The formation of nonsuperconducting hydrides in 160–170-nm-thick films of niobium is examined. We identify six elastically distinct orientation relationships $\varepsilon \text{−}{\mathrm{Nb}}_4{\mathrm{H}}_3$ takes within the matrix, solid-solution $\alpha \text{−}{\mathrm{NbH}}_x$ phase. We employ a phase field model to assess the impact of elastic energy induced by the strain of phase transformation on the morphology and transformation dynamics of $\varepsilon$ precipitates within a thin film. We consider the dimensions of the thin film, crystallographic growth direction, and diffusion rates to predict the timescale of hydride evolution. Leveraging the finite element method, we predict two-dimensional and three-dimensional equilibrium shapes of $\varepsilon$-hydrides within a bulk sample and in a thin film that has a traction-free surface. Our results suggest that niobium hydrides migrate to the free surface of the film. Precipitates which reach the free surface coarsen, while precipitates within the film dissolve. Precipitates in both two dimensions and three dimensions experience a repulsive interaction force at the free surface, that is attractive in the bulk, shown in experiment and theory of previous studies.

Thin film solar cell technologies are mainly based on polycrystalline absorber layers, which is also the case for kesterite-based photovoltaic devices. An alternative technology, which is promising and low cost, is based on kesterite-type $\mathrm{C}{\mathrm{u}}_2\mathrm{ZnSn}{\left(\mathrm{S},\mathrm{Se}\right)}_4$ (CZTSSe) monograins as absorbers, which are fixed in a polymer matrix to form a flexible solar cell. The large band tailing observed in Cu-based kesterite-type semiconductors is believed to cause voltage losses, limiting the efficiency of kesterite-based devices. Cu/Zn disorder, which is always present in these compounds, is discussed in literature as a possible reason for band tailing. The experimental determination and quantification of Cu/Zn disorder is possible by in-depth analysis of neutron diffraction data. This work reveals that the purity of copper used in the synthesis of CZTSSe monograins has an influence on the degree of Cu/Zn disorder in the semiconductor and thus on optical and PV parameters. Comparing CZTSSe monograins, less Cu/Zn disorder was observed for the monograins synthesized using copper with higher purity; the respective monograin-based solar cell shows a higher power conversion efficiency. On the other hand, the band gap energy as well as the photoluminescence maximum ($\mathrm{P}{\mathrm{L}}_{\max }$) of both monograins are the same. Applying a low-temperature annealing procedure allowed us to increase the quality of monograins synthesized using 5N copper, very close to the one grown using 6N copper. The $\mathrm{P}{\mathrm{L}}_{\max }$ slightly shifts into higher energy, which is most likely an indication of the decreased Cu/Zn disorder, either moving the defect states toward the valence band or that it reduces the formation of the tail states near the conduction band minimum.

Non-Schmid stresses, i.e., stresses that do not drive the motion of dislocations, are known to impact the core morphology of $\langle a\rangle$-type screw dislocations in $\alpha$-Ti. In this study, the interaction of the dislocation core with non-Schmid stresses is quantitatively modeled by an elastic dipole tensor characterizing the displacement field of the dislocation core. Density functional theory is used to compute the elastic dipole tensor of screw dislocations during a pyramidal and prism slip and a cross slip from a pyramidal to a prism plane. The effect of non-Schmid stress on the mobility of dislocations is discussed and the model is used to assess the properties of oriented single crystals.

$\mathrm{E}{\mathrm{r}}^{3+}-\mathrm{doped} \mathrm{Ca}{\mathrm{F}}_2$ is a promising laser gain medium for applications requiring mid-infrared radiation. It is well known that the $\mathrm{E}{\mathrm{r}}^{3+}$ ions embedded in the fluorite matrix tend to agglomerate forming so-called clusters thought to enhance the optical properties of the material. However, studies of the structure of these clusters have been limited to high doping concentrations. Furthermore, the experimental techniques used, such as extended x-ray absorption fine structure (EXAFS), provide only orientationally averaged information, which can be an issue for the unambiguous solution of the local disorder structure. Here, three-dimensional difference pair distribution function ($3\mathrm{D}-\mathrm{\Delta }\mathrm{PDF}$) analysis is applied to single-crystal diffuse scattering collected on $\mathrm{Ca}{\mathrm{F}}_2$ crystals with nominal doping levels of 1%, 3%, and 6% $\mathrm{E}{\mathrm{r}}^{3+}$. Despite the low doping concentrations and the weak diffuse scattering resulting from this, clear three-dimensionally resolved local structure information is available from the $3\mathrm{D}-\mathrm{\Delta }\mathrm{PDF}$. Comparing the experimental results to big-box simulations and analytical models, the preferred $\mathrm{E}{\mathrm{r}}^{3+}\mathrm{cluster}$ is observed to be an octahedral hexamer. Additionally, the $3\mathrm{D}-\mathrm{\Delta }\mathrm{PDF}$ and average structure information reveal that the charge compensating fluoride ions form a cuboctahedral structural motif. Combined with the $\mathrm{E}{\mathrm{r}}^{3+}$ hexamer, the structure of the preferred cluster can therefore be described as a (local structure) $\mathrm{E}{\mathrm{r}}^{3+}$ analoge to the ${\mathrm{Y}}_6{\mathrm{F}}_{37}$ clusters known from the average structure of the ordered yttrofluorite mineral tveitite. Comparison of the experimental diffuse scattering to diffuse scattering based on this local structure model shows good agreement speaking to the validity of the model.

Spin-orbit coupling facilitates the exploitation of spin degrees of freedom of an electron in the absence of any external magnetic field, opening up new possibilities for spintronics-based applications. In this work, we have conducted a detailed investigation of spin-orbit coupling-induced novel physical effects in noncentrosymmetric ${\mathrm{Ta}}_2{\mathrm{CS}}_2$, a representative member of the MXene family. We find that local symmetries and orbital compositions are responsible for the nontrivial band splitting and characteristic spin textures displayed by these systems at various high-symmetry points in the Brillouin zone. First-principles calculations, supplemented by a $\mathbf{k}·\mathbf{p}$ model Hamiltonian, demonstrate the presence of both linear and higher-order Rashba terms at the Brillouin zone (BZ) center $\mathrm{\Gamma }$, where the system exhibits little-group symmetry $C_{3v}$. Additionally, we observe valley-dependent Zeeman-type spin splitting at the non-time-reversal invariant momentum (TRIM) points $K$ and $K^{\prime }$. Furthermore, we identify that the opposite spin splitting at the $K$ and $K^{\prime }$ points arises from a complex orbital composition that induces an intrinsic orbital moment, influencing the nature of spin splitting. Our findings indicate that ${\mathrm{Ta}}_2{\mathrm{CS}}_2$ shares many key physical properties with transition metal dichalcogenides (TMDCs), making it a promising candidate for spintronic and valleytronic applications.

The realization of a Hopf-link structure in the Brillouin zone is rather rare, which hinders comprehensive exploration and understanding of such exotic nodal loop geometry. We tabulated 141 space groups which could host a Hopf-link structure derived from band crossings in high-symmetry lines and then investigated the Phonon Database at Kyoto University, which contains 10 034 materials, to search for phonon realization of the Hopf-link nodal structure based on these space groups. We found that almost all the investigated materials have nodal loops or nodal chains, while only 113 materials can host a Hopf-link structure in phonon spectra, among which 8 representative materials are manually selected to showcase the relatively clean Hopf-link structure, including ${\mathrm{LiGaS}}_2, {\mathrm{LiInSe}}_2, {\mathrm{Ca}}_2{\mathrm{Al}}_2\mathrm{Si}{\left({\mathrm{HO}}_4\right)}_2, {\mathrm{Ca}}_7{\mathrm{GeN}}_6$, Al(${\mathrm{HO})}_3, \mathrm{NaNd}{\left({\mathrm{GaS}}_2\right)}_4, {\mathrm{Ga}}_5{\left(\mathrm{PS}\right)}_3$, and ${\mathrm{RbTh}}_3{\mathrm{F}}_{13}$. The visible phonon drumhead surface states corresponding to the nodal loops in Hopf-link structure are further demonstrated using ${\mathrm{Ga}}_5{\left(\mathrm{PS}\right)}_3$. The listed 113 crystalline materials provide a good platform for experimentalists to further explore the interesting properties related to the Hopf-link structure.

In this investigation, we explored the temperature dependence of the damping parameter in Py/Cu/Gd/Ta structures using broadband ferromagnetic resonance. A noteworthy escalation in the Gilbert damping factor of Py was noted upon cooling below the magnetic ordering temperature of the Gd, particularly when Gd layer thicknesses exceed 20 nm. This observed enhancement is attributed to the phenomenon of spin pumping into the Gd layer through the Cu buffer layer. Magnetic order increases Gd's performance as a spin sink, thereby enhancing the damping parameter of Py via increased relaxation of spin current pumped into the Gd. Contrary to previous work that suggest damping enhancement in this system was due to the antiferromagnetic coupling between Py and Gd layers and not to magnetic order, the present study utilizes 10 nm thick Cu to prevent such coupling. This allows us to conclude that robust magnetic order in the spin sink enhances the damping parameter.

We present a detailed spectroscopic study of the ${}^4\mathrm{I}_{13/2}$ and ${}^4\mathrm{I}_{15/2}{\mathrm{Er}}^{3+}$ multiplets of Er:${\mathrm{CaWO}}_4$ grown without a co-dopant. Using photoluminescence and photoluminescence excitation measurements, we find multiple environments into which erbium ions are incorporated in the crystal. For the four most prevalent environments, we provide a complete assignment of the ${}^4\mathrm{I}_{13/2}$ and ${}^4\mathrm{I}_{15/2}$ sublevel energies. Polarization-dependent absorption and emission spectroscopy allow us to identify the irreducible representations of the states and determine the dipole nature of transitions. In addition, we compare the different relaxation paths within ${}^4\mathrm{I}_{13/2}$ and ${}^4\mathrm{I}_{15/2}$ multiplets via line broadening and lifetime measurements. Finally, spectral, lifetime, and polarization measurements indicate similarities between the studied environments.

Time-reversal symmetry breaking and spin-splitting phenomena, based exclusively on spin group symmetry, have been prominent topics in condensed matter physics. Until recently, magnetic materials have been classified into ferromagnetic and antiferromagnetic materials. Altermagnetism represents a newly discovered magnetic phase, characterized by zero net magnetization, similar to antiferromagnetic materials, and strong spin-dependent phenomena associated with ferromagnetic ones. The broken time-reversal symmetry in the altermagnets originates from crystal symmetries without requiring strong spin-orbit interaction. Lifting of spin degeneracy is a consequence of the preserved nonrelativistic spin group, defining the altermagnetic phase. A study of cobalt sulfide in NiAs and wurtzite phases reveals the spin momentum locked bands across off-symmetric regions in the Brillouin zone and transition temperature near room temperature. Another important consideration is the electronic correlation that influences both the electronic structure and the magnitude of spin splitting along the off-nodal lines in both atomic phases. Our findings demonstrate that CoS exhibits unconventional spin polarization order and altermagnetism phase indicating significant potential for broad theoretical and experimental research.

In recent years, several well-established 3D substrates have been considered for the van der Waals epitaxy of 2D-transition metal dichalcogenides, yet require a proper surface passivation treatment. In this work, we study the structural and electronic properties of well-ordered Se-terminated $\mathrm{GaP}{\left(111\right)}_{\mathrm{B}}$ surfaces by molecular beam epitaxy. We emphasize the key role of using a combination of atomic Hydrogen and cracked phosphine at a relatively low temperature to prepare a smooth P-rich surface with a ($2\times 2$) reconstruction of $n$ and $p$ doped GaP(111). We then investigate the evolution of the surface electronic properties after a selenium flux exposiure. The $\mathrm{GaP}{\left(111\right)}_{\mathrm{B}}$ surface exhibits a systematic change in reconstruction from a ($2\times 2$) to a ($1\times 1$) pattern, while showing a change in chemical environment mainly in the outermost P-surface layer. We show the absence of a GaSe layer formation through angle-resolved photoemission spectroscopy measurements, while demonstrating that the band structure of the Se-passivated surface originates from the $\mathrm{GaP}{\left(111\right)}_{\mathrm{B}}$ one. We then emphasize the predominant effect of a low selenium flux, while demonstrating an effective partial electronic passivation of the surface through the evolution of the band bending and the surface dipole measured with ultraviolet photoemission spectroscopy. This realization of Se-terminated $\mathrm{GaP}{\left(111\right)}_{\mathrm{B}}$ substrate paves the way to new 2D/3D heterostructure development with great interest in nanoelectronic and optoelectronic applications.

Kagome lattice decorated with $S=1/2$ spins is one of the most discussed ways to realize a quantum spin liquid. However, all previous material realizations of this model have suffered from additional complications, ranging from additional interactions to impurity effects. Recently, a new quantum kagome system has been identified in the form of averievite ${\mathrm{Cu}}_{5-x}{\mathrm{Zn}}_x{\mathrm{V}}_2{\mathrm{O}}_{10}$(CsCl), featuring a unique double-layer spacing between the kagome planes. Using muon spin spectroscopy we show that only a complete substitution (i.e., $x=2$) of interplanar copper ions leads to a quantum-disordered ground state. In contrast, the parent compound ($x=0$) exhibits long-range magnetic order, with a phase transition around 24 K. Experiments performed on the partially substituted material ($x=1$) show that the transformation proceeds through an intermediate disordered, partially frozen ground state, unaffected by pressures up to 23 kbar. Our study provides a microscopic view of the magnetism of the decoupling of the kagome layers and establishes the averievite as a new material platform for the experimental study of the fully-decoupled kagome layers.

Transition-metal oxides with an $AB{\mathrm{O}}_3$ perovskite structure exhibit significant coupling between spin, orbital, and lattice degrees of freedom, highlighting the crucial role of lattice distortion in tuning the electronic and magnetic properties of these systems. In this study, we grow a series of antiferromagnetic ${\mathrm{GdVO}}_3$ thin films on different substrates introducing various strain values. The results demonstrate that the strain not only affects the material's structure and magnetic transition temperature, but also influences the growth direction of the orthorhombic unit cell. A correlation is observed between the orientation of the orthorhombic long axis direction and the material's Néel temperature. Density functional theory calculations highlighting the link between strain, lattice distortions, and magnetic characteristics confirm these conclusions. Our findings demonstrate that the development of novel features in $R{\mathrm{VO}}_3$ through material design requires control of growth orientation through strain engineering.

In this work, we have developed CuXASNet, a dense neural network that predicts simulated Cu $L$-edge x-ray absorption spectra (XAS) from atomic structures. Featurization of the Cu local environment is performed using a component of M3GNet, a graph neural network developed for predicting the potential energy surface. CuXASNet is trained on simulated spectra from FEFF9 at the multiple scattering level of theory, and can predict the $L_3$ and $L_2$ edges for Cu sites to quantitative accuracy. To validate our approach, we compare 14 experimental spectra extracted from the literature with the predictions of CuXASNet. The agreement of CuXASNet with experiments is shown by an average mean absolute error of 0.125 and an average Spearman's correlation coefficient of 0.891, which is comparable to FEFF9's values of 0.131 and 0.898 for the same metrics. As such, CuXASNet can rapidly predict a large number of $L$-edge XAS spectra at the same accuracy as FEFF9 simulations. This can be used as a drop-in replacement for multiple scattering codes for fast screening of candidate atomic structure models of a measured system. This model establishes a general framework for Cu XAS prediction, and can be extended to more computationally expensive levels of theory and to other transition metal $L$ edges.

The mechanical behavior of most materials involves discrete “avalanche” events, where a local microscopic volume within the bulk undergoes large abrupt deformations. Such events are commonly detected and analyzed based on the acoustic emission (AE) they generate. Many materials display several deformation mechanisms simultaneously, thus calling for analysis tools that can differentiate between the AE signals they produce. We introduce a new classification method where the power-spectral densities of AE signals are mapped onto a two-dimensional space by the $t$-distributed stochastic neighbor embedding (tSNE) algorithm. To study the effectiveness and accuracy of these tools, we produced ground-truth datasets of AE signals generated by dislocation plasticity, deformation twinning, and martensitic transformation. This is achieved by loading three different alloys, each characterized by a single deformation mechanism. We show that each dataset has different distributions of AE features, thus strengthening the necessity to distinguish between AE signals generated by different deformation mechanisms. Moreover, an analysis that does not separate deformation mechanisms, and instead considers the combined datasets, provides distributions that lead to specious conclusions. The two-dimensional representation applied by our data-driven method displays three distinct clusters, which are also identified by the $k$-means clustering algorithm. The clusters match the ground-truth datasets with an accuracy of 98.6%, implying the method's capability to distinguish between different deformation mechanisms that coexist in the same material.

Achieving atomically flat and stoichiometric films of chiral antiferromagnets (AFM) with two-dimensional kagome spin lattice structures are crucial for integrating these materials in both established and emerging antiferromagnetic spintronic devices. We report a systematic study of growth and anomalous Hall effect in (111)-oriented noncollinear AFM ${\mathrm{Mn}}_{3+x}{\mathrm{Pt}}_{1-x}$ films with varying compositions, for $x=0.09$, 0.17, 0.28. Under optimized growth conditions, we obtain stoichiometric and atomically flat epitaxial ${\mathrm{Mn}}_3\mathrm{Pt}\left(111\right)$ films on Si(100) substrate, as evidenced by x-ray reflectivity and scanning probe microscopy. The magnetization measurement showed that epitaxial strain can induce a magnetic phase transition from an incommensurate spin state $\left(T_2\right)$ at $x=0.09$ to a triangular all-in/all-out AFM spin order $\left(T_1\right)$ at $x=0.17$, 0.28. The change in magnetic ground state is evident in the transport characteristics, as the $\left(T_1\right)$ state shows a robust intrinsic anomalous Hall effect (AHE) persisting to room temperature, in contrast to the $\left(T_2\right)$ state where AHE is negligible. Our studies reveal a hole-dominated conductance with room temperature anomalous Hall conductivity ranging from 5 to 16 ${\mathrm{\Omega }}^{-1}{\mathrm{cm}}^{-1}$ for $x=0.17$ and 0.28, respectively. A scaling law is established, indicating that Hall resistivity is primarily governed by the intrinsic nonvanishing Berry curvature. The experimental observation corroborates the electronic structure calculations, which predicts the massless Dirac states near Fermi level in the bulk band structure, attributed to the presence of nonsymorphic glide symmetry. Additionally, we showed that chemical tuning via Mn doping can stabilize the required $T_1$ noncollinear AFM structure which enhance the topology driven intrinsic AHE.

Epitaxial MnTe films have recently seen a surge in research into their altermagnetic semiconducting properties. However, those properties may be extremely sensitive to structural and chemical modifications. We report a detailed investigation of the synthesis of the altermagnet α-MnTe on GaAs(111), which reveals the bulk defect structure of this material, the mechanism by which it releases strain from the underlying substrate, and the impact of oxidation on its surface. X-ray diffraction measurements show that α-MnTe layers with thicknesses spanning 45 to 640 nm acquire lattice parameters different from bulk, mostly due to thermal strain caused by the substrate rather than strain from the lattice mismatch. Through high-resolution transmission electron microscopy (TEM) measurement, we then unveil a misfit dislocation array at the interface, revealing the mechanism by which lattice strain is relaxed. TEM also reveals a stacking fault in the bulk, occurring along a glide plane parallel to the interface. The combination of TEM with polarized neutron reflectometry measurements finally reveals the impact of oxidation on the chemistry of the surface of uncapped MnTe. Our findings highlight the subtle role of epitaxy in altering the structure of α-MnTe, providing potential opportunities to tune the altermagnetic properties of this material.

We report measurements of the local temperature-dependent penetration depth, $\lambda \left(T\right)$, in the kagome superconductors ${A\mathrm{V}}_3{\mathrm{Sb}}_5$ $(A=\mathrm{Cs}, \mathrm{K}, \mathrm{Rb})$ using scanning superconducting quantum interference device microscopy. Our results suggest that the superconducting order in all three compounds is fully gapped, in contrast to reports of nodal superconductivity in ${\mathrm{KV}}_3{\mathrm{Sb}}_5$ and ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$. Analysis of the temperature-dependent superfluid density, ${\rho }_s\left(T\right)$, shows deviations from the behavior expected for a single isotropic gap, but the data are well described by models incorporating either a single anisotropic gap or two isotropic gaps. Notably, the temperature dependences of $\lambda \left(T\right)$ and ${\rho }_s\left(T\right)$ in ${\mathrm{KV}}_3{\mathrm{Sb}}_5$ and ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$ are qualitatively more similar to each other than to ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, consistent with the superconducting phase-reflecting features of the normal-state band structure. Our findings provide a direct comparison of the superconducting properties across the ${A\mathrm{V}}_3{\mathrm{Sb}}_5$ family.

Charge transition levels of dopants directly influence material properties, but experimental numbers are difficult to obtain. It will be demonstrated how x-ray photoelectron spectroscopy can be applied to directly determine charge transition levels of dopants in oxides. Oxidizing and reducing treatments induce changes of the Fermi level at the surface, accompanied by changes of the oxidation state of the dopant. The approach is exemplified for $0.2\mathrm{mol}\%$ V-doped ${\mathrm{BaTiO}}_3$ bulk ceramics, revealing a ${\mathrm{V}}^{5+/3+}$ charge transition at a Fermi level $\approx 0.15\mathrm{eV}$ above the conduction-band minimum. Consequently, V is present as ${\mathrm{V}}^{5+}$ and acting as a donor in ${\mathrm{BaTiO}}_3$ for most experimental conditions.

We have investigated the electronic and magnetic structures of topological kagome ${\mathrm{Fe}}_{1-x}{\mathrm{Mn}}_x\mathrm{Sn}$ ($0\le x\le 0.3$) thin films via neutron diffraction, electronic transport measurements, and ab initio density functional theory (DFT) to understand the interplay between hole doping, magnetism, and the electronic structures. Temperature-dependent neutron diffraction measurements on parent FeSn reveal the Néel temperature to be $T_{\text{N}}\sim 355$  K and the underlying A-type antiferromagnetic ordering is associated with a wave vector $\mathit{q}=(001/2)$. Upon Mn doping to $x=0.15, T_{\text{N}}$ decreases slightly while the magnetic ordering vector remains the same. Resistivity measurements show metallic characteristics and in-plane anisotropy down to 10 K for all the investigated samples. The effects of hole doping are mapped in terms of electronic ground state calculations via DFT which show that the Dirac point is moved closer to the Fermi level ($E_{\text{F}}$) and the flat bands get pushed away from $E_{\text{F}}$ upon hole doping. However, a comparison between hole-doped ${\mathrm{Fe}}_{1-x}{\mathrm{Mn}}_x\mathrm{Sn}$ and electron-doped ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Sn}$ indicates that the Néel temperature does not scale with the position of $E_{\text{F}}$ relative to the flat band. Our results establish the antiferromagnetic state of FeSn and ${\mathrm{Fe}}_{1-x}{\mathrm{Mn}}_x\mathrm{Sn}$ films at room temperature, laying the groundwork for future studies of magnetism in kagome heterostructures.