A gap-protected zero-Hall effect state in the quantum limit of the non-symmorphic metal KHgSb.

A recurring theme in topological matter is the protection of unusual electronic states by symmetry, for example, protection of the surface states in Z2 topological insulators by time-reversal symmetry1-3. Recently, interest has turned to unusual surface states in the large class of non-symmorphic materials4-12. In particular, KHgSb is predicted to exhibit double quantum spin Hall states10. Here we report measurements of the Hall conductivity in KHgSb in a strong magnetic field B. In the quantum limit, the Hall conductivity is observed to fall exponentially to zero, but the diagonal conductivity is finite. A large gap protects this unusual zero-Hall state. We theoretically propose that, in this quantum limit, the chemical potential drops into the bulk gap, intersecting equal numbers of right- and left-moving quantum spin Hall surface modes to produce the zero-Hall state. The zero-Hall state illustrates how topological protection in a non-symmorphic material with glide symmetry may lead to highly unusual transport phenomena.

VI3 -a New Layered Ferromagnetic Semiconductor.

2D materials are promising candidates for next-generation electronic devices. In this regime, insulating 2D ferromagnets, which remain rare, are of special importance due to their potential for enabling new device architectures. Here the discovery of ferromagnetism is reported in a layered van der Waals semiconductor, VI3 , which is based on honeycomb vanadium layers separated by an iodine-iodine van der Waals gap. It has a BiI3 -type structure ( R 3 ¯ , No.148) at room temperature, and the experimental evidence suggests that it may undergo a subtle structural phase transition at 78 K. VI3 becomes ferromagnetic at 49 K, below which magneto-optical Kerr effect imaging clearly shows ferromagnetic domains, which can be manipulated by the applied external magnetic field. The optical bandgap determined by reflectance measurements is 0.6 eV, and the material is highly resistive.

Triangular Rare-Earth Lattice Materials RbBa R(BO3)2 ( R = Y, Gd-Yb) and Comparison to the KBa R(BO3)2 Analogs.

A previously unreported family of electrically insulating rare-earth borates, RbBa R(BO3)2 ( R = Y, Gd-Yb), was designed and then successfully obtained by traditional solid-state reaction. They crystallize in a monoclinic crystal system space group P21 /m (No. 11). They feature triangular planar rare-earth ( R) lattices, which are part of, for example, [Yb(BO3)2]3- infinite 2D layers. These R-based triangular lattices are stacked with layers of crystallographically ordered Rb and Ba atoms to build the 3D structures. Polycrystalline samples of RbBa R(BO3)2 were used to study the elementary magnetic properties, and millimeter-size RbBaYb(BO3)2 single crystals were grown by spontaneous nucleation for further anisotropic magnetic characterization. Antiferromagnetic spin interactions are observed for all magnetic compounds, and no long-range magnetic ordering is found down to 1.8 K. Our results suggest that this RbBa R(BO3)2 ( R = Gd-Yb) family may be of further interest both experimentally and theoretically as highly geometrically frustrated magnets.

The h-Sbx WO3+2x Oxygen Excess Antimony Tungsten Bronze.

We describe the previously unreported oxygen excess hexagonal antimony tungsten bronze is reported, with a composition of Sb0.5 W3 O10 , in the following denoted as h-Sbx WO3+2x with x=0.167, to demonstrate its analogy to classical Ax WO3 tungsten bronzes. This compound forms in a relatively narrow temperature range between 580 °C

Crystal growth and stoichiometry-dependent properties of the ferromagnetic Weyl semimetal ZrCo2-x Sn.

We report the growth of high quality bulk crystals, through crystallization from molten Sn flux, of the predicted ferromagnetic Weyl metal ZrCo2-x Sn with the L21 Heusler phase structure. The concentration of Co vacancies in the single crystals is found to be dependent on the initial concentration of Co in the flux. The saturation magnetization increases approximately linearly with decreasing Co deficiency and the ferromagnetic transition temperature changes significantly. p-type carrier conduction and an anomalous Hall effect are observed. The calculated electronic density of states of ZrCo2-x Sn shows a significant change in minority and majority spin state occupancies and a shift in the Fermi level with Co deficiency.