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The resistivity scaling of Cu electrical interconnects represents a critical challenge in Si CMOS technology. As interconnect dimensions reach below 10 nm, Cu resistivity increases significantly due to surface scattering. Topological materials have been considered for application in ultra-scaled interconnects (below 5 nm), due to their topologically protected surface states that have reduced electron scattering. Recent theoretical work on the topological chiral semimetal CoSi suggests that this material could offer lower resistivity than Cu at dimensions smaller than 10 nm. Here we investigate the scaling trend of textured and amorphous CoSi thin films, deposited by molecular beam epitaxy in a thickness range between 2 and 82.5 nm. Contrary to predictions of standard resistivity models, we report here a reduction in resistivity for thin amorphous CoSi films, which is instead consistent with surface-dominated transport. Moreover, magnetotransport measurements reveal significant enhancement of the magnetoresistance in scaled films, highlighting the complex transport mechanisms present in these highly disordered films at thicknesses of a few nanometers., (© 2024. The Author(s).)

Weyl semimetals are defined by their unique Fermi surface, comprising pairs of Weyl points of opposite chirality, connected through topological surface states. Angle-resolved photoemission spectroscopy (ARPES) has been used to verify the existence of the Weyl points and the Fermi arcs. However, ARPES is limited in resolution, leading to significant uncertainty when characterizing the shape of the Fermi surface of semimetals and measuring features such as the distance between the Weyl points. Here, to surpass the resolution of ARPES, we combine quantum oscillation measurements with transverse electron focusing experiments. These techniques offer complementary information, enabling the reconstruction of the distinctive peanut-shaped cross section of the Weyl Fermi surface and accurately determining the separation between Weyl points in the Weyl semimetal NbP. Our Letter showcases the integration of quantum oscillations and transverse electron focusing, allowing for the measurements of complex Fermi surface geometries, concurrently with carriers' transport properties, in high-mobility quantum materials.

Semiconductor transistors operate by modulating the charge carrier concentration of a channel material through an electric field coupled by a capacitor. This mechanism is constrained by the fundamental transport physics and material properties of such devices-attenuation of the electric field, and limited mobility and charge carrier density in semiconductor channels. In this work, we demonstrate a new type of transistor that operates through a different mechanism. The channel material is a Weyl semimetal, NbP, whose resistivity is modulated via a magnetic field generated by an integrated superconductor. Due to the exceptionally large electron mobility of this material, which reaches over 1,000,000 cm 2 /Vs, and the strong magnetoresistive coupling, the transistor can generate significant transconductance amplification at nanowatt levels of power. This type of device can enable new low-power amplifiers, suitable for qubit readout operation in quantum computers., (© 2024. The Author(s).)

In recent times the chiral semimetal cobalt monosilicide (CoSi) has emerged as a prototypical, nearly ideal topological conductor hosting giant, topologically protected Fermi arcs. Exotic topological quantum properties have already been identified in CoSi bulk single crystals. However, CoSi is also known for being prone to intrinsic disorder and inhomogeneities, which, despite topological protection, risk jeopardizing its topological transport features. Alternatively, topology may be stabilized by disorder, suggesting the tantalizing possibility of an amorphous variant of a topological metal, yet to be discovered. In this respect, understanding how microstructure and stoichiometry affect magnetotransport properties is of pivotal importance, particularly in case of low-dimensional CoSi thin films and devices. Here we comprehensively investigate the magnetotransport and magnetic properties of ≈25 nm Co 1- x Si x thin films grown on a MgO substrate with controlled film microstructure (amorphous vs textured) and chemical composition (0.40 < x < 0.60). The resistivity of Co 1- x Si x thin films is nearly insensitive to the film microstructure and displays a progressive evolution from metallic-like (dρ xx /d T > 0) to semiconducting-like (dρ xx /d T < 0) regimes of conduction upon increasing the silicon content. A variety of anomalies in the magnetotransport properties, comprising for instance signatures consistent with quantum localization and electron-electron interactions, anomalous Hall and Kondo effects, and the occurrence of magnetic exchange interactions, are attributable to the prominent influence of intrinsic structural and chemical disorder. Our systematic survey brings to attention the complexity and the challenges involved in the prospective exploitation of the topological chiral semimetal CoSi in nanoscale thin films and devices., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)