The peculiar band structure of semimetals exhibiting Dirac and Weyl crossings can lead to spectacular electronic properties such as large mobilities accompanied by extremely high magnetoresistance. In particular, two closely neighboring Weyl points of the same chirality are protected from annihilation by structural distortions or defects, thereby significantly reducing the scattering probability between them. Here we present the electronic properties of the transition metal diphosphides, WP2 and MoP2, which are type-II Weyl semimetals with robust Weyl points by transport, angle resolved photoemission spectroscopy and first principles calculations. Our single crystals of WP2 display an extremely low residual low-temperature resistivity of 3 nΩ cm accompanied by an enormous and highly anisotropic magnetoresistance above 200 million % at 63 T and 2.5 K. We observe a large suppression of charge carrier backscattering in WP2 from transport measurements. These properties are likely a consequence of the novel Weyl fermions expressed in this compound.

Topological insulators are characterized by an inverted band structure in the bulk and metallic surface states on the surface. In LaBi, a semimetal with a band inversion equivalent to a topological insulator, we observe surface-state-like behavior in the magnetoresistance. The electrons responsible for this pseudo-two-dimensional transport, however, originate from the bulk states rather topological surface states, which is witnessed by the angle-dependent quantum oscillations of the magnetoresistance and ab initio calculations. As a consequence, the magnetoresistance exhibits strong anisotropy with large amplitude (similar to 10(5)%)

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SrHo 2 O 4 is a geometrically frustrated magnet in which the magnetic Ho 3+ ions form honeycomb layers connected through a network of zigzag chains. At low-temperature two distinct types of short-range magnetic order can be inferred from single-crystal diffraction data, collected using both polarized and unpolarized neutrons. In the (hk0) plane the diffuse scattering is most noticeable around the k = 0 positions and its intensity rapidly increases at temperatures below 0.7 K. In addition, planes of diffuse scattering at Q = (hk ± l 2 ) are visible at temperatures as high as 4.5 K. These planes coexist with the broad peaks of diffuse scattering in the (hk0) plane at low temperatures. Correlation lengths associated with the broad peaks are L ≈ 150Å in the a-b plane and L ≈ 190Å along the c axis, while the correlation length associated with the diffuse scattering planes is L ≈ 230Å along the c axis at the lowest temperature. Both types of diffuse scattering are elastic in nature. The highly unusual coexistence of the two types of diffuse scattering in SrHo 2 O 4 is likely to be the result of the presence of two crystallographically inequivalent sites for Ho 3+ in the unit cell.