NbN films are grown on $c$-plane sapphire substrates by molecular beam epitaxy. The structural and superconducting properties of the films are characterized to demonstrate that growth parameters such as substrate temperature and active nitrogen flux affect the structural phase of films, and thereby the superconducting critical temperature. Four phases of NbN are identified for films grown in different conditions. We demonstrate that atomically flat and highly crystalline $\beta \text{−}{\text{Nb}}_2\text{N}$ films can be grown at substrate temperatures of ${1100}^{\circ }\mathrm{C}$ or higher, and that the superconducting critical temperature of phase-pure $\beta \text{−}{\text{Nb}}_2\text{N}$ films is $0.35<T_c<0.6$ K for films grown at different substrate temperatures.

The athermal irradiation-induced swelling and creep in iron under the influence of external uniaxial stress were investigated through atomic scale simulations using the creation-relaxation algorithm. The defect relaxation volume density tensors (or eigenstrains) were evaluated as a function of external uniaxial stress. When the dose exceeded the level at which isolated defects were formed, interstitial-type defect clusters were formed with polarization, resulting in crystal growth in the direction where tensile stress was applied, and growth in the other two perpendicular directions when compressive stress was applied. The concentration of vacancies, isolated self-interstitial atoms, Laves phases clusters, and dislocations in the microstructure were largely unaffected by external stress up to $\pm 1$ GPa. Biased crystal growth was primarily attributed to the anisotropic formation of new lattice planes through the coalescence of interstitial defect clusters, leading to plastic deformation depending on the direction and magnitude of the external stress.

CdO has been shown to achieve a high electron concentration N $(>{10}^{21}\mathrm{c}{\mathrm{m}}^{-3})$ and at the same time a high mobility μ $(>100\mathrm{c}{\mathrm{m}}^2/\mathrm{V}\mathrm{s})$ when doped with conventional shallow dopants (In or Ga), and consequently making it a transparent conducting oxide with very low resistivity $\rho <{10}^{-4}\mathrm{\Omega }\mathrm{cm}$. In this work, the properties of CdO thin films doped with a series of transition metal elements (CdO:TM) with partially filled $3d$ and $4d$ shells, including Sc, Ti, V, Cr, Fe, Y, Mo, and W, were investigated. We find that doping with these TM elements can effectively increase the N in CdO to a maximum N $\left(N_{\max }\right)$ of $\sim (7–12)\times {10}^{20}\mathrm{c}{\mathrm{m}}^{-3}$ with a dopant concentration $x_{\max }$ of 4–7 %. However, unlike CdO:In, the μ of CdO:TM films drops rapidly from $>100$ to $<10\mathrm{c}{\mathrm{m}}^2/\mathrm{Vs}$ as the dopant concentration $x$ increases, so that they can only achieve a minimum $\rho$ of $\sim (1–2)\times {10}^{-4}\mathrm{\Omega }\mathrm{cm}$, $\sim$ a factor of 2–3 higher than that in CdO:In. As a result, free-carrier absorption and plasma reflection effects limit their optical transparency to $<1200$ nm. For most $3d$ TM dopants, a qualitatively higher $d$-donor level $E_{d,\mathrm{donor}}$ gives rise to higher $E_{F,\max }$ or a higher $N_{\max }$. Although at low $x$, the optical band gap $E_{\mathrm{opt}}$ of CdO:TM follows the calculated values due to free-carrier effects, as $x$ increases, $E_{\mathrm{opt}}$ values are significantly higher than the calculated values. This is believed to be an effect of the anticrossing interaction of the localized $d$-levels and the extended CdO conduction-band (CB) states, giving rise to a lower occupied $E_{\text{–}}$ and an upper unoccupied $E_{+}$ subband. The restructured CBs have much flatter dispersion, which also results in a much higher effective mass $m_e^{*}$, hence it can also explain the much lower μ of CdO:TM films with high N.

We report on the magnetic and electrical properties of a ${\left({\mathrm{Mn}}_3\mathrm{Sn}\right)}_2$ triangular network kagome structured high quality Ho substituted ${\mathrm{ErMn}}_6{\mathrm{Sn}}_6$ single-crystal sample by magnetotransport measurements. ${\mathrm{Er}}_{0.5}{\mathrm{Ho}}_{0.5}{\mathrm{Mn}}_6{\mathrm{Sn}}_6$ orders antiferromagnetically at Néel temperature $T_{\mathrm{N}}\sim 350$ K followed by a ferrimagnetic (FiM) transition at $T_{\mathrm{C}}\sim 114$ K and spin-orientation transition at $T_{\mathrm{t}}\sim 20$ K. The field manifestations of these magnetic phases in the $ab$-basal plane and along the $c$ axis are illustrated through temperature-field T-H phase diagrams. In $H\parallel c$, narrow hysteresis between spin reorientation and field-induced FiM phases below $T_{\mathrm{t}}$, enhanced/strengthened FiM phase below $T_{\mathrm{C}}$ and stemming of FiM phase out of strongly coexisting antiferromagnetic and FiM phases below $T_{\mathrm{N}}$ through a non-meta-magnetic transition are confirmed to arise from strong $R$-Mn sublattices interaction. In contrast, in the $H\parallel ab$ plane, between $T_{\mathrm{N}}$ and $T_{\mathrm{C}}$, individually contributing $R$-Mn sublattices with weak antiferromagnetic interactions undergo a field-induced spin-flop quasi metamagnetic transition to FiM state. The temperature-dependent electrical resistivity suggests metallic nature with Fermi liquid behavior at low temperatures. Essentially, the current study stimulates interest to investigate the magnetic and electrical properties of mixed rare-earth layered kagome magnetic metals for possible novel and exotic behavior.

We present a comprehensive experimental and computational study on $A$-site ordered perovskite oxides ${\mathrm{YCu}}_3{\mathrm{Co}}_4{\mathrm{O}}_{12}, {\mathrm{LaCu}}_3{\mathrm{Co}}_4{\mathrm{O}}_{12}$, and ${\mathrm{BiCu}}_3{\mathrm{Co}}_4{\mathrm{O}}_{12}$ including synthesis, transport, and magnetic characterization, high-pressure application, $K$- and $L$-edge x-ray absorption spectroscopy (XAS), Co $2p$ core-level x-ray photoemission spectroscopy and density-functional theory (DFT) calculations combined with dynamical mean-field theory (DMFT) and $+U$ scheme. An insulating behavior with a valence state of $A^{3+}{\mathrm{Cu}}_3^{\sim 3+}{\mathrm{Co}}_4^{\sim 3+}{\mathrm{O}}_{12}^{2-}$ is found for the three compounds at ambient and high-pressure conditions (up to $\sim 55$ GPa). A DFT calculation for ${\mathrm{YCu}}_3{\mathrm{Co}}_4{\mathrm{O}}_{12}$ uncovers the energetics of the Cu–O and Co–O bonding formation and crystal-field splitting, leading to a narrow-gap electronic structure with a hybrid orbital and element character near the Fermi energy. The stable low-spin configuration of the Co ion is studied in comparison to a canonical perovskite cobaltite ${\mathrm{LaCoO}}_3$. A $\mathrm{DFT}+\mathrm{DMFT}$ analysis of the Cu spin-correlation function indicates that the Zhang-Rice singlet description for the ${\mathrm{CuO}}_4$ plaquette is valid, while a hybridization with the Co $3d$ orbitals also contributes to the Cu spin screening. The presence of the hybridization between the Co and Cu orbitals is shown by the $\mathrm{DFT}+\mathrm{DMFT}$ analysis for the Co $L_{2,3}$ XAS experimental spectra that exhibit unusual broad line shape. An increasing behavior of electrical resistance at elevated pressures is observed in all compounds and is interpreted based on a $\mathrm{DFT}+U$ simulation.

A first-principles method is presented to calculate the bulk modulus and its pressure derivative of a monocrystal in an arbitrary stressed state. The bulk modulus is obtained from the compliance Birch tensor, whereas its pressure derivative is calculated numerically within a nonlinear elasticity theory framework by using second- and third-order elastic constants obtained from density functional theory calculations. To demonstrate validity, generality, and accuracy, this approach is used to calculate bulk modulus and its pressure derivative of silicon and $\alpha$-quartz over finite intervals of the hydrostatic pressure, and of sodium chloride at zero hydrostatic pressure and incremental differential stress. To demonstrate impact, the method is also used to elucidate the unusual elastic softening exhibited by monoclinic hafnia under hydrostatic compression.

Metal monochalcogenides $(MX,$ $M=\mathrm{Ga}, \mathrm{In}; X=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$ offer a large variety of electronic properties depending on chemical composition, number of layers, and stacking order. InTe material has a one-dimensional chain structure, from which intriguing properties arise. Precise experimental determination of the electronic structure of InTe is needed for a better understanding of potential properties and device applications. In this study, by combining angle-resolved photoemission spectroscopy and density functional theory calculations, we demonstrate the stability of InTe in the tetragonal crystal structure, with a semiconducting character and an intrinsic $p$-type doping. The valence band maximum results in being located at the high symmetric $M$ point with a high elliptical valley, manifesting a large effective mass close to the Fermi level. The longitudinal and transverse effective masses of the $M$ valley are measured as 0.2 $m_0$ and 2 $m_0$, respectively. More specifically, we observe that the effective mass of the hole carriers is about ten times larger along the chain direction compared to the perpendicular one. Remarkably, the in-plane anisotropy of effective mass from the experiment and in theoretical calculations are in good agreement. These observations indicate a highly anisotropic character of the electronic band structure, making InTe of interest for electronic and thermoelectric applications.

Elastic moduli are among the most fundamental and important properties of solid materials, which is why they are routinely characterized in both experiments and simulations. While conceptually simple, the treatment of elastic coefficients is complicated by two factors not yet having been concurrently discussed: finite-strain and nonaffine, internal displacements. Here, we revisit the theory behind zero-temperature, finite-strain elastic moduli and extend it to explicitly consider nonaffine displacements. We further present analytical expressions for second-order derivatives of the potential energy for two-body and generic many-body interatomic potentials, such as cluster and empirical bond-order potentials. Specifically, we revisit the elastic constants of silicon, silicon carbide, and silicon dioxide under hydrostatic compression and dilatation. Based on existing and recent results, we outline the effect of multiaxial stress states as opposed to volumetric deformation on the limits of stability of their crystalline lattices.

Topological materials are of high interest due to the promise to obtain low power and fast memory devices based on efficient spin-orbit torque switching or spin-orbit magnetic state read-out. In particular, sputtered polycrystalline ${\mathrm{Bi}}_x{\mathrm{Se}}_{1-x}$ is one of the materials with more potential for this purpose since it is relatively easy to fabricate and has been reported to have a very high spin Hall angle. We study the spin-to-charge conversion in ${\mathrm{Bi}}_x{\mathrm{Se}}_{1-x}$ using the spin-pumping technique coming from the ferromagnetic resonance in a contiguous permalloy thin film. We put a special emphasis on the interfacial properties of the system. Our results show that the spin Hall angle of ${\mathrm{Bi}}_x{\mathrm{Se}}_{1-x}$ has the same sign as the one of Pt. The charge current arising from the spin-to-charge conversion is, in contrast, lower than Pt by more than one order of magnitude. We ascribe this to the interdiffusion of ${\mathrm{Bi}}_x{\mathrm{Se}}_{1-x}$ and permalloy and the changes in chemical composition produced by this effect, which is an intrinsic characteristic of the system and is not considered in many other studies.

The bulk photovoltaic effect (BPVE) of two-dimensional (2D) polar crystals has received considerable attention in recent years due to its potential applications in high-efficiency energy harvesting. Here, we propose a class of pentagonal chain-based 2D pyroelectric $\mathrm{Cu}X{X}^{\prime }Y$ $(X, X^{\prime }=\mathrm{S},\mathrm{Se},\mathrm{Te};Y=\mathrm{Cl},\mathrm{Br},\mathrm{I})$ monolayers with in-plane polarization via a high-throughput screening method. By using first-principles calculations, we show that compared to the 2D nonpolar $\mathrm{Cu}{X}_{2}Y$ compounds, the alignment between the averaged transition intensity and shift vector of the polar $\mathrm{Cu}X{X}^{\prime }Y$ materials gives rise to the enhanced shift current responses reaching up to $500\mu \mathrm{A}{\mathrm{V}}^{–2}$ in the visible range, and the magnitude of the shift current is positively related to the polarity of the $X-X^{\prime }$ bond. More importantly, we find that all the studied materials have their exfoliation energies comparable to those of existing 2D materials, implying the feasibility for preparing $\mathrm{Cu}X{X}^{\prime }Y$ monolayers by mechanical exfoliation. Our study demonstrates the potential of utilizing pentagonal chains in the design of polar materials with strong BPVE responses.

Characterizing the fundamental micromechanisms activated during plastic deformation is critical to explain the macroscopic shock response of materials and develop accurate material models. In this paper, we investigate the orientation dependence, and the mediated slip and twin systems on $\left[100\right]$ and $\left[111\right]$ bcc molybdenum single crystals shock compressed up to 18 GPa with real-time Laue x-ray diffraction measurements. We report that dislocation slip along the $\left\{110\right\}\langle 111\rangle$ and $\left\{112\right\}\langle 111\rangle$ systems is the governing deformation mechanism during compression with negligible anisotropy observed at the Hugoniot state. We provide real-time evidence that molybdenum undergoes deformation twinning along $\left\{11\overline{\phantom{b}2}\right\}\langle 111\rangle$ during shock release.

Molecular dynamics simulations for dislocation motion are conducted in a body centered cubic TaCrVW multiprincipal element alloy with different chemical randomness based on a machine learning potential. The simulated critical stress for dislocation motion in samples with an increasing level of randomness is analyzed in terms of three contributions: (1) Peierls stress (from 438 to 431 MPa), (2) strengthening from the average fault energy (from 261 MPa to near zero), and (3) strengthening due to local fluctuations of fault energy from the average value (from 394 to 566 MPa). As the alloy randomness increases, the Peierls stress as predicted from lattice distortion is rather invariant within the range studied, while there is a clear decreasing trend of the average fault energy and hence the associated strengthening. There is an increasing trend of strength contribution (3) as the alloy randomness increases, which offsets the decreasing trend of strength contribution (2). The overall strength of the TaCrVW alloy is therefore rather invariant within the range 964–1259 MPa with different randomness. The present work elucidates the physical basis of strength in the studied TaCrVW alloy.

Superconducting infinite-layer ${\mathrm{Sr}}_{1-x}{\mathrm{Eu}}_x\mathrm{Cu}{\mathrm{O}}_2$ films at optimal doping ($x\sim 0.15$) have been epitaxially grown on $\mathrm{SrTi}{\mathrm{O}}_3$(001) substrates with oxide molecular beam epitaxy. By combining x-ray diffraction and transport measurements, we have established a narrow window of growth conditions [i.e., ozone pressure, substrate temperature, ($\mathrm{Sr}+\mathrm{Eu}$)/Cu flux ratio, and postannealing] in which the superconducting infinite-layer structure can be readily achieved while eliminating any unwanted competing phases. A smaller out-of-plane lattice constant ($c<3.42\AA$) is found to be crucial to prompt superconductivity in the ${\mathrm{Sr}}_{1-x}{\mathrm{Eu}}_x\mathrm{Cu}{\mathrm{O}}_2$ films. Thickness-dependent electrical resistivity measurements reveal superconductivity even when the film thickness is thinned down to 5 nm. Furthermore, the superconducting state of the epitaxial infinite-layer films remains remarkably stable against air exposure, providing an ideal platform to explore the high-temperature superconductivity and unusual properties in cuprates.

We present the results of first-principle calculations using the Vienna Ab initio Simulation Package (vasp) for a class of organometallics labeled ${\mathit{TM}}_3{\mathrm{C}}_6{\mathrm{O}}_6$ ($\mathit{TM}=\mathrm{Sc}$, Ti, V, Cr, Fe, Co, Ni, and Cu) in the form of planar, two-dimensional, periodic freestanding layers. These materials, which can be produced by on-surface coordination on metallic surfaces, have a kagome lattice of $\mathit{TM}$ ions. Calculating the structural properties, we show that all considered materials have local magnetic moments in the ground state, but four of them (with Fe, Co, Ni, and Cu) show spin-crossover behavior or switch between magnetic and nonmagnetic states by changing the lattice constant, which could be valuable for possible epitaxy routes on various substrates. Surprisingly, we find a very large richness of electronic and magnetic properties, qualifying these materials as highly promising metal-organic topological quantum materials. We find semiconductors with nearest-neighbor ferromagnetic (FM) or antiferromagnetic (AFM) couplings for V, and Sc, Ti, and Cr, respectively, being of potential interest to study spin ice or spin liquids on the 2D kagome lattice. Other $\mathit{TM}$ ion systems combine AFM couplings with metallic behavior (Fe and Ni) or are ferromagnetic kagome metals like ${\mathrm{Cu}}_3{\mathrm{C}}_6{\mathrm{O}}_6$ with band crossings at the Fermi surface. For the latter compound, the spin-orbit coupling is shown to be responsible for small gaps which makes them a candidate material to observe the quantum anomalous Hall effect.

Antiferromagnetic order, being a ground state of a number of exotic quantum materials, is of immense interest both from the fundamental physics perspective and for driving potential technological applications. For a complete understanding of antiferromagnetism in materials, nanoscale visualization of antiferromagnetic domains, domain walls, and their robustness to external perturbations is highly desirable. Here, we synthesize antiferromagnetic FeTe thin films using molecular-beam epitaxy. We visualize local antiferromagnetic ordering and domain formation using spin-polarized scanning tunneling microscopy. From the atomically resolved scanning tunneling microscopy topographs, we calculate local structural distortions to find a high correlation with the distribution of the antiferromagnetic order. This is consistent with the monoclinic structure in the antiferromagnetic state. Interestingly, we observe a substantial domain-wall change by small temperature variations, unexpected for the low-temperature changes used compared to the much higher antiferromagnetic ordering temperature of FeTe. This is in contrast to electronic nematic domains in the cousin FeSe multilayer films, where we find no electronic or structural change within the same temperature range. Our experiments provide the atomic-scale imaging of perturbation-driven magnetic domain evolution simultaneous with the ensuing structural response of the system. The results reveal surprising thermally driven modulations of antiferromagnetic domains in FeTe thin films well below the Néel temperature.

The kagome material ${A\mathrm{V}}_3{\mathrm{Sb}}_5$ $(A=\mathrm{K}, \mathrm{Rb}, \mathrm{Cs})$ with geometry frustration hosts nontrivial topological electronic structures, electronic nematicity, the charge density wave (CDW), and superconductivity, providing an ideal platform to study the interplay between these phases. Specifically, in pressurized or substituted ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, the relationship between CDW and superconductivity is unusual and remains to be fully understood. Recently, coexisting and competing $2\times 2\times 4$ and $2\times 2\times 2$ CDW phases were discovered in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$. To investigate the evolution of the CDW phases with the substitution of V atoms, we performed x-ray diffraction experiments on ${\mathrm{Cs}(\mathrm{V}}_{1-x}{\mathrm{Ta}}_x{)}_3{\mathrm{Sb}}_5$ and ${\mathrm{Cs}(\mathrm{V}}_{1-x}{\mathrm{Nb}}_x{)}_3{\mathrm{Sb}}_5$. Our results indicate that in all substituted samples, the discrete CDW reflection points in pristine ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ change to rodlike structures along the $c^{★}$ direction. This suggests that the long-ranged three-dimensional CDW becomes quasi-two-dimensional by the substitution of V by Ta/Nb. Moreover, our temperature-dependent measurements show that there is no hysteresis behavior of CDW signals, indicating that even a slight substitution of Nb or Ta as low as 0.021 and 0.04, respectively, can easily suppress the $2\times 2\times 4$ CDW phase. These findings uncover the CDW evolution upon substitution of V atoms in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, providing insights into the microscopic mechanism of CDW and helping to understand the interplay between intertwined phases and superconductivity.

Alternative halide perovskites with characteristics similar to $\mathrm{CsPb}{X}_3$ perovskites have sparked interest over the past decade due to lead-induced toxicity and material instability. Here we utilize the technique of cation transmutation to create inorganic Pb-free halide double perovskites ${\mathrm{Cs}}_{2}M\mathrm{Sb}{X}_6$ ($M$ = Cu, Ag, Na, K, Rb, Cs, and $X=\mathrm{Cl}$, Br) and comprehensively study them from the perspective of their potential use in optoelectronic devices. Our first-principles density-functional-theory–based calculations reveal that all of these materials exhibit a cubic lattice with excellent phase stability against decomposition. Further, these systems are found to be mechanically stable and ductile in nature, with some amount of elastic anisotropy, which makes them an excellent choice for flexible materials. These materials are also found to possess interesting electronic and optical properties. While upon having $M$ = Cu, Ag, Na in ${\mathrm{Cs}}_{2}M\mathrm{Sb}{X}_6$, the system possesses an indirect band gap with a value ranging between $\sim 1.19\text{and}4.82$ eV, a transition to direct band gap with values between $\sim 4.50\text{and}5.22$ eV occurs on having heavier metals with $M$ = K, Rb, Cs. In accordance with the band gap, most of the systems are also found to exhibit excellent absorption capabilities from visible to near-ultraviolet light. Furthermore, investigations of transport and excitonic properties indicate low effective mass, excellent charge-carrier mobility ($\sim 10–{10}^3{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$), low to moderate exciton binding energy, and longer to shorter exciton lifetimes for most of the examined materials, suggesting higher quantum yield and conversion efficiency of the examined materials. Overall, our study suggests that with atomic transmutation in ${\mathrm{Cs}}_{2}M\mathrm{Sb}{X}_6$, stable and flexible lead-free halide double perovskites with superior and tunable optoelectronic properties can be achieved, which makes these materials excellent candidates for flexible optoelectronic devices, in general, and photovoltaics in particular.

Glass-ceramics feature excellent mechanical properties but tend to lack transparency due to the presence of large crystals with a different refractive index from the matrix glass. Here, we investigate the relationship between the heterogeneous microstructure, mechanical properties (hardness, crack resistance, and fracture toughness), and transparency in ${\mathrm{Na}}_2\mathrm{O}\text{–}{\mathrm{P}}_2{\mathrm{O}}_5\text{–}\mathrm{Si}{\mathrm{O}}_2$ glass-ceramics. The mechanical properties are determined by the combination of crystal type, content, and size, as well as the remaining glass-matrix structure. The crystal fraction and size increase upon heat treatment, whereas the network connectivity of the residual glass-matrix phase decreases. These observed changes have opposite effects on crack resistance and fracture toughness. Changes in crystallization behavior have a more significant effect on crack resistance relative to that on fracture toughness, while changes in crystal size have a more pronounced effect on fracture toughness. The glass-ceramic samples feature excellent transmittance and reach a maximum fracture toughness of $1.1\mathrm{MPa}{\mathrm{m}}^{0.5}$.

Motivated by the recent reports of pressure-induced engaging phenomena in van der Waals antiferromagnetic late transition metal phosphorous trisulfide compounds such as ${\mathrm{FePS}}_3, {\mathrm{NiPS}}_3$, and ${\mathrm{MnPS}}_3$, we explore the effect of pressure in an early-transition-metal-based compound, ${\mathrm{CrPS}}_3$. Our study, combining an evolutionary algorithm and first-principles calculations, establishes the existence of a pressure-induced insulator-metal transition in ${\mathrm{CrPS}}_3$ akin to that in ${\mathrm{FePS}}_3, {\mathrm{NiPS}}_3$, and ${\mathrm{MnPS}}_3$. However, while for late-transition-metal-based compounds such as ${\mathrm{FePS}}_3$ and ${\mathrm{MnPS}}_3$ the application of pressure causes a spin-state transition, in an early-transition-metal-based system it causes a valence transition, driven by the destabilization of P-P dimerization. The weakening of metal-sulfur covalency in early transition metals compared with late transition metals is found to be the origin of this contrasting behavior. The high-pressure phase is predicted to exhibit easy-axis, in-plane ferromagnetism, opening the possibility of realizing two-dimensional ferromagnetism in this class of compounds.