Symmetry-enforced topological nodal planes at the Fermi surface of a chiral magnet

Despite recent efforts to advance spintronics devices and quantum information technology using materials with non-trivial topological properties, three key challenges are still unresolved1–9. First, the identification of topological band degeneracies that are generically rather than accidentally located at the Fermi level. Second, the ability to easily control such topological degeneracies. And third, the identification of generic topological degeneracies in large, multisheeted Fermi surfaces. By combining de Haas–van Alphen spectroscopy with density functional theory and band-topology calculations, here we show that the non-symmorphic symmetries10–17 in chiral, ferromagnetic manganese silicide (MnSi) generate nodal planes (NPs)11,12, which enforce topological protectorates (TPs) with substantial Berry curvatures at the intersection of the NPs with the Fermi surface (FS) regardless of the complexity of the FS. We predict that these TPs will be accompanied by sizeable Fermi arcs subject to the direction of the magnetization. Deriving the symmetry conditions underlying topological NPs, we show that the 1,651 magnetic space groups comprise 7 grey groups and 26 black-and-white groups with topological NPs, including the space group of ferromagnetic MnSi. Thus, the identification of symmetry-enforced TPs, which can be controlled with a magnetic field, on the FS of MnSi suggests the existence of similar properties—amenable for technological exploitation—in a large number of materials.

Fabrication of a Silicide Thermoelectric Module Employing Fractional Factorial Design Principles

Thermoelectric modules can be used in waste heat harvesting, sensing, and cooling applications. Here, we report on the fabrication and performance of a four-leg module based on abundant silicide materials. While previously optimized Mg2Si0.3Sn0.675Bi0.025 is used as the n-type leg, we employ a fractional factorial design based on the Taguchi methods mapping out a four-dimensional parameter space among Mnx-εMoεSi1.75−δGeδ higher manganese silicide compositions for the p-type material. The module is assembled using a scalable fabrication process, using a Cu metallization layer and a Pb-based soldering paste. The maximum power output density of 53 μW cm–2 is achieved at a hot-side temperature of 250 °C and a temperature difference of 100 °C. This low thermoelectric output is related to the high contact resistance between the thermoelectric materials and the metallic contacts, underlining the importance of improved metallization schemes for thermoelectric module assembly.

Reach of pollution and sediment correlation with the tailings in Šibenik Bay (Croatia)

<p>To determine the influence of the historic factory of electrodes and ferroalloys on the Šibenik bay sediments, XRPD analysis were carried out. The factory was established in the city of Šibenik, on the coast of the Krka River estuary, and produced calcium carbide, and later electrodes and ferroalloys. It was active from 1900 until 1995 [1]. During that time, a large amount of produced tailings were stored nearby and on the shore of the estuary. Due to the presence of the strong winds (bora and sirocco), which can reach up to 130 km/h, the tailings material could be transported to long distances [2].</p><p>Samples of tailing were collected at the location of the former factory, which is a tailing hill today, samples of dust were collected from the rooftop of the factory in the 1980s. Other samples were taken on a 1 km distant beach in the Šibenik bay  (Beach A) and a 19 km distant beach on the island in the outer Šibenik archipelago (Beach B). Both beaches are located south-west of the factory. The samples from the beaches were taken with a corer at different depths: 0 – 3 cm, 3 – 5 cm, around 5 cm. The sample from 3 – 5 cm depth was not analysed.</p><p>Bulk sample and a fraction <63 µm were analysed on X-Ray Diffractometer. The XRPD analysis of the sediments from Beach B in the outer Šibenik archipelago shows that calcite and quartz are the most abundant phases. This mineral composition shows that distant islands were not affected by aeolian transportation of the factory dust and tailing. In the bulk samples from Beach A, in the uppermost part (0 – 3 cm depth) mineral components are calcite, aragonite, calcium manganite, bustamite ferroan and carbon, while calcite, quartz, aragonite, calcium manganite and manganosite are present in the fraction <63 µm. The sample from the depth of 5 cm at the same beach, shows calcite, aragonite and Mn-oxide, while fraction <63 µm lacks in Mn-oxide.</p><p>A bulk sample of tailings shows mineral components: calcite, quartz, calcium manganite, bustamite ferroan and gypsum which corresponds to the previous research [3], and there is also manganese silicon, manganese silicide, carbon and amorphous phase [4]. A fraction <63 µm of the tailing, shows the following mineral phases: calcite, quartz, calcium manganite and bustamite ferroan, as presented in previous research [3]. Analysis of the rooftop dust shows three phases: carbon, bustamite ferroan and manganosite, which does not correspond to the data given from the factory [3].</p><p>From the presented results, it could be concluded that the historic factory influenced sediments in the Šibenik bay, however, its influence was not detected on the Beach B 19 km to the SW, which opens the question of reach and distance to which tailings can be transported by sea and/or wind.</p><p>This work has been supported in part (samples collection) by Croatian Science Foundation under the project lP-2019-04-5832.</p>

Low-temperature electronic transport of manganese silicide shell-protected single crystal nanowires for nanoelectronics applications

Recently, core-shell nanowires have been proposed as potential electrical connectors for nanoelectronics components. A promising candidate is Mn5Si3 nanowires encapsulated in an oxide shell, due to their low reactivity and...