Two improvements to the binary structural phase field crystal (XPFC) theory are presented. The first is an improvement to the phenomenology for modelling density-density correlation functions and the second extends the free energy of the mixing term in the binary XPFC model beyond ideal mixing to a regular solution model. These improvements are applied to study kinetics of precipitation from solution. We observe a two-step nucleation pathway similar to recent experimental work [N. D. Loh, S. Sen, M. Bosman, S. F. Tan, J. Zhong, C. A. Nijhuis, P. Král, P. Matsudaira, and U. Mirsaidov, Nat. Chem. 9, 77 (2017); A. F. Wallace, L. O. Hedges, A. Fernandez-Martinez, P. Raiteri, J. D. Gale, G. A. Waychunas, S. Whitelam, J. F. Banfield, and J. J. De Yoreo, Science 341, 885 (2013)] in which the liquid solution first decomposes into solute-poor and solute-rich regions, followed by precipitate nucleation of the solute-rich regions. Additionally, we find a phenomenon not previously described in the literature in which the growth of precipitates is accelerated in the presence of uncrystallized solute-rich liquid regions.

Technological developments in high-resolution time-of-flight neutron detectors have raised the prospect of tomographic reconstruction of elastic strain fields from Bragg-edge strain images. This approach holds the potential to provide a unique window into the full triaxial stress field within solid samples. Recent work has provided an algorithm to achieve tomographic reconstruction for systems subject to in situ loads in the absence of residual stress. This paper details an experimental proof of concept for this algorithm involving the full reconstruction of a biaxial strain field within a nontrivial steel sample. Aside from a small systematic error present within individual measurements, the experiment was a success and now serves as a practical demonstration of Bragg-edge transmission strain tomography for systems under in situ loads.

A quantum spin liquid might be realized in $\alpha -{\mathrm{RuCl}}_3$, a honeycomb-lattice magnetic material with substantial spin-orbit coupling. Moreover, $\alpha -{\mathrm{RuCl}}_3$ is a Mott insulator, which implies the possibility that novel exotic phases occur upon doping. Here, we study the electronic structure of this material when intercalated with potassium by photoemission spectroscopy, electron energy loss spectroscopy, and density functional theory calculations. We obtain a stable stoichiometry at ${\mathrm{K}}_{0.5}{\mathrm{RuCl}}_3$. This gives rise to a peculiar charge disproportionation into formally ${\mathrm{Ru}}^{2+}$ ($4d^6$) and ${\mathrm{Ru}}^{3+}$ ($4d^5$). Every Ru $4d^5$ site with one hole in the $t_{2g}$ shell is surrounded by nearest neighbors of $4d^6$ character, where the $t_{2g}$ level is full and magnetically inert. Thus, each type of Ru site forms a triangular lattice, and nearest-neighbor interactions of the original honeycomb are blocked.

Semicrystalline polyethylene (PE) is attractive for a variety of mechanically demanding applications, where shock compression can occur. Although often highly crystalline, PE invariably contains nanoscale amorphous domains that influence shock propagation. Our objective in this work is to study the effects of such domains. To this end, we adopt a novel approach wherein we parametrize a simple continuum-level theory based on the shock impedance from molecular dynamics (MD) simulations. Using this theory, we predict how crystalline/amorphous interfaces attenuate shocks via energy reflection due to the impedance mismatch between the phases. The theory predicts that these interfaces attenuate weak shocks more effectively than strong shocks. We compare the theory to explicit nonequilibrium MD simulations of compressive shocks in semicrystalline PE containing nanometer-scale amorphous regions of varying size, where we analyze the pressure response and reflection of energy. The theory and simulations show good agreement for strong shocks $\left(\ge 1.0\mathrm{km}/\mathrm{s}\right)$, but for weak shocks $\left(<1.0\mathrm{km}/\mathrm{s}\right)$ the simulations show enhanced energy reflection relative to the continuum predictions. Furthermore, the simulations show an effect not captured by the continuum theory: the size of amorphous regions is important. The theory assumes a sharp (discontinuous) interface between two bulk phases and a sharp change in thermodynamic and hydrodynamic quantities at the shock front. However, the simulations show that when amorphous domains are narrow—with widths comparable to the shock front—reflection is reduced compared to the predictions. We identify several nanoscale mechanisms that reduce the impedance mismatch, and thus reduce reflection, at thin amorphous domains. First, the two-wave elastic-plastic structure of shocks in crystalline PE allows the faster-moving elastic precursor wave to compress small amorphous domains before the plastic wave arrives. Second, confinement between stiff, ordered crystalline domains increases the stiffness and chain ordering in small amorphous regions. Moreover, in terms of stiffness the interfaces are similar in width to the shock front, which may contribute to the underprediction of the theory for weak shocks, where the shock front is widest. We conclude by discussing the significance of these results, namely, how they can be applied to tune shock attenuation for particular applications.

Organic-inorganic coupling in the hybrid lead-halide perovskite is a central issue in rationalizing the outstanding photovoltaic performance of these emerging materials. Here, we compare and contrast the evolution of the structure and dynamics of hybrid ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbBr}}_3$ and inorganic ${\mathrm{CsPbBr}}_3$ lead-halide perovskites with temperature, using Raman spectroscopy and single-crystal x-ray diffraction. Results reveal a stark contrast between their order-disorder transitions, which are abrupt for the hybrid whereas smooth for the inorganic perovskite. X-ray diffraction observes an intermediate incommensurate phase between the ordered and the disordered phases in ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbBr}}_3$. Low-frequency Raman scattering captures the appearance of a sharp soft mode in the incommensurate phase, ascribed to the theoretically predicted amplitudon mode. Our work highlights the interaction between the structural dynamics of organic cation ${\mathrm{CH}}_3{\mathrm{NH}}_3{}^{+}$ and the lead-halide framework, and unravels the competition between tendencies for the organic and inorganic moieties to minimize energy in the incommensurate phase of the hybrid perovskite structure.

Results are reported for the $f$-electron intermetallic ${\mathrm{CeAuAl}}_4{\mathrm{Ge}}_2$, where the atomic arrangement of the cerium ions creates the conditions for possible geometric frustration. The magnetic susceptibility follows a Curie-Weiss temperature dependence at elevated temperatures, revealing that the cerium ions are trivalent. At lower temperatures the crystal electric field splits the Hund's rule multiplet, resulting in a weak low-temperature magnetic exchange interaction and ordering near $T_M\approx 1.4\mathrm{K}$. This occurs within a metallic Kondo lattice, where electrical resistivity and heat capacity measurements show that the Kondo-driven electronic correlations are negligible. Quantum oscillations are detected in ac-magnetic susceptibility measurements and uncover small charge carrier effective masses. Electronic structure calculations reveal that inclusion of an on-$f$-site Coulomb repulsion (Hubbard) $U$ results in antiferromagnetic order and causes the $f$-electron bands to move away from the Fermi level, resulting in electronic behavior that is dominated by the $s,p$, and $d$ bands, which are all characterized by light electron masses. Thus, ${\mathrm{CeAuAl}}_4{\mathrm{Ge}}_2$ may provide a starting point for investigating geometric magnetic frustration in a cerium lattice without strong Kondo hybridization, where calculations provide useful guidance.

We discuss a parameter-free and computationally efficient ab initio simulation approach for moderately and strongly correlated materials, the multitier self-consistent $GW+\text{EDMFT}$ method. This scheme treats different degrees of freedom, such as high-energy and low-energy bands, or local and nonlocal interactions, within appropriate levels of approximation, and provides a fully self-consistent description of correlation and screening effects in the solid. The ab initio input is provided by a one-shot $G^0{W}^0$ calculation, while the strong-correlation effects originating from narrow bands near the Fermi level are captured by a combined $GW$ plus extended dynamical mean-field (EDMFT) treatment. We present the formalism and technical details of our implementation and discuss some general properties of the effective EDMFT impurity action. In particular, we show that the retarded impurity interactions can have noncausal features, while the physical observables, such as the screened interactions of the lattice system, remain causal. As a first application, we present ab initio simulation results for ${\mathrm{SrMoO}}_3$, which demonstrate the existence of prominent plasmon satellites in the spectral function not obtainable within LDA+DMFT, and provide further support for our recent reinterpretation of the satellite features in the related cubic perovskite ${\mathrm{SrVO}}_3$. We then turn to stretched sodium as a model system to explore the performance of the multitier self-consistent $GW+\text{EDMFT}$ method in situations with different degrees of correlation. While the results for the physical lattice spacing $a_0$ show that the scheme is not very accurate for electron-gas-like systems, because nonlocal corrections beyond $GW$ are important, it does provide physically correct results in the intermediate correlation regime, and a Mott transition around a lattice spacing of $1.5a_0$. Remarkably, even though the Wannier functions in the stretched compound are less localized, and hence the bare interaction parameters are reduced, the self-consistently computed impurity interactions show the physically expected trend of an increasing interaction strength with increasing lattice spacing.

Spacer thickness $t_{\mathrm{N}}$ and annealing temperature $T_{\mathrm{anneal}}$ dependence of current perpendicular-to-plane giant magnetoresistance effects were investigated in junctions using $L{1}_2{\mathrm{Ag}}_3\mathrm{Mg}$ spacer and half-metallic ${\mathrm{Co}}_2{\mathrm{Fe}}_{0.4}{\mathrm{Mn}}_{0.6}\mathrm{Si}$ (CFMS) Heusler alloy electrodes. $t_{\mathrm{N}}$ was changed from 2–12 nm and $T_{\mathrm{anneal}}$ was changed from $450-650{}^{\circ }\mathrm{C}$ to promote the chemical ordering of the CFMS electrodes. Concerning the $t_{\mathrm{N}}$ dependence, the magnetoresistance (MR) ratio and the change of the areal resistance $\left(\mathrm{\Delta }RA\right)$ exhibited the maximum values at $t_{\mathrm{N}}=5\mathrm{nm}$. The reasons for the decrease of the MR ratio for $t_{\mathrm{N}}<5$ nm and for $t_{\mathrm{N}}>5$ nm were possibly due to an unstable antiparallel magnetization configuration and to the increased occurrence of spin scattering inside the ${\mathrm{Ag}}_3\mathrm{Mg}$ spacer, respectively. The spin-diffusion length of the ${\mathrm{Ag}}_3\mathrm{Mg}$ spacer was also estimated using the $t_{\mathrm{N}}$ dependence of $\mathrm{\Delta }RA$ and it was found to be of the order of 10–30 nm. Concerning the $T_{\mathrm{anneal}}$ dependence, $\mathrm{\Delta }RA$ and the MR ratio exhibited the maximum values at $550{}^{\circ }\mathrm{C}$, which was the optimum point in terms of the degrees of order in the CFMS layers and the ${\mathrm{Ag}}_3\mathrm{Mg}$ layer, and the (001) orientation of the layered structure. The maximum $\mathrm{\Delta }RA$ and the intrinsic MR ratio in which parasitic resistance contribution was eliminated were $25\mathrm{m}\mathrm{\Omega }\mu {\mathrm{m}}^2$ and 63%, respectively, at room temperature.

We investigate the mechanical response of a compressed monolayer of large and dense particles at a liquid-fluid interface: a granular raft. Upon compression, rafts first wrinkle; then, as the confinement increases, the deformation localizes in a unique fold. This characteristic buckling pattern is usually associated with floating elastic sheets, and as a result, particle laden interfaces are often modeled as such. Here, we push this analogy to its limits by comparing quantitative measurements of the raft morphology to a theoretical continuous elastic model of the interface. We show that, although powerful to describe the wrinkle wavelength, the wrinkle-to-fold transition, and the fold shape, this elastic description does not capture the finer details of the experiment. We describe an unpredicted secondary wavelength, a compression discrepancy with the model, and a hysteretic behavior during compression cycles, all of which are a signature of the intrinsic discrete and frictional nature of granular rafts. It suggests also that these composite materials exhibit both plastic transition and jamming dynamics.

We examine the step instability observed in Fe growth on a Cu(100) vicinal substrate in which deposition of a relatively low coverage of Fe leads to a dramatic increase in the step roughness, with a change in the step morphology from relatively straight [100] steps to a mixture of [100] and [110] steps. Our temperature-accelerated dynamics (TAD) simulations and energetics calculations indicate that the dramatic change in the step morphology is due to a variety of unexpected complex multiatom interlayer diffusion (MID) processes near step edges which lead to a competition between [100] and [110] steps, whose barriers are significantly reduced due to the existence of strong Fe-Fe and Fe-Cu interactions as well as strain effects. In contrast, TAD simulations of vicinal Cu/Cu(100) growth do not lead to an instability, in good agreement with experiments. Our results also indicate that while the instability is driven by energetics, kinetics plays a crucial role. We also present the results of TAD simulations and energetics calculations for the case of Fe/Cu(100) growth on vicinal surfaces with [110] steps. Our results in this case indicate that a variety of effects, including MID processes as well as pinning of edge-diffusing atoms, lead to the formation of protrusions with [110] steps perpendicular to the original [110] steps. These results may also provide an explanation for the experimentally observed instabilities observed in growth on vicinal Ni/Cu(100) and Co/Cu(100) surfaces with [110] steps.

The electronic and optoelectronic properties of molecular semiconductor thin films are directly linked to their extrinsic nanoscale structural characteristics such as domain size and spatial distributions. In films prepared by common solution-phase deposition techniques such as spin casting and solvent-based printing, morphology is governed by a complex interrelated set of thermodynamic and kinetic factors that classical models fail to adequately capture, leaving them unable to provide much insight, let alone predictive design guidance for tailoring films with specific nanostructural characteristics. Here we introduce a comprehensive treatment of solution-based film formation enabling quantitative prediction of domain formation rates, coverage, and spacing statistics based on a small number of experimentally measureable parameters. The model combines a mean-field rate equation treatment of monomer aggregation kinetics with classical nucleation theory and a supersaturation-dependent critical nucleus size to solve for the quasi-two-dimensional temporally and spatially varying monomer concentration, nucleation rate, and other properties. Excellent agreement is observed with measured nucleation densities and interdomain radial distribution functions in polycrystalline tetracene films. Numerical solutions lead to a set of general design rules enabling predictive morphological control in solution-processed molecular crystalline films.

Spin pumping (SP) and the spin Seebeck effect (SSE), two of the most common methods for generating a pure spin current from ferromagnetic insulators, are considered to share similar physical mechanisms. However, a systematic study of the fundamental difference of their working principle is missing. In this Rapid Communication, we present experimental evidence of the contrast in a pure spin current generated by SP and SSE, based on results from yttrium iron garnet (YIG) with various crystalline properties. It is shown that while the SP-induced spin current could be two-orders-of-magnitude different between the polycrystalline and epitaxial films, the SSE-excited spin current is surprisingly insensitive to the different crystal structures. Our results clearly distinguish the coherent mechanism of SP from the noncoherent mechanism of the SSE. Consequently, the robust SSE voltage against poor crystallinity proves that the SSE is a powerful tool to explore pure spin current physics, and suggests that polycrystalline YIG films are a promising candidate for spin caloritronic applications.

Electrical conductivity and high dielectric constant are in principle self-excluding, which makes the terms insulator and dielectric usually synonymous. This is certainly true when the electrical carriers are electrons, but not necessarily in a material where ions are extremely mobile, electronic conduction is negligible, and the charge transfer at the interface is immaterial. Here we demonstrate in a perovskite-derived structure containing five-coordinated Ti atoms, a colossal dielectric constant (up to ${\text{10}}^9)$ together with very high ionic conduction ${\text{10}}^{-3}\text{S}{\text{cm}}^{-1}$ at room temperature. Coupled investigations of $I\text{−}V$ and dielectric constant behavior allow us to demonstrate that, due to ion migration and accumulation, this material behaves like a giant dipole, exhibiting colossal electrical polarization (of the order of $\text{0.1}\text{C}{\text{cm}}^{-2})$. Therefore it may be considered as a “ferro-ionet” and is extremely promising in terms of applications.

Although copper and bismuth do not form any compounds at ambient conditions, two intermetallics, $\mathrm{CuBi}$ and ${\mathrm{Cu}}_{11}{\mathrm{Bi}}_7$, were recently synthesized at high pressures. Here we report on the discovery of additional copper-bismuth phases at elevated pressures with high densities from ab initio calculations. In particular, a ${\mathrm{Cu}}_2\mathrm{Bi}$ compound is found to be thermodynamically stable at pressures above 59 GPa, crystallizing in the cubic Laves structure. In strong contrast to ${\mathrm{Cu}}_{11}{\mathrm{Bi}}_7$ and CuBi, cubic ${\mathrm{Cu}}_2\mathrm{Bi}$ does not exhibit any voids or channels. Since the bismuth lone pairs in cubic ${\mathrm{Cu}}_2\mathrm{Bi}$ are stereochemically inactive, the constituent elements can be closely packed and a high density of 10.52 g/${\mathrm{cm}}^3$ at 0 GPa is achieved. The moderate electron-phonon coupling of $\lambda =0.68$ leads to a superconducting temperature of 2 K, which exceeds the values observed both in ${\mathrm{Cu}}_{11}{\mathrm{Bi}}_7$ and CuBi, as well as in elemental Cu and Bi.

Recent progress in materials informatics has opened up the possibility of a new approach to accessing properties of materials in which one assays the aggregate properties of a large set of materials within the same class in addition to a detailed investigation of each compound in that class. Here we present a large scale investigation of electronic properties and correlated magnetism in Ce-based compounds accompanied by a systematic study of the electronic structure and $4f$-hybridization function of a large body of Ce compounds. We systematically study the electronic structure and $4f$-hybridization function of a large body of Ce compounds with the goal of elucidating the nature of the $4f$ states and their interrelation with the measured Kondo energy in these compounds. The hybridization function has been analyzed for more than 350 data sets (being part of the IMS database) of cubic Ce compounds using electronic structure theory that relies on a full-potential approach. We demonstrate that the strength of the hybridization function, evaluated in this way, allows us to draw precise conclusions about the degree of localization of the $4f$ states in these compounds. The theoretical results are entirely consistent with all experimental information, relevant to the degree of $4f$ localization for all investigated materials. Furthermore, a more detailed analysis of the electronic structure and the hybridization function allows us to make precise statements about Kondo correlations in these systems. The calculated hybridization functions, together with the corresponding density of states, reproduce the expected exponential behavior of the observed Kondo temperatures and prove a consistent trend in real materials. This trend allows us to predict which systems may be correctly identified as Kondo systems. A strong anticorrelation between the size of the hybridization function and the volume of the systems has been observed. The information entropy for this set of systems is about 0.42. Our approach demonstrates the predictive power of materials informatics when a large number of materials is used to establish significant trends. This predictive power can be used to design new materials with desired properties. The applicability of this approach for other correlated electron systems is discussed.

We report a combination of x-ray and neutron diffraction studies, Mössbauer spectroscopy, and muon spin relaxation (${\mu }^{+}\mathrm{SR}$) measurements to probe the structure and magnetic properties of the semiconducting $\beta -\mathrm{C}{\mathrm{e}}_2{\mathrm{O}}_2\mathrm{FeS}{\mathrm{e}}_2$ oxychalcogenide. We report a structural description in space group $Pna{2}_1$ which is consistent with diffraction data and second harmonic generation measurements and reveal an order-disorder transition on one Fe site at $T_{\mathrm{OD}}\approx 330\mathrm{K}$. Susceptibility measurements, Mössbauer, and ${\mu }^{+}\mathrm{SR}$ reveal antiferromagnetic ordering below $T_{\mathrm{N}}=86\mathrm{K}$ and more complex short range order above this temperature. 12 K neutron diffraction data reveal a modulated magnetic structure with $\mathbf{q}=0.444{\mathbf{b}}_{\mathrm{N}}{}^{*}$.

A mechanism of anomalous tension-compression (T-C) asymmetry in ultrafine-grained (UFG) metals is proposed using large-scale atomistic simulations and dislocation theory. Unlike coarse-grained metals, UFG Al exhibits remarkable T-C asymmetry of the yield stress. The atomistic simulations reveal that the yield event is not related to intragranular dislocations but caused by dislocation nucleation from the grain boundaries (GBs). The dislocation core structure associated with the stacking fault energy in Al is strongly affected by the external stress compared with Cu; specifically, high tensile stress stabilizes the dissociation into partial dislocations. These dislocations are more likely to be nucleated from GBs and form deformation twins from an energetic viewpoint. The mechanism, which is different from well-known mechanisms for nanocrystalline and amorphous metals, is unique to high-strength UFG metals and can explain the difference in T-C asymmetry between UFG Cu and Al.

We demonstrate the use of selective thermal evaporation to separate and purify small molecular weight polymers into highly monodisperse polymers over an extended range of polymerization index. By exploiting the calculated dependence of polymer vapor pressure on polymerization index $N$ and temperature $T$, we can isolate individual components $(N$-mers) of an initially polydisperse mixture. To demonstrate this ability, we consider polystyrene samples of $M_w=600$ g/mol and $M_w=890$ g/mol with narrow molecular weight distributions, as well as a $M_w=1200$ g/mol sample with a broader distribution. In each case we are able to separate the sample into milligram quantities of many different components. Using this technique, we have been able to isolate $N$-mers from 3 to 13. We use differential scanning calorimetry to measure the $T_g$ values of these components, and find that the components have the same $T_g$ values independent of the $M_w$ or polydispersity of the sample they originate from. We find that even initially narrow molecular weight distributions have many different components whose $T_g$ values can differ by more than 50 K. Calculations suggest the isolated components have $M_w/M_n$ values less than 1.001 and through a second iteration of the process could become as low as 1.000 003. The measured $T_g$ values for the $N$-mers as well as large $N$ polymers are well described by a simple relation derived from the Fox equation for the $T_g$ of mixtures.

The combination of charge and spin degrees of freedom with electronic correlations in condensed matter systems leads to a rich array of phenomena, such as magnetism, superconductivity, and novel conduction mechanisms. While such phenomena are observed in bulk materials, a richer array of behaviors becomes possible when these degrees of freedom are controlled in atomically layered heterostructures, where one can constrain dimensionality and impose interfacial boundary conditions. Here, we unlock a host of unique, hidden electronic and magnetic phase transitions in $\mathrm{NdNi}{\mathrm{O}}_3$ while approaching the two-dimensional (2D) limit, resulting from the differing influences of dimensional confinement and interfacial coupling. Most notably, we discover a phase in fully 2D, single-layer $\mathrm{NdNi}{\mathrm{O}}_3$, in which all signatures of the bulk magnetic and charge ordering are found to vanish. In addition, for quasi-two-dimensional layers down to a thickness of two unit cells, bulk-type ordering persists but separates from the onset of insulating behavior in a manner distinct from that found in the bulk or thin-film nickelates. Using resonant x-ray spectroscopies, first-principles theory, and model calculations, we propose that the single-layer phase suppression results from an alternative mechanism of interfacial electronic reconstruction based on ionicity differences across the interface, while the phase separation in multilayer $\mathrm{NdNi}{\mathrm{O}}_3$ emerges due to enhanced 2D fluctuations. These findings provide insights into the intertwined mechanisms of charge and spin ordering in strongly correlated systems in reduced dimensions and illustrate the ability to use atomic layering to access hidden phases.

Electronic charge rearrangements at interfaces between organic molecules and solid surfaces play a key role in a wide range of applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. It is common to utilize electrostatics and Pauli pushback to control the interface electronic properties, while the ubiquitous van der Waals (vdW) interactions are often considered to have a negligible direct contribution (beyond the obvious structural relaxation). Here, we apply a fully self-consistent Tkatchenko-Scheffler vdW density functional to demonstrate that the weak vdW interactions can induce sizable charge rearrangements at hybrid metal/organic systems (HMOS). The complex vdW correlation potential smears out the interfacial electronic density, thereby reducing the charge transfer in HMOS, changes the interface work functions by up to 0.2 eV, and increases the interface dipole moment by up to 0.3 Debye. Our results suggest that vdW interactions should be considered as an additional control parameter in the design of hybrid interfaces with the desired electronic properties.