In-plane optical anisotropy in ReS2 flakes determined by angle-resolved polarized optical contrast spectroscopy.

Various in-plane anisotropic properties are observed for the layered semiconducting transition metal dichalcogenide (TMD), rhenium disulfide (ReS2) due to its reduced symmetry. The understanding of these unique anisotropic behaviors in ReS2 will promote its applications in optoelectronics. In this work, angle-resolved polarized optical contrast spectroscopy has proved to be an efficient, quantitative, and non-destructive method to probe the optical anisotropy in ReS2 flakes with different thicknesses. The contrast value of ReS2 displays the maximum intensity when the polarization of incident light is along the Re-Re chain direction, while the contrast shows the minimum value when the polarization is perpendicular. An empirical equation for in-plane anisotropic refractive index calculation has been proposed and the angle-resolved polarized optical contrasts of 1-3-layer ReS2 are calculated. The calculation results show good agreements with the experimental observations. This indicates that the proposed equation is indeed appropriate for the quantitative understanding of birefringence and dichroism in ReS2 flakes. Our results not only shed light on the identification of crystal axes in anisotropic materials by using angle-resolved polarized contrast spectroscopy, but also provide quantitative information about anisotropy in anisotropic materials such as ReS2.

Pressure-Induced Phase Transition in Weyl Semimetallic WTe2.

Tungsten ditelluride (WTe2 ) is a semimetal with orthorhombic Td phase that possesses some unique properties such as Weyl semimetal states, pressure-induced superconductivity, and giant magnetoresistance. Here, the high-pressure properties of WTe2 single crystals are investigated by Raman microspectroscopy and ab initio calculations. WTe2 shows strong plane-parallel/plane-vertical vibrational anisotropy, stemming from its intrinsic Raman tensor. Under pressure, the Raman peaks at ≈120 cm-1 exhibit redshift, indicating structural instability of the orthorhombic Td phase. WTe2 undergoes a phase transition to a monoclinic T' phase at 8 GPa, where the Weyl states vanish in the new T' phase due to the presence of inversion symmetry. Such Td to T' phase transition provides a feasible method to achieve Weyl state switching in a single material without doping. The new T' phase also coincides with the appearance of superconductivity reported in the literature.

(SP-4-4)-[Hydrogen N-({2-[(2S)-1-benzyl-pyrrolidine-2-carboxamido]phen-yl}(phen-yl)methyl-ene)-l-glutamato(2-)]nickel(II).

In the mol-ecule of the title complex, [Ni(C(30)H(29)N(3)O(5))], the Ni atom is coordinated in a distorted square-planar geometry by three N and one O atoms. The aromatic rings are oriented at dihedral angles of 29.01 (3), 79.73 (3) and 83.37 (3)°. The remaining rings adopt envelope conformations with the C and N atoms at the flap positions. In the crystal structure, inter-molecular O-H⋯O hydrogen bonds link the mol-ecules into chains along the b axis. There is also a weak C-H⋯π inter-action.