Observation of topological superconductivity in a stoichiometric transition metal dichalcogenide 2M-WS2

Topological superconductors (TSCs) are unconventional superconductors with bulk superconducting gap and in-gap Majorana states on the boundary that may be used as topological qubits for quantum computation. Despite their importance in both fundamental research and applications, natural TSCs are very rare. Here, combining state of the art synchrotron and laser-based angle-resolved photoemission spectroscopy, we investigated a stoichiometric transition metal dichalcogenide (TMD), 2M-WS₂ with a superconducting transition temperature of 8.8 K (the highest among all TMDs in the natural form up to date) and observed distinctive topological surface states (TSSs). Furthermore, in the superconducting state, we found that the TSSs acquired a nodeless superconducting gap with similar magnitude as that of the bulk states. These discoveries not only evidence 2M-WS₂ as an intrinsic TSC without the need of sensitive composition tuning or sophisticated heterostructures fabrication, but also provide an ideal platform for device applications thanks to its van der Waals layered structure.

Molecular identification of hemoplasma and piroplasma species from Rattus edwardsi based on sequences analysis of ribosomal DNA, China

The present study provides the first report on the molecular epidemiological data regarding infection by hemoplasma and piroplasma species in wild Rattus edwardsi, from China. In the current study, blood samples were investigated from 32 wild Rattus edwardsi from Hunan (23) and Guangxi (9) provinces, China. The prevalence of hemoplasma and piroplasma was 65.63% (21/32) and 6.25% (2/32), respectively. Phylogenetic analyses indicated that hemoplasmas (HQ183731, HQ183732) derived from wild Rattus edwardsi in China, can be grouped into a solitary clade closely related to H. muris (HMU82963) and M. haemomuris (AB758435). In addition, it was shown that piroplasmas from this study have very close genetic distance to other unidentified piroplasma species isolated from China (AB242140) and Japan (AB188086). The results suggested that hemoplasmas isolated in this study should be represented as a new genotype. Piroplasmas on the other hand needs more sequenced samples in its life-cycle and evidence to check its taxonomic status. These data may have important implications for researching on the epidemiology and population biology as well as for studying the taxonomy status of hemoplasmas and piroplasmids of wild rodents.

Coexistence of superconductivity and antiferromagnetism in (Li0.8Fe0.2)OHFeSe

Iron selenide superconductors exhibit a number of unique characteristics that are helpful for understanding the mechanism of superconductivity in high-Tc iron-based superconductors more generally. However, in the case of AxFe2Se2 (A = K, Rb, Cs), the presence of an intergrown antiferromagnetic insulating phase makes the study of the underlying physics problematic. Moreover, FeSe-based systems intercalated with alkali metal ions, NH3 molecules or organic molecules are extremely sensitive to air, which prevents the further investigation of their physical properties. It is therefore desirable to find a stable and easily accessible FeSe-based superconductor to study its physical properties in detail. Here, we report the synthesis of an air-stable material, (Li0.8Fe0.2)OHFeSe, which remains superconducting at temperatures up to ~40 K, by means of a novel hydrothermal method. The crystal structure is unambiguously determined by a combination of X-ray and neutron powder diffraction and nuclear magnetic resonance. Moreover, antiferromagnetic order is shown to coexist with superconductivity. This synthetic route opens a path for exploring superconductivity in other related systems, and confirms the appeal of iron selenides as a platform for understanding superconductivity in iron pnictides more broadly.

New layered materials: syntheses, structures, and optical and magnetic properties of CsGdZnSe3, CsZrCuSe3, CsUCuSe3, and BaGdCuSe3

Four new quaternary selenides CsGdZnSe3, CsZrCuSe3, CsUCuSe3, and BaGdCuSe3 have been synthesized with the use of traditional high-temperature solid-state experimental methods. These compounds are isostructural with KZrCuS3, crystallizing with four formula units in the orthorhombic space group Cmcm. Cell constants (A) at 153 K are CsGdZnSe3 4.1684(7), 15.765(3), 11.0089(18); CsZrCuSe3 3.903(2), 15.841(10), 10.215(6); CsUCuSe3 4.1443(7), 15.786(3), 10.7188(18); and BaGdCuSe3 4.1839(6), 13.8935(19), 10.6692(15). The structure of these ALnMSe3 compounds (A = Cs, Ba; Ln = Zr, Gd, U; M = Cu, Zn) is composed of 2 to infinity [LnMSe3(n-)] (n = 1, 2) layers separated by A atoms. The Ln atom is octahedrally coordinated to six Se atoms, the M atom is tetrahedrally coordinated to four Se atoms, and the A atom is coordinated to a bicapped trigonal prism of eight Se atoms. Because there are no Se-Se bonds in the structure, the oxidation state of A is 1+ (Cs) or 2+ (Ba), that of Ln is 3+ (Gd) or 4+ (Zr, U), and that of M is 1+ (Cu) or 2+ (Zn). CsGdZnSe3 and BaGdCuSe3, which are paramagnetic, obey the Curie-Weiss law and have effective magnetic moments of 7.87(6) and 7.85(5) muB for Gd(3+), in good agreement with the theoretical value of 7.94 muB. Optical transitions at 1.88 and 2.92 eV for CsGdZnSe3 and 1.96 eV for BaGdCuSe3 were deduced from diffuse reflectance spectra.

Syntheses and structures of the infinite chain compounds Cs(4)Ti(3)Se(13), Rb(4)Ti(3)S(14), Cs(4)Ti(3)S(14), Rb(4)Hf(3)S(14), Rb(4)Zr(3)Se(14), Cs(4)Zr(3)Se(14), and Cs(4)Hf(3)Se(14)

The alkali metal/group 4 metal/polychalcogenides Cs(4)Ti(3)Se(13), Rb(4)Ti(3)S(14), Cs(4)Ti(3)S(14), Rb(4)Hf(3)S(14), Rb(4)Zr(3)Se(14), Cs(4)Zr(3)Se(14), and Cs(4)Hf(3)Se(14) have been synthesized by means of the reactive flux method at 823 or 873 K. Cs(4)Ti(3)Se(13) crystallizes in a new structure type in space group C(2)(2)-P2(1) with eight formula units in a monoclinic cell at T = 153 K of dimensions a = 10.2524(6) A, b = 32.468(2) A, c = 14.6747(8) A, beta = 100.008(1) degrees. Cs(4)Ti(3)Se(13) is composed of four independent one-dimensional [Ti(3)Se(13)(4-)] chains separated by Cs(+) cations. These chains adopt hexagonal closest packing along the [100] direction. The [Ti(3)Se(13)(4-)] chains are built from the face- and edge-sharing of pentagonal pyramids and pentagonal bipyramids. Formal oxidation states cannot be assigned in Cs(4)Ti(3)Se(13). The compounds Rb(4)Ti(3)S(14), Cs(4)Ti(3)S(14), Rb(4)Hf(3)S(14), Rb(4)Zr(3)Se(14), Cs(4)Zr(3)Se(14), and Cs(4)Hf(3)Se(14) crystallize in the K(4)Ti(3)S(14) structure type with four formula units in space group C(2)(h)()(6)-C2/c of the monoclinic system at T = 153 K in cells of dimensions a = 21.085(1) A, b = 8.1169(5) A, c = 13.1992(8) A, beta = 112.835(1) degrees for Rb(4)Ti(3)S(14);a = 21.329(3) A, b = 8.415(1) A, c = 13.678(2) A, beta = 113.801(2) degrees for Cs(4)Ti(3)S(14); a = 21.643(2) A, b = 8.1848(8) A, c = 13.331(1) A, beta = 111.762(2) degrees for Rb(4)Hf(3)S(14); a = 22.605(7) A, b = 8.552(3) A, c = 13.880(4) A, beta = 110.919(9) degrees for Rb(4)Zr(3)Se(14); a = 22.826(5) A, b = 8.841(2) A, c = 14.278(3) A, beta = 111.456(4) degrees for Cs(4)Zr(3)Se(14); and a = 22.758(5) A, b = 8.844(2) A, c = 14.276(3) A, beta = 111.88(3) degrees for Cs(4)Hf(3)Se(14). These A(4)M(3)Q(14) compounds (A = alkali metal; M = group 4 metal; Q = chalcogen) contain hexagonally closest-packed [M(3)Q(14)(4-)] chains that run in the [101] direction and are separated by A(+) cations. Each [M(3)Q(14)(4-)] chain is built from a [M(3)Q(14)] unit that consists of two MQ(7) pentagonal bipyramids or one distorted MQ(8) bicapped octahedron bonded together by edge- or face-sharing. Each [M(3)Q(14)] unit contains six Q(2)(2-) dimers, with Q-Q distances in the normal single-bond range 2.0616(9)-2.095(2) A for S-S and 2.367(1)-2.391(2) A for Se-Se. The A(4)M(3)Q(14) compounds can be formulated as (A(+))(4)(M(4+))(3)(Q(2)(2-))(6)(Q(2-))(2).

New Layered Materials: Syntheses, Structures, and Optical Properties of K2TiCu2S4, Rb2TiCu2S4, Rb2TiAg2S4, Cs2TiAg2S4, and Cs2TiCu2Se4

The new compounds K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiAg(2)S(4), Cs(2)TiAg(2)S(4), and Cs(2)TiCu(2)Se(4) have been synthesized by the reactions of A(2)Q(3) (A = K, Rb, Cs; Q = S, Se) with Ti, M (M = Cu or Ag), and Q at 823 K. The compounds Rb(2)TiCu(2)S(4), Cs(2)TiAg(2)S(4), and Cs(2)TiCu(2)Se(4) are isostructural. They crystallize with two formula units in space group P4(2)/mcm of the tetragonal system in cells of dimensions a = 5.6046(4) A, c = 13.154(1) A for Rb(2)TiCu(2)S(4), a =6.024(1) A, c = 13.566(4) A for Cs(2)TiAg(2)S(4), and a =5.852(2) A, c =14.234(5) A for Cs(2)TiCu(2)Se(4) at 153 K. Their structure is closely related to that of Cs(2)ZrAg(2)Te(4) and comprises [TiM(2)Q(4)(2)(-)] layers, which are separated by alkali metal atoms. The [TiM(2)Q(4)(2)(-)] layer is anti-fluorite-like with both Ti and M atoms tetrahedrally coordinated to Q atoms. Tetrahedral coordination of Ti(4+) is rare in the solid state. On the basis of unit cell and space group determinations, the compounds K(2)TiCu(2)S(4) and Rb(2)TiAg(2)S(4) are isostructural with the above compounds. The band gaps of K(2)TiCu(2)S(4), Rb(2)TiCu(2)S(4), Rb(2)TiAg(2)S(4), and Cs(2)TiAg(2)S(4) are 2.04, 2.19, 2.33, and 2.44 eV, respectively, as derived from optical measurements. From band-structure calculations, the optical absorption for an A(2)TiM(2)Q(4) compound is assigned to a transition from an M d and Q p valence band (HOMO) to a Ti 3d conduction band.

Syntheses, structures, and physical properties of LnAsTe (Ln = La, Pr, Sm, Gd, Dy, Er)

Six rare-earth arsenic tellurides have been synthesized by the reactions of the rare-earth elements (Ln) with As and Te at 1123 K. LaAsTe (a = 7.8354(11) A, b = 4.1721(6) A, c = 10.2985(14) A, T = 153 K), PrAsTe (a = 7.728(2) A, b = 4.1200(11) A, c = 10.137(3) A, T = 153 K), SmAsTe (a = 7.6180(16) A, b = 4.0821(9) A, c = 9.991(2) A, T = 153 K), GdAsTe (a = 7.5611(15) A, b = 4.0510(8) A, c = 9.920(2) A, T = 153 K), DyAsTe (a = 7.4951(13) A, b = 4.0246(7) A, c = 9.8288(17) A, T = 153 K), and ErAsTe (a = 7.4478(1) A, b = 4.0078(1) A, c = 9.7552(2) A, T = 153 K) crystallize with four formula units in the orthorhombic space group D2h16-Pnma. These compounds are isostructural and belong to the beta-ZrSb2 structure type. In each compound, the Ln atoms are coordinated by a tricapped trigonal prism of four As atoms and five Te atoms. The entire three-dimensional structure is built up by the motif of the LnAs4Te5 tricapped trigonal prisms. Infinite nonalternating zigzag As chains are found along the b axis, with As-As distances in these compounds ranging from 2.5915(5) to 2.6350(9) A. Conductivity measurements in the direction of these As chains indicate that PrAsTe is metallic whereas SmAsTe and DyAsTe are weakly metallic. Antiferromagnetic transitions occur in SmAsTe and DyAsTe at 3 and 9 K, respectively. DyAsTe above 9 K follows the Curie-Weiss law.