Topologically protected interface mode in plasmonic waveguide arrays

Recent realization of nontrivial topological phases in photonic systems has provided unprecedented opportunities in steering light flow in novel manners. Based on the Su–Schriffer–Heeger (SSH) model, a topologically protected optical mode was successfully demonstrated in a plasmonic waveguide array with a kinked interface that exhibits a robust nonspreading feature. However, under the same excitation conditions, another antikinked structure seemingly cannot support such a topological interface mode, which appears to be inconsistent with the SSH model. Theoretical calculations are carried out based on the coupled‐mode theory, in which the mode properties, excitation conditions, and the robustness are studied in detail. It is revealed that under the exact eigenstate excitations, both kinked and antikinked structures do support such robust topological interface modes; however, for a realistic single‐waveguide input only the kinked structure does so. It is concluded that the symmetry of interface eigenmodes plays a crucial role, and the odd eigenmode in a kinked structure offers the capacity to excite the nonspreading interface mode in the realistic excitation of a one‐waveguide input. Our finding deepens the understanding of mode excitation and propagation in coupled waveguide systems, and could open a new avenue in optical simulations and photonic designs.

     

Photonic Floquet topological insulators in atomic ensembles

The feasibility of realizing a photonic Floquet topological insulator (PFTI) in an atomic ensemble is demonstrated. The interference of three coupling fields will split energy levels periodically, to form a periodic refractive index structure with honeycomb profile that can be adjusted by different frequency detunings and intensities of the coupling fields. This in turn will affect the appearance of Dirac cones in momentum space. When the honeycomb lattice sites are helically ordered along the propagation direction, gaps open at Dirac points, and one obtains a PFTI in an atomic vapor. An obliquely incident beam will be able to move along the zigzag edge of the lattice without scattering energy into the PFTI, due to the confinement of edge states. The appearance of Dirac cones and the formation of a photonic Floquet topological insulator can be shut down by the third‐order nonlinear susceptibility and opened up by the fifth‐order one.

     

Inverse hydrogen bonds between SiH_4 and hydrides of Na,Mg and Be

The optimized geometries of the three complexes between MeHn (Me=Na,Mg,Be;n=1 or 2) and SiH4 have been calculated at the B3LYP/6-311++g**,MP2/6-311++g(3df,3pd) and MP2/aug-cc-pvtz levels,respectively.The red-shift inverse hydrogen bonds (IHBs) based on Si-H,an electron donor,were reported.The calculated binding energies with basis set super-position error (BSSE) correction of the three complexes are-5.98,-8.65 and-3.96 kJ mol-1 (MP2/6-311++g(3df,3pd)),respectively,which agree with the results obtained via M...     

SIMS accurate determination of matrix composition of topological crystalline insulator material Pb1 − xSnxSe

Substitutional alloy Pb_1 − xSn_xSe is a new class of electronic materials called topological crystalline insulators, which at the temperature range from 0 K to 300 K exhibit topological state at compositions in the range 0.18 < x < 0.40 (in the rock-salt structure). In this report, we present a secondary ion mass spectrometry (SIMS) analysis technique to provide accurate Pb and Sn composition based on the measurement of PbCs⁺ and SnCs⁺ cluster ions intensities. Studies of Pb_1 − xSn_xSe bulk samples with various values of x show that x/(1 − x) is linear in relation to the intensity ratio of PbCs⁺/SnCs⁺ over the range from x = 0.15 to x = 0.41. This technique allows us to obtain an accurate Sn content for multilayered heterostructures, quantum wells containing Pb_1 − xSn_xSe with different x values for each layer.     

Synthesis, structure and luminescence properties of metal-organic frameworks based on benzo-bis(imidazole)

Metal-organic frameworks(MOFs)constructed from conjugated organic ligands are candidates for hybrid photoactive materials with potential applications.Compared to that from the ligands only,the intensity and wavelength of the luminescence could be tuned after they were incorporated in extended framework.In this report,by using an organic ligand with azolate moiety,benzo-bis(imidazole)(H2BBI),we synthesized two new MOF structures.Framework 1([Co(H2BBI)(DMSO)2Cl2]n,DMSO=dimethyl sulfoxide),constructed from tetrahedral Co(II)and H2BBI,exhibits zigzag 1D structure.Meanwhile,framework 2([Cu2(H2BBI)3(DMSO)6(NO3)4]n),a layered structure with hcb topology,was assembled from tetragonal pyramidal Cu(II)and H2BBI.Furthermore,2 exhibits strong luminescence emission(ex=280 nm).A blue shift of 40 nm(from 359 nm to 319 nm)was observed in framework 2 compared to the free ligand,which could be explained by the ligand-to-metal charge transfer in the network.     

A three‐dimensional CdII coordination framework: poly[di‐μ2‐aqua‐{μ2‐1,4‐bis[(1H‐1,2,4‐triazol‐1‐yl)methyl]benzene‐κ2N4:N4′}di‐μ3‐terephthalato‐κ3O:O′:O′′‐dicadmium(II)]

The title Cd^II coordination polymer, [Cd(C₁₀H₈O₄)(C₁₂H₁₂N₆)_0.5(H₂O)]_n, has been obtained by the hydrothermal method and studied by single‐crystal X‐ray diffraction, elemental analysis, thermogravimetric analysis, IR spectroscopy and fluorescence spectroscopy. The compound forms a novel three‐dimensional framework with 3,8‐connected three‐dimensional binodal {4.5²}₂{4².5¹⁰.6¹².7.8³} topology. An investigation of its photoluminescence properties shows that the compound exhibits a strong fluorescence emission in the solid state at room temperature.     

Unexpected Room‐Temperature Ferromagnetism in Nanostructured Bi2Te3

There is an urgent need for the development in the field of the magnetism of topological insulators, owing to the necessity for the realization of the quantum anomalous Hall effect. Herein, we discuss experimentally fabricated nanostructured hierarchical architectures of the topological insulator Bi₂Te₃ without the introduction of any exotic magnetic dopants, in which intriguing room‐temperature ferromagnetism was identified. First‐principles calculations demonstrated that the intrinsic point defect with respect to the antisite Te site is responsible for the creation of a magnetic moment. Such a mechanism, which is different from that of a vacancy defect, provides new insights into the origins of magnetism. Our findings may pave the way for developing future Bi₂Te₃‐based dissipationless spintronics and fault‐tolerant quantum computation.     

高斯涡旋光束的傍轴度

按单色光束傍轴度的定义,对高斯涡旋光束的傍轴度进行了研究.使用角谱表示法推导出高斯涡旋光束傍轴度的解析公式,用此研究了傍轴度和高斯涡旋光束参数之间的关系.结果表明,随背景高斯光束束腰宽度和光涡旋离轴参数的增加及随光涡旋拓扑电荷的减少,高斯涡旋光束的傍轴度增加.对所得结果用傍轴度与远场发散角间的关系做了物理解释.