We report on the geometrically frustrated two-dimensional triangular-lattice magnets A2La2NiW2O12 (A=Sr,Ba) studied mostly by means of neutron powder diffraction (NPD) and muon-spin rotation and relaxation (μSR) techniques. The chemical pressure induced by the Ba-for-Sr substitution suppresses the ferromagnetic (FM) transition from 6.3 K in the Ba compound to 4.8 K in the Sr compound. We find that the R3¯ space group reproduces the NPD patterns better than the previously reported R3¯m space group. Both compounds adopt the same magnetic structure with a propagation vector k=(0,0,0), in which the Ni2+ magnetic moments are aligned ferromagnetically along the c axis. The zero-field μSR results reveal two distinct internal fields (0.31 and 0.10 T), caused by the long-range FM order. The small transverse muon-spin relaxation rates reflect the homogeneous internal field distribution in the ordered phase and, thus, further support the simple FM arrangement of the Ni2+ moments. The small longitudinal muon-spin relaxation rates, in both the ferromagnetic and paramagnetic states of A2La2NiW2O12, indicate that spin fluctuations are rather weak. Our results demonstrate that chemical pressure indeed changes the superexchange interactions in A2La2NiW2O12 compounds, with the FM interactions being dominant.

We report on the magnetic and electrical properties of a (Mn3Sn)2 triangular network kagome structured high quality Ho substituted ErMn6Sn6 single-crystal sample by magnetotransport measurements. Er0.5Ho0.5Mn6Sn6 orders antiferromagnetically at Néel temperature TN∼350 K followed by a ferrimagnetic (FiM) transition at TC∼114 K and spin-orientation transition at Tt∼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∥c, narrow hysteresis between spin reorientation and field-induced FiM phases below Tt, enhanced/strengthened FiM phase below TC and stemming of FiM phase out of strongly coexisting antiferromagnetic and FiM phases below TN through a non-meta-magnetic transition are confirmed to arise from strong R-Mn sublattices interaction. In contrast, in the H∥ab plane, between TN and TC, 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.

Predictions of a topological electronic structure in the skutterudite TPn3 family (T=transition metal, Pn=pnictogen) are investigated via magnetoresistance, quantum oscillation, and angle-resolved photoemission experiments on RhSb3, a semimetal with low carrier density. Electronic band structure calculations and symmetry analysis of RhSb3 indicate this material to be a zero-gap semimetal protected by symmetry with inverted valence and conduction bands that touch at the Γ 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 (∼1.3×106 m/s), high carrier mobility [∼14 m2/(Vs)], 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 RhSb3 as representative of a material family of topological semimetals with symmetry-enforced Fermi degeneracy at the high-symmetry points.

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.

A recent experiment of polycrystalline WB2 with hP3 (space-group 191, prototype MgB2) and hP12 (space-group 194, prototype WB2) structures was reported to realize 17-K superconductivity (SC) at 90 GPa, and the hP3 structure is believed to be responsible for this emergent SC. However, a microscopic understanding of what makes the hP3 structure so different from the hP12 structure and why the hP3 can feature such strong electron-phonon coupling (EPC) SC is still missing. Here, based on first-principles calculations, we found that in the hP3 structure, W d orbitals contribute most to electronic occupation near the EF, and dz2 orbitals of two neighboring W atoms have some hybridization to form weak σ bonds. The further EPC analysis indicates that the dominant dz2 states are strongly coupled with the out-of-plane phonon modes by stretching the W−Wσ bond, thereby yielding a large superconducting gap and high Tc of ∼35 K. By contrast, for the hP12 structure, two neighboring W atoms are isolated without charge hybridization to form the covalent bonds, and, accordingly, their phonon modes become very stiffened, which cannot effectively couple to W d orbital states associated with a lower Tc of ∼4 K. Therefore, our findings not only provide an explanation for the emergent strong EPC SC in the hP3 structure, but also have important implications for the design of high-Tc superconductors among transition metal borides.

We present a comprehensive experimental and computational study on A-site ordered perovskite oxides YCu3Co4O12, LaCu3Co4O12, and BiCu3Co4O12 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 A3+Cu3∼3+Co4∼3+O122− is found for the three compounds at ambient and high-pressure conditions (up to ∼55 GPa). A DFT calculation for YCu3Co4O12 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 LaCoO3. A DFT+DMFT analysis of the Cu spin-correlation function indicates that the Zhang-Rice singlet description for the CuO4 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 DFT+DMFT analysis for the Co L2,3 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 DFT+U simulation.

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.

A simple stochastic model of solute drag by moving grain boundaries (GBs) is presented. Using a small number of parameters, the model describes solute interactions with GBs and captures nonlinear GB dynamics, solute saturation in the segregation atmosphere, and the breakaway from the atmosphere. The model is solved by kinetic Monte Carlo (KMC) simulations with time-dependent transition barriers. The non-Markovian nature of the KMC process is discussed. In this paper (which is Paper I of this work), the model is applied to planar GBs driven by an external force. The model reproduces all basic features of the solute drag effect, including the maximum of the drag force at a critical GB velocity. The force-velocity functions obtained depart from the scaling predicted by the classical models by Cahn and Lücke-Stüwe, which are based on more restrictive assumptions. The paper sets the stage for an accompanying paper [Paper II, Phys. Rev. Mater. 7, 063404 (2023)] in which the GB will be treated as a two-dimensional solid-on-solid interface.

Quantum tunneling rotors in a zeolitic imidazolate framework ZIF-8 can provide insights into local gas adsorption sites and local dynamics of porous structure, which are inaccessible to standard physisorption or x-ray diffraction sensitive primarily to long-range order. Using in situ high-resolution inelastic neutron scattering at 3 K, we follow the evolution of methyl tunneling with respect to the number of dosed gas molecules. While nitrogen adsorption decreases the energy of the tunneling peak, and ultimately hinders it completely (0.33 meV to zero), argon substantially increases the energy to 0.42 meV. Ab initio calculations of the rotational barrier of ZIF-8 show an exception to the reported adsorption sites hierarchy, resulting in anomalous adsorption behavior and linker dynamics at subatmospheric pressure. The findings reveal quantum tunneling rotors in metal-organic frameworks as a sensitive atomistic probe of local physicochemical phenomena.

GeSn is a promising group-IV semiconductor material for on-chip Si photonics devices and high-mobility transistors. These devices require the use of doped GeSn regions, achieved preferably in situ during epitaxy. From the electronic valence point of view, p-type dopants of group-IV materials include B, Al, Ga, and In. The latter element has never been investigated as p-type dopant in GeSn. In this work, we explore in situ In p-type doping of GeSn grown by molecular beam epitaxy. We demonstrate that In acts as a surfactant during epitaxial growth of GeSn:In, accumulating on surface and inducing Sn segregation in the form of mobile Sn-In liquid droplets, strongly affecting the local composition of the material. In nondefective GeSn, we measure a maximal In incorporation of 2.8×1018 cm−3, which is two orders of magnitude lower than the values reported in the literature for in situ p-type doping of GeSn. We further show that In induces the nucleation of defects at low growth temperatures, hindering out-of-equilibrium growth processes for maximization of dopant incorporation. This work provides insights on the limitations associated with in situ In doping of GeSn and discourages its utilization in GeSn-based optoelectronic devices.

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 [100] and [111] 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 {110}〈111〉 and {112}〈111〉 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 {11b2¯}〈111〉 during shock release.

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 Na2O–P2O5–SiO2 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 1.1MPam0.5.

Due to its phenomenal thermoelectric properties, SnSe has received increased interest, triggering systematic studies of both electronic and vibrational properties and the associated coupling. Recent experimental work claims that orthorhombic SnSe sustains a one-dimensional large polaron with a dimension of about 2 nm. In search of its theoretical signature, we first establish the level of precision that can be reached in describing the electronic structure of SnSe by means of ab initio density functional and many-body perturbation theories. As the characterization of band extrema by means of effective masses plays a crucial role in determining polaron properties, we signal the existence of a broad variation of such quantity among the various ab initio methodologies employed and in the available experimental data. The impact of electron-phonon coupling is then analyzed by employing the recently developed generalized Fröhlich model as well as the nonadiabatic Allen-Heine-Cardona formalism, and their relative accuracy is rationalized. We found that, although the vast majority of band extrema in SnSe cannot sustain a large one-dimensional polaron with a radius as small as 2 nm, there is one case in which another type of polaron emerges, indeed one-dimensional, but with an unusual oscillating electronic density of an approximate real space period of ∼3 nm that evokes a stack of disks. Such type of polaron is obtained from two theoretical treatments: a fixed Gaussian ansatz for the polaron wave function and a variational approach, both within the Fröhlich formalism. We hypothesize that such cylindrical polaron might be found in other materials with extended, shallow double-well band extrema.

An intermittent pattern is observed in the modeling of interfacial cyclic-loading crack growth at high-angle grain boundaries in ternary Fe-Ni-Cr alloys. Different from conventional wisdom of stress-intensity factor, the abrupt crack advances are found driven by extreme value statistics—namely, the aggregation of atoms with most compressive residual stresses. In addition, inherently non-affine atomic stress fluctuations are discovered, and the fluctuations peak at intermediate level of chemical heterogeneity, causing the fastest crack growth. Implications of such nonmonotonic mechanism in regard to the origin of intermediate-temperature embrittlement phenomena are also discussed.

The first sharp diffraction peak (FSDP) in the reciprocal-space structure factor S(Q) of glasses has been associated with their medium-range order (MRO) structure, but the real-space origin remains debated. While some progress has been made in the case of silicate and borate glasses, the MRO structure of phosphate glasses has not been studied in detail. Here, we apply persistent homology (PH), a topological data analysis method, to extract the MRO features and deconvolute the FSDP of zinc phosphate glasses. To this end, the oxygen, phosphorus, and zinc atoms in the atomic configurations of the glasses are regarded as vertices weighted by initial atom radii for PH computation before decomposing their contributions to the FSDP. To determine the vertex weights, we vary the oxygen (O) radius systematically and set the radii of zinc (Zn) and phosphorus (P) atoms based on the positions of the first peak in the O-Zn and O-P partial radial distribution functions. These configurations with varying atom radii are used as inputs for PH computation, allowing us to assess the contributions of the different ring structures to the MRO. In turn, this comparison between the computed and measured S(Q) gives rise to an optimized oxygen radius for the best agreement. The optimized vertex weight (oxygen radius) is found to have a physical meaning based on the covalent and ionic bonding characters. Finally, using the optimized atom radii, we are able to decompose the hierarchical structural contributions to the FSDP.

The ferroelectric material usually exhibits temperature-dependent spontaneous polarization, known as pyroelectricity, which can be used to directly convert thermal energy to electricity from ambient low-grade waste heat. When utilizing the structural phase transformations of the material, the conversion capability can be magnified, consequently the device performance can be strongly boosted by orders of magnitude. However, common ferroelectric oxides suffer mechanical fatigue and functional degradation over cyclic phase transformations, hindering widespread applications of the energy conversion device. In this paper, we investigate the mechanical and functional reversibility of the material by lattice tuning and grain coarsening. We discover the lead-free compound Ba(Ce0.005Zr0.005)Ti0.99O3−0.10(Ba0.7Ca0.3)TiO3 (BaCeZrTiO3−0.10BaCaTiO3) satisfying the compatibility condition among all present phases by its lattice parameters, making the phase transformations highly reversible. We demonstrated that the energy conversion device with equiaxial coarse grains exhibits exceptional fatigue resistance, with stable pyroelectric current output at 4µA/cm2 over 3000 energy conversion cycles. Our work opens another way to fabricate high-performance materials that advances the pyroelectric energy conversion for practical applications in engineering.

The Weyl semimetal CeAlGe is a promising material to study nontrivial topologies in real and momentum space due to the presence of a topological magnetic phase. Our results at ambient pressure show that the electronic properties of CeAlGe are extremely sensitive to small stoichiometric variations. In particular, the topological Hall effect (THE) present in CeAlGe is absent in some samples of almost identical chemical composition. The application of external pressure favors the antiferromagnetic ground state. It also induces a THE where it was not visible at ambient pressure. Furthermore, a small pressure is sufficient to drive the single region of the THE in magnetic fields into two different ones. Our results reveal an extreme sensitivity of the electronic properties of CeAlGe to tiny changes in its chemical composition, leading to a high tunability by external stimuli. We can relate this sensitivity to a shift in the Fermi level and to domain walls.

Alternative halide perovskites with characteristics similar to CsPbX3 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 Cs2MSbX6 (M = Cu, Ag, Na, K, Rb, Cs, and X=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 Cs2MSbX6, the system possesses an indirect band gap with a value ranging between ∼1.19and4.82 eV, a transition to direct band gap with values between ∼4.50and5.22 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 (∼10–103cm2V−1s−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 Cs2MSbX6, 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.

We study the modification of the magnetocrystalline anisotropy (MCA) of Co slabs induced by several different conjugated molecular overlayers, i.e., benzene, cyclooctatetraene, naphthalene, pyrene, and coronene. We perform first-principles calculations based on density functional theory and the magnetic force theorem. Our results indicate that molecular adsorption tends to favor a perpendicular MCA at surfaces. A detailed analysis of various atom-resolved quantities, accompanied by an elementary model, demonstrates that the underlying physical mechanism is related to the metal-molecule interfacial hybridization and, in particular, to the chemical bonding between the molecular C pz and the out-of-plane Co dz2 orbitals. This effect can be estimated from the orbital magnetic moment of the surface Co atoms, a microscopic observable accessible to both theory and experiments. As such, we suggest a way to directly assess the MCA modifications at molecule-decorated surfaces, overcoming the limitations of experimental studies that rely on fits of magnetization hysteresis loops. Finally, we also study the interface between Co and both C60 and Alq3, two molecules that find widespread use in organic spintronics. We show that the modification of the surface Co MCA is similar on adsorption of these two molecules, thereby confirming the results of recent experiments.

The introduction of obstacles (e.g., precipitates) for controlling dislocation motion in molecular structures is a prevalent method for designing the mechanical strength of metals. Owing to the nanoscale size of the dislocation core (≤1 nm), atomic modeling is required to investigate the interactions between the dislocation and obstacles. However, conventional empirical potentials are not adequately accurate in contrast to calculations based on density functional theory (DFT). Therefore, the atomic-level details of the interactions between the dislocations and obstacles remain unclarified. To this end, in this paper, we applied an artificial neural network (ANN) framework to construct an atomic potential by leveraging the high accuracy of DFT. Using the constructed ANN potential, we investigated the dynamic interaction between the (a0/2)〈111〉{110} edge dislocation and obstacles in body-centered cubic (bcc) iron. When the dislocation crossed the void, an ultrasmooth and symmetric half-loop was observed for the bowing-out dislocation. Except for the screw dislocation, the Peierls stress of all the dislocations predicted using the ANN was <100 MPa. More importantly, the results confirmed the formation of an Orowan loop in the interaction between a rigid sphere and dislocation. Furthermore, we discovered a phenomenon in which the Orowan loop disintegrated into two small loops during its interaction with the rigid sphere and dislocation.