Search

The control of the speed of terahertz waves is always a challenge since the bandgap of most optical materials is much larger beyond meV with subtle nonlinear susceptibility. Moiré metasurfaces are shown to exhibit wide tunable optical properties and extraordinary physical phenomena at specific commensurate angles. These can be achieved by a careful design of the metasurface to manipulate terahertz slow light. Herein, we demonstrate a triple layer Moiré metasurface with a distinct electromagnetically induced transparency (EIT) phenomenon at commensurate angles. The proposed metasurface is composed of an intrinsic square lattice embedded into another Moiré photonic superlattice made of twisted square lattice at commensurate angles of 10.39° and 7.63°. The coupling between adjacent meta-atoms on the combined metasurface leads to destructive interference of dual trapped lattice modes, which results in a transparency window at the terahertz band. A maximum group delay of 9.76 ps is found at the transparent window of 0.84 THz when the commensurate angle is 10.39°. When the commensurate angle reduces to 7.63°, the transparency window shifts to 0.57 THz with a 5.96 ps group delay. The coupled Lorentz oscillator model indicates that the nonlinear optical susceptibility at transparency windows is above zero. Our results create an approach to tune the EIT as well as slow light in the terahertz band. Our device can have potential applications in terahertz signal processing and storage. [ABSTRACT FROM AUTHOR]

The recent discovery of a Weyl semimetal in TaAs offers the first Weyl fermion observed in nature and dramatically broadens the classification of topological phases. However, in TaAs it has proven challenging to study the rich transport phenomena arising from emergent Weyl fermions. The series MoxW1-xTe2 are inversion-breaking, layered, tunable semimetals already under study as a promising platform for new electronics and recently proposed to host Type II, or strongly Lorentz-violating, Weyl fermions. Here we report the discovery of a Weyl semimetal in MoxW1-xTe2 at x=25%. We use pump-probe angle-resolved photoemission spectroscopy (pump-probe ARPES) to directly observe a topological Fermi arc above the Fermi level, demonstrating a Weyl semimetal. The excellent agreement with calculation suggests that MoxW1-xTe2 is a Type II Weyl semimetal. We also find that certain Weyl points are at the Fermi level, making MoxW1-xTe2 a promising platform for transport and optics experiments on Weyl semimetals.

We report the low-temperature magneto-transport in the bulk-insulating single crystal of topological insulator Sn doped Bi1.1Sb0.9Te2S. Shubnikov-de Haas oscillations appear with their reciprocal frequency proportional to cos θ , demonstrating the dominant transport of topological surface states. While the magnetic field rotates on the sample surface, the planar Hall effect arises with sizeable oscillations following a relation of cos θ sin θ. Its amplitude reaches the maximum at the lowest temperature and drops to nearly zero at temperature higher than 100 K. All these evidences consolidate such planar Hall oscillations as another golden criterion on the topological surface transport. [ABSTRACT FROM AUTHOR]

The high performance MnCoNiO (MCN) ceramic materials are successfully fabricated using nanoparticles which are synthesized by the reverse microemulsion method. The morphology, crystal structure and particle size distribution of MCN nanoparticles are characterized by the XRD, SEM, TEM and HRTEM. The results show the well single tetragonal spinel structure and the narrow particle size distribution about 40 nm. As the sintering temperature increasing from 1000 to 1250 °C, all the MCN ceramic samples prepared by above-mentioned nanoparticles show the same single tetragonal spinel structure. The thermal sensitive properties with high values of ρ, B, E, and α of MCN ceramics at different sintering temperatures are in the range of 68,805-497,730 Ω cm, 4578-5159 K, 0.395-0.445 eV, and −5.2 to −5.8 %/K, respectively. These features indicate that the microstructure and electrical properties of MCN ceramics are relevant to the sintering temperature. [ABSTRACT FROM AUTHOR]

WO3·nH2O microcrystals with different shapes have been synthesized via a facile inorganic hydrothermal route. By controlling the amount of Na2SO4 in the precursor solution, hexagonal WO3·0.33H2O nanoplates, WO3 nanorods, and octahedron-shaped WO3·0.5H2O crystals have been obtained, highlighting the role of Na2SO4 in the growth of WO3·nH2O crystals. Based on the experimental observations, we have discussed the growth mechanisms of the WO3·nH2O crystals. The adsorption ability and photocatalytic activities of tungsten trioxide hydrates have also been investigated, and the results show that the WO3·0.33H2O nanoplates with large surface areas show the largest adsorption ability, and WO3·0.5H2O octahedral microcrystals with large bare crystal face exhibit the highest photodegradation performance in these samples, rendering their potential application in the treatment of organic pollutants. [ABSTRACT FROM AUTHOR]

Highlights: [•] Single (100)-oriented MCNO thin films were deposited on MgO substrate. [•] NTC thin film was prepared through LMBE technique for the first time. [•] The prepared thin films achieved epitaxial growth. [•] The prepared thin films achieved epitaxial growth. [ABSTRACT FROM AUTHOR]

The discovery of a new type-II Dirac semimetal in Ir 1- x Pt x Te 2 with optimized band structure is described. Pt dopants protect the crystal structure holding the Dirac cones and tune the Fermi level close to the Dirac point. The type-II Dirac dispersion in Ir 1- x Pt x Te 2 is confirmed by angle-resolved photoemission spectroscopy and first-principles calculations. Superconductivity is also observed and persists when the Fermi level aligns with the Dirac points. Ir 1- x Pt x Te 2 is an ideal platform for further studies on the exotic properties and potential applications of type-II DSMs, and opens up a new route for the investigation of the possible topological superconductivity and Majorana physics., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)