Pressure-Induced Electronic Topological Transition and Superconductivity in Topological Insulator Bi₂Te_2.1Se_0.9

One approach to discovering topological superconductors is establishing superconductivity based on well-identified topological insulators. However, the coexistence of superconductivity and a topological state is always arcane. In this paper, we report how pressure tunes the crystal structure, electronic structure, and superconductivity in topological insulator Bi2Te2.1Se0.9. At ∼2.5 GPa, the abnormal changes in c/a and the full width at half-maximum of the A1g1 mode indicate the occurrence of an electronic topological transition. The pressure-induced superconductivity in Bi2Te2.1Se0.9 pinned with an electronic topological transition presents at 2.4 GPa, which is far below the structural phase transition pressure of 8.4 GPa. These results suggest that the appearance of an electronic topological transition is closely correlated with superconductivity in the initial phase, where the topological surface state persists. Our work clarifies the complex electronic structure of Bi2Te2.1Se0.9 and sheds light on the mechanism for superconductivity in topological insulators

Visualizing Optical Phase Anisotropy in Black Phosphorus

Layered black phosphorus has triggered enormous interest since its recent emergence. Compared to most other two-dimensional materials, black phosphorus features a moderate band gap and pronounced in-plane anisotropy, which stems from the unique atomic-puckering crystal structure. The future potential of black phosphorus in optoelectronics demands a deeper understanding of its unique anisotropic behavior. In particular, the phase information on light when interacting with the material is imperative for many applications in the optical regime. In this work we have comprehensively studied a wide range of optical anisotropic properties of black phosphorus, including the Raman scattering, extinction spectra, and phase retardance by utilizing conventional spectral measurements and a uniquely developed interferometric spectroscopy and imaging technique. The phase retardance of light passed through black phosphorus is exploited in conjunction with polarization interferometric techniques to demonstrate an optical contrast an order of magnitude higher than a purely polarization-based measurement could offer

High Pressure Structural Investigation of Benzoic Acid: Raman Spectroscopy and X‑ray Diffraction

The structural stability of benzoic acid (C₆H₅COOH, BA), a hydrogen-bonded molecular crystal, has been investigated by Raman spectroscopy and angle-dispersive X-ray diffraction (ADXRD) up to ∼18 GPa at room temperature. Under ambient conditions, benzoic acid molecules are arranged in two sets of parallel planes and held together by hydrogen bonding and van der Waals interactions. Small changes (e.g., emergence of new peaks, splitting of original peaks) can be observed in the Raman spectra at high pressures. However, no obvious changes can be observed in the X-ray diffraction measurements, which rules out any symmetry/structure changes within this pressure range. The pressure dependence of lattice parameters is presented, which shows monotonously decrease without any anomalies. The experimental isothermal pressure–volume data are well fitted by the third-order Birch–Murnaghan equation of state, yielding bulk modulus <i>B</i>₀ = 41.7(6) GPa and a first pressure derivative <i>B</i>₀^′ = 4.5(4). Axial compressibility shows obvious anisotropy, the <i>a</i> axis is more compressible than <i>b</i> and <i>c</i> axes. Moreover, the near symmetrization limit of hydrogen bonds at high pressures is proposed from the first-principles calculations. Based on the Raman, XRD, and the first-principles calculations analysis, we propose that the high pressure structural stability of benzoic acid is associated with the special hydrogen-bonded dimer structure

Giant Chiral Optical Response from a Twisted-Arc Metamaterial

We demonstrate enormously strong chiral effects from a photonic metamaterial consisting of an array of dual-layer twisted-arcs with a total thickness of ∼λ/6. Experimental results reveal a circular dichroism of ∼0.35 in the absolute value and a maximum polarization rotation of ∼305°/λ in a near-infrared wavelength region. A transmission of greater than 50% is achieved at the frequency where the polarization rotation peaks. Retrieved parameters from measured quantities further indicate an actual optical activity of 76° per λ and a difference of 0.42 in the indices of refraction for the two circularly polarized waves of opposite handedness

Rational Design of Deep-Ultraviolet Nonlinear Optical Materials in Fluorooxoborates: Toward Optimal Planar Configuration

Rational Design of Deep-Ultraviolet Nonlinear Optical Materials in Fluorooxoborates: Toward Optimal Planar Configuratio

Unigenes annotatation and characteristics of homology search of unigenes against the nr database.

<p>A: Venn diagram of number of unigenes annotated by BLASTx with an E-value threshold of 10^-5 against the 5 databases. B: E-value distribution of the top BLAST hits against the nr database for each unique sequence. C: Similarity distribution of the top BLAST hits against the nr database for each unique sequence. D: Species distribution of unigenes in the nr database.</p

Metal Thiophosphates with Good Mid-infrared Nonlinear Optical Performances: A First-Principles Prediction and Analysis

The family of metal thiophosphates is an important but long-ignored compound system of the nonlinear optical (NLO) materials with desirable properties for the mid-infrared (mid-IR) coherent light generation. In the present work, the mid-IR NLO capabilities of metal thiophosphate crystals are systematically investigated based on their structure–property relationship. The linear and nonlinear optical properties of these crystals are predicted and analyzed using the first-principles calculations. In particular, several metal thiophosphate compounds are highlighted to exhibit good mid-IR NLO performances, as supported by the primary experimental results. These candidates would greatly promote the development of the mid-IR NLO functional materials

Midinfrared Nonlinear Optical Thiophosphates from LiZnPS₄ to AgZnPS₄: A Combined Experimental and Theoretical Study

Our earlier theoretical calculation and preliminary experiment highlighted LiZnPS₄ as a good mid-infrared (mid-IR) nonlinear optical (NLO) material. However, this compound suffers from problems including corrosion of the silica tubes, a pungent smell, deliquescence, and incongruent-melting behavior in the further single crystal growth and applications. In order to overcome these problems, herein, we investigate the analogues of LiZnPS₄ and propose that AgZnPS₄ would be a good candidate. The combination of experimental and theoretical study demonstrates that AgZnPS₄ exhibits a much stronger NLO effect than that of LiZnPS₄ despite the relatively smaller energy band gap. More importantly, AgZnPS₄ melts congruently with a melting point as low as 534 °C, much lower than those of traditional IR NLO crystals, and is nondeliquescent with enough stability in the air. Such a good crystal growth habit and chemical stability enable AgZnPS₄ to possess much better overall performance for the practical mid-IR NLO applications

Ploidy analysis and phenotypic characterization of autopolyploid.

<p>A: Ploidy analysis of 2<i>x</i> (A1), 3<i>x</i> (A2), 4<i>x</i> (A3) woad by flow cytometer. B: Mitotic metaphase of 4<i>x</i> plant with 28 chromosomes (B1) and 2<i>x</i> plant with 14 chromosomes (B2). C-G: Morphological differences between diploid and autotetraploid, C-G: plantlets, inflorescence, flowers, pollen grains and siliques of autotetraploid (left) and diploid (right). Scale bars: B, F = 10 μm; C = 10 cm; D, E, G = 1 cm.</p