Although oxide glasses have many unique properties, their range of applications remains limited by their brittleness. By mimicking the microstructure of composite materials, the presence of controlled nanoscale phase separation in glass could overcome this limitation. However, the nature of the toughening mechanism induced by such nanostructuring remains poorly understood. Here, based on peridynamic simulations, we investigate the effect of nanoscale phase separation on the crack propagation mechanism. We show that phase separation can significantly increase glass's toughness (with up to a 90% increase in the fracture energy for the range of conditions investigated herein). The extent of toughening is found to arise from a balance between the overall cohesion of the phase-separated glass and the propensity for crack deflection. This suggests that controlled nanoscale phase separation is a promising route toward the development of tough, yet optically transparent glasses.

Large unsaturated magnetoresistance has been recently reported in numerous semimetals. Many of them have a topologically nontrivial band dispersion, such as Weyl nodes or lines. Here, we show that elemental antimony displays the largest high-field magnetoresistance among all known semimetals. We present a detailed study of the angle-dependent magnetoresistance and use a semiclassical framework invoking an anisotropic mobility tensor to fit the data. A slight deviation from perfect compensation and a modest variation with magnetic field of the components of the mobility tensor are required to attain perfect fits at arbitrary strength and orientation of magnetic field in the entire temperature window of study. Our results demonstrate that large orbital magnetoresistance is an unavoidable consequence of low carrier concentration and the subquadratic magnetoresistance seen in many semimetals can be attributed to field-dependent mobility, expected whenever the disorder length scale exceeds the Fermi wavelength.

The origin of nematicity, i.e., in-plane rotational symmetry breaking, and in particular the relative role played by spontaneous unidirectional ordering of spin, orbital, or charge degrees of freedom, is a challenging issue of magnetism, unconventional superconductivity, and quantum Hall effect systems, discussed in the context of doped semiconductor systems such as ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}, {\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$, and Ga(Al)As/${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells, respectively. Here, guided by our experimental and theoretical results for ${\mathrm{In}}_{1-x}{\mathrm{Fe}}_x\mathrm{As}$, we demonstrate that spinodal phase separation at the growth surface (that has a lower symmetry than the bulk) can lead to a quenched nematic order of alloy components, which then governs low-temperature magnetic and magnetotransport properties, in particular the magnetoresistance anisotropy whose theory for the $C_{2v}$ symmetry group is advanced here. These findings, together with earlier data for ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$, show under which conditions anisotropic chemical phase separation accounts for the magnitude of transition temperature to a collective phase or merely breaks its rotational symmetry. We address the question to what extent the directional distribution of impurities or alloy components setting in during the growth may account for the observed nematicity in other classes of correlated systems.

We perform a combined experimental and theoretical study of a magnetic-field $\left(B\right)$-induced evolution of magnetic and ferroelectric properties in an antiferromagnetic material $\mathrm{Pb}\left(\mathrm{TiO}\right){\mathrm{Cu}}_4{\left({\mathrm{PO}}_4\right)}_4$, whose structure is characterized by a staggered array of ${\mathrm{Cu}}_4{\mathrm{O}}_{12}$ magnetic units with convex geometry known as square cupola. Our experiments show a $B$-induced phase transition from a previously reported low-$B$ linear magnetoelectric phase to a high-$B$ magnetoelectric phase, which accompanies a ${90}^{\circ }$ flop of electric polarization and gigantic magnetodielectric effect. Moreover, we observe a $B$-induced sign reversal of ferroelectric polarization in the high-$B$ phase. Our model and first-principles calculations reveal that the observed complex magnetoelectric behavior is well explained in terms of a $B$-dependent electric polarization generated in each ${\mathrm{Cu}}_4{\mathrm{O}}_{12}$ unit by the so-called exchange-striction mechanism. The present study demonstrates that the materials design based on the magnetic structural unit with convex geometry deserves to be explored for developing strong magnetoelectric couplings.

Conventional magnetic imaging techniques have observed magnetic domains in the polished surface of Nd-Fe-B sintered magnets, but the mechanical processing involved introduces numerous defects that facilitate the nucleation of reversed domains, thereby masking the interior domain structure. Here, we utilize high-field synchrotron x-ray magnetic circular dichroism microscopy to map the elemental and magnetic distributions in the polished and fractured surfaces of a Nd-Fe-B sintered magnet throughout its entire demagnetization process. As the applied field is varied, the domains in the fractured surface behave completely differently from those in the polished surface, thereby unmasking the interior domain structure and behavior. The area-averaged fractured surface coercivity is ${\mu }_0{H}_{\mathrm{c}}^{\mathrm{frac}}=0.85\mathrm{T}$ which is much higher than the area-averaged polished surface coercivity, ${\mu }_0{H}_{\mathrm{c}}^{\mathrm{pol}}=0.5\mathrm{T}$. Most of the local magnetic hysteresis loops are positively or negatively biased from the zero of the field axis. The highest coercivity grains, some of which exceed 2 T, are almost always located in the vicinity of strongly oppositely biased adjacent grains. This indicates that these oppositely biased grains are strongly influencing the magnetostatic field at the sample surface.

We use resonant and nonresonant x-ray diffraction measurements in combination with first-principles electronic structure calculations and Monte Carlo simulations to study the relationship between crystal structure and multiferroic orders in the orthorhombic perovskite manganites, $\mathrm{o}\text{−}R{\mathrm{MnO}}_3$ ($R$ is a rare-earth cation or Y). In particular, we focus on how the internal lattice parameters (Mn-O bond lengths and Mn-O-Mn bond angles) evolve under chemical pressure and epitaxial strain, and the effect of these structural variations on the microscopic exchange interactions and long-range magnetic order. We show that chemical pressure and epitaxial strain are accommodated differently by the crystal lattice of $\text{o-}R{\mathrm{MnO}}_3$, which is key for understanding the difference in magnetic properties between bulk samples and strained films. Finally, we discuss the effects of these differences in the magnetism on the electric polarization in $\mathrm{o}\text{−}R{\mathrm{MnO}}_3$.

A lately discovered 1144 phase has generated significant interest for its high superconducting temperatures, disorder-free doping, and various chemical substitutions. However, it has only been found in iron arsenides ($AB{\mathrm{Fe}}_4{\mathrm{As}}_4$), and cations are limited to +1 or +2 valence states (e.g., alkali metals, alkaline earth elements, and Eu). Whether more 1144 phases could be stabilized and whether intriguing properties exist are questions of general interest. In this work, we investigate 1144 iron and cobalt arsenides with tri-valence cations (La, Y, In, Tl, Sm, Gd). We study phase stability among other competing phases: 122 solution phase and phase decomposition. With La as the cation, we predict room-temperature stable 1144 structures: $\mathrm{La}A{\mathrm{Fe}}_4{\mathrm{As}}_4$ ($A=\mathrm{K}$, Rb, and Cs). Other La-contained 1144 structures tend to form solution phase. The solubility of La is estimated and compared with the experiment. By contrast, we do not find stable 1144 structures with Y as the cation. For In and Tl as cations, two 122-phase compounds are remarkably stable: ${\mathrm{InCo}}_2{\mathrm{As}}_2$ and ${\mathrm{TlCo}}_2{\mathrm{As}}_2$, which adds to our knowledge about the In(Tl)-Co-As phase diagram. Stable 1144 phases are found in ${\mathrm{InKCo}}_4{\mathrm{As}}_4$ and ${\mathrm{InRbCo}}_4{\mathrm{As}}_4$. With Sm and Gd as cations, 1144- or 122-phase iron arsenides are generally unstable. Among structures investigated, we recognize two critical factors for 1144-phase stability: size effect and charge balance, which yields a merging picture with the rule found in previous 1144 systems. Moreover, $\mathrm{La}A{\mathrm{Fe}}_4{\mathrm{As}}_4$ ($A=\mathrm{K}$, Rb, and Cs), ${\mathrm{InCo}}_2{\mathrm{As}}_2$, and ${\mathrm{TlCo}}_2{\mathrm{As}}_2$ are exhibiting semimetal features and a two-dimensional Fermi surface, similar to iron superconductors.

The recent discovery of the large anomalous Hall effect (AHE) in noncollinear kagome antiferromagnets $\mathrm{M}{\mathrm{n}}_{3}X$ ($X=\mathrm{Sn}$, Ge) has highlighted compounds and alloys based on a combination of Mn and X. As the spin Hall effect (SHE) and AHE share the same origin, the injection of pure spin current into alloys based on Mn and X could potentially engender a large SHE. Here, we report that our spin Seebeck and the spin pumping measurements both reveal that doping Mn with 18% Sn strikingly increases the spin Hall angle of the amorphous/nanocrystalline Mn-Sn alloy by as much as 20 times while the resistivity is reduced by ten times compared with pure Mn. Our study not only serves as an essential reference for pure spin current phenomena in Mn-based alloys but may also offer a promising method for exploring future energy-saving spin Hall materials.

The reduction of the energy dissipation induced by defects is essential to achieve the ultrahigh-quality-factor mechanical resonators for the applications of quantum platform and high-sensitivity microelectromechanical (MEMS) and nanoelectromechanical system (NEMS) sensors. Single-crystal diamond (SCD) is the ideal material for high-quality-factor mechanical resonators due to its outstanding mechanical properties and intrinsic low-energy dissipation. To achieve mechanical resonators with extreme properties as well as high reliability, it is desirable to develop all-SCD mechanical resonators. By using a smart-cut method and atomic layer etching to remove the defects within the resonators, we achieve the SCD-on-SCD mechanical resonators with ultrahigh quality factors of over one million at room temperature. The quality factors are one or more orders of magnitude higher than those of the state-of-the-art MEMS cantilevers based on polycrystalline diamond, single-crystal silicon, and other crystal materials. The diamond MEMS resonators would be highly promising for sensor application as well as for the scheme for coupling with quantum centers in diamond.

We investigate the metallic surface state in ultrathin films of ${\mathrm{BaTiO}}_3$ by angle-resolved photoemission spectroscopy. We find Fermi-surface contours derived from the Ti $3d{t}_{2g}$ conduction band, similar as in ${\mathrm{SrTiO}}_3$ but with broader spectral features due to enhanced quasiparticle scattering. Oxygen vacancies created in the x-ray beam spot allow for reversible in situ doping control up to surface carrier densities as high as ${10}^{14}{\mathrm{cm}}^{-2}$, but vacancy migration into the subsurface at $T\ge 285\mathrm{K}$ quenches the surface state. Our analysis suggests that the charge state of oxygen vacancies in ultrathin films is predominantly $2+$, which limits charge-carrier trapping and the formation of localized defect states.

This work presents the emergence of superconductivity in Re-substituted topological Weyl semimetal ${\mathrm{MoTe}}_2$. Re substitution for Mo sites leads to a sizable enhancement in the superconducting transition temperature ($T_c$). A record high $T_c$ at ambient pressure in a $1T^{\prime }-{\mathrm{MoTe}}_2$ (room-temperature structure) related sample is observed for the ${\mathrm{Mo}}_{0.7}{\mathrm{Re}}_{0.3}{\mathrm{Te}}_2$ composition ($T_c=4.1\mathrm{K}$; in comparison, ${\mathrm{MoTe}}_2$ shows a $T_c$ of 0.1 K). The experimental and theoretical studies indicate that Re substitution is doping electrons and facilitates the emergence of superconductivity by enhancing the electron-phonon coupling and density of states at the Fermi level. Our findings, therefore, open a new way to further manipulate and enhance the superconducting state together with the topological states in two-dimensional van der Waals materials.

III–V semiconductor nanowires have shown great potential in various quantum transport experiments. However, realizing a scalable high-quality nanowire-based platform that could lead to quantum information applications has been challenging. Here, we study the potential of selective area growth by molecular beam epitaxy of InAs nanowire networks grown on GaAs-based buffer layers, where Sb is used as a surfactant. The buffered geometry allows for substantial elastic strain relaxation and a strong enhancement of field effect mobility. We show that the networks possess strong spin-orbit interaction and long phase-coherence lengths with a temperature dependence indicating ballistic transport. With these findings, and the compatibility of the growth method with hybrid epitaxy, we conclude that the material platform fulfills the requirements for a wide range of quantum experiments and applications.

Controllable local electronic conduction in otherwise insulating materials can be created by arranging two opponent ferroelectric polarizations in a head to head (or tail to tail) configuration. Using an effective trailing field of dc biased tip motion, charged domain walls have been artificially created in the context of tip-based nanolithography. However, the charged domain wall formed by a trailing field is unstable because of elastic interaction at the boundary between poling and nonpoling regions, finally resulting in ferroelastic back-switching. Here, we report that nanoscale plate structures under strain relaxation can provide a promising opportunity for stabilization and manipulation of a charged domain wall using a highly anisotropic mechanical boundary condition that restricts the unique ferroelastic domain configuration. We demonstrate that a ferroelectric ${\mathrm{BiFeO}}_3$ nanoplate subjected to compressive misfit strain at the bottom but less external stress on the side walls exhibits radial-quadrant in-plane ferroelectric domain structures. Electronic conduction is significantly enhanced near the side walls and the magnitude of electrostatic conductivity is adjustable up to about 20 times by 180° ferroelectric switching that is protected by the clamped ferroelastic domain. Our findings provide a pathway to controllable nanoelectronic logic devices by tuning a charged ferroelectric domain wall.

We perform a systematic materials informatics search for two-dimensional (2D) ferromagnetic materials (2DFM) in the Inorganic Crystal Structure Database (ICSD). The key indicator in the search is that the candidates have a 2D network composed of magnetic atoms and heavy atoms. From the 187,093 entries in the ICSD, the search identified 15 candidates whose magnetic order are then determined by first-principles calculations and Curie temperatures obtained by either analytical solution or Monte Carlo simulation of the 2D Ising model. For the 15 candidates, eight materials have ferromagnetic order including three known structural prototypes and the two 2DFM materials discovered in recent experiments. More importantly, the search produced two new structural prototypes and a very promising material, ${\mathrm{Cr}}_3{\mathrm{Te}}_4$, which has a calculated Curie temperature one order of magnitude higher than the others.

The recent realization of topological electronic states such as Dirac and Weyl fermions in real materials and their potential for future energy and electronics applications has motivated interest in the study of new forms of topological behavior embodied through new materials. ${\mathrm{Pd}}_3\mathrm{Pb}$ is one such candidate predicted recently to host unique topological features, including a dispersionless band near the Fermi level and triple nodal points hosting Dirac fermions and open Fermi arcs. Here, we report the crystal growth and electric transport properties of ${\mathrm{Pd}}_3\mathrm{Pb}$. Our low field magnetoresistance measurements indicate an anisotropic Fermi surface. We found that ${\mathrm{Pd}}_3\mathrm{Pb}$ manifests a large transverse magnetoresistance, which reaches 650% at 1.8 K and 14 T, and pronounced Shubnikov-de Haas (SdH) oscillations. Preliminary analysis of the field dependence of the SdH oscillations points to the likelihood of nontrivial Berry phase in ${\mathrm{Pd}}_3\mathrm{Pb}$. Further studies in high field limit are desirable to extend the realization of the topological properties of the predicted novel fermions in this material.

Reconstructing the three-dimensional (3D) size and shape distribution of randomly oriented grains using only images of cross sections remains an important challenge. Even for ellipsoids, a solution is only possible when they are solids of revolution, and may still be numerically unstable. Here we show that crystallographic orientation data, for example from electron back-scatter diffraction (EBSD), provides enough additional information to obtain moments of the 3D grain distribution, provided grain shapes can be assumed to align with crystal axes. We show that this moment method can give an average 3D grain size and shape (with error estimate) which is rigorous for ellipsoids and a good approximation for cuboidal grains, indicating that it may be a useful technique for polycrystalline materials in general. High throughput image analysis and EBSD now make the necessary sample sizes practical. We illustrate by applying the method to a basaltic rock specimen.

The noncentrosymmetric Weyl semimetal candidate ${\mathrm{MoTe}}_2$ was investigated through neutron-diffraction and transport measurements at pressures up to 1.5 GPa and at temperatures down to 40 mK. Centrosymmetric and noncentrosymmetric structural phases were found to coexist in the superconducting state. Density functional theory (DFT) calculations reveal that the strength of the electron-phonon coupling is similar for both crystal structures. Furthermore, it was found that by controlling nonhydrostatic components of stress, it is possible to mechanically control the ground-state crystal structure. This allows for the tuning of crystal symmetry in the superconducting phase from centrosymmetric to noncentrosymmetric. DFT calculations support this strain control of crystal structure. This mechanical control of crystal symmetry gives a route to tuning the band topology of ${\mathrm{MoTe}}_2$ and possibly the topology of the superconducting state.

The line tension model of obstacle hardening is modified to account for the thermally activated, kink-limited glide of $1/2\langle 111\rangle$ screw dislocations, allowing application to the plastic flow of bcc metals. Using atomistically informed dislocation mobility laws, Frenkel-Kontorova simulations, and a simplified dislocation-obstacle model, we identify a size effect for intermediate obstacle densities, where the activation energy for screw dislocation motion halves once the obstacle density falls below a critical value. Our model shows striking agreement with fracture experiments across a wide range of unirradiated and irradiated bcc metals. In particular, we demonstrate that the presence of defects in the crystal lattice can at most double the brittle to ductile transition temperature.

Intralayer deformation in van der Waals (vdW) heterostructures is generally assumed to be negligible due to the weak nature of the interactions between the layers, especially when the interfaces are found incoherent. In the present work, graphene-phosphorene vdW heterostructures are investigated with the density functional theory (DFT). The challenge of treating a nearly incommensurate (very large) supercell in DFT is bypassed by considering different energetic quantities in the grand canonical ensemble, alternative to the formation energy, in order to take into account the mismatch elastic contribution of the different layers. In the investigated heterostructures, it is found that phosphorene contracts by $\sim 4\%$ in the armchair direction when compared to its free-standing form. This large contraction leads to important changes in terms of electronic properties, with the direct electronic optical transition of phosphorene becoming indirect in specific vdW heterostructures. More generally, such a contraction indicates strong substrate effects in supported or encapsulated phosphorene—neglected hitherto—and paves the way to substrate-controlled stresstronic in such 2D crystal. In addition, the stability of these vdW heterostructures is investigated as a function of the rotation angle between the layers and as a function of the stacking composition. The alignment of the specific crystalline directions of graphene and phosphorene is found energetically favored. In parallel, several models based on DFT-estimated quantities are presented; they allow notably a better understanding of the global mutual accommodation of 2D materials in their corresponding interfaces, that is predicted to be non-negligible even in the case of incommensurate interfaces.

We demonstrate experimental evidence for the existence of an optimal thickness that yields the maximum third-harmonic (TH) signal in thick multilayer graphene (MLG). We measure the layer-dependent TH signal from MLG on a quartz substrate for $N$ graphene layers ranging from $\sim 3$ to 50. Theoretical predictions of the layer-dependent TH signal are compared with experiment, including those measured using atomic force and optical microscopy. We find the optimal TH signal for $N\approx 24$, in good agreement with two theoretical models: one in which the graphene layers are assumed isolated but contribute coherently, and one in which the MLG is assumed as one continuous thin film. Our measurements reveal that for MLG, the stacking property of the linear and nonlinear conductivities are found to be remarkably preserved up to the very thick layers $\left(N\sim 50\right)$, i.e., ${\sigma }_{N,g}^{\left(i\right)}=N{\sigma }_g^{\left(i\right)}$, where $i=1$ and 3, respectively, and ${\sigma }_g^{\left(i\right)}$ is the corresponding monolayer conductivity.