Recently the kagome compounds have inspired enormous interest and made some great progress such as in the field of superconductivity and topology. Here we predict a different kagome magnesium triboride $\left(\mathrm{Mg}{\mathrm{B}}_3\right)$ superconductor with a calculated $T_c\sim 12.2\mathrm{K}$ and $T_c\sim 15.4$ K by external stress, the potentially highest among the reported diverse kagome-type superconductors. We reveal its various exotic physical properties including the van Hove singularity, flat-band, multiple Dirac points, and nontrivial topology. The system can be described by a two-band model with highly anisotropic superconducting gaps on Fermi surfaces. Its topological and nodal superconducting nature is unveiled by a recently developed symmetry indicators method. Our results suggest that $\mathrm{Mg}{\mathrm{B}}_3$ can be a new platform to study exotic physics in the kagome structure, and pave a way to seek for more superconductors and topological materials with $X{Y}_3\text{−}\mathrm{type}$ kagome lattice.

The suppressed diffusion of Al in ${\gamma }^{\prime }$ precipitates of Co-based superalloys is suspected to be one of the reasons for the selective formation of alumina during the early-stage oxidation above $900{}^{\circ }\mathrm{C}$. In order to scrutinize this assumption, the diffusion properties of Al, Co, and W in a prototype structure of the ${\gamma }^{\prime }$ phase, $\mathrm{L}{1}_2-{\mathrm{Co}}_3(\mathrm{Al},\mathrm{W})$, are investigated in a combined density functional theory (DFT) and kinetic Monte Carlo (KMC) study. A particular challenge in simulating diffusion in this ordered phase is the representation and evaluation of numerous migration pathways on the $\mathrm{L}{1}_2$ sublattices. With specified diffusion models for the $\mathrm{L}{1}_2$ structure and random solid solution ($\gamma$ phase), our KMC results reveal that Al diffusivity in the $\gamma$ phase with the same stoichiometric composition is more than two orders of magnitude higher than in the $\mathrm{L}{1}_2$ ordered ${\gamma }^{\prime }$ phase at $900{}^{\circ }\mathrm{C}$. Furthermore, in our rapid thermal exposure experiments for a model Co-based superalloy, the formation of alumina nuclei is observed preferentially in the $\gamma$ channels while the Al content is comparable in both channels and precipitates before oxidation. Combining these insights from experiment and simulation, the sluggish diffusion of Al in ${\gamma }^{\prime }$ appears to be a key factor in the selective formation of alumina observed in these systems.

In this work, we form alloyed transition-metal dichalcogenides (TMDs), ${\mathrm{Mo}}_{1–x}{\mathrm{W}}_x{\mathrm{Se}}_2$, through a hydrothermal synthesis procedure. Due to the identical effective ionic radius of the cations, the common-anionic alloys did not experience any lattice strain. A complete series of the common-anionic TMD alloys could thereby be synthesized; their nanosheets were formed by a liquid exfoliation method. The electronic properties of the alloyed nanosheets in their monolayer, bilayer, and trilayer forms were recorded separately through scanning tunneling spectroscopy (STS) in an extremely localized manner. From the STS studies, which have a correspondence to the density of states of the semiconductors, we have deliberated on their electronic properties and commented on the band edges of the nanosheets in the alloy series. The transport gap of the alloys in their monolayer, bilayer, and trilayer forms exhibited band-gap bowing, and also a layer-number-dependent bowing coefficient. That is, the bowing phenomenon interestingly occurred only in the few-layered TMD alloys and diminished to finally vanish in thicker nanosheets. The conduction band has been found to be responsible for such a nonlinear behavior of the transport gap; the results could be explained in terms of the molecular orbitals which form the band. The results have established a coherent description of the band-gap tuning in atomically thin 2D TMD alloys.

High-quality, ultrathin superconducting films are required for advanced devices such as hot-electron bolometers, superconducting nanowire single-photon detectors, and quantum applications. Using hybrid physical-chemical vapor deposition, we show that ${\mathrm{MgB}}_2$ films as thin as 4 nm can be fabricated on the carbon-terminated $6H$-SiC (0001) surface with a superconducting transition temperature above 33 K and a rms roughness of 0.7 nm. Remarkably, the film quality is a function of the SiC surface termination, with the C-terminated surface preferred to the Si-terminated surface. To understand the ${\mathrm{MgB}}_2$ thin film/SiC substrate interactions giving rise to this difference, we characterized the interfacial structures using Rutherford backscattering spectroscopy/channeling, electron-energy-loss spectroscopy, and x-ray photoemission spectroscopy. The ${\mathrm{MgB}}_2$/SiC interface structure is complex and different for the two terminations. Both terminations incorporate substantial unintentional oxide layers influencing ${\mathrm{MgB}}_2$ growth and morphology, but with a different extent, intermixing, and interface chemistry. In this paper, we report measurements of transport, resistivity, and the critical superconducting temperature of ${\mathrm{MgB}}_2$/SiC that are different for the two terminations, and they link interfacial structure variations to observed differences. The result shows that the C face of SiC is a preferred substrate for the deposition of ultrathin superconducting ${\mathrm{MgB}}_2$ films.

${\mathrm{Co}}_2{\mathrm{Mn}}_2\mathrm{C}$ thin films were synthesized via vacuum carburization of the host CoMn alloy films based on a conventional gas-solid reaction to demonstrate the effect of C, a common light element, on the magnetic and spintronic materials. The crystal structure transitioned from the disordered face-centered-cubic CoMn to the $L{1}_0$-like ${\mathrm{Co}}_2{\mathrm{Mn}}_2\mathrm{C}$, for which the lattice constant increased from 0.356 to 0.378 nm. The C $1s$ x-ray photoemission spectra of the ${\mathrm{Co}}_2{\mathrm{Mn}}_2\mathrm{C}$ film indicated hybridization in C-Co and C-Mn and a homogeneous concentration of C in the film. The enhancement of both the saturation magnetization and the anomalous Hall conductivity (${\sigma }_{xy}$) was induced by C, attributing to the magnetic transition to the ferrimagnetic spin order. The surface flatness and high ${\sigma }_{xy}$ are promising characteristics for spintronic applications such as the spin-anomalous Hall effect. The atom- and spin-resolved density of states (DOS) via first-principles calculations revealed that face-centered Mn(II) and Co could be significantly influenced by C because of p-d hybridization, resulting in enhanced spin polarization of the DOS at the Fermi level of ∼0.82. These results demonstrate that the use of C could be an essential way to boost material properties in the future.

The proton conductors barium zirconate (${\mathrm{BaZrO}}_3$, or BZO), barium cerate (${\mathrm{BaCeO}}_3$, or BCO), and their alloys have attracted considerable interest as solid-state electrolytes in solid-oxide fuel and electrolysis cells. However, the reasons for their non-negligible electrical conductivity, which can limit their performance, are not fully understood. To address that question, we use first-principles calculations based on density functional theory to study the properties of hole and electron polarons in BZO and BCO. We confirm that hole polarons form in both materials, slightly more favorably in BCO. Electron polarons, on the other hand, are stable only in BCO and in Ce-containing alloys; in pure BZO, electron polaron states are unfavorable relative to free carriers, though they become accessible when Ce impurities are introduced. In general, doped BZO and BCO will have negligible electron concentrations, but larger concentrations of holes and hole polarons may be present. Avoiding extreme O-rich conditions and limiting dopant concentrations are key strategies for reducing significant $p$-type electrical leakage. Our results provide physical insights into the different electronic behaviors of BZO and BCO, which can be used to optimize their performance as pure ionic conductors.

${\mathrm{CeCd}}_3{\mathrm{P}}_3$ and ${\mathrm{CeCd}}_3{\mathrm{As}}_3$ compounds adopt the hexagonal ${\mathrm{ScAl}}_3{\mathrm{C}}_3$-type structure, where magnetic Ce ions on a triangular lattice order antiferromagnetically below $T_{\text{N}}\sim 0.42$ K. Their crystalline electric field (CEF) level scheme has been determined by fitting magnetic susceptibility curves, magnetization isotherms, and Schottky anomalies in specific heat. The calculated results, incorporating the CEF excitation, Zeeman splitting, and molecular field, are in good agreement with the experimental data. The CEF model, with ${\mathrm{Ce}}^{3+}$ ions in a trigonal symmetry, explains the strong easy-plane magnetic anisotropy that has been observed in this family of materials. A detailed examination of the CEF parameters suggests that the fourth-order CEF parameter $B_4^3$ is responsible for the strong CEF-induced magnetocrystalline anisotropy, with a large $ab$-plane moment and a small $c$-axis moment. The reliability of our CEF analysis is assessed by comparing the current study with earlier reports of ${\mathrm{CeCd}}_3{\mathrm{As}}_3$. For both ${\mathrm{CeCd}}_3{X}_3$ ($X=\mathrm{P}$ and As) compounds, less than 40% of $Rln\left(2\right)$ magnetic entropy is recovered by $T_{\text{N}}$ and full $Rln\left(2\right)$ entropy is achieved at the Weiss temperature ${\theta }_p$. Although the observed magnetic entropy is reminiscent of delocalized $4f$-electron magnetism with significant Kondo screening, the electrical resistivity of these compounds follows a typical metallic behavior. Measurements of thermoelectric power further validate the absence of a Kondo contribution in ${\mathrm{CeCd}}_3{X}_3$.

Three-dimensional discrete dislocation dynamics simulations are used to study strain-controlled plastic deformation of face-centered cubic aluminium single crystals. After describing the rate and size dependence of the average stress-strain curves, we study the power-law distributed strain bursts and find a universal power-law exponent $\tau \approx 1.0$ for all imposed strain rates. This is then followed by the characterization of the average avalanche shapes which reveals the two key physical regimes in dislocation plasticity dominant at small and large strain rates, respectively. We discuss the dependence on the loading rate and compare our observations with previous studies of strain-controlled two-dimensional systems of discrete dislocations as well as of quasistatic stress-controlled loading of aluminium single crystals.

One of the main challenges for the synthesis and application of the promising hard-magnetic compound $\mathrm{Ce}{\mathrm{Fe}}_{11}\mathrm{Ti}$ is the formation of Laves phases that are detrimental for their thermodynamic stability and magnetic properties. In this paper, we present an ab initio based approach to modify the stability of these phases in the Ce-Fe-Ti system by additions of $3d$ and $4d$ elements. We combine highly accurate free-energy calculations with an efficient screening technique to determine the critical annealing temperature for the formation of $\mathrm{Ce(Fe,X)}{}_{11}\mathrm{Ti}$. The central findings are the dominant role of the formation enthalpy at $T=0$ K on chemical trends and the major relevance of partial chemical decompositions. Based on these insights, promising transition metals to promote the stability of the hard-magnetic phase, such as Zn and Tc, were predicted. The comparison with suction casting and reactive crucible melting experiments for Ce-Fe-Ti-X (X = Cu, Ga, Co, and Cr) highlights the relevance of additional phases and quaternary elements.

Ge-rich hexagonal SiGe alloys have recently emerged as new direct-gap semiconductors with unprecedented potential for integration of photonics on silicon. We present a comprehensive first-principles investigation of optical, transport, and thermoelectric properties of pure and doped hexagonal ${\mathrm{Si}}_x{\mathrm{Ge}}_{1-x}$ alloys based on density-functional theory calculations, the Boltzmann transport equation, and the generalized quasichemical approximation to obtain alloy averages of electronic properties. At low temperatures, phase decomposition into the hexagonal elementary crystals is thermodynamically favored, but around and above room temperature random alloys are predicted to be stable. While hexagonal Si has an indirect band gap, the gap of hexagonal Ge is direct with very weak optical transitions at the absorption edge. The alloy band gap remains direct for a Si content below 45% and the oscillator strength of the lowest optical transitions is efficiently enhanced by alloying. The optical spectra show clear trends and both absorption edges and prominent peaks can be tuned with composition. The dependence of transport coefficients on carrier concentration and temperature is similar in cubic and hexagonal alloys. However, the latter display an anisotropic response due to the reduced hexagonal symmetry. In particular, the transport mass exhibits a significant directional dependence. Seebeck coefficients and thermoelectric power factors of $n$-doped alloys show nonmonotonous variations with the Si content independently of temperature.

Transition-metal halides can host a large variety of novel phenomena, such as magnetism in the monolayer limit, quantum spin liquid and spiral spin liquid states, topological magnons, and chiral phonons. Sizable high-quality single crystals are necessary for investigations of magnetic and lattice excitations by, for example, inelastic neutron scattering. In this paper, we review a less well-known vapor transport technique, self-selecting vapor growth, and report our growths of transition-metal halides using this technique. We report the growth and characterizations of sizable single crystals of $\alpha \text{−}{\mathrm{RuCl}}_3, {\mathrm{CrCl}}_3, {\mathrm{Ru}}_{1-x}{\mathrm{Cr}}_x{\mathrm{Cl}}_3$, and ${\mathrm{CrBr}}_3$. In order to expedite the conversion of starting powder to single crystals, we modified the technique by cooling the growth ampoule through an appropriate temperature range. Our work shows that the self-selecting vapor transport technique can provide large single crystals of transition-metal halides, demonstrating its potential for providing high-quality single crystals of quantum materials.

Topological insulators in which the Fermi level is in the bulk gap and intersects only a topological surface state (the Dirac cone) are of special interest in the current research. In the last decades, a fine-tuning of the chemical composition of topological insulators has been carefully explored in order to control the Fermi level position with respect to the Dirac surface state. Taking the ${\mathrm{SnBi}}_2{\mathrm{Te}}_4$ crystal as a case study, we provide a characterization of its electronic structure by means of angle-resolved photoemission spectroscopy and first-principles calculations. We show that, going away from the Brillouin zone center, bulk band states energetically overlap with the Dirac cone at the Fermi level, thus providing an unwanted as well as hidden contribution to the transport properties of the material. In addition, the comparison between experimental results of the band structure with state-of-the-art simulations, implemented taking into account the number of defects, leads to useful insights on the existing limits in the description of this material.

The advent of germanium telluride as a promising ferroelectric Rashba semiconductor for spintronic applications requires the growth of nanometer-thick films of high crystalline quality. In this study, we have elucidated the initial growth stages of GeTe on Si(111)-Sb by scanning tunneling microscopy and low energy electron diffraction. We demonstrate the presence of an initial 0.35-nm-thick GeTe buffer layer followed by the 2D growth of GeTe via Frank-Read sources of atomic steps. As shown by core level spectroscopy, Sb is acting as a surfactant during growth up to a 5-nm-thick film. X-ray diffraction, transmission electron microscopy, and low energy electron microscopy evidence that numerous mirror domains and in-plane misorientations appear early in the growth process and are gradually buried at the film/substrate interface. The use of a miscut Si substrate close to Si(111) allows suppressing these defects from the early beginning of growth.

Spinel cobalt vanadate ${\mathrm{CoV}}_2{\mathrm{O}}_4$ has been grown on (001) ${\mathrm{SrTiO}}_3$ substrates. Using torque magnetometry experiments, we find that the previously observed temperature-induced anisotropy change, where the easy axis changes from the out-of-plane [001] direction to a biaxial anisotropy with planar <100> easy axes, occurs in a gradual second-order structural phase transition. This paper characterizes this transition and the magnetic anisotropies in the (001), (100), and $\left(\overline{1}10\right)$ rotation planes, and explores their field dependence up to 30 T. Below 80 K, hysteretic features appear around the hard axes, i.e., the out-of-plane direction in $\left(\overline{1}10\right)$ and (010) rotations and the planar <110> directions in (001) rotations. This is due to a Zeeman energy that originates from the lag of the magnetization with respect to the applied magnetic field as the sample is rotated. The appearance of the hysteresis, which persists up to very high fields, shows that the anisotropy at low temperature is rather strong. Additionally, field-dependent distortions to the symmetry of the torque response in increasing applied fields shows that magnetostriction plays a large role in determining the direction and magnitude of the anisotropy.

While ultra-thin layers of the ${\mathrm{LaNiO}}_3$ film exhibit a remarkable metal-insulator transition as the film thickness becomes smaller than a few unit cell (u.c.), the formation of possible oxygen vacancies and their effects on the correlated electronic structure have been rarely studied using first principles. Here, we investigate the effects of the surface termination and the oxygen vacancy position on the electronic properties and vacancy energetics of ${\mathrm{LaNiO}}_3$ ultra-thin films under the compressive strain using density functional theory plus U $(\mathrm{DFT}+\mathrm{U})$. We find that oxygen vacancies can be easily formed in the Ni layers with the ${\mathrm{NiO}}_2$ terminated surface (0.5 u.c. and 1.5 u.c. thickness) compared to the structures with the LaO terminated surface and the in-plane vacancy is energetically favored than the out-of-plane vacancy. When two vacancy sites are allowed, the Ni square plane geometry is energetically more stable in most cases as two oxygen vacancies tend to stay near a Ni ion. Strong anisotropy between the in-plane and out-of-plane vacancy formation as well as the layer and orbital dependent electronic structure occur due to strain, surface termination, charge reconstruction, and quantum confinement effects. The in-plane vacancy of the ${\mathrm{NiO}}_2$ terminated structure is favored since the released charge due to the oxygen vacancy can be easily accommodated in the $d_{x^2-y^2}$ orbital, which is less occupied than the $d_{z^2}$ orbital. Remarkably, the oxygen vacancy structure containing the Ni square-plane geometry becomes an insulating state in $\mathrm{DFT}+\mathrm{U}$ with a sizable band gap of 1.2 eV because the large crystal field splitting between $d_{z^2}$ and $d_{x^2-y^2}$ orbitals in the square-plane favors an insulating state and the Mott insulating state is induced in other Ni sites due to strong electronic correlations. In the thin-film structure without oxygen vacancies, the strong correlation effect in $\mathrm{DFT}+\mathrm{U}$ drives a pseudogap ground state at the Fermi energy, similarly as the experimental photo-emission spectra; however, the variation of the $\mathrm{DFT}+\mathrm{U}$ electronic structure depending on the surface termination becomes weaker compared to those obtained in DFT.

Due to its three-dimensional bulk-insulating nature and better room-temperature thermoelectric properties, ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ is widely explored as potential thermoelectric material and topological insulator. Here, we report the effect of smaller atoms (Ge, Se) doping on the evolution of the temperature-dependent optical phonon modes in polycrystalline single-phase ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. While undoped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ exhibits crystal inversion symmetry lowering in the investigated temperature range, the doped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ retains the inversion symmetry below 270 K. As a result, the IR-active $A_{1u}^2$ phonon mode, which arises due to the lowering of crystal inversion symmetry, disappears in the doped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ below 270 K. The increase in the full width at half maxima of Raman peaks and reduction in the phonon lifetime with an increase in temperature confirm the optical phonon decay in doped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$, and hence lattice thermal conductivity is expected to decrease at higher temperatures. The lattice thermal conductivity estimated from the optical phonon modes is in line with the experimentally measured value, which affirms that optical phonon vibrations dominate the lattice thermal conductivity of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. At low temperature, the Ge-Se codoped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ shows a fourfold enhancement of the Seebeck coefficient compared to that of undoped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. Our results give an insight into the optical phonon decay mechanism in the doped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ and corroborate that optical phonons play a vital role in the lattice thermal conductivity of polycrystalline ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. Also, it is found that Se-Ge codoped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ can be used as an efficient near-room temperature thermoelectric material.

Globular proteins undergo heat-induced denaturation and eventually gelation at significantly elevated temperatures. The present study provides pathways to control temperature-driven protein gelation, having potential applications in a wide range of fields, from medicine to cosmetics to the food industry. The sol-gel transitions have been directed via modifying interprotein (electrostatic and hydrophobic) interactions by complexation of protein with amphiphiles. The heat-induced gelation of bovine serum albumin protein (anionic) is prevented in the presence of anionic sodium dodecyl sulfate (SDS) surfactant without significantly altering its native conformation. The specific binding of SDS monomers on the oppositely charged sites of protein increases the electrostatic repulsion between protein molecules, thereby suppressing the protein gelation. On the other hand, incorporating nonionic decaoxyethylene $n-\mathrm{dodecylether}$ (${\mathrm{C}}_{12}{\mathrm{E}}_{10}$) surfactant along with ionic surfactant reverses this scenario, and the solution state of the bovine serum albumin-SDS system undergoes gelation. The preferential binding of SDS with ${\mathrm{C}}_{12}{\mathrm{E}}_{10}$ nonionic surfactant forms detached mixed micelles, resulting in the release of the SDS monomers from protein, hence reverting the SDS-induced prevention of protein gelation. The results are counterintuitive and explained based on the interplay of hydrophobic and electrostatic interactions among protein molecules, as probed by small-angle neutron scattering, dynamic light scattering, and rheology.

Irreversible deformation of crystals is often characterized by stochastic scale-free distributed intermittent local plastic bursts. Quenched obstacles with short-range interaction were found to limit the size of these events, which was termed as a transition from wild to mild fluctuations. Here, we show by analyzing the local yield thresholds in a discrete dislocation model that a dynamic length scale can be introduced based on weakest link principles, and this scale characterizes the extension of plastic events. The interplay between long-range dislocation interactions and short-range quenched disorder is found to destroy scale-free dynamical correlations, thus leading to event localization (that is, shortening of the length scale) which explains the crossover between the wild and mild regimes. Several methods are presented to determine the dynamic length scale which can be generalized to other types of heterogeneous materials.

In this paper, density functional theory calculations are adopted to systematically study the magnetic-structure anisotropy association and strain induced structure variants switching behavior of ferroelastic $1{\mathrm{T}}^{\prime }\text{−}{\mathrm{CrS}}_2$ and ${\mathrm{CrSe}}_2$. We find that the easy magnetization axis is always perpendicular to Cr-Cr zigzag chain in the ferromagnetic (FM) $1{\mathrm{T}}^{\prime }$ phase. In addition, the mechanical strain can alter the relative thermodynamic stability among the three different crystal orientation variants of both the FM and nonmagnetic (NM) $1{\mathrm{T}}^{\prime }$ phase. These two facts lay the ground for strain-controlled magnetic moment rotation of the FM $1{\mathrm{T}}^{\prime }$ phase. A prototypical design and operating mechanism of a strain-controlled $1{\mathrm{T}}^{\prime }$-FM/NM/FM heterostructure spin valve are presented. Our finding offers a potential solution to reduce energy consumption in miniaturized spintronics devices.