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

Materials research has driven the development of modern nano-electronic devices. In particular, research in magnetic thin films has revolutionized the development of spintronic devices1,2 because identifying new magnetic materials is key to better device performance and design. Van der Waals crystals retain their chemical stability and structural integrity down to the monolayer and, being atomically thin, are readily tuned by various kinds of gate modulation3,4. Recent experiments have demonstrated that it is possible to obtain two-dimensional ferromagnetic order in insulating Cr2Ge2Te6 (ref. 5) and CrI3 (ref. 6) at low temperatures. Here we develop a device fabrication technique and isolate monolayers from the layered metallic magnet Fe3GeTe2 to study magnetotransport. We find that the itinerant ferromagnetism persists in Fe3GeTe2 down to the monolayer with an out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition temperature, Tc, is suppressed relative to the bulk Tc of 205 kelvin in pristine Fe3GeTe2 thin flakes. An ionic gate, however, raises Tc to room temperature, much higher than the bulk Tc. The gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2 opens up opportunities for potential voltage-controlled magnetoelectronics7-11 based on atomically thin van der Waals crystals.

Gate-tunable Room-temperature Ferromagnetism in Two-dimensional Fe 3 GeTe 2

We show that the pseudorelativistic physics of graphene near the Fermi level can be extended to three dimensional (3D) materials. Unlike in phase transitions from inversion symmetric topological to normal insulators, we show that particular space groups also allow 3D Dirac points as symmetry protected degeneracies. We provide criteria necessary to identify these groups and, as an example, present ab initio calculations of β-cristobalite BiO(2) which exhibits three Dirac points at the Fermi level. We find that β-cristobalite BiO(2) is metastable, so it can be physically realized as a 3D analog to graphene.

Dirac Semimetal in Three Dimensions

The ability to tune material properties using gating by electric fields is at the heart of modern electronic technology. It is also a driving force behind recent advances in two-dimensional systems, such as the observation of gate electric-field-induced superconductivity and metal-insulator transitions. Here, we describe an ionic field-effect transistor (termed an iFET), in which gate-controlled Li ion intercalation modulates the material properties of layered crystals of 1T-TaS2. The strong charge doping induced by the tunable ion intercalation alters the energetics of various charge-ordered states in 1T-TaS2 and produces a series of phase transitions in thin-flake samples with reduced dimensionality. We find that the charge-density wave states in 1T-TaS2 collapse in the two-dimensional limit at critical thicknesses. Meanwhile, at low temperatures, the ionic gating induces multiple phase transitions from Mott-insulator to metal in 1T-TaS2 thin flakes, with five orders of magnitude modulation in resistance, and superconductivity emerges in a textured charge-density wave state induced by ionic gating. Our method of gate-controlled intercalation opens up possibilities in searching for novel states of matter in the extreme charge-carrier-concentration limit.

http://absimage.aps.org/image/MAR15/MWS_MAR15-2014-020259.pdf

Gate-tunable phase transitions in thin flakes of 1T-TaS$_{2}$

The interaction of Li(+) with single and few layer graphene is reported. In situ Raman spectra were collected during the electrochemical lithiation of the single- and few-layer graphene. While the interaction of lithium with few layer graphene seems to resemble that of graphite, single layer graphene behaves very differently. The amount of lithium absorbed on single layer graphene seems to be greatly reduced due to repulsion forces between Li(+) at both sides of the graphene layer.

http://ma.ecsdl.org/content/MA2010-02/6/375.full.pdf

The Interaction of Li+ with Single-Layer and Few Layers Graphene

Ternary compound HfCuP: An excellent Weyl semimetal with the coexistence of type-I and type-II Weyl nodes.

Superconductors with a nontrivial band structure are promising to realize a topological superconducting state. Herein, we report the presence of a topological phase in a well-known superconductor, NaAlSi. Our first-principles computations show that NaAlSi naturally possesses four nodal lines in the kz = 0 and kz = π planes and hosts clear drumhead surface states. Comparing with those identified in other superconductors, the nodal line band structure of NaAlSi can more favor experimental detection on considering that: (1) it possesses four nodal lines in total in the system; (2) all the nodal lines appear slightly below the Fermi level; (3) the nodal lines do not coexist with other fermions or extraneous bands. Our findings indicate that NaAlSi is an excellent material platform to investigate the entanglement of superconducting and topological nodal line states.

Topological nodal line state in superconducting NaAlSi compound

Topological metals/semimetals, as novel topological states of matter, have been well investigated in nonmagnetic and ferromagnetic materials. Here, by performing band structure calculations, we report the discovery of rich topological states in an antiferromagnetic metal β-Fe2PO5. When spin–orbit coupling (SOC) is not considered, it hosts a Weyl nodal line, Dirac point, and Dirac nodal line near the Fermi level. In particular, the Weyl nodal line in β-Fe2PO5 is formed by the crossing bands from a single spin channel. Such a fully spin-polarized Weyl nodal line has not been identified in realistic AFM materials before. The Dirac point and Dirac nodal line in β-Fe2PO5 occur in a specific high-symmetry path, and are formed by the crossing bands from both spin channels, showing different signatures with the Weyl nodal line. When SOC is taken into account, the Weyl nodal line is retained, and the Dirac nodal point and nodal line degenerate into their Weyl counterparts. The existence of rich fermionic states in antiferromagnetic β-Fe2PO5 not only provides an excellent platform to study the entanglement between magnetism and topological states, but also shows great potential in topological antiferromagnetic spintronics applications.

Topological nodal lines and nodal points in the antiferromagnetic material β-Fe2PO5

Mn2C monolayer: A superior anode material offering good conductivity, high storage capacity and ultrafast ion diffusion for Li-ion and Na-ion batteries

Weizhen Meng

Papers

Ternary compound HfCuP: An excellent Weyl semimetal with the coexistence of type-I and type-II Weyl nodes.

Topological nodal line state in superconducting NaAlSi compound

Topological nodal lines and nodal points in the antiferromagnetic material β-Fe2PO5

Mn2C monolayer: A superior anode material offering good conductivity, high storage capacity and ultrafast ion diffusion for Li-ion and Na-ion batteries

Ferromagnetic two-dimensional metal-chlorides MCl (M = Sc, Y, and La): Candidates for Weyl nodal line semimetals with small spin-orbit coupling gaps