Valence-Ordered Thin-Film Nickelate with Tri-component Nickel Coordination Prepared by Topochemical Reduction.

The metal-hydride-based "topochemical reduction" process has produced several thermodynamically unstable phases across various transition metal oxide series with unusual crystal structures and nontrivial ground states. Here, by such an oxygen (de-)intercalation method we synthesis a samarium nickelate with ordered nickel valences associated with tri-component coordination configurations. This structure, with a formula of SmNiO as revealed by four-dimensional scanning transmission electron microscopy (4D-STEM), emerges from the intricate planes of {303} ordered apical oxygen vacancies.

Minority-spin conducting states in Fe substituted pyrite CoS.

There has been a longstanding debate whether the pyrite CoSor its alloys with FeSare half metallic. We argue using first principles calculations that there is a finite occupation of minority-spin states at the Fermi level throughout the series Co1-xFeS. Although the exchange-correlation functional influences the specifics of the electronic structure, we observe a similar trend with increasing Fe concentration in both local density approximation and generalized gradient approximation calculations.

The phonon thermal Hall angle in black phosphorus.

The origin of phonon thermal Hall Effect (THE) observed in a variety of insulators is yet to be identified. Here, we report on the observation of a thermal Hall conductivity in a non-magnetic elemental insulator, with an amplitude exceeding what has been previously observed. In black phosphorus (BP), the longitudinal (κ), and the transverse, κ, thermal conductivities peak at the same temperature and at this peak temperature, the κ/κ/B is ≈ 10-10 T.

Observation of Poiseuille flow of phonons in black phosphorus.

The travel of heat in insulators is commonly pictured as a flow of phonons scattered along their individual trajectory. In rare circumstances, momentum-conserving collision events dominate, and thermal transport becomes hydrodynamic. One of these cases, dubbed the Poiseuille flow of phonons, can occur in a temperature window just below the peak temperature of thermal conductivity.

Competing covalent and ionic bonding in Ge-Sb-Te phase change materials.

Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases.

The performance of in situ grown Schottky-barrier single wall carbon nanotube field-effect transistors.

Electrical transport measurements were used to study device behavior that results from the interplay of defects and inadvertent contact variance that develops in as-grown semiconducting single wall carbon nanotube devices with nominally identical Au contacts. The transport measurements reveal that as-grown nanotubes contain defects that limit the performance of field-effect transistors with ohmic contacts. In Schottky-barrier field-effect transistors the device performance is dominated by the Schottky barrier and the nanotube defects have little effect.