${\mathrm{MnSiN}}_2$ is a transition-metal nitride with Mn and Si ions displaying an ordered distribution on the cation sites of a distorted wurtzite-derived structure. The ${\mathrm{Mn}}^{2+}$ ions reside on a three-dimensional (3D) diamondlike covalent network with strong superexchange pathways. We simulate its electronic structure and find that the N anions in ${\mathrm{MnSiN}}_2$ act as $\sigma$- and $\pi$-donors, which serve to enhance the N-mediated superexchange, leading to the high Néel ordering temperature of $T_N$ = 443 K. Polycrystalline samples of ${\mathrm{MnSiN}}_2$ were prepared to reexamine the magnetic structure and resolve previously reported discrepancies. An additional magnetic canting transition is observed at $T_{\mathrm{cant}}$ = 433 K and the precise canted ground-state magnetic structure has been resolved using a combination of density functional theory (DFT) calculations and powder neutron diffraction. The calculations favor a $G$-type antiferromagnetic spin order with lowering to $P{c}^{\prime }$. Irreducible representation analysis of the magnetic Bragg peaks supports the lowering of the magnetic symmetry. The computed model includes a ${10}^{\circ }$ rotation of the magnetic spins away from the crystallographic $c$ axis consistent with measured powder neutron diffraction data modeling and a small canting of $0.6{}^{\circ }$.

Topological insulators are promising materials in condensed-matter physics on the grounds that they host a peculiar spin texture that can generate very high spin-to-charge current interconversion, significantly relevant for up-and-coming low-energy-consumption spintronics devices. The goal of this study is to explore a promising family of topological materials showing distinctive properties such as high tunability—the half-Heuslers. We focus on the epitaxial growth of PdYBi and PtYBi thin films, which were grown and characterized on a series of interconnected UHV setups, allowing us to get a full set of in situ surface characterizations, such as electron diffraction, scanning tunneling microscopy, and angle-resoled photoemission spectroscopy. Ex situ structural characterization using standard x-ray diffraction and scanning transmission electron microscopy were used to control the crystalline quality and chemical ordering in the thin films. Angle-resolved photoemission spectroscopy was performed and reveals the presence of linear states around the $\mathrm{\Gamma }$ point of the Brillouin zone. Furthermore, we carry out thermospin transport measurements using on-chip devices with a designed geometry for a controlled heat propagation to test the potential interconversion efficiency of our compounds, finding a larger value of the spin Seebeck coefficient than that of platinum for different thicknesses for both PdYBi and PtYBi. This observation opens a pathway to develop efficient spin interconversion materials using half-Heuslers.

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.

Electron-electron ($e\text{−}e$) and electron-phonon ($e$-ph) interactions are challenging to describe in correlated materials, where their joint effects govern unconventional transport, phase transitions, and superconductivity. Here we combine first-principles $e$-ph calculations with dynamical mean-field theory (DMFT) as a step toward a unified description of $e\text{−}e$ and $e$-ph interactions in correlated materials. We compute the $e$-ph self-energy using the DMFT electron Green's function and combine it with the $e\text{−}e$ self-energy from DMFT to obtain a Green's function including both interactions. This approach captures the renormalization of quasiparticle dispersion and spectral weight on equal footing. Using our method, we study the $e$-ph and $e\text{−}e$ contributions to the resistivity and spectral functions in the correlated metal ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. In this material, our results show that $e\text{−}e$ interactions dominate transport and spectral broadening in the temperature range we study ($50–310$ K), while $e$-ph interactions are relatively weak and account for only $\sim 10\%$ of the experimental resistivity. We also compute effective scattering rates and find that the $e\text{−}e$ interactions result in scattering several times greater than the Planckian value $k_{B}T$, whereas $e$-ph interactions are associated with scattering rates lower than $k_{B}T$. Our work demonstrates a first-principles approach to combine electron dynamical correlations from DMFT with $e$-ph interactions in a consistent way, advancing quantitative studies of correlated materials.

We examine the effects of Pt vacancies on the magnetotransport properties of Weyl semimetal candidate GdPtSb films, grown by molecular beam epitaxy on $c$-plane sapphire. Rutherford backscattering spectrometry and x-ray diffraction measurements suggest that phase-pure ${\mathrm{GdPt}}_x\mathrm{Sb}$ films can accommodate up to $15\%$ of Pt vacancies ($x=0.85$), which act as acceptors, as measured by the Hall effect. Two classes of electrical transport behavior are observed. Pt-deficient films display metallic temperature-dependent resistivity ($d\rho /dT>0$). The longitudinal magnetoresistance (LMR, magnetic field $\mathbf{B}$ parallel to electric field $\mathbf{E}$) is more negative than transverse magnetoresistance (TMR, $\mathbf{B}\perp \mathbf{E}$), consistent with the expected chiral anomaly for a Weyl semimetal. The combination of Pt-vacancy disorder and doping away from the expected Weyl nodes, however, suggests that conductivity fluctuations may explain the negative LMR rather than chiral anomaly. Samples closer to stoichiometry display the opposite behavior: semiconductorlike resistivity ($d\rho /dT>0$) and more negative TMR than LMR. Hysteresis and other nonlinearities in the low-field Hall effect and magnetoresistance suggest that spin-disorder scattering and possible topological Hall effect may dominate the near-stoichiometric samples. Our findings highlight the complications of transport-based identification of Weyl nodes but point to possible topological spin textures in GdPtSb.

Nitride perovskites are an emerging class of materials that have been predicted to display a range of interesting physics and functional properties, but they are highly underexplored due to the difficulty of synthesizing oxygen-free nitrides. ${\mathrm{LaWN}}_3$, recently reported as the first oxygen-free nitride perovskite, exhibited polar symmetry and a large piezoelectric coefficient. However, the predicted ferroelectric switching was hindered by a large leakage current, which motivates better understanding of the electronic structure and optical properties of this material. In this article, we study the structure and optoelectronic properties of thin film ${\mathrm{LaWN}}_3$ in greater detail, employing combinatorial techniques to correlate these properties with cation stoichiometry. We report a two-step synthesis method that utilizes a more common radio frequency substrate bias instead of a nitrogen plasma source, yielding nanocrystalline films that are subsequently crystallized by ex situ annealing. We investigate the crystal structure and composition of the combinatorial films produced by this method, finding polycrystalline La-rich films and highly textured W-rich films. The measured optical absorption onset (2.5–3.5 eV) and temperature- and magnetic field-dependent resistivity (0.0055–2 $\mathrm{\Omega }$ cm for W-rich and La-rich ${\mathrm{LaWN}}_3$, respectively) are consistent with semiconducting behavior and are highly sensitive to cation stoichiometry, which may be related to amorphous impurities: metallic W or ${\mathrm{WN}}_x$ in W-rich samples and insulating ${\mathrm{La}}_2{\mathrm{O}}_3$ in La-rich samples. The fractional magnetoresistance is linear and small, consistent with defect scattering, and a W-rich sample has n-type carriers with high densities and low mobilities. We demonstrate a photoresponse in ${\mathrm{LaWN}}_3$: The resistivity of a La-rich sample is enhanced by $\sim 28$% under illumination and at low temperature, likely due to a defect trapping mechanism. The physical properties of ${\mathrm{LaWN}}_3$ are highly sensitive to cation stoichiometry, like many oxide perovskites, which therefore calls for precise composition control to utilize the interesting properties observed in this nitride perovskite.

Halide pervoskites are an important class of semiconducting materials that hold great promise for optoelectronic applications. In this work we investigate the relationship between vibrational anharmonicity and dynamic disorder in this class of solids. Via a multiscale model parametrized from first-principles calculations, we demonstrate that the non-Gaussian lattice motion in halide perovskites is microscopically connected to the dynamic disorder of overlap fluctuations among electronic states. This connection allows us to rationalize the emergent differences in temperature-dependent mobilities of prototypical ${\mathrm{MAPbI}}_3$ and ${\mathrm{MAPbBr}}_3$ compounds across structural phase transitions, in agreement with experimental findings. Our analysis suggests that the details of vibrational anharmonicity and dynamic disorder can complement known predictors of electronic conductivity and can provide structure-property guidelines for the tuning of carrier transport characteristics in anharmonic semiconductors.

Ammonium sulphate ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$ (AS) has recently been shown to display giant barocaloric and electrocaloric effects when its paraelectric-ferrielectric transition at $\sim 225$ K is driven by hydrostatic pressure or an electric field, respectively. Important aspects of the structural evolution in this context are coupling of strain to molecular librational modes, distortions, and rotations of ${{\mathrm{NH}}_4}^{+}$ and ${{\mathrm{SO}}_4}^{2-}$ groups, and to changes in hydrogen bonding. Resonant ultrasound spectroscopy (RUS) has been used to reveal subtle elastic and anelastic relaxation processes of single crystals of AS through the temperature interval 5–300 K that are indicative of (i) coupling of strain to the driving order parameter, modified by a transformation microstructure, and (ii) of hysteretic effects that are attributed to different dynamics of displacive and order/disorder components of the phase transition. At high temperatures, partial chemical decomposition results in the formation of triammonium hydrogen disulphate ${\left({\mathrm{NH}}_4\right)}_3\mathrm{H}{\left({\mathrm{SO}}_4\right)}_2$ (AHS) which displays elastic and anelastic anomalies associated with phase transitions at $\sim 265$, 139, 132, and 72 K. Freezing of defects coupled with strain occurs at temperatures below $\sim 35$ K in both AS and AHS.

In situ synthesized semiconductor/superconductor hybrid structures became an important material platform in condensed matter physics. Their development enabled a plethora of novel quantum transport experiments with focus on Andreev and Majorana physics. The combination of InAs and Al has become the workhorse material and has been successfully implemented in the form of one-dimensional structures and two-dimensional electron gases. In contrast to the well-developed semiconductor parts of the hybrid materials, the direct effect of the crystal nanotexture of Al films on the electron transport still remains unclear. This is mainly due to the complex epitaxial relation between Al and the semiconductor. Here, we present characterization of Al thin films grown on shallow InAs two-dimensional electron gas systems by molecular beam epitaxy. Using a growth approach based on an intentional roughening of the epitaxial interface, we demonstrate growth of grain-boundary-free Al. We show that the implemented roughening does not negatively impact either the electron mobility of the two-dimensional electron gas or the basic superconducting properties of the proximitized system. This is an important step in understanding the role of properties of the InAs/Al interface in hybrid devices. Ultimately, our results provide a growth approach to achieve a high-degree of epitaxy in lattice-mismatched materials.

Predictions of a topological electronic structure in the skutterudite ${\mathrm{TPn}}_3$ family ($T=\text{transition metal}$, $Pn=\text{pnictogen}$) are investigated via magnetoresistance, quantum oscillation, and angle-resolved photoemission experiments on $\mathrm{Rh}{\mathrm{Sb}}_3$, a semimetal with low carrier density. Electronic band structure calculations and symmetry analysis of $\mathrm{Rh}{\mathrm{Sb}}_3$ indicate this material to be a zero-gap semimetal protected by symmetry with inverted valence and conduction bands that touch at the $\mathrm{\Gamma }$ point close to the Fermi level. Transport experiments reveal an unsaturated linear magnetoresistance that approaches a factor of 200 at 60 T magnetic fields and quantum oscillations observable up to 150 K that are consistent with a large Fermi velocity ($\sim 1.3\times {10}^6$ m/s), high carrier mobility [$\sim 14$ ${\mathrm{m}}^2/\left(\mathrm{V}\mathrm{s}\right)$], and the existence of a small three-dimensional hole pocket. A very small, sample-dependent effective mass falls to values as low as 0.018(2) of the bare electron mass and scales with the Fermi wave vector. This, together with a nonzero Berry's phase and the location of the Fermi level in the linear region of the valence band, suggests $\mathrm{Rh}{\mathrm{Sb}}_3$ as representative of a material family of topological semimetals with symmetry-enforced Fermi degeneracy at the high-symmetry points.

Single crystals were grown and characterized to investigate the physical properties and magnetic ground state of $\mathrm{Ba}{\mathrm{Nd}}_2\mathrm{Pt}{\mathrm{O}}_5$, a candidate to host physics of the Shastry-Sutherland model. Analysis of single crystal x-ray diffraction data yields an updated crystal structure, similar to the prior report but now in space group $P4$/mbm. Magnetization and specific heat measurements reveal an antiferromagnetic transition at ${\mathrm{T}}_N=1.9\mathrm{K}$ and a large magnetic anisotropy with in-plane magnetization much larger than out-of-plane magnetization. Single crystal neutron diffraction at zero field reveals a propagation vector of $\left(\frac{1}{2}\frac{1}{2}\frac{1}{2}\right)$ for the magnetic ground state as compared to the $\left(\frac{1}{2}\frac{1}{2}0\right)$ wave vector observed in the related body-centered material $\mathrm{Ba}{\mathrm{Nd}}_2\mathrm{Zn}{\mathrm{O}}_5$. The ground state is found to be a fully compensated antiferromagnet with diffraction data well fitted within the magnetic space group $P_{\mathrm{S}}\text{−}1$ (BNS setting #2.7). The ordered moment is mostly in the basal plane with nearest neighbors forming ferromagnetic dimers, however it also has a finite out-of-plane component unlike the related easy-plane materials $\mathrm{Ba}{\mathrm{Nd}}_2\mathrm{Zn}{\mathrm{O}}_5$ and $\mathrm{Ba}{\mathrm{Nd}}_2\mathrm{Zn}{\mathrm{S}}_5$. Field-induced transitions are observed below $T_{\mathrm{N}}$ when the field is applied within the basal plane, and in-plane anisotropy of the associated critical fields is observed. The magnetization is strongly impacted by misalignment of the field away from high symmetry directions. These results suggest complex magnetic structures may arise in the field-induced states, and they highlight the need for extreme care when studying this and related Shastry-Sutherland materials.

Transient binding between associating macromolecules can cause qualitative changes to chain dynamics, including modes of conformational relaxation and diffusion, through tethering effects imparted by long-range connectivity. In this work, the role of binding on short-time segmental dynamics in associative polymer gels is investigated by neutron spin-echo (NSE) measurements on a class of model artificial coiled-coil proteins with a systematically varied architecture, probing timescales of 0.1–130 ns, and length scales close to the molecular radius of gyration. The results illustrate effects of transient cross-linking on chain dynamics on different timescales, manifested in changes in segmental relaxation behavior with variations in strand length, chain concentration, and sticker distribution (endblock- vs midblock-functionalized). In all gels, a short-time cooperative diffusion mode is seen over all wave vectors, analogous to a semidilute solution, with no transitions seen at any known structural length scale. However, the diffusion coefficients are found to decrease with increasing junction density across all gels, with the strand length and number of stickers per chain in each gel appearing to play a relatively minor role. The slowing of cooperative diffusion with junction density contrasts with classical predictions of a greater restoring force for fluctuation dissipation due to the increased elasticity, suggesting additional effects of the coiled-coil junctions such as an enhancement in local viscosity that slows dynamics. Notably, the relaxation rates for all gels can be rescaled by the interjunction spacing inferred from small-angle neutron scattering, where they collapse onto a master curve suggestive of self-similar dynamics even in networks with different strand lengths and chain architectures. On long timescales (but shorter than the junction exchange time), a slowing of network relaxation is observed, resulting in a nondecaying plateau in the spin-echo amplitude attributed to a freezing of chain dynamics due to tethering. A characteristic length scale corresponding to the extent of dynamic fluctuations is estimated for each gel, which appears to be smaller than the interjunction spacing but similar to the correlation blob size of the overlapping strands. The results indicate an important role of transient binding on molecular-scale dynamics in associative polymer gels, even on timescales shorter than the junction exchange time, in addition to its effects on long-range self-diffusion previously observed.

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.

Antiferroelectricity is a state of matter that has so far eluded a clear-cut definition. Even in the best-known material realization, ${\mathrm{PbZrO}}_3$, the physical nature of the driving force towards an antipolar order has not been settled yet. Here, by building a Landau-like continuum Hamiltonian from first principles via an exact long-wave approach, we reconcile the existing theories in terms of a single physical mechanism. In particular, we find that a formerly overlooked trilinear coupling between tilts, tilt gradients, and polarization provides a surprisingly accurate description of the energetics and structure of the antiferroelectric ground state of ${\mathrm{PbZrO}}_3$. We discuss the relevance of our findings to other ferrielectric and incommensurate polar structures that were recently observed in perovskites.

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.

Here we present $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ and $\mathrm{Eu}{\mathrm{V}}_3{\mathrm{Sb}}_4$, two compounds exhibiting slightly distorted vanadium-based kagome nets interleaved with zigzag chains of divalent ${\mathrm{Yb}}^{2+}$ and ${\mathrm{Eu}}^{2+}$ ions. Single crystal growth methods are reported alongside magnetic, electronic, and heat capacity measurements. $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ is a nonmagnetic metal with no collective phase transitions observed between 60 mK and 300 K. Conversely, $\mathrm{Eu}{\mathrm{V}}_3{\mathrm{Sb}}_4$ is a magnetic kagome metal exhibiting easy-plane ferromagneticlike order below $T_{\text{C}}=32$ K with hints of modulated spin texture under low field. With $\mathrm{Yb}{\mathrm{V}}_3{\mathrm{Sb}}_4$ and $\mathrm{Eu}{\mathrm{V}}_3{\mathrm{Sb}}_4$ we demonstrate another direction for the discovery and development of vanadium-based kagome metals while incorporating the chemical and magnetic degrees of freedom offered by a rare-earth sublattice.

The enthalpy change involved in metal oxide reduction is a key quantity in various processes related to energy conversion and storage and is of particular interest for computational prediction. Often this prediction involves the simulation of a high-temperature reduction process with a 0-K methodology like density functional theory (DFT), and it is not infrequent for the high temperature and 0-K stable crystal structures to differ. This introduces a conundrum with regard to the choice of crystal structure to utilize in the computation, with approaches in the literature varying and experimental validation remaining scarce. In this work, we address both the crystal structure conundrum and the experimental validation, and then apply the insights we gain to guide a high-throughput search for new materials for solar thermochemical water-splitting applications. By computing the $\mathrm{DFT}+U$ oxygen-vacancy formation energy ($\mathrm{\Delta }{E}_{vf}$) of a selection of $AB{\text{O}}_3$ compounds and comparing different crystal structures for each composition, we highlight the issues that arise when the structure utilized in the computation is dynamically unstable at 0 K, namely the presence of an artificial lowering of $\mathrm{\Delta }{E}_{vf}$, and the lack of convergence of $\mathrm{\Delta }{E}_{vf}$ with cell size. We solve these limitations by identifying and employing a suitable surrogate dynamically stable structure. We then validate the predictive power of our calculations against appositely generated experimental measurements of reduction enthalpy for a series of Hubbard $U$ values, finding an accuracy ranging between 0.2–0.6 eV/O. In light of such conclusions, we revise and expand a previous a high-throughput DFT study on $AB{\mathrm{O}}_3$ perovskite oxides. We provide a list of candidate STCH materials, highlight trends with redox-active cation and structural distortion, and identify ${\mathrm{Mn}}^{4+}$, ${\mathrm{Mn}}^{3+}$, and ${\mathrm{Co}}^{3+}$ as the most promising redox-active cations.

Ytterbium-doped $\mathrm{CsPb}{\mathrm{Cl}}_3$ is the leading candidate for a quantum-cutting coating on silicon solar cells to increase their efficiencies and durability by converting each incident ultraviolet and blue photon with energies $>2.5$ eV to two 1.25-eV near-infrared (NIR) photons. This approach can potentially increase silicon solar cell efficiencies above the Quessier limit. While photoluminescence quantum yields (PLQYs) approaching 200% have been demonstrated with thin films made using colloidal particle synthesis and nanocrystal dispersions, there is increased interest in physical vapor deposition as a large-area scalable method. We investigated the effect of Yb concentration and the annealing environment on the film structure, morphology, and optical properties, including the NIR PLQY. We found that subtle differences in the postdeposition annealing protocol significantly affect PLQY. Specifically, the highest PLQY ($\sim 70\%$) is achieved by annealing the films in an ${\mathrm{N}}_2$-filled glovebox first, followed by a second annealing step in air, both at $350{}^{\circ }\mathrm{C}$. X-ray photoelectron spectroscopy reveals that this approach anneals bulk defects, brings Yb to the surface, and forms a passivating oxide layer on the surface whose major component appears to be ${\mathrm{Yb}}_2{\mathrm{O}}_3$. Both surface oxidation and Yb segregation to the surface suppress grain growth during annealing. In addition, annealing only in air stops Yb segregation toward the surface. Annealing in ${\mathrm{N}}_2$ brings Yb to the surface but does not form a robust oxide. In contrast, annealing in ${\mathrm{N}}_2$, followed by annealing in air, brings Yb toward the surface and forms a passivating oxide, resulting in the highest PLQY.

Parametrized tight-binding models fit to first-principles calculations can provide an efficient and accurate quantum mechanical method for predicting properties of molecules and solids. However, well-tested parameter sets are generally only available for a limited number of atom combinations, making routine use of this method difficult. Furthermore, many previous models consider only simple two-body interactions, which limits accuracy. To tackle these challenges, we develop a density functional theory database of nearly 1 000 000 materials, which we use to fit a universal set of tight-binding parameters for 65 elements and their binary combinations. We include both two-body and three-body effective interaction terms in our model, plus self-consistent charge transfer, enabling our model to work for metallic, covalent, and ionic bonds with the same parameter set. To ensure predictive power, we adopt a learning framework where we repeatedly test the model on new low-energy crystal structures and then add them to the fitting data set, iterating until predictions improve. We distribute the materials database and tools developed in this paper publicly.

The electrostatic self-assembly of charged Brownian objects typically occurs in cases of short-range interactions. The objects form Coulombic materials that are close-packed and have long-range order. Here, we present a system in which two kinds of non-Brownian millimeter-sized beads tribocharge differently, experience long-range electrostatic interactions, and still form ordered two-dimensional structures. We provide a complete characterization of the kinetics of formation of these materials, as the total number of beads is held constant and the relative number of beads that tribocharge negatively or positively is modified. We agitate the beads by shaking the dish in which they are contained. We show that the beads commonly adopt a transient structure that we call a rosette. A rosette consists of a central bead surrounded by six close-packed neighbors of a different kind. The symmetry of the final structure depends on the relative number of negatively and positively charged beads, and it is not necessarily the same as that of the transient structure. Our results bear important implications in the de novo design of Coulombic materials given our ability to isolate transient structures, identify the moment of their appearance, and quantify the impact of agitation, tribocharging, and Coulombic energy minimization on their persistence.