physical grains with dimensions close to 5 μm. We have also utilized the behavior of the peak in the χ″ component as a function of applied magnetic fields to build a H vs Tphase diagram for these compounds. Some interesting features were observed in this H vs Tphase diagram: (1) a H α, α=2/3, dependence at low applied magnetic fields (H≤2 kOe) and high temperatures, and (2) an abrupt increase in the magnitude of the exponent at high fields and low temperatures. The behavior at low fields and high temperatures suggests that the magnetic response of the system is mainly controlled by a disordered Josephson network. Possible connections between these two different behaviors are discussed.

Magnetic properties of polycrystalline Sm2−xCexCuO4−y at high magnetic fields

http://absimage.aps.org/image/MAR06/MWS_MAR06-2005-000420.pdf

M. B. Maple

Papers

Interaction between TLS and the conduction electrons in actinide arsenoselenides: a high-pressure study

Improved superconducting properties of MgB2

Ultrahigh vacuum compatible superconducting quantum interference device magnetometer system for studies of magnetic thin films

Magnetic properties of polycrystalline Sm2−xCexCuO4−y at high magnetic fields

Flux jumps in irradiated MgB$_{2}$ dense samples