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

Weyl and Dirac semimetals are three-dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry. As three-dimensional analogs of graphene, they have generated much recent interest. Deep connections exist with particle physics models of relativistic chiral fermions, and, despite their gaplessness, to solid-state topological and Chern insulators. Their characteristic electronic properties lead to protected surface states and novel responses to applied electric and magnetic fields. The theoretical foundations of these phases, their proposed realizations in solid-state systems, and recent experiments on candidate materials as well as their relation to other states of matter are reviewed.

Weyl and Dirac semimetals in three-dimensional solids

The MN+1AXN phases: A new class of solids

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

We systematically study topological phases of insulators and superconductors (or superfluids) in three spatial dimensions. We find that there exist three-dimensional (3D) topologically nontrivial insulators or superconductors in five out of ten symmetry classes introduced in seminal work by Altland and Zirnbauer within the context of random matrix theory, more than a decade ago. One of these is the recently introduced ${\mathbb{Z}}_{2}$ topological insulator in the symplectic (or spin-orbit) symmetry class. We show that there exist precisely four more topological insulators. For these systems, all of which are time-reversal invariant in three dimensions, the space of insulating ground states satisfying certain discrete symmetry properties is partitioned into topological sectors that are separated by quantum phase transitions. Three of the above five topologically nontrivial phases can be realized as time-reversal invariant superconductors. In these the different topological sectors are characterized by an integer winding number defined in momentum space. When such 3D topological insulators are terminated by a two-dimensional surface, they support a number (which may be an arbitrary nonvanishing even number for singlet pairing) of Dirac fermion (Majorana fermion when spin-rotation symmetry is completely broken) surface modes which remain gapless under arbitrary perturbations of the Hamiltonian that preserve the characteristic discrete symmetries, including disorder. In particular, these surface modes completely evade Anderson localization from random impurities. These topological phases can be thought of as three-dimensional analogs of well-known paired topological phases in two spatial dimensions such as the spinless chiral $({p}_{x}\ifmmode\pm\else\textpm\fi{}i{p}_{y})$-wave superconductor (or Moore-Read Pfaffian state). In the corresponding topologically nontrivial (analogous to ``weak pairing'') and topologically trivial (analogous to ``strong pairing'') 3D phases, the wave functions exhibit markedly distinct behavior. When an electromagnetic U(1) gauge field and fluctuations of the gap functions are included in the dynamics, the superconducting phases with nonvanishing winding number possess nontrivial topological ground-state degeneracies.

Classification of topological insulators and superconductors in three spatial dimensions

The 700 °C isothermal sections of the phase diagrams of the ternary systems Sr—Ag—Ge and Sr—Au—Ge and the 800 °C isothermal sections of Sr—Ag—Si and Sr—Au—Si are determined in the Ge,Si-rich region for Sr contents up to33.3 at%.

Phase Relations and Crystal Structures in the Ternary Systems Sr‐{Ag, Au}‐{Si, Ge}.

The crystal structure of the quaternary so-called π-phase, which was originally solved from photographic single crystal data, has been refined from single crystal automatic four circle counter data. Single crystals were obtained from the residue of a slowly cooled melt of nominal composition (in at %) Al74.1Fe0.5Mg8.4Si17.0, which was dissolved in butanol. The composition of the π-phase crystal was Al9Fe1Mg3.5Si5.0. The π-phase crystallizes in a unique structure type (Al9FeMg3Si5-type) with the noncentrosymmetric hexagonal space group P 6 2m−D 3 3h , No. 189. The lattice parameters obtained from a Gandolfi camera were a=0.6625(2) nm and c=0.7910(4) nm, Z=1. For 366 reflections (‖F0‖≥3σ) the residual values are R=∑ (‖ΔF‖/∑‖F0‖)=0.064, Rw=0.075. Whereas previous structure determinations claimed full atom order, the present refinement clearly indicates that the crystal structure is partially ordered with a random distribution of 0.94 Al+0.06 Mg in the 6i-sites. Furthermore, whilst lattice and atom parameter essentially correspond to the values derived earlier, the new composition as a result of the refinement (Al8.7Fe1Mg3.3Si5) is in close agreement with the experimental composition Al9FeMg3.5Si5.

Refinement of the Crystal Structure π-Al9FeMg3Si5.

Density Functional Study of Structural and Phase Stabilities for LnMn2 Laves Phases (Ln: Sc, Y, Lu, Ti, Zr, Hf).

Semiconducting clathrate-type I compounds are of considerable interest for thermoelectric materials.

Crystal Structure and Physical Properties of Quaternary Clathrates Ba8ZnxGe46-x-ySiy, Ba8(Zn,Cu)xGe46-x and Ba8(Zn,Pd)xGe46-x.

A series of selected ternary holmium germanides with platinum group metals was synthesized and characterized by room temperature X-ray powder diffraction: Ho3(Ru,Os)4Ge13 (Y3Co4Ge13-type). Ho2(Ru,Os)Ge2 (Sc2CoSi2-type), Ho(Ru,Pd1)2Ge2 (CeGa2Al2-type), Ho(Ru,Ir,Pt)Ge (TiNiSi-type), HoAuGe (LiGaGe-type), Ho2Ru3Ge5 (U2Co3Si5-type), Ho3Ru2Ge3 (Hf3Ni2Si3-type), Ho5Os4Ge10 (Sc5Co4Si10-type). Ho3Pd4Ge4 (Gd3Cu4Ge4-type) and HoPdGe (CeCu2-type). Magnetic measurements of the HoMGe compounds revealed that Ho3(Ru,Os)4Ge13, Ho5Os4Ge10, HoPtGe and HoPt2Ge2 are paramagnets above T = 4.5 K. Ho2Ru3Ge5, HoRuGe, Ho3Pd4Ge4 and HoAuGe are ferromagnets. HoRu2Ge2 and HoPd2Ge2 are metamagnets. Ho2(Ru,Os)Ge2, Ho3Ru2Ge3, HoIrGe as well as HoPdGe undergo an antiferromagnetic ordering at higher temperatures, whereas a spin reorientation to a ferromagnetic spin alignment occurs at lower temperatures. No superconductivity was observed down to around 2 K.

Peter Rogl

Papers

Phase Relations and Crystal Structures in the Ternary Systems Sr‐{Ag, Au}‐{Si, Ge}.

Refinement of the Crystal Structure π-Al9FeMg3Si5.

Density Functional Study of Structural and Phase Stabilities for LnMn2 Laves Phases (Ln: Sc, Y, Lu, Ti, Zr, Hf).

Crystal Structure and Physical Properties of Quaternary Clathrates Ba8ZnxGe46-x-ySiy, Ba8(Zn,Cu)xGe46-x and Ba8(Zn,Pd)xGe46-x.

Magnetic Behavior of Holmium‐Platinum Group Metal‐Germanium Ternary Alloys.