Dielectric particles of the same material exchange electrical charge during collisions or sliding contacts, yet the underlying charge-exchange mechanism is still not understood. The fact that particles can become highly charged as a result of this effect has significant consequences for many settings, both in nature and industry, such as thunderstorms, volcanic eruptions, particle aggregation during meteorite and planet formation, and the clogging of industrial granular systems. Toward understanding these systems, great efforts have been made to develop precise in situ measurements for particle charge, e.g., to determine ensemble charge distributions or measure exchange during individual contacts. Here, we present experimental results concerning the particle size scaling of the stationary-state charge distributions of oxide particles in the sub-millimeter range. We measure the charge distributions for large ensembles of monodisperse ${\mathrm{ZrO}}_2$:${\mathrm{SiO}}_2$ composite spheres, ranging from 172 to $545\mathrm{\mu }\mathrm{m}$ in diameter. These distributions are non-Gaussian and collapse to a single master curve when plotted as functions of the surface charge density $\mathrm{\Sigma }=q/4\pi R^2$. X-ray fluorescence and atomic force microscopy measurements show that the differences in the measured charge distributions are not due to variations in chemical composition or surface roughness, but rather to size alone. Our findings provide constraints on microscopic models for charge exchange, namely that they should lead to steady-state distributions that are non-Gaussian and scale in a specific way with particle size.

Refractory high-entropy alloys show promising resistance to irradiation, yet little is known about the fundamental nature of radiation-induced defect formation. Here, we simulate threshold displacement energies in equiatomic MoNbTaVW using an accurate machine-learned interatomic potential, covering the full angular space of crystal directions. The effects of local chemical ordering are assessed by comparing results in random and short-range-ordered MoNbTaVW. The average threshold displacement energy in the random alloy is $44.3\pm 0.15\mathrm{eV}$, and slightly higher, $48.6\pm 0.15\mathrm{eV}$, in the short-range-ordered alloy. Both are significantly lower than in any of the constituent pure metals. We identify the mechanisms of defect creation and find they are mainly dependent on the masses of the recoiling and colliding elements. Low thresholds are generally found when heavy atoms (W, Ta) displace and replace the lightest atoms (V). The average threshold energies, when separated by recoiling element, are consequently ordered inversely according to their mass, opposite to the trend in the pure metals where W has by far the highest thresholds. However, the trend in the alloy is reversed when considering the cross sections for defect formation in electron irradiation, due to the mass-dependent recoil energies from the electrons.

Recent intensive studies in metallic kagome systems have revealed various correlated topological and electronic states, leading to their spintronic applications. The kagome ferromagnetic metal ${\mathrm{Fe}}_3\mathrm{Sn}$ has been found to host a topological nodal plane near the Fermi energy and exhibits large transverse transport responses. Here we report the fabrication of the epitaxial thin films of ${\mathrm{Fe}}_3\mathrm{Sn}$ and the observation of its large anomalous Nernst effect (ANE). Structural and magnetic measurements reveal (0001)-orientated epitaxial growth of kagome $D{0}_{19}$ ${\mathrm{Fe}}_3\mathrm{Sn}$ and the magnetic easy plane along the substrate plane. Moreover, transport measurements confirm the large ANE of 2.4 µV/K at room temperature, comparable to that of the bulk polycrystalline samples. The obtained ${\mathrm{Fe}}_3\mathrm{Sn}$ film should be useful for thermoelectric applications, because the binary compound based on inexpensive elements exhibits large spontaneous ANE voltage under an out-of-plane heat current due to the magnetic and electronic states stabilized by the magnetic anisotropy.

Dealloyed nanoporous metals with a hierarchical structure provide model systems for low-density structural and functional nanomaterials. It has been suggested that these materials are distinguished by particularly stringent design principles, with precisely defined characteristic length scales, and with geometrically similar structures on each hierarchy level, and that the length scales can be independently tuned on each level. Studying nanoporous gold made by two-step dealloying, we here demonstrate the tunability of the microstructure, independently for the upper and the lower hierarchy level. Small-angle (SAXS) and ultrasmall-angle x-ray scattering (USAXS) revealed sharp interference peaks corresponding to each of the two levels, confirming the stringent structural definition. Exploiting USAXS, we resolve and study upper-hierarchy-level ligament spacings of up to 600 nm. The length scales inferred from the peak positions correlate excellently with structure sizes determined by analysis of electron micrographs. This suggests a scaling factor that allows for size conversion between the two approaches. Furthermore, the analysis of the small-angle scattering enables a characterization of the volume-specific surface area, in good agreement with the estimate based on the ligament size and the leveled-wave model as an approximate description of the material's microstructure.

For layered materials, the interlayer stacking is a critical degree of freedom tuning electronic properties, while its microscopic characterization faces great challenges. The transition-metal dichalcogenide $1T\text{−}\mathrm{Ta}{\mathrm{S}}_2$ represents a novel example, in which the stacking pattern is not only enriched by the spontaneous occurrence of the intralayer charge density wave, but also recognized as a key to understand the nature of the low-temperature insulating phase. We exploit the ${}^{33}\mathrm{S}$ nuclei in a $1T\text{−}\mathrm{Ta}{\mathrm{S}}_2$ single crystal as sensitive probes of the local stacking pattern via quadrupolar coupling to the electron density distribution nearby, by combining nuclear magnetic resonance (NMR) measurements with the state-of-the-art first-principles electric-field gradient calculations. The applicability of our proposal is analyzed through temperature, magnetic-field, and angle-dependent NMR spectra. Systematic simulations of a single $1T\text{−}\mathrm{Ta}{\mathrm{S}}_2$ layer, bilayers with different stacking patterns, and typical stacking orders in three-dimensional (3D) structures unravel distinct NMR characteristics. Particularly, one 3D structure achieves a quantitative agreement with the experimental spectrum, which clearly rationalizes the coexistence of two types of interfacial environments. Our method may find general applications in the studies of layered materials.

Low-dimensional materials can display enhanced electronic, magnetic, and quantum properties. We use the topological scaling algorithm to identify all sufficiently metastable materials in the Materials Project database to identify bulk crystals with one-dimensional (1D) structural motifs: Five hundred fifty-one crystals that are within 50 meV ${\mathrm{atom}}^{-1}$ of the thermodynamic hull display 1D motifs, where 293 of these contain $d$-valence elements, which we focus on in this work. After exfoliating nanowires from 263 of these materials and calculating their thermodynamic stability using density functional theory, 103 nanowires meet per-atom and per-Ångström thermodynamic stability criteria. We illustrate for three nanowire systems that a variety of local minima can be present in these systems, demonstrating one case of a Peierls distortion. The wires display a broad diversity of electronic and magnetic properties of these nanowires, with 14 metals, 7 half-metals, and 82 semiconductors and insulators, and 41 nanowires displaying magnetic moments ranging from 0.1 to $5{\mu }_B$ per $d$-valence species when assuming ferromagnetic order. A subset of these chains are investigated for the impact of magnetic ordering, identifying 1D ${\mathrm{FeCl}}_3$ to be most stable in an antiferromagnetic state. The electronic and magnetic properties of the identified 1D materials could enable applications in spintronic and quantum devices.

Pressure is a unique tuning parameter for probing the properties of materials, and it has been particularly useful for studies of electronic materials such as high-temperature cuprate superconductors. Here we report the effects of quasihydrostatic compression produced by a neon pressure medium on the structures of bismuth-based high-${\mathit{T}}_{\mathit{c}}$ cuprate superconductors with the nominal composition ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}}_{n-1}{\mathrm{Cu}}_n{\mathrm{O}}_{2n+4+\delta }$ ($n=1,2,3$) up to 155 GPa. The structures of all three compositions obtained by synchrotron x-ray diffraction can be described as pseudotetragonal over the entire pressure range studied. We show that previously reported pressure-induced distortions and structural changes arise from the large strains that can be induced in these layered materials by nonhydrostatic stresses. The pressure-volume equations of state (EOS) measured under these quasihydrostatic conditions cannot be fit to single phenomenological formulation over the pressure ranges studied, starting below 20 GPa. This intrinsic anomalous compression as well as the sensitivity of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}}_{n-1}{\mathrm{Cu}}_n{\mathrm{O}}_{2n+4+\delta }$ to deviatoric stresses provide explanations for the numerous inconsistencies in reported EOS parameters for these materials. We conclude that the anomalous compressional behavior of all three compositions is a manifestation of the changes in electronic properties that are also responsible for the remarkable nonmonotonic dependence of ${\mathit{T}}_{\mathit{c}}$ with pressure, including the increase in ${\mathit{T}}_{\mathit{c}}$ at the highest pressures studied so far for each. Transport and spectroscopic measurements up to megabar pressures are needed to fully characterize these cuprates and explore higher possible critical temperatures in these materials.

We present the growth and basic magnetic and transport properties of ${\mathrm{Cr}}_{1+x}{\mathrm{Pt}}_{5-x}\mathrm{P}$. We show that single crystals can readily be grown from a high-temperature solution created by adding dilute quantities of Cr to Pt-P based melts. Like other 1–5–1 compounds, ${\mathrm{Cr}}_{1+x}{\mathrm{Pt}}_{5-x}\mathrm{P}$ adopts a tetragonal P4/mmm structure composed face-sharing ${\mathrm{CrPt}}_3$ like slabs that are broken up along the $c$ axis by sheets of P atoms. EDS and x-ray diffraction measurements both suggest ${\mathrm{Cr}}_{1+x}{\mathrm{Pt}}_{5-x}\mathrm{P}$ has mixed occupancy between Cr and Pt atoms, similar to what is found in the closely related compound ${\mathrm{CrPt}}_3$, giving real compositions of ${\mathrm{Cr}}_{1.5}{\mathrm{Pt}}_{4.5}\mathrm{P}$ $(x=0.5)$. We report that ${\mathrm{Cr}}_{1.5}{\mathrm{Pt}}_{4.5}\mathrm{P}$ orders ferromagnetically at ${\mathit{T}}_C=464.5$ K with a saturated moment of $\approx 2.1{\mu }_{\mathit{B}}/\mathrm{Cr}$ at 1.8 K. Likely owing to the strong spin-orbit coupling associated with the large quantity of high Z, Pt atoms, ${\mathrm{Cr}}_{1.5}{\mathrm{Pt}}_{4.5}\mathrm{P}$ has exceptionally strong planar anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and 300 K, respectively. The resistance of ${\mathrm{Cr}}_{1.5}{\mathrm{Pt}}_{4.5}\mathrm{P}$ has a metallic temperature dependence with relatively weak magnetoresistance. Electronic band structure calculations show that ${\mathrm{CrPt}}_5\mathrm{P}$ has a large peak in the density of states near the Fermi level, which is split into spin majority and minority bands in the ferromagnetic state. Furthermore, the calculations suggest substantial hybridization between $\mathrm{Cr}\text{−}3d$ and $\mathrm{Pt}\text{−}5d$ states near the Fermi level, in agreement with the experimentally measured anisotropy.

Resistive random-access memories are promising for nonvolatile memory and brain-inspired computing applications. High variability and low yield of these devices are key drawbacks hindering reliable training of physical neural networks. In this paper, we show that doping an oxide electrolyte, ${\mathrm{Al}}_2{\mathrm{O}}_3$, with electronegative metals makes resistive switching significantly more reproducible, surpassing the reproducibility requirements for obtaining reliable hardware neuromorphic circuits. Based on density functional theory calculations, the underlying mechanism is hypothesized to be the ease of creating oxygen vacancies in the vicinity of electronegative dopants due to the capture of the associated electrons by dopant midgap states and the weakening of Al-O bonds. These oxygen vacancies and vacancy clusters also bind significantly to the dopant, thereby serving as preferential sites and building blocks in the formation of conducting paths. We validate this theory experimentally by implanting different dopants over a range of electronegativities in devices made of multiple alternating layers of ${\mathrm{Al}}_2{\mathrm{O}}_3$ and WN and find superior repeatability and yield with highly electronegative metals, Au, Pt, and Pd. These devices also exhibit a gradual SET transition, enabling multibit switching that is desirable for analog computing.

We demonstrate that nature has produced a close-packed helical twisted filamentous material in the biomineralization of the mollusk. In liquid crystals, twist–bend nematics have been predicted and observed. We present and analyze evidence that the helical biomineral microstructure of mollusk shells may be formed from such a liquid-crystal precursor.

The Stoner criterion allows only three single elements possessing room-temperature (RT) ferromagnetism: cobalt (Co), nickel (Ni), and iron (Fe). Although these three elements have played central roles in magnetism-based materials, their large work function ($4.5\sim 5.2\mathrm{eV}$) is becoming a non-negligible obstacle for realization of spin devices using nonmetallic materials with finite energy gaps, because injection of electron spins into these nonmetallic materials is strongly hampered due to the large Schottky barrier height. Hence, a novel ferromagnetic or ferrimagnetic material simultaneously possessing RT ferromagnetism or ferrimagnetism and high Fermi energy is strongly required. Here, we show that an Fe-based alloy, iron-gadolinium (FeGd), allows circumvention of the obstacle. Surprisingly, only 20% of Gd incorporation in Fe dramatically modulates the Fermi energy from −4.8 to −3.0 eV, which is the largest modulation in all metallic alloys reported thus far. The coexistence of ferrimagnetism and nonzero spin polarization at RT of FeGd supports its abundant potential for future applications in low-carrier-density materials such as monolayer, organic, and nondegenerate inorganic semiconductors.

The emergence of long-range magnetic order in noncentrosymmetric compounds has stimulated interest in the possibility of exotic spin transport phenomena and topologically protected spin textures for applications in next-generation spintronics. Polar magnets, with broken symmetries of spatial inversion and time reversal, usually host chiral spin textures. This work reports on a wurtzite-structure polar magnetic metal, identified as $A{A}^{\prime }$-stacked ${\left({\mathrm{Fe}}_{0.5}{\mathrm{Co}}_{0.5}\right)}_5\mathrm{Ge}{\mathrm{Te}}_2$, which exhibits a Néel-type skyrmion lattice as well as a Rashba-Edelstein effect at room temperature. Atomic resolution imaging of the structure reveals a structural transition as a function of Co-substitution, leading to the emergence of the polar phase at 50% Co. This discovery reveals an unprecedented layered polar magnetic system for investigating intriguing spin topologies, and it ushers in a promising new framework for spintronics.

Understanding the role of disorder, and the correlations that exist within it, is one of the defining challenges in contemporary materials science. However, there are few material systems, devoid of other complex interactions, that can be used to systematically study the effects of crystallographic conflict on correlated disorder. Here, we report extensive diffuse x-ray scattering studies on the epitaxially stabilized alloy ${\text{U}}_{1-x}{\text{Mo}}_x$, showing that a new form of intrinsically tuneable correlated disorder arises from a mismatch between the preferred symmetry of a crystallographic basis and the lattice upon which it is arranged. Furthermore, combining grazing incidence inelastic x-ray scattering and state-of-the-art ab initio molecular dynamics simulations, we discover strong disorder-phonon coupling. This breaks global symmetry and dramatically suppresses phonon lifetimes compared to alloying alone, providing an additional design strategy for phonon engineering. These findings have implications wherever crystallographic conflict can be accommodated, and they may be exploited in the development of future functional materials.

Achieving on-demand control of the valley degree of freedom is essential for valley-based information science and technology. Optical and magnetic control of the valley degree of freedom in monolayer transition-metal dichalcogenide (TMD) semiconductors has been studied extensively. However, electrical control of the valley polarization has remained a challenge. Here we demonstrate switching of the valley polarization in monolayer $\mathrm{WS}{\mathrm{e}}_2$ by electrical gating. This is achieved by coupling a $\mathrm{WS}{\mathrm{e}}_2$ monolayer to a two-dimensional (2D) layered magnetic insulator $\mathrm{Cr}{\mathrm{I}}_3$. The valley degeneracy in $\mathrm{WS}{\mathrm{e}}_2$ is lifted by the magnetic proximity effect. The valley polarization is switched through gate control of the interlayer spin-flip transition in 2D $\mathrm{Cr}{\mathrm{I}}_3$, which switches the magnetization of the $\mathrm{Cr}{\mathrm{I}}_3$ layer adjacent to the $\mathrm{WS}{\mathrm{e}}_2$ layer. The effect is manifested by a sign change in the photoluminescence handedness of $\mathrm{WS}{\mathrm{e}}_2$. Our results provide the basis for high-speed and energy-efficient gate control of the valley degree of freedom in monolayer TMD semiconductors.

Two-dimensional electron gases (2DEGs) can form at the surface of oxides and semiconductors or in carefully designed quantum wells and interfaces. Depending on the shape of the confining potential, 2DEGs may experience a finite electric field, which gives rise to relativistic effects such as the Rashba spin-orbit coupling. Although the amplitude of this electric field can be modulated by an external gate voltage, which in turn tunes the 2DEG carrier density, sheet resistance and other related properties, this modulation is volatile. Here, we report the design of a “ferroelectric” 2DEG whose transport properties can be electrostatically switched in a nonvolatile way. We generate a 2DEG by depositing a thin Al layer onto a $\mathrm{SrTi}{\mathrm{O}}_3$ single crystal in which 1% of Sr is substituted by Ca to make it ferroelectric. Signatures of the ferroelectric phase transition at 25 K are visible in the Raman response and in the temperature dependences of the carrier density and sheet resistance that shows a hysteretic dependence on electric field as a consequence of ferroelectricity. We suggest that this behavior may be extended to other oxide 2DEGs, leading to novel types of ferromagnet-free spintronic architectures.

When exposed to air, metallic yttrium dihydride ${\mathrm{YH}}_2$ films turn into insulating and transparent yttrium oxyhydride (YHO). The incorporation of oxygen causes the lattice expansion of ${\mathrm{YH}}_2$ and the emergence of photochromic properties, i.e., YHO darkens reversibly when illuminated with light of adequate energy and intensity. However, the adequate bleaching of the photodarkened samples once the illumination has stopped is much faster in air than in inert atmosphere. According to this experimental evidence, the photochromic mechanism has to be related to an oxygen diffusion and exchange process. Since this process is accompanied by a lattice expansion/contraction, it can be said that YHO “breathes” when subjected to illumination/darkness cycling. Another interesting side effect of the breathing is the unexpected enhancement of the hydrophobicity of the YHO samples under illumination. A theoretical model able to explain the breathing in YHO is presented, together with the discussion of other alternative explanations.

The magnetic properties of a material are determined by a subtle balance between the various interactions at play, a fact that makes the design of new magnets a daunting task. High-throughput electronic structure theory may help to explore the vast chemical space available and offers a design tool to the experimental synthesis. This method efficiently predicts the elementary magnetic properties of a compound and its thermodynamical stability, but it is blind to information concerning the magnetic critical temperature. Here we introduce a range of machine-learning models to predict the Curie temperature $T_{\mathrm{C}}$ of ferromagnets. The models are constructed by using experimental data for about 2500 known magnets and consider the chemical composition of a compound as the only feature determining $T_{\mathrm{C}}$. Thus we are able to establish a one-to-one relation between the chemical composition and the critical temperature. We show that the best model can predict $T_{\mathrm{C}}$'s with an accuracy of about 50 K. Most importantly our model is able to make predictions in regions of the chemical space, where only a small fraction of the data was considered for training. Furthermore, it is able to assess the uncertainty of such predictions. This is demonstrated by tracing the $T_{\mathrm{C}}$ of binary intermetallic alloys along their composition space and for the Al-Co-Fe ternary system.

Determination of the adsorption structure of water molecules on metal surfaces is an imperative challenge to understanding the mechanisms of the wetting process and water-related heterogeneous catalysis. We identify water monolayers formed on Ni(111) via low-temperature atomic force microscopy, which enables the visualization of individual water molecules in monolayers with higher spatial resolution than scanning tunneling microscopy. On the terraces of Ni(111) at 150 K, water forms monolayers comprising fused pentagonal, hexagonal, and heptagonal rings. Water adsorbates on step sites assemble in a different manner, forming a hydrogen-bonding network with fused pentagonal and octagonal rings aligned in the step direction. Because similar water networks with pentagonal rings have been proposed in monolayers or their defect sites on other metal surfaces, our structural characterization of ${\mathrm{H}}_2\mathrm{O}/\mathrm{Ni}\left(111\right)$ provides an insight into water adsorption structures on metals.

Contact electrification, or tribocharging, is pertinent to a broad range of industrial and natural processes involving dielectric materials. However, the basic mechanism by which charge is transferred between insulators is still unclear. Here, we use a simple apparatus that brings two macroscopic surfaces into repeated contact and measures the charge on the surfaces after each contact. We vary the temperature of the surfaces and find that increasing temperature leads to a decrease in the magnitude of charge transfer. When paired with a Monte Carlo simulation and thermogravimetric analysis measurements, our results support a mechanism where adsorbed surface water is crucial for charge exchange. Our setup is easily extendable to a variety of industrially relevant materials.

The thermodynamic state of lipid interfaces was observed during shock wave induced cavitation in water with submicrosecond resolution, using the emission spectra of hydration-sensitive fluorescent probes colocalized at the interface. The experiments show that the cavitation threshold is lowest near a phase transition of the lipid interface. The cavitation collapse time and the maximum state change during cavitation are found to be a function of both the driving pressure and the initial state of the lipid interface. The experiments show dehydration and crystallization of lipids during the expansion phase of cavitation, suggesting that the heat of vaporization is absorbed from within the interface, which is adiabatically uncoupled from the free water. The study underlines the critical role of the thermodynamic state of the interface in cavitation dynamics, which has mechanistic implications for ultrasound-mediated drug delivery, acoustic nerve stimulation, ultrasound contrast agents, and the nucleation of ice during cavitation.