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

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Topological insulators are new states of quantum matter which cannot be adiabatically connected to conventional insulators and semiconductors. They are characterized by a full insulating gap in the bulk and gapless edge or surface states which are protected by time-reversal symmetry. These topological materials have been theoretically predicted and experimentally observed in a variety of systems, including HgTe quantum wells, BiSb alloys, and Bi2Te3 and Bi2Se3 crystals. Theoretical models, materials properties, and experimental results on two-dimensional and three-dimensional topological insulators are reviewed, and both the topological band theory and the topological field theory are discussed. Topological superconductors have a full pairing gap in the bulk and gapless surface states consisting of Majorana fermions. The theory of topological superconductors is reviewed, in close analogy to the theory of topological insulators.

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Topological insulators and superconductors

Graphene’s success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in...

/pdf/progress-challenges-and-opportunities-in-two-dimensional-1sweg4hljr.pdf

Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene

Using combined scanning tunneling microscopy (STM) measurements and first-principles electronic structure calculations, we extensively studied the atomic and electronic properties of a $\sqrt{7}$-InBi overlayer on Si(111). We propose and demonstrate an effective experimental process to successfully form a large well-ordered $\sqrt{7}$ surface by depositing Bi atoms on the In-Si(111)-$4\ifmmode\times\else\texttimes\fi{}1$ substrate. The STM images exhibit a honeycomb pattern. After performing an exhaustive computational search, we identified the atomic structures of the surface at In and Bi coverages of 6/7 and 3/7 monolayers, respectively. We discovered a trimer model with a lower energy than the previously proposed model. The simulated STM images of trimer models confirm the presence of the honeycomb pattern in accord with our experimental STM images. Most importantly, we found that the surface is robust, preserving the topologically nontrivial phase. Our edge state calculations verify that the InBi overlayer on Si(111) is indeed a two-dimensional (2D) topological insulator (TI). Moreover, hybrid functional calculations result in band gaps up to 70 meV, which is high enough for room-temperature experiments. Our findings lay the foundation for the materials realization of 2D TIs by growing an InBi overlayer on a Si(111) substrate.

Growth of a predicted two-dimensional topological insulator based on InBi-Si(111)-√7×√7

Ultrathin bilayers (BLs) of bismuth have been predicated to be a two-dimensional (2D) topological insulator. Here we report on a new route to manufacture the high-quality Bi bilayers from a 3D topological insulator, a top-down approach to prepare large-area and well-ordered Bi(111) BL with deliberate hydrogen etching on epitaxial Bi2Se3 films. With scanning tunneling microscopy (STM) and X-ray photoelectron spectra (XPS) in situ, we confirm that the removal of Se from the top of a quintuple layer (QL) is the key factor, leading to a uniform formation of Bi(111) BL in the van der Waals gap between the first and second QL of Bi2Se3. The angle resolved photoemission spectroscopy (ARPES) in situ and complementary density functional theory (DFT) calculations show a giant Rashba splitting with a coupling constant of 4.5 eV A in the Bi(111) BL on Bi2Se3. Moreover, the thickness of Bi BLs can be tuned by the amount of hydrogen exposure. Our ARPES and DFT study indicated that the Bi hole-like bands increase with i...

Selective Hydrogen Etching Leads to 2D Bi(111) Bilayers on Bi2Se3: Large Rashba Splitting in Topological Insulator Heterostructure

http://absimage.aps.org/image/MAR16/MWS_MAR16-2015-001680.pdf

Prediction of an arc-tunable Weyl Fermion metallic state in Mo$_x$W$_{1-x}$Te$_2$

The magnetic properties of ${\text{NaVO}}_{2}$ are investigated using full-potential linearized augmented plane-wave method. We perform calculations for three structures. For the rhombohedral structure at 100 K, the ${t}_{2g}$ orbitals of V ions are split into upper ${a}_{1g}$ and lower ${e}_{g}^{\ensuremath{'}}$ orbitals by a trigonal distortion of compression. For the monoclinic structure at 91.5 K, the system behaves such as a frustrated spin lattice with spatially anisotropic exchange interactions. For another monoclinic structure at 20 K, the magnetic frustration is relieved by a lattice distortion which is driven by a certain orbital ordering and the long-range magnetic ordering is thus formed. Moreover, the small magnetic moment originates from the compensation of orbital moment for the spin moment.

Orbitally relieved magnetic frustration in NaVO2

http://absimage.aps.org/image/MAR16/MWS_MAR16-2015-004740.pdf

Hsin Lin

Papers

Growth of a predicted two-dimensional topological insulator based on InBi-Si(111)-√7×√7

Selective Hydrogen Etching Leads to 2D Bi(111) Bilayers on Bi2Se3: Large Rashba Splitting in Topological Insulator Heterostructure

Prediction of an arc-tunable Weyl Fermion metallic state in Mo$_x$W$_{1-x}$Te$_2$

Orbitally relieved magnetic frustration in NaVO2

Prediction of two-dimensional topological insulator by forming surface alloy on Au/Si(111) substrate