Materials Science
An Atlas and Design Rules for Single- and Dual-Atom Alloys
Fabian Berger, Yicheng Wang, E. Charles H. Sykes et al. (+1 more)
A long-standing goal across heterogeneous catalysis, materials science, and condensed matter physics is to design
alloys with prescribed local atomic arrangements. Recent experiments show that dilute trimetallic
alloys unlock chemistries inaccessible to bimetallics, but realizing this potential requires knowing which dopant structures form across an enormous compositional space. Using density functional theory screening, we construct an atlas spanning transition metal single- and dual-atom
alloys in Cu and Ag surfaces, which we validate by scanning tunneling microscopy. The stability follows an electron count: dopants pair most strongly when their combined d-electron count approaches ten. Host metal and surface facet can be used to tune the resulting active site motifs, while size mismatch and
spin explain variations around this trend. We further introduce a reactor-anchor concept, in which one dopant anchors a second, otherwise bulk-segregating dopant at the surface. Together, these results establish design principles for engineering
alloys with targeted active site structures.
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All authors Fabian Berger, Yicheng Wang, E. Charles H. Sykes, Angelos Michaelides
Materials Science · Cross-listed from cs.LG
Physics-based prediction, uncertainty quantification and decision-making for IN718 crystallographic texture intensity across LPBF defocus regimes
Yisheng Lu, John Riris, Jie Song et al. (+2 more)
Reliable prediction of crystallographic texture in
laser powder bed fusion is critical for linking process conditions with anisotropic response and for qualification. However, black-box models may fail under shift and cannot distinguish weak data support from loss of physical validity. This study develops a two-stage physics-based model for <001> || BD (build direction) texture in Inconel 718. Stage 1 maps process variables to melting mode and melt pool geometry. Stage 2 predicts texture by combining an empirical physics model with a random-forest residual model. A k-nearest-neighbor weight attenuates residual corrections for poorly supported queries, while a study-specific areal beam-power-density criterion withholds predictions outside the adopted conduction envelope. Conformal intervals are evaluated on the retained physics-valid set, and SHAP and Sobol analyses assess residual sensitivity. Under a controlled leave-one-defocus-out evaluation, the physics anchor achieved R^2 = 0.778, against -0.001 for the black-box model and 0.750 for the gated hybrid. Under leave-one-group-out cross-validation, the gated hybrid reached R^2 = 0.592 against 0.538 for the black-box model. Retained-set coverage was 92.9% at a mean full width of 3.65 multiples of a uniform distribution (MUD) under grouped cross-validation and 100% at a width of 3.21 MUD under transfer to a withheld +80 mm defocus regime. An illustrative mapping produced a retained BD elastic-modulus span of 127-187 GPa. On nine conditions from a separately built sample set, the framework withheld three, attenuated three, and matched the measured ordering for the rest. Separating data applicability, physics validity, and predictive uncertainty into distinct decisions lets the framework transfer where an unconstrained model does not, and withhold predictions where no model class performs adequately.
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All authors Yisheng Lu, John Riris, Jie Song, Yao Fu, Jie Chen
Materials Science
Epitaxial inversion of spontaneous polarization in {\epsilon}-Ga2O3
Yan Wang, Zhigao Xie, Weihua Tang et al. (+1 more)
Polar wide bandgap
semiconductors offer the unique capability to manipulate internal electric fields and induce two-dimensional electron gases (2DEG). The emerging orthorhombic {\epsilon}-Ga2O3 is a promising candidate owing to its large spontaneous polarization (Psp). However, exploiting this material is hindered by fundamental ambiguities surrounding its absolute Psp vectors and the inability to govern its epitaxial direction. Here we show the resolution of the absolute Psp vectors in {\epsilon}-Ga2O3 and control of its macroscopic polarity via substrate engineering. By correlating interferometric piezoresponse with atomic configurations, we establish an identification criterion where opposing polarities are assigned through the
geometric elevation within an asymmetric four-atom sequence. Guided by this signature, we demonstrate that epitaxy on Al-polar AlN and sapphire yields uniformly Ga-polar (upward Psp) and O-polar (downward Psp) architectures, respectively, whereas deteriorated crystallinity disrupts this registry and triggers mixed-polarity. This atomic-to-macroscopic correlation eliminates long-standing ambiguities regarding absolute polar orientations in non-centrosymmetric oxides. Analogous to mature III-Nitride architectures, this blueprint provides the foundational platform for designing macroscopic polarization discontinuities at heterointerfaces, unlocking {\epsilon}-Ga2O3 for advanced polarization electronics.
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All authors Yan Wang, Zhigao Xie, Weihua Tang, Chee Keong Tan
Materials Science
Gauge-including neural-network quantum Monte Carlo for molecules in magnetic fields
Chengye Lü, Weizhong Fu, Xin-gao Gong et al. (+1 more)
External
magnetic fields, through their coupling to orbital and
spin motion, complicate the correlated electronic states and impose coordinate-dependent phases on the wavefunction, thereby making accurate electronic structure calculations substantially more demanding. Recently, neural network-based
quantum Monte Carlo (NNQMC) has emerged as a highly accurate approach to study
nucleus-free systems in
magnetic fields. For molecular systems, however, things get more complicated as the
magnetic field would introduce a rapidly varying phase in the region far from the gauge origin. Here we introduce a gauge-including phase factor that acts directly on the full many-electron wavefunction and accounts for the prescribed
magnetic phase, leaving a smoother correlated residual for the network to learn. This factor greatly improves molecular translation consistency and size consistency, providing a route for studying systems in
magnetic fields with NNQMC. Upon this approach, we reproduce weak-field magnetizabilities and strong-field bond contraction in \ce{H2}. We further apply the method to selected transitions in the \ce{CN} red and \ce{C2} Swan systems at
magnetic fields relevant to white dwarfs. The \ce{CN} transition exhibits a much larger field-induced shift than its \ce{C2} counterpart, suggesting its potential as a probe of white-dwarf
magnetic fields.
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All authors Chengye Lü, Weizhong Fu, Xin-gao Gong, Hongjun Xiang
Materials Science · Cross-listed from physics.chem-ph
Atomic-scale structure of static screening in noble-metal nanoparticles from clusters to the conductor limit
Pulkit Joshi and Marek Sierka
The static screening response of a metallic nanoparticle is encoded in its induced charge density. Integrated observables such as the dipole moment or the polarizability do not determine this density, because many different screening profiles yield the same integrals. We show that in noble-metal nanoparticles the screening charge is atomically structured, with facet, edge, and vertex sites responding differently from a smooth classical conductor. This structure survives in a surface layer of about one atomic width even when the integrated response has reached the conductor limit, and it is absent from continuum descriptions. To resolve it across size, morphology, and composition, we calibrate an atomistic charge-dipole model for Ag and Au nanoparticles directly to first-principles induced-density profiles. The calibration includes the short-range kinetic and exchange-correlation contribution to the hardness kernel that a purely electrostatic model omits, reducing the induced-density-profile error by about a factor of 2.5. A single averaged parameter set per element predicts clusters withheld from the fit and transfers without adjustment to Ag/Au core-shell, alloyed, and elongated particles. A continuous fast multipole implementation of the model scales almost linearly with the number of atoms and reaches several-million-atom particles, far beyond the reach of first-principles methods.
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Materials Science
Photoresponse properties of single-crystalline thick film based on high-entropy topological insulator (Bi3/4Sb1/4)2(Te2/5Se2/5S1/5)3
Alexei Vasilev, Marina Zhezhu and Oleg Ivanov
High-
entropy topological
insulator (Bi3/4Sb1/4)2(Te2/5Se2/5S1/5)3 has been for the first time prepared by self-propagating high-temperature synthesis and melting methods. Single-crystalline thick-filmed sample with thickness of ~0.1 mm was applied to examine the photoresponse properties by using room-temperature chopped-light technique. Photodetector based on (Bi3/4Sb1/4)2(Te2/5Se2/5S1/5)3 demonstrated strong photovoltaic response under irradiation of a white LED light, covering 420-730 nm range. The photocurrent increases from ~20 to ~55 mkA with the increase in intensity from 100 to 600 W/m2 that is originated from the increase in the number of non-
equilibrium carriers generated by light. Room-temperature responsivity and detectivity of the photodetector are ~8.7 mA/W and ~109 Jones, respectively.
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Materials Science
Adaptive Substrate Support Based on Thin-Film Piezoelectric Actuators
Ertuğ Şimşek, Bas Jansen, Marcelo Ackermann et al. (+1 more)
Advanced lithography scanners require extreme substrate flatness in the range of nanometers to prevent focus errors. Such a flatness is challenging to reach and maintain using static substrate supports. Active correction concepts using bulk piezoelectric or linear actuators become prohibitive due to wiring and volume limitations, considering the thousands of pillars required. In this work, we present to our knowledge the first ever demonstration of an active substrate support concept based on thin-film piezoelectric actuators. The working principle, fabrication steps, and characterization of a proof-of-principle device, supported by finite element modeling (FEM), are presented in detail. The fabricated device shows a displacement above 9 nm, which is sufficient to correct some of the focus errors in lithography systems. We foresee that this new concept may open the way towards smaller chip dimensions and improved yield.
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All authors Ertuğ Şimşek, Bas Jansen, Marcelo Ackermann, Muharrem Bayraktar
Materials Science
Low Temperature Halide Assisted HVPE Growth of Single Crystal AlN Films
K. Udwary, M. Smeaton, J.S. Mangum et al. (+6 more)
Low defect, single polarity aluminum nitride layers grown by halide vapor phase epitaxy (HVPE) methods have classically needed growth temperatures well exceeding 1100{\deg}C with many of the best results being grown in the range of 1400{\deg}C. These high temperatures have typically been required to obtain Al-polar AlN films with smooth morphologies and high crystalline quality. However, these elevated temperatures make the use of quartz reactor chambers difficult, as quartz begins to soften at 1200{\deg}C, and requires specially designed reactors. This study examines the use of anhydrous hydrogen chloride (HCl) gas, injected directly to the growth surface, to suppress inverted polarity grains that form at low growth temperatures. This method allows for high quality, single
crystal AlN layers with a growth temperature of just 1000{\deg}C in a quartz reactor chamber. With this method, AlN layers of 5 um thickness were grown on c-plane (0 0 0 1) sapphire, with a growth rate of 20 um/hour, and a resulting full-width at half-maximum (FWHM) of symmetric (0 0 0 2) rocking curve reflection under 400 arcsec and asymmetric (1 0 -1 2) reflection under 1000 arcsec. Electron backscatter diffraction measurements showed the suppression of inversion domains with increasing free HCl, resulting in smoother and higher quality films.
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All authors K. Udwary, M. Smeaton, J.S. Mangum, R. Gannon, G. Dodson, B. Tellekamp, K.L. Schulte, J.H. Leach, J. Simon
Materials Science · Cross-listed from cond-mat.str-el
Orbital-Induced Peierls Transitions: How Orbitals Orchestrate Lattice Instability
T. Mizokawa and S.V. Streltsov
The Peierls transition is typically regarded as a phenomenon inherent to one-dimensional (1D) materials. However, orbital degrees of freedom can induce this instability even in higher dimensions. Two mechanisms are primarily responsible. First, the anisotropic shape of $p$ and $d$ orbitals can lead to effective "1D-zation" of the electronic spectrum. Second, orbital degrees of freedom can lift band degeneracy by shifting bands relative to each other via the local or band Jahn-Teller effect, thereby affecting the nesting of the Fermi surface. The orbital-induced Peierls effect is most commonly observed when ligand octahedra surrounding transition metals share edges, and less frequently in face-sharing geometries. In this review, we discuss the underlying physical mechanisms, the materials in which this phenomenon occurs, the characteristics of the high-temperature undistorted phase, and the role of local effects such as the formation of molecular orbitals.
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Materials Science
Hypothesis-Driven Autonomous Materials Synthesis with Multimodal LLM Agents
Izumi Takahara, Kazunori Nishio, Akira Aiba et al. (+4 more)
Self-driving laboratories can explore synthesis conditions autonomously, but their decision-making layer is typically a black-box optimizer, and the output is a set of optimized samples, with the measurements reduced to predefined scalar objectives and the reasons behind success left unarticulated. Here we present SynAgent, a framework in which large
language model
agents operate an automated experimental system and maintain an explicit, revisable understanding of the synthesis process as the campaign's primary output. Starting with no predefined analysis pipeline, SynAgent adaptively generates analysis skills for newly acquired data and evolves this understanding through
multimodal reasoning over experimental data such as X-ray diffraction patterns and electron micrographs. The
evolution is guided by a verify-falsify scheme, in which the
agent deliberately challenges its own hypotheses by testing conditions predicted to fail as well as those predicted to succeed. In a single campaign of 18 autonomous experiments using LiCoO2 (001) thin-film deposition as a testbed, SynAgent synthesized highly crystalline films and evolved an understanding of how the substrate temperature governs crystallization, discovering an abrupt threshold and a narrow optimal growth window at 650-690 {\deg}C. These results extend autonomous experimentation beyond optimized samples to testable, human-readable understanding.
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All authors Izumi Takahara, Kazunori Nishio, Akira Aiba, Shigeru Kobayashi, Takao Nakajima, Taro Hitosugi, Teruyasu Mizoguchi
Materials Science
Nonempirical Time-Dependent Density Functional Theory Framework for Nonlocal Exchange–Correlation Potentials
Zhandos A. Moldabekov, Michele Pavanello, Thomas D. Gawne et al. (+2 more)
Advanced, orbital-dependent exchange–correlation (XC) functionals can significantly improve the description of electronic structural properties, but they substantially worsen spectral properties that are computed within standard linear-response time-dependent density functional theory frameworks. This is not a failure of the underlying Kohn-Sham states, but due to a formal inconsistency in the treatment of the dynamic density response when the non-locality of the XC potential is not taken into account consistently on the level of the full off-diagonal density
matrix. To avoid these complexities, we present a non-empirical additive correction $\Delta f_\textnormal{xc}(\mathbf{q},\omega)$ to the dynamic XC kernel that re-enforces the exact f-sum rule of the non-local KS
Hamiltonian within TDDFT. Comparing our new results against a representative set of accurate experimental measurements (ambient aluminum, silicon and carbon, as well as heated and compressed aluminum) reveals a dramatic improvement in all cases without any additional computational cost. The corresponding extension to the open-source GPAW code is made freely available online. We further investigate the implications of non-local pseudopotentials and show that the non-locality has an important, physically motivated effect that is indispensable to capture the correct plasmon dispersion in lieu of full all-electron simulations. In addition to being important for the estimation of a plethora of dynamic and spectral properties, our work constitutes an important step towards a universal XC functional that can be used to estimate all kinds of observables with high accuracy. Finally, we outline the potential utility of our framework for the development of advanced non-local XC functionals, and suggest a new way to rigorously verify non-local pseudopotentials against experimental measurements of collective excitations.
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All authors Zhandos A. Moldabekov, Michele Pavanello, Thomas D. Gawne, Jan Vorberger, Tobias Dornheim
Materials Science
ERAF4XRD: A multimodal agentic framework for constructing validated experimental X-ray diffraction databases from scientific literature
Afnan Mostafa, William Ratcliff, Simon J. L. Billinge et al. (+1 more)
The scientific literature contains decades of experimental measurements that remain difficult to access as structured data for modern AI and data-driven research. Much of this information is distributed across figures, captions, text, and tables, requiring experimental data and their context to be identified, connected, and verified before they can be reused. Here we introduce ERAF4XRD (Experiment Reader Agentic Framework for X-Ray Diffraction), a fully automated
multimodal (i.e., image and text), multi-
agent framework that reconstructs validated X-ray diffraction (XRD) records from scientific publications. ERAF4XRD downloads and screens documents, identifies XRD figures, extracts and links metadata to the corresponding experimental data, and validates outputs against source evidence using an independent validation
agent. On a manually curated
benchmark of 273 scientific publications containing 3,150 candidate figures, ERAF4XRD achieved up to 98.7% accuracy for XRD figure identification and generated 1,400 metadata values across 22 fields. Independent manual assessment of the final validated records yielded 98.5% precision and 90.7% recall, with no unsupported metadata observed among 443 evaluated fields. By moving beyond information extraction to the reconstruction and validation of linked experimental records, ERAF4XRD establishes an automated approach for transforming published scientific information into machine-readable experimental
datasets for AI and data-driven science.
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All authors Afnan Mostafa, William Ratcliff, Simon J. L. Billinge, Niaz Abdolrahim
Materials Science
Thermally Desorbable InN Capping Layers for Nitride Surface Science
Mellie Lemon, Amitayush Thakur, Anthony Rice et al. (+5 more)
Group III-nitride thin films are essential for optoelectronic and power devices, where surface and interface quality critically influence performance. It is often necessary to transfer these films through atmosphere for processing or characterization steps, which can introduce significant surface contamination. Here we demonstrate a technique to protect the surface of III-N films during atmospheric exposure by capping with sacrificial InN layers. Using molecular beam epitaxy grown AlGaN films as our representative protected material, we take advantage of the lower decomposition and desorption temperatures of InN and metallic In to remove the protective cap layer in situ via thermal desorption without damaging the AlGaN film beneath. Angle-resolved photoemission spectroscopy (ARPES) measurements of the valence band dispersion in Al0.4Ga0.6N demonstrate that the film surface is recovered after InN decapping, highlighting the versatility of this process in allowing further surface-sensitive characterization of films that had been exposed to air.
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All authors Mellie Lemon, Amitayush Thakur, Anthony Rice, Glenn Teeter, Michelle Smeaton, Renae Gannon, Jessica L. McChesney, M. Brooks Tellekamp
Materials Science · Cross-listed from cond-mat.mes-hall
Layer-Dependent Vibrational and Optical Properties of $\mathrm{Mo}{0.58}\mathrm{W}{0.42}\mathrm{Se}_2$ Alloy
Szymon Socha, Tomasz Wozniak, Elena Blundo et al. (+7 more)
Semiconducting Mo$_x$W$_{1-x}$Se$_2$
alloys provide a versatile platform for tailoring the optical properties of two-dimensional materials through both composition and layer thickness. Here, we systematically investigate mechanically exfoliated Mo$_{0.58}$W$_{0.42}$Se$_2$ flakes ranging from monolayer (1L) to nine layers by combining Raman scattering (RS), photoluminescence (PL), reflectance contrast (RC) spectroscopy, and first-principles
phonon calculations. Thirteen RS peaks are identified, including the low-frequency interlayer shear mode, whose thickness dependence is well described by a linear-chain model, yielding an interlayer force constant of $K_s=(2.996\pm0.015)\times10^{19}$ N m$^{-3}$. PL measurements reveal a crossover from the direct-bandgap 1L to indirect-bandgap multilayers. The thickness
evolution of the indirect optical transition is quantitatively reproduced using a
quantum-confinement model, yielding an out-of-plane reduced effective mass of $\mu_\perp=0.75 m_0$. RC spectroscopy reveals four excitonic resonances. While the A and B
excitons associated with the $K^\pm$ valleys remain nearly independent of layer thickness, the higher-energy C and D resonances originating from the band-nesting regions exhibit pronounced
redshifts, reflecting substantial thickness-induced modifications of the electronic band structure. These results establish comprehensive spectroscopic fingerprints of flake thickness, interlayer coupling, and electronic structure in Mo$_x$W$_{1-x}$Se$_2$
alloys and provide a reliable, non-destructive framework for their optical characterization.
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All authors Szymon Socha, Tomasz Wozniak, Elena Blundo, Malgorzata Brzoska, Grzegorz Krasucki, Piotr Wrobel, Antonio Polimeni, Adam Babinski, Maciej R. Molas, Katarzyna Olkowska-Pucko
Materials Science
A Pseudoscalar Representation Mapping from Parent-Group Vibrational Normal Modes to Symmetry-Adapted Magnetic Structures
Yachao Liu, Haibo Niu and Vei Wang
Conventional approaches classify
symmetry-allowed
magnetic configurations but do not by themselves establish a direct, mode-resolved correspondence with parent-
lattice vibrations. Here, we formulate a universal determinant-induced pseudoscalar twist for all 32 crystallographic point groups, establishing an exact representation-to-geometry correspondence between parent vibrations and
magnetic order. Within the paramagnetic gray group $G\times\Theta_{\mathcal{T}}$, the spatial twist determines
symmetry-defined
magnetic geometry, while time-reversal parity independently specifies
magnetic character. Each parent
phonon irrep $\Gamma$ maps to $\Gamma_{\mathrm{mag}}=\Gamma\otimes\Gamma_{\mathrm{ps}}$, preserving multiplicities and yielding the projection identity $P_{\mathrm{mag},mn}^{(\Gamma\otimes\Gamma_{\mathrm{ps}})}=P_{\mathrm{ph},mn}^{(\Gamma)}$ under the common Cartesian realization. This establishes the Template Principle: parent vibrational modes furnish real-space templates whose
symmetry-enforced nodal
manifolds are inherited exactly. Applied to monolayer $\mathrm{Cd}_2\mathrm{N}_3$, the framework identifies the ferrimagnetic ground state from the parent $A_{2u}$ sector, confirmed by first-principles calculations, alongside cluster
magnetic octupoles and antiferromagnetic
manifolds. It further provides an a priori parent-group criterion for screening
symmetry-allowed linear
magnetic responses.
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Materials Science
The role of disconnections in redox-induced phase transformation of metal oxides
Martina Ruffino, Baptiste Bienvenu, Xuyang Zhou et al. (+2 more)
Detailed atomic-level understanding of the phase transformation between magnetite (${\rm Fe_3 O_4}$) and haematite (${\rm Fe_2 O_3}$) is lacking, despite widespread interest in redox reactions of metal oxide systems. While the magnetite-to-haematite transformation entails the addition of oxygen to the system and thus a net diffusive flux, haematite formations have been reported to grow along well-defined habits on the close-packed $\{0001\}_{\rm Fe_2 O_3}//\{111\}_{\rm Fe_3 O_4}$ planes. The propagation of the phase interface in the bulk is thus thought to maintain the oxygen sublattice fixed up to a shear, and to require long-range
diffusion of iron ions. In this letter we propose interfacial steps with dislocation character, i.e. disconnections, as the elementary defects propagating the transformation. We use the topological model of interfacial defects to predict three disconnection modes for the system, and we employ scanning transmission electron microscopy to ascertain their presence in a haematite/magnetite interface of a partially oxidised magnetite powder. Using atomistic simulations, we determine the
equilibrium structures of the disconnections, and study their motion and how they accomplish the transformation, obtaining excellent agreement with atomic-resolution experimental observations.
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All authors Martina Ruffino, Baptiste Bienvenu, Xuyang Zhou, Dierk Raabe, Yan Ma
Materials Science
Rapid Parameter Estimation from Photoluminescence Decays of Halide Perovskite Thin Films
Robin Heumann, Toby Rudolph, Gaosheng Huang et al. (+2 more)
Extracting material parameters from experimental data is often challenging if no invertible analytical equation can be used to link the data with the quantities of interest. If the link between experiment and material parameters is given mathematically by a set of non-linear differential equations, these must be solved repeatedly during the traditional fitting procedure, resulting in long optimization times and limited insight into parameter uncertainty. Here, we present a parameter estimation workflow specifically aimed at transient photoluminescence measurements performed on lead-halide perovskite films. This workflow is accelerated using artificial neural networks for rapid comparison between experiment and simulation. An advantage of the method is the ability to rapidly scan multidimensional material parameter spaces and identify correlations between parameters that provide insights into the physics of non-radiative recombination in halide perovskites. Finally, we compare steady-state and transient photoluminescence and show how uncertainty in parameters such as the defect density can be reduced by including steady-state data in the parameter estimation workflow.
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All authors Robin Heumann, Toby Rudolph, Gaosheng Huang, Thomas Kirchartz, Chris Dreessen
Materials Science
Electronic Origins of Elastic Behavior in Rocksalt, Zinc-Blende and Wurtzite 3d Transition-Metal Nitrides
Jesus Cañas and Oliver Ambacher
We present a comprehensive ab-initio study of the elastic properties of the IV-period transition metal nitrides, highlighting the correlation between their mechanical behavior and electronic structure. By analyzing the electronic density of states, we reveal how the occupation of bonding or antibonding orbitals determines the
evolution of elastic properties along the period. Furthermore, we examine trends across different
crystal structures, specifically comparing rocksalt, zincblende and wurtzite phases, to uncover how variations in
crystal symmetry and atomic coordination influence their elastic properties.
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Materials Science
Complex magnetic properties of EuAgAs single crystals
Karolina Kowalczyk, Kamila Komędera, Janusz Przewoźnik et al. (+6 more)
EuAgAs is an antiferromagnetic topological material exhibiting intriguing
magnetic behavior. We investigate its structural,
magnetic, and local electronic properties using X ray diffraction, Mössbauer spectroscopy, dc magnetization, ac susceptibility, and heat capacity measurements. The results confirm antiferromagnetic ordering below $T_\text{N}$ and reveal pronounced
magnetic anisotropy and several field induced metamagnetic transitions. We construct the
magnetic phase diagram of EuAgAs, identifying several distinct
magnetic regions. The field and temperature dependent behavior observed suggests a noncollinear
magnetic structure in the low field regime. The sequence of field induced transitions resembles that observed in centrosymmetric rare earth compounds hosting skyrmion phases, suggesting that competing
magnetic interactions may play an important role in stabilizing the observed
magnetic states.
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All authors Karolina Kowalczyk, Kamila Komędera, Janusz Przewoźnik, Łukasz Gondek, Czesław Kapusta, Wojciech Tabiś, Michał Babij, Lan Maria Tran, Damian Rybicki
Materials Science
Direct observation of phonon mode with an antisymmetric Raman tensor
Shangfei Wu, Shang Ren, Kai Du et al. (+4 more)
Phonon angular momentum, characterized by circular or elliptical motion of atoms, plays a decisive role in diverse phenomena, ranging from the
phonon Hall effect,
phonon magnetic moment, Einstein-de Haas effect, Weyl
phonons, and driven chiral
phonons. The
phonon modes with an antisymmetric Raman tensor, which carry an intrinsic
phonon angular momentum in a pseudovector
symmetry channel, have been overlooked in the past in the chiral
phonon community. Here, we report the detection of this type of
phonon mode using polarization-resolved Raman spectroscopy. We observe a
phonon at 266cm$^{-1}$ in the antiferromagnetic chiral phase of Cr$_2$O$_3$ in the $A_2$-pseudovector
symmetry channel. This $A_2$ mode's frequency and the elliptical motion are captured by first-principles
phonon calculations, which treat both
lattice and
spins on an equal footing as 'slow' degrees of freedom. This mode gets Raman activity due to the presence of Cr vacancies in Cr$_2$O$_3$ that locally break the twofold rotational
symmetry perpendicular to the threefold axis. Our results provide a new way to detect the novel
symmetry-forbidden $A_2$
phonon modes with an antisymmetric Raman tensor in a pseudovector
symmetry channel.
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All authors Shangfei Wu, Shang Ren, Kai Du, Xianghan Xu, Sang-Wook Cheong, David Vanderbilt, Girsh Blumberg
Materials Science
Quantum electrodynamics of equilibrium systems: A rigorous Maxwell-regularized functional-theoretic formulation
Markus Penz, Christian Jöns, Michael Ruggenthaler et al. (+1 more)
A framework for
quantum electrodynamics of
equilibrium systems is proposed that takes the Maxwell equations as foundational and links them to the structure of density-functional theory for the
quantum system. By switching from purely internal observables like the one-particle density to combined internal and external quantities, the external sources and their energy are taken into account. A fully regularized functional theory emerges that avoids the usual representability problems. With the Kohn-Sham construction that links to an auxiliary uncoupled system, the ultra-violet cutoff can be removed and one arrives at a fully renormalized and non-perturbative light-matter description. Regularized forms of density-functional theory with and without
magnetic fields appear as boundary cases, while the emergent physical picture reproduces the macroscopic Maxwell equations.
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All authors Markus Penz, Christian Jöns, Michael Ruggenthaler, Angel Rubio
Materials Science
Nitrogen based electride superconductor Nb5Ir3N under pressure: multifunctional physical properties from DFT based first-principles investigation
M. Abdul Hadi Shah, J.H. Abir and S.H. Naqib
Discovery and study of superconducting electrides have opened new avenues in condensed matter physics, driven by their intriguing multifunctional features spanning ambient and high-pressure regimes. This work investigates the ternary nitride
superconductor Nb5Ir3N under pressure ranging from 0 to 20 GPa via density functional theory based simulations. Estimated structural parameters agree well with the available data, confirming their reliability and supporting the validity of this analysis. Negative formation enthalpy, together with evaluated elastic constants and
phonon spectra, confirm the structural, thermodynamic, mechanical, and dynamical stability of Nb5Ir3N over the entire pressure range. Pressure dependent elastic constants and polycrystalline elastic moduli are investigated. The compound is categorized as ductile in light of estimated mechanical indices. Elastic anisotropy factors indicate that Nb5Ir3N remains anisotropic, with the degree of anisotropy gradually decreasing as pressure increases. Electronic band structure and density of states are calculated with and without
spin orbit coupling to investigate its influence on the electronic structure. Calculated optical response reveals substantial intraband contributions in the low energy region, intense ultraviolet absorption, and strong reflectivity. The spectra exhibit optical anisotropy and a broadening at higher pressures. Pressure induced superconducting features are also discussed qualitatively.
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Materials Science
Disentangling Strain and Ti3+ Contributions to the Anomalous Hall Effect in Epitaxial RuO2 Films
S. G. Jeong, A. Santhosh, S. Lee et al. (+7 more)
The anomalous Hall effect (AHE) reported in epitaxial RuO2/TiO2 has been attributed to a strain-stabilized
magnetic state, but strain can be entangled with Ru-Ti intermixing and interfacial charge redistribution, which can produce Ti3+ and potentially localized moments. Here, we disentangle these contributions using Ti-alloyed RuO2
heterostructures in which abundant Ti3+ states are retained while epitaxial strain is independently changed. The strained and relaxed films have nearly identical Ti/Ru compositions and comparable Ti3+ fractions, yet a pronounced nonlinear AHE appears only in the coherently strained film, while the relaxed
heterostructure exhibits an almost linear Hall response. Spectroscopic ellipsometry further shows that the AHE-active strained state is accompanied by a reconstruction of the itinerant electronic response, including enhanced
metallicity and longer carrier relaxation times. These results show that Ti3+ formation alone is insufficient to generate the anomalous Hall state and identify epitaxial strain, through its modification of the itinerant RuO2 electronic structure, as the dominant control parameter.
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All authors S. G. Jeong, A. Santhosh, S. Lee, S. Sheikh, U. M. Jayathilake, T. -L. Lee, T. Low, A. X. Gray, S. A. Chambers, B. Jalan
Materials Science
High-performance orbital-torque magnetic memory on the 300-mm platform
Dinggui Zeng, Yang Gao, Jinyu Duan et al. (+24 more)
Contemporary
memory technologies are increasingly constrained by the fundamental trilemma of storage capacity, access latency, and power consumption. Among the emerging technologies,
spin-orbit torque
magnetic random-access
memory (SOT-MRAM) shows promise to circumvent these challenges, owing to its fast switching dynamics and high endurance. However, the application of SOT-MRAM is hindered by the relatively low write and read efficiencies, resulting in a large bitcell area and an insufficient sensing margin. Meanwhile, the involvement of an ultrathin
spin-source channel, typically within a few nanometers, imposes technological challenges for mass production. Here, we resolve these issues on a 300-mm wafer platform by exploiting the emerging orbital degree of freedom and the resultant orbital torque (OT) from the relatively thick Ti/W bilayer. In particular, OT
memory nanodevices exhibit a giant tunnel magnetoresistance (TMR) of 182%, nanosecond-scale response, 1012 endurance, together with an enhanced switching efficiency (E_b/I_c), which consequently enables an ultra-low write energy of less than 0.1 pJ/bit. Our findings demonstrate that orbital angular momentum can be implemented for building energy-efficient MRAM devices, offering a practical pathway towards low-latency
memory that is demanded for high-performance computing and AI applications.
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All authors Dinggui Zeng, Yang Gao, Jinyu Duan, Lei Zhao, Yuhao An, Xing He, Jintao Ke, Yonglong Ga, Shasha Wang, Zhenghui Ji, Muyuan Chen, Hengan Zhou, Xuejie Xie, Enlong Liu, Junlu Gong, Qijun Guo, Yihui Sun, Zejie Zheng, Weiming He, Xiaolei Yang, Fantao Meng, Yaohua Wang, Hongxin Yang, Delin Zhang, Yong Jiang, Wanjun Jiang, Shikun He
Materials Science
Magnetically coupled charge-transport crossover and giant negative magnetoresistance in iodine-incorporated Cr$_2$Se$_3$
Bikash Das, Shibnath Mandal, Kapildeb Dolui et al. (+12 more)
We report the synthesis and comprehensive investigation of iodine-incorporated $Cr_2Se_3$, a non-van der Waals quasi-two-dimensional
magnetic material, using structural,
magnetic, transport, spectroscopic, and first-principles methods. Magnetization and electron
spin resonance measurements reveal an antiferromagnetically ordered state below $T_N \approx 52$ K. At higher temperatures, a second, broader anomaly emerges near $T^* \approx 150$ K, coinciding with a shallow minimum in the temperature-dependent resistivity that resembles a metal-to-
insulator-like crossover. Hall measurements indicate predominantly hole-like conduction at high temperatures ($\geq$ 150 K), while the nonlinear Hall response below T*, together with an anomaly in the third-harmonic electrical signal, suggests the emergence of mobility-dependent multichannel and spatially inhomogeneous transport. A large, non-saturating negative magnetoresistance reaching approximately -78% at 25 K and 12 T further demonstrates strong coupling between charge transport and the
magnetic state. Temperature-dependent Raman spectroscopy reveals no
symmetry-changing structural transition near T*, whereas angle resolved photoemission spectroscopy (ARPES) measurements show no major reconstruction of the electronic structure occupied across the crossover. Taken together, these results identify the high-temperature anomaly as a broad magnetically coupled transport crossover arising from the interplay of short-range
magnetic correlations, chemical disorder, and redistribution among competing conduction channels. These findings demonstrate that anion incorporation provides an effective route to tuning the coupled electronic and
magnetic properties of non-layered Cr$_2$Se$_3$, establishing this system as a promising platform for investigating correlated transport and emergent spintronic functionalities in transition-metal chalcogenides.
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All authors Bikash Das, Shibnath Mandal, Kapildeb Dolui, Oleksi Laguta, Sambit Choudhury, Suvadip Masanta, Tanima Kundu, Jorge Andres Navarro Giraldo, Alexey Barinov, Shibabrata Nandi, Kai Rossnagel, Sanjoy Kr Mahatha, Rajib Mondal, Petr Neugebauer, Subhadeep Datta