Accessing metastable structural states in high-entropy alloys (HEAs) offers a promising route to tailor material properties, yet the use of high pressure to engineer such states remains underexplored. Here, we report the pressure-driven synthesis of a unique metastable dual-BCC microstructure in a near-equimolar ReNbTiZrHf alloy. Starting from an ambient two-phase mixture of hexagonal (C14-derived) and body-centered cubic (BCC) phases, compression induces a selective, diffusionless transformation of the hexagonal constituent into a second, crystallographically distinct BCC polymorph, while the original BCC phase remains stable. Upon decompression, the pressure-induced BCC phase is kinetically trapped, yielding a dual-BCC state that is inaccessible via conventional thermal processing. The pressure-stabilized BCC polymorph is Re-enriched and inherits the exceptional stiffness of its hexagonal parent (bulk modulus $\sim 290$ GPa), creating a composite microstructure with pronounced elastic and mechanical contrast relative to the softer original BCC matrix $(\sim 180 \mathrm{GPa})$. These findings demonstrate that pressure can effectively navigate the flat free-energy landscapes of chemically complex alloys, establishing a robust pathway for polymorph engineering and metastable phase design in refractory HEAs.

Er-doped ${\mathrm{Al}}_2{\mathrm{O}}_3$ is a promising host for telecom-band integrated photonics. Here we combine ab initio calculations with a symmetry-resolved analysis to elucidate substitutional Er on the Al site $\left({\mathrm{Er}}_{\mathrm{Al}}\right)$ in $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$. First-principles relaxations confirm the structural stability of ${\mathrm{Er}}_{\mathrm{Al}}$. We then use the local trigonal crystal-field symmetry to classify the Er-derived impurity levels by irreducible representations and to derive polarization-resolved electric-dipole selection rules, explicitly identifying the symmetry-allowed $f-d$ hybridization channels. Kubo-Greenwood absorption spectra computed from Kohn-Sham states quantitatively corroborate these symmetry predictions. Furthermore, we connect the calculated intra-$4f$ line strengths to Judd-Ofelt theory, clarifying the role of $4f-5d$ admixture in enabling optical activity. Notably, we predict a characteristic absorption near 1.47 $\mu \mathrm{m}$ (telecom band), relevant for on-chip amplification and emission. To our knowledge, a symmetry-resolved first-principles treatment of Er:${\mathrm{Al}}_2{\mathrm{O}}_3$ with an explicit Judd-Ofelt interpretation has not been reported, providing a transferable framework for tailoring rare-earth dopants in wide-band-gap oxides for integrated photonics. Our results for the optical spectra are in good agreement with experimental data. The resulting symmetry-based selection rules translate directly to polarization-dependent coupling in ${\mathrm{Al}}_2{\mathrm{O}}_3$ integrated photonic waveguides and resonators, enabling device-level design of TE/TM-mode interaction with Er emitters in the 1.5-$\mu \mathrm{m}$ telecom band.

Compositional trends in III-V ternary nanowires grown by the vapor-liquid-solid method were extensively studied over the past decade. Conversely, the wurtzite-zincblende polytypism was investigated mainly for binary III-V nanowires. The crystal phase changes in III-V ternary nanowires and even the key parameters determining the preferred crystal structure of such nanowires remain largely unknown. Here, we try to fill the gap by presenting a model for the crystal phase in vapor-liquid-solid III-V ternary nanowires based on the surface energy analysis. Our approach is based on the known phase diagram of GaAs nanowires, and allows one to identify the crystal phase as a function of the droplet contact angle and composition. We show a qualitative trend agreement of the phase diagrams with the available experimental data on $\mathrm{I}{\mathrm{n}}_x\mathrm{G}{\mathrm{a}}_{1-x}\mathrm{As}, \mathrm{A}{\mathrm{l}}_x\mathrm{G}{\mathrm{a}}_{1-x}\mathrm{As}$, and $\mathrm{Ga}{\mathrm{P}}_x\mathrm{A}{\mathrm{s}}_{1-x}$ nanowires. We also discuss the general crystal phase trends and the remaining uncertainties that should be circumvented to enable the full description and compositional control of these complex growth systems.

We investigate the manipulation of weakly bound graphene nanoribbons (GNRs) on the Au(111) surface using large amplitude scanning force microscopy. The GNRs are fabricated in situ via surface-assisted Ullmann coupling. Mobile GNRs are identified in scanning images by increased noise due to their weak binding. Their mobility is reduced when they are part of an extended GNR network. Even during passive imaging, interactions between the tip and the GNR can induce slight movements, allowing us to approximate the corrugation of the surface binding potential. We demonstrate tip-induced rotation and lateral displacement of GNRs perpendicular to their axis, during which the ribbon is partially lifted from the surface. Based on first-principles calculations, we construct a two-dimensional potential energy landscape and perform climbing image nudged elastic band calculations to approximate energy barriers for translation. Both approaches show that the barrier strongly depends on the GNR orientation. In addition, we find that beyond a critical length, GNRs become effectively immobilized due to increased energy barriers and reduced flexibility. The theoretical results align well with the observed outcomes of the manipulation experiments.

Hydrogen uptake in brownmillerite perovskites ${\mathrm{A}}_2{\mathrm{B}}_2{\mathrm{O}}_5$ offers an (electro)chemically accessible route to tune functional properties, but mechanistic understanding and design rules for hydrogen-responsive oxides remain limited. Here, we employ density functional theory (DFT) to quantify how H absorption affects electronic structure, magnetic exchange, and anisotropy in representative ${\mathrm{Sr}}_2{\mathrm{Fe}}_2{\mathrm{O}}_5$ and ${\mathrm{Sr}}_2{\mathrm{Co}}_2{\mathrm{O}}_5$ oxides. We find that hydrogenation introduces a localized ${\mathrm{e}}^{-}$ that stabilizes near the ${\mathrm{H}}^{+}$, with B-site dependent preference. The resulting lattice distortions and redistribution of charge density modify exchange coupling and cant the Néel vector, giving rise to weak ferromagnetism. We also show that absorption energies are highly sensitive to ${\mathrm{H}}^{+}–{\mathrm{e}}^{-}$ arrangements and magnetic order, varying by up to 1 eV across different settings. This sensitivity demands consistent treatment of charge localization and spin states, together with careful choice of computational parameters. Extending to a variety of experimentally reported ${\mathrm{A}}_2{\mathrm{B}}_2{\mathrm{O}}_5$ compositions, we identify candidates with favorable H uptake and uncover a trend linking more favorable absorption to a higher B-site $d$-electron count. We also demonstrate that the preferential ${\mathrm{H}}^{+}$ absorption site in these materials is governed by local O–O separations and lattice flexibility, which describe the ability of the framework to accommodate ${\mathrm{H}}^{+}$-induced distortions. Finally, benchmarks of universal machine-learning interatomic potentials reveal uncertainties of about 1 eV for site-resolved absorption energies, motivating descriptor-based surrogate models and targeted DFT validation. Together, these results establish practical design rules for hydrogen-responsive oxides relevant to iono-electronic devices, sensors, and electrically tunable spin functionality.

Understanding the mechanisms of helium-induced damage in zirconium alloys used in nuclear reactors is essential for ensuring both reactor safety and the longevity of materials. However, atomistic simulation of helium (He) in $\alpha$ -zirconium ( $\alpha$ -Zr) has proven to be challenging due to the limitations of conventional empirical potentials. In this study, we developed a deep-potential (DP) model to explore the diffusion and nucleation behavior of He in $\alpha$ -Zr through molecular dynamics simulations. The DP model demonstrates strong consistency with density functional theory (DFT) results in predicting elastic constants, phonon spectra, and thermodynamic properties, significantly outperforming traditional empirical potentials. We found that helium atoms preferentially occupy the basal octahedral (BO) and tetrahedral (T) interstitial sites in $\alpha$ -Zr, with a diffusion activation energy of 0.34 eV. Increased concentrations of He in $\alpha$ -Zr lead to lattice distortions, which degrade the material's mechanical properties. The process of He bubble aggregation shows characteristics of dynamic equilibrium, and the size of the He clusters in $\alpha$ -Zr is positively correlated with temperature.

We demonstrate precise control of magnetism in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin films through careful synthesis by molecular beam epitaxy, achieving minimal defects and accurate layer thickness control. By optimizing Mn-Bi-Te ratios and growth temperatures, we minimize detrimental self-doping effects and accurately target integer-layer films. X-ray diffraction and reflectivity provide quantitative measures of film quality and thickness. When these macroscale probes of structure and thickness are integrated with magnetotransport measurements, a striking even-odd layer dependence of the anomalous Hall effect is revealed. Odd-layer films exhibit a large hysteresis up to the Néel temperature ($\sim 25\mathrm{K}$), consistent with noncompensated antiferromagnetism, while even-layer films show minimal response, as expected for an antiferromagnet. The sign of the anomalous Hall effect exhibits a sign reversal for intrinsic magnetism versus magnetism associated with defects. This work identifies critical factors for inducing pure, noncompensated ferromagnetism and reveals the characteristics of the intrinsic anomalous Hall effect in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, which together is a step toward realizing the zero-field quantum anomalous Hall effect in topological materials.

The silicon-hydrogen system is of key interest for solar-cell devices, including both crystalline and amorphous modifications. Elemental amorphous Si is now well understood, but the atomic-scale effects of hydrogenating the silicon matrix remain to be fully explored. Here, we present a machine-learned interatomic potential model based on the atomic cluster expansion (ACE) framework that can describe a wide range of Si-H phases, from crystalline and amorphous bulk structures to surfaces and molecules. We perform numerical and physical validation across a range of hydrogen concentrations and compare our results to experimental findings. Our work constitutes an advancement toward the exploration of large structural models of $a$-Si:H at realistic device scales.

This work presents a systematic study of the pressure evolution of the electronic structure of ZrSiS using bulk magnetotransport measurements under hydrostatic pressure and first-principles calculations. Magnetoresistance measured at four pressure points (0.25, 0.47, 1.55, and 2.10 GPa) exhibits clear Shubnikov-de Haas oscillations characterized by five dominant frequencies, $F_{\alpha }=17$, $F_{\beta }=37$, $F_{\gamma }=93$, $F_{\delta }=138$, and $F_{\epsilon }=242\mathrm{T}$, which remain nearly unchanged with increasing pressure. To probe the pressure evolution of the electronic states, the Berry phase $\left({\mathrm{\Phi }}_{\mathrm{B}}\right)$ was extracted from Landau level fan diagram analyses. The extracted ${\mathrm{\Phi }}_{\mathrm{B}}$ values for the $\alpha$ and $\epsilon$ orbits show a systematic evolution with pressure, changing from values close to $\pi$ at low pressure toward values approaching zero above $\sim 0.47$ GPa, suggesting a possible change in the electronic topology near this pressure. To further examine the evolution of the band topology, we calculated the topological invariants calculations. The results suggest nontrivial states at low pressures and a tendency toward trivial states at higher pressures, consistent with the experimentally observed evolution of the Berry phase. To further investigate the underlying electronic structure, first-principles calculations were performed up to 16 GPa. The calculated band structures reveal multiple Dirac crossings near the Fermi level derived primarily from Zr $d$ and S $p$ orbitals, which remain robust under pressure. Phonon dispersion calculations show no imaginary modes up to 16 GPa, confirming the dynamical stability of ZrSiS under hydrostatic compression. The combined experimental and theoretical results indicate that pressure modifies the electronic states without a pronounced reconstruction of the Fermi surface, highlighting the role of subtle changes in the electronic structure. These findings provide insight into pressure-driven electronic evolution in nodal-line semimetals and related quantum materials.

The electrochemical instability of Sn-based halide perovskites in aqueous media is commonly linked to surface electron accumulation and defect-assisted oxidation of ${\mathrm{Sn}}^{2+}$ to ${\mathrm{Sn}}^{4+}$. Here, we examine how interfacial coupling in a cesium tin chloride (${\mathrm{CsSnCl}}_3)$-molybdenum disulfide $\left({\mathrm{MoS}}_2\right)$ (CSC–MS, 10%) composite electrode influences charge distribution and electrochemical behavior. Electrochemical and spectroscopic measurements indicate trends consistent with effective electronic redistribution at the interface between $n$-type ${\mathrm{CsSnCl}}_3$ and $p$-type 2H-${\mathrm{MoS}}_2$, suggestive of a type-II–like alignment. Mott-Schottky analysis yields an apparent flat-band offset on the order of several hundred millivolts, which reflects an effective interfacial capacitance response rather than a uniquely defined junction potential in the heterogeneous composite electrode. Correlated trends in x-ray photoelectron spectroscopy, impedance spectroscopy, and kinetic analyses support reduced near-surface electron density in ${\mathrm{CsSnCl}}_3$ and an enhanced pseudocapacitive response. In addition, ${\mathrm{MoS}}_2$ contributes hydrophobic basal planes and electronically active edge states that cooperatively improve interfacial stability, electronic percolation, and charge transport. As a result, the composite exhibits a kinetically extended aqueous operating window approaching 2.3 V under scan conditions and mixed charge-storage behavior in which reversible ${\mathrm{Sn}}^{2+}/{\mathrm{Sn}}^{4+}$ redox processes are contributory but not exclusive. These results provide a physically consistent, though not uniquely resolved, picture of how interfacial coupling and composite engineering can enhance the aqueous pseudocapacitive performance of lead-free halide perovskite electrodes.

Hydrogen isotope transport in plasma-facing components is a critical issue for nuclear fusion devices, as it directly affects fuel retention, permeation, and material integrity. In ITER-like divertor designs, tungsten monoblocks are bonded to copper-based heat sinks, forming W/Cu interfaces that play a key role in hydrogen migration from the plasma-facing surface toward the coolant. At the atomic scale, such interfacial regions present additional challenges, as interstitial diffusion is inherently more complex than in bulk materials due to asymmetries in the energy landscape and modified atomic coordination. This asymmetry restricts the development of macroscopic kinetic models, as it requires considering a large number of flux balance equations. Consequently, metallic interfaces are often assumed to be in local thermodynamic equilibrium, ensuring chemical potential continuity. These assumptions, widely employed in macroscopic rate equations codes, are examined in this study. A methodology is proposed to reduce the number of equations needed for flux balance across metallic interfaces, eliminating the necessity of assuming local thermodynamic equilibrium or chemical potential continuity while enabling implementation in reaction diffusion codes. Given its relevance for nuclear fusion devices, we apply the approach to hydrogen diffusion at the tungsten/copper interface as a case study. The resulting reduced kinetic model accurately reproduces both the time to reach steady-state conditions and the hydrogen concentration profile.

The unique optoelectronic properties of organic semiconductors make them attractive candidates for functional electronic devices. Organic molecules exhibiting singlet fission—a process in which a photoexcited singlet exciton converts into two triplet excitons—hold particular promise for enhancing the efficiency of organic optoelectronic devices. Once generated, triplet excitons decay either through triplet-triplet annihilation (TTA) or interaction with trap states. Identifying these decay pathways is essential for understanding and controlling the performance of organic semiconductors. Modulated photocurrent (MPC) spectroscopy is a useful technique for extracting information about various parameters of the trap states of inorganic and organic semiconductors. Recently, it was shown that in organic semiconductors the MPC is highly sensitive to exciton-trap interactions, where excitons dissociate into mobile holes. Here, using this approach, we present a new spectroscopic method based on MPC for extracting both the triplet exciton density and the density of traps involved in their dissociation in two-terminal organic devices: rubrene single crystals and pentacene thin films. Furthermore, we show that the characteristic dependence of triplet exciton density on the light generation rate enables the separation of different decay pathways. Our results reveal that triplet exciton decay is dominated by TTA in rubrene crystals, while in pentacene films it primarily proceeds via triplet-trap interactions.

The structural and scintillation properties of pure and Ce-doped ${\mathrm{Y}}_3{\mathrm{Sc}}_x{\mathrm{Al}}_{5-x}{\mathrm{O}}_{12}$ $(x=0, 0.05, 1.16, \text{and} 2)$ crystals were systematically investigated. High-resolution ${}^{45}\mathrm{Sc}$ and ${}^{27}\mathrm{Al}$ magic angle spinning nuclear magnetic resonance spectroscopy revealed that $\mathrm{S}{\mathrm{c}}^{3+}$ ions predominantly occupy octahedral sites, effectively replacing $\mathrm{A}{\mathrm{l}}^{3+}$ ions, while antisite Sc at Y dodecahedral positions remains below 0.2 at.%. Sc incorporation into ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ induces strong exciton emission at 320–324 nm, nearly 10 times higher than that of reference ${\mathrm{Bi}}_4{\mathrm{Ge}}_3{\mathrm{O}}_{12}$ (BGO) crystal, even at low Sc concentrations (5 at.%). $\mathrm{C}{\mathrm{e}}^{3+}$ doping introduces characteristic $5d^1\to 4f$ emission at 518 nm, accelerates scintillation decay, and in combination with $\mathrm{M}{\mathrm{g}}^{2+}$ codoping, promotes the formation of $\mathrm{C}{\mathrm{e}}^{4+}$ ions that enable a fast radiative de-excitation pathway. ${\mathrm{Y}}_3{\mathrm{Sc}}_2{\mathrm{Al}}_3{\mathrm{O}}_{12}$: Ce exhibits a maximum scintillation light yield of 80–84% relative to BGO with a mean decay time of 85–110 ns. Thermostimulated liminescence and electron paramagnetic resonance studies indicate that holes are mainly trapped at oxygen ions near Sc ions (${\mathrm{O}}^{-}$ centers), while electrons are primarily localized at Sc antisite ions near oxygen vacancies ($\mathrm{S}{\mathrm{c}}^{2+}\text{–}{\mathrm{V}}_{\mathrm{O}}$ centers), affecting scintillation kinetics. Density functional theory calculations confirm that $\mathrm{S}{\mathrm{c}}^{3+}$ at the dodecahedral site forms a deep electron trap. These results highlight the key role of Sc and Ce in tuning emission, decay dynamics, and defect-mediated processes in Sc-admixed multicomponent garnet scintillators.

Cation self-diffusion plays a key role in the microstructure evolution of a wide range of materials, including oxide nuclear fuels. Growing evidence indicates that small defect clusters can make a substantial contribution to cation transport in these oxides. Quantifying this contribution is nevertheless challenging because of complex defect chemistry, strong correlations between cation and anion migration, and the existence of multiple competing migration mechanisms. In this work, we compute bulk cation self-diffusion coefficients in stoichiometric ${\mathrm{UO}}_2$ and ${\mathrm{PuO}}_2$ by explicitly accounting for small vacancy clusters (cation–anion divacancies and Schottky defects) in addition to isolated cation vacancies. Our approach combines a systematic exploration of cluster migration pathways using ART-nouveau with the calculation of cluster transport coefficients through the KineCluE code, which rigorously incorporates the influence of local atomic environments and kinetic correlations on defect migration. These transport coefficients are then coupled with equilibrium cluster concentrations to obtain self-diffusion coefficients directly comparable with experimental data. We find that small vacancy clusters are significantly more mobile than isolated cation vacancies and dominate the overall diffusion process. In ${\mathrm{UO}}_2$, the resulting self-diffusion coefficients are consistent with the most reliable experimental datasets, whereas in ${\mathrm{PuO}}_2$ the predictions are discussed in light of the limited data currently available. Although vacancy clusters exhibit higher mobility in ${\mathrm{PuO}}_2$, the overall self-diffusion coefficient is lower than in ${\mathrm{UO}}_2$ because of the larger cation vacancy formation energy predicted by our defect model. Beyond actinide oxides, this work demonstrates how defect clusters can be systematically integrated into diffusion calculations and provides transferable insights and input data for fuel behavior models.

It is known that cuprate artificial high-$T_C$ superlattices (AHTS) with period $d$, composed of quantum wells confining interface space charge in stoichiometric Mott insulator layers ($S$), with thickness $L$, at the interface with overdoped normal metallic cuprate layers ($N$) show a superconducting dome by tuning the geometric $L$ over $d$ ratio of the SNSN superlattice with the top predicted by quantum material design engineering quantum size effects. Here we report high-field magnetotransport measurements up to 41 Tesla of AHTS across the entire superconducting dome. The results show the universal upward-concave behavior of the temperature-dependent upper critical magnetic field in low-$T_C$ samples at the rising edge and drop edge of the dome, providing strong evidence consistent with two-band superconductivity in agreement with multigap theory used for quantum design of the SNSN superlattices. The measured superconducting coherence length demonstrates that atomic-scale engineering controls not only the critical temperature but also the intrinsic pair size at Fano-Feshbach resonances physics paving the way toward next-generation quantum devices and shedding light on unconventional superconductivity.