The motion of microdroplets under thermal gradients, also known as thermomigration (TM), plays a critical role in a wide range of surface phenomena and technological applications. In this work, we study the TM behavior of Au-Ge micro-droplets on Ge(111) surfaces and show that the droplet motion leads to the formation of atomically flat terraces, which are essential for thin film epitaxy. Experimental observations are combined with a microscopic model to investigate droplet motion and the formation of flat atomic terraces. Our results show that, at low temperatures, droplet velocity increases with size, but this size dependence diminishes as the temperature rises. The microscopic model we develop is based on thermally activated detachment, diffusion, and attachment of solute (Ge) atoms across the droplet, driven by a temperature-dependent concentration difference between the leading edge and the trailing edge. The model reproduces the experimental trends. Our results provide insights into the fundamental mechanisms of droplet TM and suggest ways to control surface morphology.

Tunable electronic properties in magnetic materials lead to novel physical phenomena that have the potential to be exploited in the design of new spintronic devices. Here, we report the effect of uniaxial stress on the anomalous Hall effect (AHE) in the hexagonal frustrated antiferromagnetic Heusler compound ${\mathrm{Mn}}_3\mathrm{Ge}$. Our x-ray diffraction results show that the $c/a$ ratio varies linearly with strain when stress is applied along the $a$ axis, as well as a significantly higher Young's modulus along the $c$ direction. The linear behavior of the $c/a$ ratio under uniaxial stress mirrors that seen under hydrostatic pressure up to 1.8 GPa, but results in a characteristically different behavior of the AHE. Stress applied along the $a$ axis induces a distortion in the $ab$ plane, smoothing the abrupt jump in the AHE signal at zero magnetic field. In contrast, stress applied along the $c$ axis has little effect, presumably due to the higher Young's modulus. We argue that this is due to pronounced changes in magnetic order.

We investigate the chiral magnet $\mathrm{CoTeMo}{\mathrm{O}}_6$ (CTMO), an orthorhombic $\mathrm{P}{2}_1{2}_{1}2$ system with a canted antiferromagnetic structure and weak ferromagnetism along the $a$ axis. Despite lacking a unique polar axis in its crystal structure, CTMO exhibits significant magnetodielectric coupling, which is consistent with a spin-dependent p-d hybridization mechanism. Using single-crystal magnetization, neutron diffraction, and magnetocapacitance measurements, complemented by inelastic neutron scattering, we identify that the magnetic behavior of CTMO can be described by an anisotropic Hamiltonian with magnetic moments interpolating between two limit representations: spin-orbit entangled $J_{\mathrm{eff}}=1/2$ and spin-only $S=3/2$ moments. Depending on the representation, a Dzyaloshinskii-Moriya interaction or a site-dependent off-diagonal single-ion anisotropy leads to the formation of a canted magnetic structure. A comparative study with $\mathrm{MnTeMo}{\mathrm{O}}_6$ (MTMO), which has a collinear antiferromagnetic structure and negligible magnetodielectric coupling, confirms the crucial role of noncollinearity and intrinsic magnetic interactions in spin-driven dielectric responses. These results highlight the broader relevance of the p-d hybridization mechanism in insulating magnets and motivate further studies on magnetoelectric coupling in CTMO.

Interfaces between molecular layers and ferromagnetic materials, named spinterfaces, have been widely studied on account of the intriguing magnetic phenomena associated with the spin-polarized hybrid interface states, and of possible innovative applications. This work starts exploring the opportunities given by coupling molecular layers and antiferromagnetic materials, focusing on the magnetoelectric antiferromagnetic insulator ${\mathrm{Cr}}_2{\mathrm{O}}_3$. Antiferromagnets are currently of great interest for the future development of spintronics and magnonics applications, since they are stable against external fields and they show dynamic behaviors at much higher frequencies, compared to ferromagnets. On the other hand, interacting with the magnetic structure of an antiferromagnet is more challenging. A possible approach is that of establishing an antiferromagnetic spinterface, in such a way that external stimuli acting on the molecular side can influence the substrate magnetic parameters. Self-assembled monolayers of FePc (iron phthalocyanine) are prepared on thin ${\mathrm{Cr}}_2{\mathrm{O}}_3$ films, and the morphological, structural, electronic, and magnetic properties of the resulting antiferromagnetic spinterface are experimentally and theoretically investigated. We observe flat-lying molecular layers that develop a long-range magnetic ordering of the magnetic moments associated with Fe ions. Our calculations support the conclusion that such ordering is established through the interaction at the interface between FePc and ${\mathrm{Cr}}_2{\mathrm{O}}_3$.

Ultrawide bandgap semiconductors such as $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ are ideal materials for next-generation power electronic devices. Electronic and mechanical properties of $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ can be tuned by alloying with other sesquioxides, notably ${\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{In}}_2{\mathrm{O}}_3$. Moreover, by tuning the In content of a ${\left({\mathrm{In}}_x{\mathrm{Al}}_{1-x}\right)}_2{\mathrm{O}}_3$ alloy, its lattice constants can be matched to those of ${\mathrm{Ga}}_2{\mathrm{O}}_3$, while preserving a large conduction-band offset. In view of potential applications to $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$-based heterostructure, we performed atomistic modeling of ${\left({\mathrm{In}}_x{\mathrm{Al}}_{1-x}\right)}_2{\mathrm{O}}_3$ alloys using density functional theory to investigate thermodynamic and electrical properties of conventional group IV dopants (Si, Sn, C, Ge), alternative metal donors (Ta, Zr, Hf), and acceptors (Mg, Zn, Cu). The hybrid Heyd–Scuseria–Ernzerhof functional (HSE06) is used to accurately quantify the defect formation energies, ionization levels, and concentrations over a wide range of experimentally relevant conditions for the oxygen chemical potential and temperature. In our atomistic models, Hf and Zr show favorable properties as alternative donors to Si and other group IV impurities, especially under oxygen-poor conditions. Our findings also suggest that acceptors Mg, Zn, and Cu, while they cannot promote $p$ doping, can be still beneficial for the compensation of unintentionally $n$-doped materials, e.g., to generate semi-insulating layers and improve rectification.

We observed an anomalous bending and transmission at the Bragg condition by crystal stacking fault. Two macroscopic and sharp deflections were observed in the proximity of the interface of stacking faults inside a diamond crystal due to the x-ray translation effect. Anomalous high transmissivity through the crystal was observed due to the x-ray translation toward the interface and due to some possible topological effect. The Berry phase for translated x-rays enables us to identify the type of stacking faults existing in the crystal by the angular dependence of the amount of x-ray translation.

We present thermal conductivity data on single crystals of ${\mathrm{YAlO}}_3$ and ${\mathrm{YbAlO}}_3$ for temperatures between 2 K and 300 K and the heat current along $b$ and $c$. Both materials are very good thermal conductors in the investigated temperature range. The thermal conductivity in these electrical insulators is caused by phonons. The effect of Y-Yb exchange is found to be rather small despite the considerable difference in density and average atomic mass. For ${\mathrm{YAlO}}_3$, we find a moderate thermal conductivity anisotropy with weak temperature dependence and a ratio of $c$ to $b$ direction between at most 1 and 2.2. It is discussed in terms of the velocities of sound and relevant scattering processes. For ${\mathrm{YbAlO}}_3$ the small crystal size limits the precision of absolute thermal conductivity values and does not allow drawing conclusions on the anisotropy. Our results on ${\mathrm{YAlO}}_3$ confirm that the material is suitable for applications requiring a good thermal conductivity at temperatures down to liquid helium, such as lasers, substrates, and detectors.

We theoretically study the ultrafast optical control of multiple valley states in two‐dimensional (2D) tin sulfide (SnS) monolayers, a member of the layered group-IV monochalcogenides, which is a promising class of materials for overcoming current challenges in valleytronics. By combining time‐dependent density functional theory with Maxwell's equations, we simulate how both linearly and circularly polarized ultrashort laser pulses affect the electronic excitation dynamics and valley polarization in SnS. Our results reveal that the corrugated phosphorene-like crystal structure of SnS monolayers leads to the emergence of both linear and circular dichroism, allowing flexible manipulation of multivalley excitation by simply adjusting the light polarization. Moreover, the interplay between broken inversion symmetry and spin-orbit coupling gives rise to distinct Berry curvature effects and spin-valley coupling, thereby enabling circular dichroism. Furthermore, we propose that tuning the carrier‐envelope phase of few-cycle femtosecond laser pulses can achieve subcycle, ultrafast switching among multiple valley states. These findings provide further insight into valley dynamics in 2D materials and may contribute to future developments in valleytronics applications.

Using a computational crystal structure search in the Li-Fe-B ternary system, we predict a stable phase of $\mathrm{L}{\mathrm{i}}_3\mathrm{F}{\mathrm{e}}_8{\mathrm{B}}_8$, featuring 1D channels that enable rapid Li-ion transport. Ab initio molecular dynamics simulations show that the Li-ion diffusion coefficient in $\mathrm{L}{\mathrm{i}}_3\mathrm{F}{\mathrm{e}}_8{\mathrm{B}}_8$ surpasses that of common electrode and conductive additive materials by several orders of magnitude. The high diffusion in $\mathrm{L}{\mathrm{i}}_3\mathrm{F}{\mathrm{e}}_8{\mathrm{B}}_8$ can be explained by the Frenkel–Kontorova model, which describes an incommensurate state between the Li diffusion chain and the periodic potential field caused by the FeB backbone structure. The favorable lithium-ion diffusivity and mechanical properties of $\mathrm{L}{\mathrm{i}}_3\mathrm{F}{\mathrm{e}}_8{\mathrm{B}}_8$ make it a promising conductive additive for battery materials. An external magnetic field can further manipulate the properties of this material due to its predicted itinerant ferromagnetism, which also offers a platform for exploring spin-dependent phenomena.

Nernst effect, a transverse electric current induced by a temperature gradient, is a promising tool for revealing emergent phases of condensed matter. We find a Nernst coefficient plateau in low carrier density topological insulators, as a signature of 1D Weyl points in the quantum limit of the weak topological insulator. The plateau height is inversely proportional to the impurity density, suggesting a way to engineer infinitely large Nernst effects. The Nernst plateau also exists in strong topological insulators, at the bottom of the lowest Landau band. We show that these plateaus have been overlooked in the previous experiments and we highlight the experimental conditions to observe them. Our results may inspire more investigations of employing anomalous Nernst effect to identify emergent phases of condensed matter.

Superconducting thin metallic films, functioning as supercurrent gate-tunable transistors, have considerable potential for future quantum electronic devices. Despite extensive research, a comprehensive microscopic quantitative mechanism that elucidates the control or suppression of supercurrents in thin films remains elusive. Focusing on NbN, a prototypical material, and starting from a phenomenological ansatz that links the critical electric field with the kinetic energy parameter needed to break Cooper pairs, we provide a quantitative analysis of the critical current using Eliashberg theory in the dirty limit without adjustable parameters. The critical kinetic energy value is identified, corresponding to the maximum supercurrent that can flow in the thin film. The peak in supercurrent density as a function of the Cooper pairs' kinetic energy arises from the interplay between the increase in supercurrent due to increased kinetic energy and the depairing effect when the kinetic energy becomes sufficiently large. The critical value of the pair's kinetic energy is subsequently employed to estimate the critical value of an external electric field required to suppress superconductivity in the sample. This estimation is in parameter-free agreement with the experimental observations. Although the disorder reduces the temperature dependence of the gating effect on the critical current, at the same time, it increases the unscreened critical electric field needed to suppress superconductivity. This enables the proposal of methods to control and reduce the critical field value necessary to suppress superconductivity in superconducting electronics.

Aluminum-magnesium alloys are widely used in engineering, but their susceptibility to hydrogen embrittlement and intergranular corrosion limits their applications. Understanding these phenomena requires accurate atomistic modeling of the ternary Al-Mg-H system, which has been hindered by the lack of reliable interatomic potentials. This work presents a ternary atomic cluster expansion (ACE) potential for Al-Mg-H, trained on an extensive density functional theory dataset using active learning. The ACE potential accurately reproduces a wide range of properties, including defect energetics, phase stability, and diffusion coefficients. Thanks to its outstanding computational efficiency, ACE can be employed in large-scale atomistic simulations that help elucidate the nanoscale mechanisms of hydrogen-related degradation in Al-Mg alloys.

Deep-level transient spectroscopy measurements were conducted on He-implanted $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ thin films to study the $E_4^{*}$ level, which is a known irradiation-induced defect that is energetically positioned $1.5\mathrm{e}\mathrm{V}$ below the conduction band minimum. We find that the formation of $E_4^{*}$ after implantation is strongly dependent on a reverse-bias annealing step, where the activation energy for the thermally-activated introduction of $E_4^{*}$ is estimated to be $\sim 2.4\mathrm{e}\mathrm{V}$. Contrary to previous reports, we find, for some of the measured diodes, that the level is stable upon subsequent measurements. From first-principles calculations of the intrinsic defects, we find that the properties of the $V_{\text{O1}}$ and $V_{\text{O3}}$ configurations of the oxygen vacancy closely agree with the experimental observations for the $E_4^{*}$ level. A model is suggested where the reverse bias lowers the Fermi-level position in the depletion region of the diode and changes the relative formation energies of the possible configurations of the oxygen vacancy; the formation of $E_4^{*}$ then results from an increase in the relative stability of the O1 and O3 configurations of $V_{\mathrm{O}}$.

PEDOT:Tos is a promising conducting polymer for electronic and bioelectronic applications, yet its charge transport is affected by various factors and remains challenging to optimize. This study investigates the impact of solvent posttreatment on PEDOT:Tos thin films, exploring its influence on morphology and electrical conductivity. A combined experimental-theoretical approach is employed, integrating molecular dynamics, density functional theory, and transport calculations on one hand and conductivity, GIWAXS and XPS measurements on the other hand. Moreover, we developed a machine learning (ML) framework based on convolutional neural networks with the Coulomb matrix as the predictor, and transfer integrals for multiscale transport calculations as targets. Our results reveal that solvent-induced morphological changes strongly affect charge transport, with the ML model effectively reproducing observed conductivity. The developed ML model dramatically boosts the speed of mobility calculations, enabling the analysis of large-scale polymer films that were previously beyond computational reach.

The recently identified multiprincipal-element alloy (MEA), known as GRX-810, exhibits a dramatic improvement in the creep resistance at elevated temperatures. Initial studies have identified segregation atmospheres around the oxide-dispersion particles, which likely contribute to this phenomenon. However, the many details remain elusive, especially the co-segregation effects. Such effects include both substitutional and interstitial type segregation, leading to a complex alloying environment. To investigate these segregation effects, Monte Carlo/ab initio based molecular dynamics (MC/AIMD) hybrid simulations were performed. Coupled with an algorithm to identify potential interstitial sites, evaluation of the joint interstitial and substitutional segregation events was made possible. The simulations have revealed critical elements of carbon segregation near the oxide-dispersoid particles, where carbon atoms are repelled from the oxygen-terminated metal-yttria interface but attracted to the yttrium-terminated interface. This discovery identifies critical distinctions between yttrium-based oxide dispersoids, which control critical solute atmospheres.

We introduce the Cyrrhus spin ice geometry, a variant of decimated square ice patterns that exhibits a form of magnetic frustration known as vertex frustration. Using synchrotron-based photoemission electron microscopy, we present a temperature-dependent study of magnetic moment fluctuations in this dipolar Cyrrhus lattice. The results confirm key signatures of vertex frustration marked by an elevated presence of energetically unfavorable moment configurations and a strong adherence to an emergent ice rule. Analyzing the observed dynamics within the framework of the Thirumalai-Mountain stress metric reveals near-zero values for the relaxation exponent, suggesting ergodicity-breaking dynamics.