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 ternary phase YbPdxGa11−x has been synthesized from the elements by high frequency argon melting. An extended homogeneous region at 600 °C has been established from X-ray powder data for 2.3≤×≤3.4. The crystal structure of YbPd3Ga8 has been derived from X-ray single crystal counter data: partially ordered BaHg11-type, space group Pm 3 m (O1h, No. 221), a=8.4346(5) A: RF=0.054 for 176 independent reflections with I>2σ. YbPdxGa11−x samples are temperature independent Pauli-type paramagnets for x≤3. Increasing the palladium content to x>3 leads to an enhanced f–d electron interaction, and a variation of the magnetic moment due to valence instabilities (4f14→4f13) is established using X-ray absorption spectroscopy.

Crystal Structure and Valence Behavior of YbPdxGa11‐x.

EuPt4B (I), Eu3Pt7B2 (II), and Eu5Pt18B6-x (III) are synthesized by arc melting of the constituent elements using excess Eu due to its high volatility.

Structural and Physical Properties Diversity of New CaCu5-Type Related Europium Platinum Borides.

Phase relations were established in the Sr-poor part of the ternary systems Sr–Ni–Si (900 °C) and Sr–Cu–Si (800 °C) by light optical microscopy, electron probe microanalysis and X-ray diffraction on as cast and annealed alloys. Two new ternary compounds SrNiSi3 (BaNiSn3-type) and SrNi9−xSi4+x (own-type) were found in the Sr–Ni–Si system along with previously reported Sr(NixSi1−x)2 (AlB2-type). The crystal structure of SrNi9−xSi4+x (own-type, x=2.7, a=0.78998(3), c=1.1337(2) nm; space group P4/nbm) was determined from X-ray single crystal counter to be a low symmetry derivative of the cubic, parent NaZn13-type. At higher Si-content X-ray Rietveld refinements reveal the formation of a vacant site (□) corresponding to a formula SrNi5.5Si6.5□1.0. Phase equilibria in the Sr–Cu–Si system are characterized by the compounds SrCu2−xSi2+x (ThCr2Si2-type), Sr(CuxSi1−x)2 (AlB2-type), SrCu9−xSi4+x (0≤x≤1.0; CeNi8.5Si4.5-type) and SrCu13−xSix (4≤x≤1.8; NaZn13-type). The latter two structure types appear within a continuous solid solution. Neither a type-I nor a type-IX clathrate compound was encountered in the Sr–{Cu,Ni}–Si systems. Structural details are furthermore given for about 14 new ternary compounds from related alloy systems with Ba.

Ternary Systems Sr—{Ni,Cu}—Si: Phase Equilibria and Crystal Structure of Ternary Phases.

Investigations of the magnetic phase diagram of Ce(RuxRh1−x)3B2 were complemented by detailed specific heat and susceptibility measurements revealing complex magnetic order without spontaneous magnetisation. This regime follows the ferromagnetic phase on Rh/Ru substitution for x≳0.06.

Thermodynamic properties of Ce(RuxRh1−x)3B2

The crystal structures of the compounds CeRuAl and CeRhAl were studied by single crystal X-ray diffraction. Both compounds crystallize in the orthorhombic LaNiAl type with space group Pnma (No. 62) and are related to the structure types of hexagonal ZrNiAl and orthorhombic TiNiSi. Parameters for CeRuAl and CeRhAl are: a  = 7.2057(2) A, b =  4.0589(1) A, c  = 15.8728(5) A; R F  = 0.023; a  = 7.107(2) A, b =  4.2237(10) A, c  = 15.965(3) A; R F  = 0.032, respectively.

Peter Rogl

Papers

Crystal Structure and Valence Behavior of YbPdxGa11‐x.

Structural and Physical Properties Diversity of New CaCu5-Type Related Europium Platinum Borides.

Ternary Systems Sr—{Ni,Cu}—Si: Phase Equilibria and Crystal Structure of Ternary Phases.

Thermodynamic properties of Ce(RuxRh1−x)3B2

Crystal Structures of Isotypic Aluminides CeRuAl and CeRhAl.