Alloy engineering offers a powerful route to tailor the optoelectronic properties of two-dimensional semiconductors. However, a comprehensive understanding of how alloy composition simultaneously affects the electronic structure, excitonic response, vibrational properties, and spin-valley physics remains limited. Here, we investigate monolayer ${\mathrm{MoS}}_{2x}{\mathrm{Se}}_{2(1-x)}$ alloys across the full composition range using optical spectroscopy. We demonstrate continuous tuning of the optical gap over $\sim 0.35\mathrm{eV}$, accompanied by a systematic reduction of the A-B exciton splitting, in agreement with density functional theory calculations. Temperature-dependent measurements reveal a progressive increase of the average phonon energy from Se-rich to S-rich alloys that follows a simple reduced-mass scaling model. Polarization-resolved spectroscopy further shows a monotonic increase of the circular polarization from nearly zero in ${\mathrm{MoSe}}_2$ to $\sim 15\%$ in ${\mathrm{MoS}}_2$ at 78 K. The observed evolution of the polarization is attributed to alloy-induced modifications of the electronic structure that modify bright-dark exciton mixing and the associated valley depolarization. These findings establish alloy engineering as an effective strategy for controlling excitonic properties in transition-metal-dichalcogenide monolayers.

We report a comprehensive, multitechnique study of bismuth oxide growth on Au(111) under different conditions such as temperature and exposure to molecular oxygen. By combining synchrotron-based x-ray photoelectron spectroscopy and diffraction with low-energy electron diffraction and scanning tunneling microscopy, we elucidate the structural evolution of the system during controlled oxidation and subsequent annealing. We find that Bi deposition induces well-defined surface reconstructions, whereas oxidation triggers the formation of a complex sequence of bismuth oxide domains. High-resolution spectroscopic and diffraction data enable us to identify an oxide structure consistent with the (201) surface of $\beta \text{−}{\mathrm{Bi}}_2{\mathrm{O}}_3$. In addition, angle-resolved photoemission experiments and work function measurements reveal substantial electronic modifications triggered by a complex interplay of segregation of Bi and Au. Notably, a work function of 3.4 eV is achieved for oxidation at 423 K. These results provide benchmark structural and electronic insights into the Bi oxide/Au(111) system and establish a framework for integrating ${\mathrm{Bi}}_2{\mathrm{O}}_3$ as a contact material in devices using two-dimensional semiconductors, where it can enable low contact resistance.

The layered organic conductor $\kappa \text{−}{\left(\mathrm{BETS}\right)}_2\mathrm{Mn}{\left[\mathrm{N}{\left(\mathrm{CN}\right)}_2\right]}_3$ is a strongly correlated electron system exhibiting a metal-insulator transition at $T_{\text{MI}}\approx 25\mathrm{K}$ and unusual equilibrium and nonequilibrium dynamics above and below $T_{\text{MI}}$, respectively, caused by electronic ferroelectricity. However, at higher temperatures ($T^{*}=102\mathrm{K}$), another transition, associated with the formation of an incommensurate superstructure, has been reported, but its origin has not been clarified. By using resistance noise spectroscopy to investigate the low-frequency charge carrier dynamics as well as thermal expansion measurements, we find strong indications for a structural order-disorder transition of the BETS molecules' terminal ethylene groups, which manifests itself in a pronounced maximum in the noise magnitude around $T^{*}\approx 100\mathrm{K}$. Performing computational studies of the energy landscapes of the BETS cations and the Mn[N(CN)${}_2{]}_3$ polymeric anion, we find evidence suggesting that the observed structural transition is due to a possibly glassy freezing of the dicyanamide ligands in the anion layer.

Chemical short-range order (CSRO) critically underpins the physical properties of complex face-centered cubic (FCC) alloys, yet its reliable identification by electron diffuse scattering is often impeded by thermal diffuse scattering (TDS). This work revisits the kinematic theory of first-order TDS to establish a generalizable connection between characteristic TDS features and phonon dispersion relations in FCC systems. Simulations of pure Ni TDS patterns indicate that the commonly observed $1/3\left\{422\right\}$ and $1/2\left\{311\right\}$ peaks and diffuse streaking in $\left[11\overline{1}\right]$ and $\left[11\overline{2}\right]$ zone axes result from low-frequency transverse acoustic $\left\{111\right\}$ (L-branch) phonons in FCC lattices. We experimentally confirm that these hallmark features persist in complex FCC alloys, including a ${\left(\mathrm{CrCoNi}\right)}_{93}{\mathrm{Al}}_4{\mathrm{Ti}}_2\mathrm{Nb}$ medium-entropy alloy and an Fe-17Cr-3Ni-9Mn-3Cu-0.3N-0.14C austenitic stainless steel, and confirm their TDS origin through temperature-dependent measurements. We also discuss how TDS can confound CSRO characterization at the $1/3\left\{422\right\}$ and $1/2\left\{311\right\}$ positions in complex FCC alloys and propose practical strategies for robust CSRO analysis: targeting reflections in orientations where TDS and CSRO peaks separate in reciprocal space, such as the $1/3\left\{511\right\}$ positions in $\left[11\overline{4}\right]$. These results provide a transferable, physics-based approach for interpreting electron diffuse scattering in FCC metals and complex alloys and for designing diffraction measurements that isolate CSRO from ubiquitous TDS.

${\mathrm{Ce}}_2{\mathrm{Te}}_5$ is a layered $f$-electron van der Waals magnet in which reduced dimensionality and inequivalent Ce sites give rise to competing magnetic interactions. We investigate its magnetic ground state using muon spin relaxation ($\mu \mathrm{SR}$), neutron powder diffraction (NPD), and inelastic neutron scattering (INS). Zero-field $\mu \mathrm{SR}$ reveals an onset of static magnetism below $T_{\mathrm{C}}=5.0\left(1\right)\mathrm{K}$, followed by an additional anomaly in the internal field at $T_2=2.3\left(2\right)\mathrm{K}$, consistent with features observed in bulk thermodynamic and transport measurements. In contrast, NPD data collected between $0.05–8\mathrm{K}$ reveal a single long-range ordered magnetic phase below $T_{\mathrm{C}}$, with the magnetic Bragg intensities vanishing at $T_{\mathrm{C}}$ with no evidence for additional structural or magnetic phase transitions down to base temperature. The ordered state is characterized by a commensurate propagation vector $\mathbf{k}=(0,0,0)$ and ferromagnetic alignment of Ce moments along the crystallographic $b$ axis. Remarkably, only one of the two crystallographically distinct Ce sites carries an ordered moment of $\approx 0.85\left(3\right){\mu }_{\mathrm{B}}$ per Ce at 0.05 K. INS measurements establish the crystal-electric-field (CEF) energy scale of ${\mathrm{Ce}}^{3+}$, revealing low-lying excitations at 7.94 and 21.46 meV and a Kramers-doublet ground state with strong single-ion anisotropy. These results demonstrate that ${\mathrm{Ce}}_2{\mathrm{Te}}_5$ undergoes a single symmetry-breaking magnetic transition, while additional low-temperature anomalies reflect subtle modifications of the ordered state driven by competing interactions and CEF effects.

Since the prediction and observation of topological Weyl semimetals (chiral TSMs), there have been enormous efforts to characterize further condensed matter realizations of chiral fermions. These efforts were dramatically accelerated by the subsequent discovery of a profound link between low-energy topological and lattice chirality in structurally chiral crystals. Though TSMs are well understood in the limit of perfect translation symmetry, real solid-state materials host defects and disorder, and may even be rendered amorphous down to all but the smallest system length scales. Previous theoretical studies have concluded that chiral TSMs transition into trivial diffusive metals at moderate disorder scales, raising concerns that chiral TSM states may only be accessible in highly crystalline samples. In this work, we in contrast identify large families of chiral TSMs that instead persist under strong structural disorder—even into the amorphous regime. We show that amorphous chiral TSM phases can be stabilized in particular by the presence of long-range order in the local structural chirality. We present extensive analytic and numerical calculations demonstrating the existence of both Weyl and higher-charge chiral fermions in amorphous metals whose topology and spin and orbital angular momentum textures are tunable via the interplay of average symmetry and geometry. To distinguish and generate new realizations of strongly disordered chiral fermions, we introduce an analytic approach grounded in symmetry group theory. We then introduce an amorphous Wilson loop numerical method to identify chiral fermions in metals with 3D structural disorder. Our findings bridge the crystalline and strongly disordered regimes of chiral TSMs, and indicate a clear route toward engineering geometry-enforced topology in noncrystalline materials and metamaterials.

The existence of multiple amorphous states, or polyamorphism, remains one of the most debated phenomena in disordered matter, particularly regarding its microscopic origin and impact on glassy dynamics. Profiting of the enhanced data quality provided by brilliant synchrotrons, we combined high pressure x-ray photon correlation spectroscopy and x-ray diffraction to investigate the atomic dynamics-structure relationship in a ${\mathrm{Au}}_{49}{\mathrm{Cu}}_{26.9}{\mathrm{Si}}_{16.3}{\mathrm{Ag}}_{5.5}{\mathrm{Pd}}_{2.3}$ metallic glass at room temperature. We identify a structural and dynamical crossover near 3 GPa, marked by avalanchelike massive atomic rearrangements that promote the system toward increasingly compact atomic cluster connections. This crossover superimposes a pressure-induced acceleration of the atomic motion recently reported and signals the onset of a transitional state, potentially linked to the nucleation of a different phase within the glass, characterized by the coexistence of two amorphous states with distinct relaxation processes. These results provide evidence for a sluggish, continuous polyamorphic transformation, even in the absence of marked structural discontinuities.

We report on the fabrication and characterization of patterned high mobility two-dimensional electron gases (2DEG) formed on ${\mathrm{SrTiO}}_3$ (STO) substrate surfaces by hydrogen plasma exposure. The resulting devices consistently showed high electron mobilities up to $7400{\mathrm{cm}}^2/\left(\mathrm{V}\mathrm{s}\right)$. A large range of electron density was systematically explored by controlled aging of the sample between cooldowns, including the expected range for the STO 2DEG superconducting dome. No superconducting transition was observed down to the base temperature of approximately 10 mK. This suggests suppression of superconductivity in high mobility quasi-two-dimensional ${\mathrm{SrTiO}}_3$ electron gas, likely linked to vertical confinement and electronic orbital rearrangement. We systematically explored electrostatic gate modulation in this 2DEG system and its scaling with electron density and side gate geometry. In contrast with our initial expectation, we observed an improvement of achievable total modulation for larger side gate to channel separation. At low electron density, stochastic channel pinch-off events were observed, creating quasiballistic constrictions with irregular conductance quantization. This epitaxy-free and high mobility oxide material platform offers a promising route towards patterning quantum devices.

We report the synthesis and comprehensive investigation of single-crystalline ${\mathrm{Tb}}_2{\mathrm{IrAl}}_4{\mathrm{Ge}}_2$ and ${\mathrm{Er}}_2{\mathrm{IrAl}}_4{\mathrm{Ge}}_2$, the first Ir-based members of the $L{n}_{2}M{\mathrm{Al}}_4{\mathrm{Ge}}_2$ family. Both compounds crystallize in the tetragonal ${\mathrm{Tb}}_2{\mathrm{NiAl}}_4{\mathrm{Ge}}_2$-type structure (space group $I4/mmm$) and exhibit easy-axis magnetic anisotropy with the crystallographic $c$ axis as the preferred magnetization direction. ${\mathrm{Tb}}_2{\mathrm{IrAl}}_4{\mathrm{Ge}}_2$ undergoes antiferromagnetic ordering below $T_N=25\mathrm{K}$ and develops a sequence of field-induced metamagnetic transitions accompanied by pronounced magnetotransport anomalies, including a nonlinear Hall response. In contrast, ${\mathrm{Er}}_2{\mathrm{IrAl}}_4{\mathrm{Ge}}_2$ exhibits three successive zero-field magnetic transitions and a substantially richer low-temperature magnetic phase diagram comprising multiple competing field-induced phases confined to relatively modest magnetic fields. The differences between the Tb- and Er-based compounds demonstrate the wide range of magnetic behavior that can be realized within the ${\mathrm{Tb}}_2{\mathrm{NiAl}}_4{\mathrm{Ge}}_2$-type structure. More broadly, the successful realization of Ir-based $L{n}_{2}M{\mathrm{Al}}_4{\mathrm{Ge}}_2$ compounds considerably expands the accessible chemical space of this family and opens a route to the exploration of related $4d$- and $5d$-based aluminogermanides.

While bulk bcc plasticity is traditionally governed by screw dislocation glide, prismatic dislocation loops are proposed as an essential pathway for strain accommodation under severe, local constraints. This experimental study on pure W, as a model bcc system, demonstrates that prismatic dislocation half-loops can develop and propagate in a triaxial stress field as imposed by nanoindentation. Using electron channeling contrast imaging, the Burgers vector of emitted dislocation half-loops is determined to be 1/2 $\langle 111\rangle$ and the punching-out process is studied during progressive stages of imposed strain. Long arrays of dislocation half-loops are emitted during the initial displacement burst (pop-in) and continue to propagate during subsequent loading. Although energetic considerations indicate that loop formation alone cannot account for the total plastic deformation energy—implying a concurrent contribution from glide mechanisms—these findings reveal that plastic flow under severe hydrostatic stress gradients can be accommodated via non-Schmid loop punching. Crucially, the unique slip system multiplicity of the bcc lattice yields highly mobile, circular loop geometries that stand in stark contrast to the faceted loops typical of fcc metals.

Interpretable AI can reveal physical principles governing intricate materials properties by uncovering explicit relationships between physical parameters and target properties. The sure-independence screening and sparsifying operator (SISSO) symbolic regression approach identifies analytical expressions that correlate a target property with a small set of parameters, termed materials genes, selected from a large pool of candidates. However, multiple gene combinations can yield equally accurate SISSO models, with individual genes contributing with different weights. Here, we establish a derivative-based sensitivity analysis that enhances interpretability, thereby enabling deeper physical insight. This analysis also reveals how distinct gene combinations encode equivalent information and identifies valence orbital radii, nuclear charges, and their products as the key quantities governing the equilibrium lattice constant of perovskites.

We investigate the spin Hall effect (SHE) in a van der Waals (vdW) ferromagnet ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ (FGT) with a Curie temperature $T_{\mathrm{C}}$ of 310 K utilizing the spin-torque ferromagnetic resonance method. In synchronization with the emergence of the ferromagnetic phase resulting in the anomalous Hall effect (AHE), a noticeable enhancement in the SHE was observed below $T_{\mathrm{C}}$. On the other hand, the SHE shows a different temperature dependence from the AHE: the effective spin Hall conductivity is clearly enhanced with decreasing temperature unlike the anomalous Hall conductivity, reflecting the variation in the band structure accompanied by the complicated magnetic ordering of the FGT. The results provide a deep understanding of the SHE in magnetic materials to open a new route for novel functionalities in vdW materials-based spintronic devices.

Giant responses over wide temperature ranges in relaxor ferroelectrics remain a puzzling phenomenon in solid state physics. Rapid-quenching x-ray diffraction demonstrates pronounced kinetic suppression of macroscopic structural ordering in ($1-x$)Pb(${\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}$)${\mathrm{O}}_3\text{−}x{\mathrm{PbTiO}}_3$ near the morphotropic phase boundary. Independently, neutron scattering reveals scale-free spatial and temporal correlations of polar nanoregions over the temperature range associated with the giant dielectric response. Taken together, these observations support a kinetic picture in which sluggish structural ordering allows near-critical relaxor fluctuations to persist over an extended temperature range.

Machine learning interatomic potentials (MLIPs) are routinely used to model diverse atomistic phenomena, yet parameterizing them to accurately capture solid-state phase transformations remains difficult. We present error metrics and data-generation schemes designed to streamline the parameterization of MLIPs for modeling precipitation in multicomponent alloys. We developed an algorithm that enumerates symmetrically distinct transformation pathways connecting chemical decorations of different parent crystal structures. Additionally, we introduce the weighted Kendall-$\tau$ coefficient and its semigrand-canonical generalization as metrics for quantifying MLIP accuracy in predicting low-temperature thermodynamics. We apply these approaches to parameterize an MLIP for a dilute Mg–Nd alloy. The resulting potential reproduces the complex early stage precipitation behavior observed experimentally. Large-scale atomistic simulations reveal competition between order-disorder and structural transformations. Furthermore, these results suggest a continuous transition between high-symmetry hcp and bcc crystal structures during aging heat treatments.

We report a comparative neutron single crystal diffraction study of the structural and magnetic properties of layered halides ${\mathrm{CrCl}}_3$ and $\alpha \text{−}{\mathrm{RuCl}}_3$. They host a honeycomb arrangement of transition metal ions with distinct electronic configurations and undergo a first-order structural transition between high-temperature $C2/m$ and low-temperature $R\overline{3}$. Both compounds show a step-like change in the $c$-lattice parameter across the structure transition. In contrast, the in-plane lattice response is quite different: $\alpha \text{−}{\mathrm{RuCl}}_3$ exhibits an abrupt hysteretic change across the transition accompanied by progressive crystalline degradation upon thermal cycling, whereas ${\mathrm{CrCl}}_3$ shows a smooth in-plane lattice evolution and remains structurally robust. Magnetically, ${\mathrm{CrCl}}_3$ orders into an A-type antiferromagnetic structure at $T_N=14$ K and exhibits pronounced diffuse magnetic scattering extending up to about 40 K. $\alpha \text{−}{\mathrm{RuCl}}_3$ shows no observable magnetic diffuse scattering above its zigzag antiferromagnetic ordering temperature $T_N=7.6$ K. These results suggest that the contrasting structural responses arise from an interplay between interlayer sliding energetics, stacking-strain coupling, and elastic accommodation of the stacking transition. The distinct chemical bonding and electronic configurations of the two compounds provide a microscopic basis for their different lattice responses to the structure transition and magnetic correlations.

Element-specific magnetism at the atomic scale is important in low-dimensional materials such as thin magnetic films and quantum dots, where interfacial and surface effects can give rise to novel behavior. However, probing magnetism specific to the topmost atomic layer remains a key experimental challenge. Here, we introduce a synchrotron x-ray scanning tunneling spectroscopy approach that enables detection and quantification of surface magnetism via x-ray-excited electron tunneling. By illuminating a scanning tunneling microscope tip-sample junction with circularly polarized x-rays tuned to the Ni $L_{2,3}$ absorption edges, ensemble-averaged and surface atomic-layer x-ray magnetic circular dichroism are simultaneously measured on a $\sim 2.5$-monolayer-thick Ni film grown on a Cu(111) surface. Measurements are performed at substrate temperatures of 90 and 22 K. The results reveal enhanced orbital and spin magnetic moments in the outermost atomic layer as compared to the ensemble-averaged moments of the thin Ni film at both temperatures. This work establishes an experimental method for quantitative, element-specific magnetometry with atomic-layer sensitivity using x-rays.

Negatively charged nitrogen-vacancy $\left({\mathrm{NV}}^{-}\right)$ centers located a few nanometers below the diamond surface are key quantum defects for nanoscale sensing of external spins. However, the creation of shallow ${\mathrm{NV}}^{-}$ centers with high yield remains a materials challenge. Here, we demonstrate that high-angle ion implantation enhances the creation efficiency of shallow ${\mathrm{NV}}^{-}$ centers. By implanting ${}^{15}\mathrm{N}$ ions at angles exceeding ${60}^{\circ }$, we achieve high ${\mathrm{NV}}^{-}$ yields approaching 10% with effective ${\mathrm{NV}}^{-}$ depths below 10 nm. These yields are significantly higher than those typically reported for shallow ${\mathrm{NV}}^{-}$ creation. The enhanced ${\mathrm{NV}}^{-}$ yield is consistent with an increased vacancy-to-nitrogen ratio in the near-surface region, which is expected to promote NV formation during annealing. The created ${\mathrm{NV}}^{-}$ ensembles show coherence properties comparable to those of single shallow ${\mathrm{NV}}^{-}$ centers at similar depths, and allow detection of nuclear spins in van der Waals materials attached to the diamond surface. Our results establish geometric control of ion implantation as a simple and broadly applicable approach to engineer shallow vacancy-related quantum defects.

Bi is predicted to be an efficient generator of spin–orbit torques (SOTs), with charge-to-spin conversion efficiency comparable to those of prototypical heavy metals, such as Ta, W, and Pt. However, experimental reports provide widely scattered interconversion efficiencies, while the origin of the large conversion signal in Bi/Ag bilayers remains controversial. Here, we investigate charge-to-spin conversion in epitaxial and polycrystalline Bi-based magnetic heterostructures by measuring the damping-like SOT using magneto-optic Kerr effect magnetometry, complemented by structural and spectroscopic analyses and comparison with harmonic Hall resistance measurements. We show that inserting an Ag spacer between Bi(001) and metallic ferromagnets (FeCo or Ni) enhances the SOT efficiency by more than one order of magnitude, reaching an effective spin Hall conductivity of approximately $2\times {10}^5(\hslash /2e)\mathrm{S}/\mathrm{m}$, in excellent agreement with theoretical expectations for bulk Bi. This enhancement can be consistently explained by the preservation of the structural and chemical integrity of Bi—otherwise compromised by the direct deposition of a ferromagnetic overlayer—rather than by Rashba spin–orbit coupling at the Bi/Ag interface. We show that Ag forms an atomically sharp, chemically inert interface with Bi that, unlike other metallic spacers such as Al and Cu, prevents interdiffusion and solid-state dewetting while enabling efficient charge-to-spin conversion. Angle-resolved photoemission spectroscopy reveals no measurable enhancement of the Rashba spin splitting at the Bi(001) surface upon Ag deposition. Comparative studies across epitaxial, polycrystalline, and intentionally surface-oxidized Bi films, beyond oxygen doses known to destroy Bi(001) surface states, reveal that structural disorder has a negative impact on the SOT efficiency. Meanwhile, the retention of 72% of the SOT efficiency following oxygen exposure indicates a dominant bulk contribution to spin-current generation in Bi/Ag heterostructures, yielding an effective Bi spin Hall angle of approximately 1. By establishing a direct correlation between atomic-scale integrity and charge-to-spin conversion, this study provides design principles to improve the reliability of Bi-based SOT devices and offers a robust framework for interpreting spin–charge interconversion in Bi and Bi/Ag systems.

We demonstrate experimentally how the nucleation of skyrmions in an $\mathrm{Ir}, \mathrm{Co}$, and $\mathrm{Pt}$ based magnetic multilayer is affected by introducing a layer dependent sign for the Dzyaloshinskii-Moriya interaction (DMI). In one stack, the bottom half of the stack is given a positive DMI and the top half a negative DMI, and as a result, the in-plane component of the dipolar field is aligned parallel to the effective field of the DMI in every layer, enhancing the effective DMI. We show that this enhanced DMI facilitates the nucleation and stability of skyrmions using both current-driven and laser-induced skyrmion nucleation. In the devices with an enhanced effective DMI, the density of nucleated skyrmions is greater by up to a factor $\sim 20$ and skyrmions can be observed in stronger magnetic fields—suggesting that their stability is also improved. These results show that skyrmion nucleation depends strongly on the magnitude of the effective DMI in a magnetic multilayer and that the dipolar field within such a multilayer presents an effective route towards controlling the effective DMI, and thereby, the nucleation of chiral magnetic textures.