Topological materials discovery by large-order symmetry indicators.

Crystalline symmetries play an important role in the classification of band structures, and their richness leads to various topological crystalline phases. On the basis of our recently developed method for the efficient discovery of topological materials using symmetry indicators, we explore topological materials in five space groups ( S G s), which are diagnosed by large-order symmetry indicators (ℤ8 and ℤ12) and support the coexistence of several kinds of gapless boundary states in a single compound. We predict many candidate materials; some representatives include Pt3Ge ( S G 140 ), graphite ( S G 194 ), XPt3 ( S G 221 , X = Sn, Pb), Au4Ti ( S G 87 ), and Ti2Sn ( S G 194 ). As by-products, we also find that AgXF3 ( S G 140 , X = Rb, Cs) and AgAsX ( S G 194 , X = Sr, Ba) are good Dirac semimetals with clean Fermi surfaces. The proposed materials provide a good platform for studying the novel properties emerging from the interplay between different types of boundary states

Spin alignment of vector meson in e+e- annihilation at Z0 pole

We calculate the spin density matrix of the vector meson produced in e+e- annihilation at Z^0 pole. We show that the data imply a significant polarization for the antiquark which is created in the fragmentation process of the polarized initial quark and combines with the fragmenting quark to form the vector meson. The direction of polarization is opposite to that of the fragmenting quark and the magnitude is of the order of 0.5. A qualitative explanation of this result based on the LUND string fragmentation model is given.Comment: 15 pages, 2 fgiures; submitted to Phys. Rev.

2′-(3-Bromo-5-chloro-2-hydroxy­benzyl­idene)isonicotinohydrazide methanol solvate

The title Schiff base compound, C13H9BrClN3O2·CH4O, was derived from the condensation reaction of 3-bromo-5-chloro­salicylaldehyde with isonicotinohydrazide. The dihedral angle between the benzene and pyridine rings is 5.9 (2)°. In the crystal structure, mol­ecules are linked through N—H⋯O, O—H⋯O, and O—H⋯Br inter­molecular hydrogen bonds, forming dimers and chains. There is also an intramolecular O—H⋯N hydrogen bond