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Physics Condensed Matter Materials Science

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Wednesday 1 April

Materials Science

Cryogenic stabilization of molecular hydrogen in dense cubic ice

Tomasz Poręba, Leon Andriambariarijaona, Richard Gaal et al. (+5 more)

Hydrogen is widely regarded as a cornerstone of future low-carbon energy technologies, yet the lack of safe, efficient, and reversible solid-state storage materials remains a major barrier to its large-scale deployment. Although porous frameworks and metal hydrides have been extensively explored, far less is known about the ability of dense molecular solids to stabilize hydrogen at near-ambient pressure. Here we show that fully crystalline cubic ice, despite its non-porous nature, can retain molecular hydrogen as an interstitial guest following controlled decompression from a high-pressure hydrogen hydrate precursor. Using synchrotron X-ray diffraction, neutron diffraction, and Raman spectroscopy, we demonstrate that hydrogen is retained within the ice structure up to about 130 K, producing reproducible lattice expansion and distinct spectroscopic signatures. We further show that pure cubic ice can be partially refilled with hydrogen at 0.18 GPa and 130 K, while fully hydrogen-filled cubic structure can be preserved at the same pressure up to 90 K. The retained hydrogen content reaches several percent of the parent hydrate composition, corresponding to gravimetric and volumetric storage densities comparable to those of interstitial hydrogen in metals. These results reveal an unexpected ability of a dense hydrogen-bonded crystal structure to host molecular hydrogen without permanent porosity or chemical bonding, establishing cubic ice as a minimal model for hydrogen-lattice interactions. More broadly, our findings identify dense hydrogen-bonded solids as an unexplored class of materials for hydrogen storage physics, with implications extending from energy materials to planetary and astrophysical ice environments.
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All authors Tomasz Poręba, Leon Andriambariarijaona, Richard Gaal, Kazuki Komatsu, Gaston Garbarino, Thomas Hansen, Stanislav Savvin, Livia E. Bove

Materials Science · Cross-listed from cond-mat.supr-con

Emergent superconductivity at 16.3 K in an altermagnetic candidate Na$_{2-x}$V$_2$Se$_2$O with broken inversion symmetry

Y. Sun, Z. Yin, T. Zhang et al. (+14 more)

Altermagnets (AMs), characterized by zero net magnetization and momentum-dependent spin splitting, are anticipated to hold significant potential for generating multiple exotic and uncommon superconducting states. However, superconductivity has not yet been realized in AMs to date. Recently, two-dimensional (2D) V$_2$Ch$_2$O (Ch = Se, Te) monolayers, as well as AV$_2$Ch$_2$O (A = K, Rb, Cs) crystals containing [V$_2$Ch$_2$O]$^{\delta -}$ building layers, have been predicted and/or demonstrated to be promising altermagnetic materials. Our preliminary attempts to explore superconductivity in these materials by applying pressure or chemical doping were unsuccessful. Here we report the discovery of superconductivity at a relatively high transition temperature of ~ 16.3 K in a newly synthesized layered compound, Na$_{2-x}$V$_2$Se$_2$O, a variant of AV$_2$Ch$_2$O. In this structure, the [V$_2$Ch$_2$O]$^{\delta -}$ layers are interspersed with double layers of Na$^+$ instead of a single layer of A$^+$, with sodium sites being only half-filled. This new family of layered vanadium oxychalcogenides, lacking inversion symmetry, represents an intriguing platform for exploring altermagnetic superconductors, and holds the potential to reveal novel phenomena, such as topological states, van Hove singularities, and finite-momentum superconductivity. Furthermore, this material acts as a "bridge" between the cuprate/nickelate and iron-pnictide high temperature superconductors, providing new hope and opportunity to expand the category of layered superconductors with higher critical temperatures (T$_c$) and enhancing our understanding of the underlying mechanisms in these systems.
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All authors Y. Sun, Z. Yin, T. Zhang, L. Wang, B. Ruan, Y. Huang, J. He, W. Zhu, M. Ma, J. Bai, J. Cheng, Q. Dong, C. Li, P. Liu, Q. Liu, C. Zhang, G. Chen

Materials Science · Cross-listed from physics.optics

Fractal hierarchy enables exponential scaling of topological boundary states

Limin Song, Zhichan Hu, Ziteng Wang et al. (+7 more)

Exponential growth describes an extremely rapid process ubiquitous across mathematics and diverse physical, biological, and technological systems. Here, we introduce a class of fractal-inspired lattices that combine long-range periodic order with self-similar hierarchy, establishing a structural motif that enables exponential scaling of topological boundary states. We demonstrate this phenomenon in (i) a quasi-one-dimensional lattice chain constructed from Koch-curve unit cells and (ii) a two-dimensional periodic tiling lattice composed of Sierpinski-gasket unit cells. We show that, for suitable coupling parameters, both the number of topological boundary states $N_{\ell}$ and the number of topological minigaps $M_{\ell}$ grow exponentially with the fractal generation index $\ell$. We find that $N_{\ell}$ is an integer multiple of $M_{\ell}$, with the integer determined by the underlying symmetry. This hierarchical scaling law is captured by multi-topological-phase theory and confirmed experimentally in laser-written photonic lattices. Our results identify fractal hierarchy as a materials architecture principle for controlling boundary-state multiplicity, revealing an interplay between topology, self-similar geometry, and periodic order. More broadly, this work suggests a route to synthetic materials and integrated photonic platforms in which large numbers of robust boundary modes can be engineered within compact architectures.
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All authors Limin Song, Zhichan Hu, Ziteng Wang, Domenico Bongiovanni, Liqin Tang, Daohong Song, Roberto Morandotti, Jingjun Xu, Hrvoje Buljan, Zhigang Chen

Materials Science

Laser-generated CuPdAgPtAu High-Entropy Alloy Nanoparticles – Thermal Segregation Threshold and Elemental Segregation

Felix Pohl, Robert Stuckert, Florent Calvo et al. (+5 more)

High-entropy alloy nanoparticles synthesized via laser ablation in liquid are promising for catalysis due to their ability to form simple solid solutions despite chemical complexity. In this study, noble metal HEA NPs (CuPdAgPtAu) are produced from equimolar and Cu- or Ag-enriched bulk targets. Advanced electron microscopy, XRD, and atomistic simulations are used for structural and compositional analysis. Equimolar targets and NPs exhibit a single fcc phase. In contrast, Cu- or Ag-enriched targets show phase segregation into two fcc phases, which is not observed in the synthesized NPs. Simulations predict segregation tendencies, including Ag surface enrichment and Pt core enrichment due to surface energy differences. However, experimentally, individual NPs remain compositionally homogeneous. Thermal stability studies reveal that phase segregation can be induced post-synthesis. Upon heating, Cu-Ag segregation occurs, forming a second fcc phase similar to bulk targets. These findings demonstrate that rapid quenching during laser ablation suppresses thermodynamically driven segregation and stabilizes metastable solid solutions under kinetic control. Subsequent slow heating overcomes kinetic barriers, enabling equilibrium phase formation at higher temperatures. The thermal stability of these NPs and their tunable composition, including Cu enrichment beyond equilibrium limits, make them promising for high-temperature catalytic applications while reducing noble metal usage.
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All authors Felix Pohl, Robert Stuckert, Florent Calvo, Oleg Prymak, Christoph Rehbock, Ulrich Schürmann, Stephan Barcikowski, Lorenz Kienle

Materials Science

First principles study of thermoelectric properties of $\text{Nb}_2\text{Co}_2\text{InSb}$ and $\text{Nb}_2\text{Co}_2\text{GaSb}$ double half-Heuslers

Rajeev Ranjan

Valence electron count (VEC) 18 half-Heusler (hH) alloys are considered promising for high-temperature thermoelectric applications due to their high Seebeck coefficient, mechanical stability, and robustness. However, their relatively large lattice thermal conductivity ($k_{L}$) significantly limits their thermoelectric performance. Introducing mass disorder at lattice sites is an effective approach to suppress $k_{L}$ through enhanced phonon scattering. For instance, NbCoSn exhibits a low figure of merit ($zT \sim 0.05$) despite having a reasonably high power factor of 2.1~$\text{mW}/\text{mK}^{2}$ at room temperature, mainly due to its large lattice thermal conductivity, reported to be 13.25~$\text{W}/\text{mK}$ experimentally and 18~$\text{W}/\text{mK}$ theoretically. In this work, we explore the thermoelectric properties of $\text{Nb}_2\text{Co}_2\text{InSb}$ and $\text{Nb}_2\text{Co}_2\text{GaSb}$, which can be regarded as derivatives of NbCoSn with substitution at the Sn site. Both ordered and Special Quasirandom Structures (SQSs) are considered to understand the role of configurational disorder. Energetic analysis indicates that the ordered phase is most stable for $\text{Nb}_2\text{Co}_2\text{InSb}$, whereas the SQS phase is energetically favored for $\text{Nb}_2\text{Co}_2\text{GaSb}$. The lattice thermal conductivity is evaluated using the Debye-Callaway model, yielding values in the range of 5.5-6.9~$\text{W}/\text{mK}$ for $\text{Nb}_2\text{Co}_2\text{InSb}$ and 4.7-5.8~$\text{W}/\text{mK}$ for $\text{Nb}_2\text{Co}_2\text{GaSb}$ at room temperature. These values are significantly lower than those of the parent NbCoSn system, highlighting the effectiveness of mass disorder in reducing thermal conductivity. The results suggest that these double half-Heusler compounds are promising candidates for improved thermoelectric performance.
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Materials Science

A comparison of the spin-phonon behaviour of Fe$_2$P-based magnetocaloric materials

Mikael S. Andersson, Simon R. Larsen, Erna K. Delczeg-Czirjak et al. (+7 more)

Magnetic refrigeration can provide an environmentally friendly technology to reduce significantly the energy consumption of cooling devices. To retain the sustainability of the device, all parts must be made from abundant materials, excluding e.g. rare earth elements. As such, materials based on Fe$_2$P have shown great potential for magnetocaloric devices. In this study, Fe$_2$P and FeMnP$_{0.55}$Si$_{0.45}$, have been studied using magnetometry, neutron scattering and theoretical modelling with the aim to understand the ferromagnetic transition, related to the magnetocaloric effect. Analysis of the diffraction data of Fe$_2$P showed that it is the Fe$_{3g}$-site that drives the magnetic transition as the Fe$_{3f}$ does not have any magnetic contribution at the magnetic transition temperature. For FeMnP$_{0.55}$Si$_{0.45}$, the magnetic transition is more gradual, on both sites, with coexistence of the para- and ferromagnetic phases close to the magnetic transition. The temperature dependent magnetic structure behaviour are well in agreement with our first principles calculations. Both Fe$_2$P and FeMnP$_{0.55}$Si$_{0.45}$ showed two distinct regions, at different length scales, in their S(Q,$\omega$) spectra. The two length scales can be modelled using a different set of magnetic spin states (S), using S$\rm _{Fe}$~=~2 and S$\rm _{Mn}$~=~2.5, consistent with the ground state of the magnetic atoms. QENS at low Q (Q~\textless{}~0.5~Å) shows similar magnetic processes in both compounds with uncorrelated magnetism below the magnetic transition temperature. The uncorrelated state highlights that the magnetic anisotropy does not play a major role in the formation of the magnetic state. Furthermore, this emphasises the existence of a two part system in FeMn(P,Si)-based compounds, that drives the magnetic transition and in turn the magnetocaloric effect.
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All authors Mikael S. Andersson, Simon R. Larsen, Erna K. Delczeg-Czirjak, Antonio Corona, Jacques Ollivier, Wiebke Lohstroh, Helen Y. Playford, Cheng Li, Pascale P. Deen, Johan Cedervall

Materials Science

Microscopic Theory of Superionic Phase Transitions: Nonadiabatic Dynamics and Many-Body Effects

Jiaming Hu, Zhichao Guo, Jingyi Liang et al. (+1 more)

Superionic phase transitions have attracted extensive interest for decades due to their promising applications and rich underlying physics. In particular, complicated many-body effects and nonadiabatic dynamics are believed to play essential roles, limiting the explanatory power of phenomenological approaches and obscuring the microscopic mechanisms at play. In this work, we develop a unified theoretical framework for describing solid-state ionic conduction. After reviewing the conventional approximations, we construct a general lattice model that applies to both normal ionic and superionic conductors. By incorporating the nonadiabatic concerted-hopping mechanism and the many-body Coulomb interaction within a self-consistent mean-field scheme, we identify these two effects as the fundamental driving forces behind type-I and type-II superionic phase transitions, respectively. Our model directly reproduces key experimental observations. Within this unified framework, we further provide a comprehensive comparison between the two types of transitions. Overall, our work offers microscopic insight into superionic phase transitions and provides guidance for the design and optimization of advanced solid-state ionic conductors.
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All authors Jiaming Hu, Zhichao Guo, Jingyi Liang, Bartomeu Monserrat

Materials Science

Spontaneous structural reconstructions and properties of ultrathin triangular ZnSe nanoplatelets

Alexander I. Lebedev

Two-dimensional (2D) materials have revolutionized all areas of development of high-performance electronic devices. In particular, the unique electronic and optical properties of II–VI semiconductor nanoplatelets have been found to be very promising for optoelectronics. However, not all properties of this intriguing class of materials are yet known. A new, previously unknown hexagonal 2D structure of ZnSe nanoplatelets whose energy is lower than the energies of all previously studied systems is found from first-principles calculations. This structure appears as a result of spontaneous reconstruction of the wurtzite structure and differs from it by the stacking order of the bulk and near-surface Zn atomic layers. The phonon spectrum, electronic structure, and band gap of the obtained nanoplatelets are calculated. The phonon spectra of the nanoplatelets are in complete agreement with the spectra observed in experiment and differ strongly from the vibrational spectra of ZnSe nanoclusters. The adsorption of ZnCl$_2$ and $L$-cysteine molecules on the surface of the nanoplatelets is studied and is shown to be accompanied by yet another spontaneous reconstruction of the hexagonal structure into a tetragonal one and a new rearrangement of Zn atoms in the near-surface layers. Calculations of the natural optical activity of nanoplatelets covered with $L$-cysteine reveal an increase in the specific (calculated per chiral molecule) optical activity, which is especially strong for the Janus structures, as compared to the free $L$-cysteine molecule.
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Materials Science

Strain-tunable multipiezo effects in Janus monolayer Cr2SSe: Selective reversal of valley polarization and single-spin-channel anomalous valley Hall effect

Quan Shen, Jianing Tan, Tao Yao et al. (+2 more)

Altermagnetism, the third class of collinear magnetic order, uniquely combines a zero net magnetization with spin polarized bands in reciprocal space, opening new avenues for two dimensional valleytronics and spintronics. Here, using first principles calculations, we predict that the Janus monolayer Cr2SSe, which possesses intrinsic inversion symmetry breaking, hosts a strain tunable multipiezo effect and exhibits distinctive valleytronic properties. The system displays pronounced spin splitting and band inversion at the X and Y high symmetry points in the Brillouin zone, giving rise to robust spin-valley locking. The degeneracy of these valleys is protected by diagonal mirror symmetry. Application of uniaxial strain breaks this symmetry, concurrently inducing piezovalley, piezoelectric, and piezomagnetic responses, a manifestation of the multipiezo effect. Critically, strain applied along orthogonal crystallographic directions yields opposite valley polarization, while under small compressive strain, we achieve selective reversal of valley polarization, enabling independent control of valence and conduction band valleys and promoting a single-spin-channel anomalous valley Hall effect. These findings establish a pathway for low-power, non volatile manipulation of valley degrees of freedom and enhanced spin transport efficiency, providing a theoretical foundation for the design of energy-efficient valleytronic devices.
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All authors Quan Shen, Jianing Tan, Tao Yao, Wenhu Liao, Jiansheng Dong

Materials Science

Contemporary Insights into Electronic Structure and Microscopic Transport in Nodal-Line Semimetals

Ashutosh S. Wadge, Pardeep K. Tanwar, Giuseppe Cuono et al. (+1 more)

Topological semimetals have emerged as an important class of quantum materials with novel electronic responses and unconventional transport phenomena. Among them, nodal-line semimetals are distinguished by band crossings that extend along one-dimensional lines in momentum space rather than occurring at discrete points, forming closed loops, chains, or extended lines. The stability of these nodal structures is governed by crystalline symmetries such as mirror, spin-rotation, and nonsymmorphic operations, which give rise to characteristic topological invariants and surface states, including drumhead-like bands. In this review, we present a comprehensive overview of the theoretical framework and experimental realization of nodal-line semimetals, with particular emphasis on symmetry protection and the consequences of symmetry breaking. We discuss the classification of nodal-line structures, their evolution into other topological phases, and their signatures in electronic structure measurements and transport phenomena. Special attention is given to insights obtained from angle-resolved photoemission spectroscopy and related probes. By bringing together symmetry analysis, band topology, and experimental observations, this review aims to clarify the relationship between topology, magnetism, and measurable electronic responses in nodal-line semimetals. These considerations highlight their potential as a versatile platform for next-generation topological electronic functionalities and emergent quantum phenomena beyond conventional paradigms.
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All authors Ashutosh S. Wadge, Pardeep K. Tanwar, Giuseppe Cuono, Carmine Autieri

Materials Science

Beyond Beryllium: AI-Accelerated Materials Discovery for Interstellar Spacecraft Shielding

Yue Li, Xu Pan and Kaiyuan Guo

Project Daedalus (1973–1978), the most detailed interstellar probe design study ever conducted, specified a 9 mm beryllium erosion shield to protect the spacecraft payload during its 5.9 light-year cruise to Barnard's Star at 12% of the speed of light. This design, however, predated both the isolation of two-dimensional materials and the development of graph neural network (GNN) property predictors. Here, we systematically screen 20 candidate materials–spanning conventional aerospace metals, transition metal dichalcogenides, and ultra-high-temperature ceramics–using density functional theory (DFT) data from the JARVIS database (76,000 materials) with independent validation by the Atomistic Line Graph Neural Network (ALIGNN). We evaluate candidates across four criteria: specific mechanical stiffness (KV/rho), sputtering resistance, thermal neutron absorption cross-section, and thermodynamic stability. Our screening identifies hexagonal boron nitride (h-BN) and boron carbide (B4C) as dual-function materials offering simultaneous mechanical protection and neutron radiation shielding, and we propose a graphene/h-BN/polymer layered heterostructure shield design that achieves an estimated 47% mass reduction relative to the original beryllium specification. These findings will become immediately actionable upon the successful development of fusion pulse propulsion, which we note remains an outstanding engineering challenge.
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Materials Science · Cross-listed from cond-mat.soft

Organic Electrochemical Transistor Arrays with Integrated Lipid-Sealed Femtolitre Chambers for Simultaneous Electrical and Optical Detection of Membrane Protein Activity

S. Kojima, S. Rawat, M. Sanchez Miranda et al. (+4 more)

We report a scalable method for fabricating arrays of fifty-two ion-sensitive PEDOT:PSS organic electrochemical transistors (OECTs) on glass coverslips, each incorporating an integrated fluoropolymer microwell sealed with a lipid bilayer for simultaneous electrical and fluorescence microscopy studies of membrane proteins. The architecture addresses a key limitation of existing OECT arrays by providing every transistor with an independent fluid reservoir sealed by its own isolated segment of lipid bilayer, thereby confining membrane protein diffusion to a defined sensing region. Microwells containing a dye-labelled $50$~mM KCl solution were sealed with lipid bilayers and overlaid with a dye-free $100$~mM KCl solution. Following addition of $\alpha$-hemolysin, formation of heptameric pores enabled K$^{+}$ ions to diffuse into the microwells and dye molecules to diffuse out, producing concurrent decreases in transistor conductance and fluorescence intensity. This integrated platform combines electrical and optical readout within independently addressable sensing sites and provides a versatile, scalable foundation for larger transistor arrays and the investigation of diverse membrane proteins reconstituted into lipid bilayers.
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All authors S. Kojima, S. Rawat, M. Sanchez Miranda, J.G. Gluschke, H. Noji, L.K. Lee, A.P. Micolich

Materials Science

Revealing buried ferroelectric topologies by depth-resolved electron diffraction imaging

Ting-Ran Liu, Koushik Jagadish, Xiangwei Guo et al. (+10 more)

Nanoscale topological polar textures promise new functionalities for ferroelectric memories and logic, yet their three-dimensional structure and mesoscale organization remain experimentally inaccessible. Here we introduce depth-resolved electron diffraction imaging (DREDI), a fast, non-destructive, method that maps polarization with <50 nm lateral and <10 nm depth sensitivity within fraction of a second. Its high acquisition speed enables the first continuous polarization mapping across six orders of magnitude in length scale, from nanometers to millimeters. Using epitaxial BiFeO3 films, DREDI reveals a hidden depth evolution of polar textures: surface 71-degree stripes evolve into subsurface flux-closure vortices that bifurcate into three-fold vertices near the bottom interface. Cross-sectional multi-slice electron ptychography and phase-field modeling confirm these buried configurations and attribute them to strain heterogeneity and ferroelastic twinning in the SrRuO3 electrode. Large-area analysis further shows that vertex-like frustration forms a mesoscale percolating network above a critical length scale of 4 um. DREDI enables real-time, volumetric studies of buried topological textures in ferroic nanomaterials.
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All authors Ting-Ran Liu, Koushik Jagadish, Xiangwei Guo, Maya Ramesh, Peter Meisenheimer, Harish Kumarasubramanian, Sajid Husain, Ann V. Ngo, Amir Avishai, Jayakanth Ravichandran, Darrell G. Schlom, Ramamoorthy Ramesh, Yu-Tsun Shao

Materials Science

Magnetoelastic instabilities in kagome antiferromagnet Mn3-xGa

Linxuan Song, Feng Zhou, Guilin Lu et al. (+5 more)

We present a systematic study of the structural, magnetic, and transport properties of hexagonal Mn3-xGa alloys, revealing a series of composition-controlled emergent phenomena. By tuning the Mn concentration, we uncover distinct lattice responses, including a zero thermal expansion-like volume compensation behavior in Mn-poor compositions and a magnetoelastic-driven, field-assisted structural phase transition in Mn-rich samples. These lattice instabilities are accompanied by correlated magnetic and transport anomalies, including metamagnetic transitions, negative magnetoresistance, and anomalous Hall sign reversal. First-principles calculations demonstrate that the Hall sign reversal originates from crystal-symmetry breaking rather than magnetic reorientation alone. Our results establish composition as the key control parameter governing magnetoelastic coupling in Mn3-xGa, providing a unified framework to tailor structural, magnetic, and topological transport properties in kagome antiferromagnets and reconcile previously disparate experimental observations.
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All authors Linxuan Song, Feng Zhou, Guilin Lu, Liang Yao, Xuekui Xi, Yong-Chang Lau, Youguo Shi, Wenhong Wang

Materials Science

Radio-Frequency-Driven Reshaping of the Mesoscale Charge-Density-Wave Landscape in 1T-TaS2 Thin-Film Devices

Maedeh Taheri, Zahra Ebrahim Nataj, Nick Sesing et al. (+4 more)

Radio-frequency excitation directly reshapes the mesoscale charge-density-wave landscape in quasi-two-dimensional 1T-TaS2 thin films. Under combined RF and DC bias, the hysteretic current-voltage characteristics associated with the nearly commensurate-incommensurate transition are strongly altered, displaying RF-driven collapse, branching, and multiple step-like features that depend on frequency and drive amplitude. In-situ Raman measurements show enhanced intensity and linewidth narrowing of low-frequency CDW phonon modes, consistent with reduced dephasing and increased coherence of the periodic lattice distortion under RF drive. This behavior is captured by combining an overdamped time-dependent Ginzburg-Landau description of the commensurate CDW with a morphology-informed percolative resistor-capacitor transport model. The simulations indicate that oscillatory driving anneals frustrated domain configurations, reduces domain-wall density, and reorganizes the discommensuration network, while the transport model reproduces the resulting hysteresis, avalanche-like pathways, and RF-induced conductance steps. RF driving therefore provides an effective route for controlling collective electron-phonon order and accessing metastable transport states in 1T-TaS2, with implications for reconfigurable RF electronics, memory, and unconventional computing based on correlated materials.
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All authors Maedeh Taheri, Zahra Ebrahim Nataj, Nick Sesing, Topojit Debnath, Tina T. Salguero, Roger K. Lake, Alexander A. Balandin

Materials Science

Bipolar plates for the next generation of proton exchange membrane fuel cells (PEMFCs): A review of the latest processing methods for unconventional flow channels

Zahra Kazemi and Kamran Behdinan

The rapid, unsustainable depletion of finite fossil fuel resources and their environmental consequences demand the deployment of affordable clean and sustainable energy solutions. Polymer electrolyte membrane fuel cell (PEMFC) technology is an important pathway in decarbonization of modern energy systems, especially when fueled by high-purity green hydrogen. In PEMFCs, bipolar plates largely determine cell efficiency, longevity, and affordability, which in turn depends on both material selection and design of the embedded flow channels. Conventional manufacturing processes have long been used to fabricate standard bipolar plate designs; however, they are incompatible with unconventional, intricate geometries due to their insufficient resolution and precision in fabrication of fine features, and reliance on multi-step post-processing modifications that limit their design adaptability. This lack of design flexibility impedes the translation of innovative laboratory-scale concepts to industrial-scale production and their practical adoption. In recent years, a growing body of research publications and patent disclosures has reported advanced manufacturing methods, such as additive manufacturing, capable of producing intricate bipolar plate geometries at competitive costs. However, a discussion of these manufacturing approaches, along with an assessment of their scalability and industrial readiness, remains absent in the literature. This study aims to fill this gap. It outlines recent progress and proposes future research directions toward affordable and efficient bipolar plate solutions for advanced PEMFC systems.
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Materials Science

Robust $d$-wave altermagnetism in $\mathrm{XCr_2Y_2O}$ (X=K, Rb, Cs; Y=S, Se, Te) family

San-Dong Guo

The $\mathrm{KV_2Se_2O}$, $\mathrm{Rb_{1-\delta}V_2Te_2O}$ and $\mathrm{Cs_{1-\delta}V_2Te_2O}$ are experimentally confirmed to adopt either C-type or G-type antiferromagnetic configuration, corresponding to apparent or hidden altermagnetism. However, their nearly degenerate energies lead to inconsistent experimental assignments between the two antiferromagnetic configurations. Here, we predict that the experimentally synthesized $\mathrm{RbCr_2Se_2O}$ is a robust $d$-wave altermagnetic metal, since the energy difference between C-type and G-type configurations is large, which is independent of electron correlation strength and van der Waals interaction. Upon applying in-plane uniaxial strain, $\mathrm{RbCr_2Se_2O}$ can generate a net total magnetic moment via a direct piezomagnetic effect, which is distinct from semiconductor that typically requires carrier doping in addition to strain. This provides an experimental strategy for distinguishing the G-type antiferromagnetic configuration, in which the total magnetic moment remains zero under uniaxial strain. Our work presents an isostructural $d$-wave altermagnetic $\mathrm{RbCr_2Se_2O}$ analogous to $\mathrm{KV_2Se_2O}$, $\mathrm{Rb_{1-\delta}V_2Te_2O}$ and $\mathrm{Cs_{1-\delta}V_2Te_2O}$, which can facilitate further experimental verification. Furthermore, these results are universal across materials of this family $\mathrm{XCr_2Y_2O}$ (X=K, Rb, Cs; Y=S, Se, Te), thus expanding the family of altermagnets.
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Materials Science

Comparative study of room temperature and quench condensed bismuth films: morphology and electronic characteristics

Yulia Kirina, Prakash Sharma, Wyatt Thomas et al. (+4 more)

A comparison between properties of bismuth thin films deposited at substrate temperatures of 296 K (room temperature) and 77 K (quench condensed) is studied across epitaxial, amorphous, and van der Waals substrates. The experiments demonstrate changes in crystallinity, morphology, and electrical transport arising from the influence of substrate temperature. Moreover, the work highlights changes in grain size, roughness, X-ray diffraction peak intensities, and preferred orientation between the two deposition temperatures. The orientation of the films deposited at 77 K is preferentially (110), compared to (111) for films deposited at room temperature. Films grown at 77 K differ from those deposited at room temperature, exhibiting lower surface roughness but smaller grain size, which leads to increased electrical resistivity in quench condensed films. The decrease of substrate temperature during the deposition appears to induce slightly more strain in depositions on the amorphous and van der Waals substrates than on the epitaxial substrates. Lastly, quench condensed films exhibit lower carrier mobility and lower carrier density compared to room temperature films. This study elucidates previously incompletely understood processes in bismuth deposition and raises new questions regarding growth on van der Waals surfaces.
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All authors Yulia Kirina, Prakash Sharma, Wyatt Thomas, Tristan Anderson, Arya G. Pour, Victoria Soghomonian, Jean J. Heremans

Materials Science

AI-assisted Human-in-the-Loop Web Platform for Structural Characterization in Hard drive design

Utkarsh Pratiush, Huaixun Huyan, Maryam Zahiri Azar et al. (+4 more)

Scanning transmission electron microscopy (STEM) has become a cornerstone instrument for semiconductor materials metrology, enabling nanoscale analysis of complex multilayer structures that define device performance. Developing effective metrology workflows for such systems requires balancing automation with flexibility; rigid pipelines are brittle to sample variability, while purely manual approaches are slow and subjective. Here, we present a tunable human-AI-assisted workflow framework that enables modular and adaptive analysis of STEM images for device characterization. As an illustrative example, we demonstrate a workflow for automated layer thickness and interface roughness quantification in multilayer thin films. The system integrates gradient-based peak detection with interactive correction modules, allowing human input at the design stage while maintaining fully automated execution across samples. Implemented as a web-based interface, it processes TEM/EMD files directly, applies noise reduction and interface tracking algorithms, and outputs statistical roughness and thickness metrics with nanometer precision. This architecture exemplifies a general approach toward adaptive, reusable metrology workflows - bridging human insight and machine precision for scalable, standardized analysis in semiconductor manufacturing. The code is made available at https://github.com/utkarshp1161/thickness-mapping-webapp
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All authors Utkarsh Pratiush, Huaixun Huyan, Maryam Zahiri Azar, Esmeralda Yitamben, Allen Bourez, Sergei V Kalinin, Vasfi Burak Ozdol

Tuesday 31 March

Materials Science · Cross-listed from physics.geo-ph

Correlative Microstructural Analysis of a Weathered Nantan Meteorite Fragment

Graeme J. Francolini, Brendan V. Dyck, Paul Mack et al. (+1 more)

The weathering of iron-rich phases within meteorites is a multi-stage process that significantly alters the microstructure and chemical composition based both on the environmental condition at the location of landing and the exposure time since the fall. This work investigates the resulting phases of this process in a correlative and comparative manner using a naturally weathered Nantan meteorite fragment. Techniques including X-ray Photoelectron Spectroscopy (XPS), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Fluorescence Spectroscopy (XRF) were used for chemical and compositional determination and X-ray Diffraction (XRD) and Electron Backscatter Diffraction (EBSD) for phase determination and microstructural analysis. The combination of these techniques revealed the meteorite matrix to be predominantly composed of magnetite, with goethite and maghemite present as secondary phases. The meteorite had two pairs of distinct regions, one separated by Ni content and the other by grain size and Cl distribution. The Ni content regions are believed to have formed from a former Widmanstätten pattern, with the high ($\geq$2.6 at%) and low ($\leq$0.9 at%) Ni regions from plessite and kamacite, respectively. The kamacite and taenite within the plessite are suggested to have weathered through distinct mechanisms. The grain size regions were separated by a visible boundary 100-200 $\mu$m wide where grains transitioned rapidly from fine to elongated grains and the Cl content changed from low and dispersed to concentrated spots. Lastly, a brecciated phase was found within the sample and was identified as a large cohenite grain which exhibited signs of weathering, including vein-like extensions of the matrix composed of NiO and magnetite, and deposits of iron and nickel carbonates.
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All authors Graeme J. Francolini, Brendan V. Dyck, Paul Mack, Ben Britton

Materials Science · Cross-listed from physics.geo-ph

Iron spin crossover in ferropericlase and its effect on lower-mantle thermal conductivity

Alexander F. Goncharov, Irina Chuvashova, Eric Edmund et al. (+29 more)

Thermal conductivity of Earths lower mantle controls heat transfer across the core-mantle boundary (CMB) and strongly influences mantle convection. We report direct measurements of the thermal conductivity of single-crystal ferropericlase (Mg$_{1-x}$Fe$_x$O, $x = 0.09$-0.13), the second most abundant lower-mantle mineral, using optical laser flash and X-ray free-electron laser heating in diamond-anvil cells up to $\sim2200$~K and 130~GPa. These experiments provide the first conductivity data for ferropericlase at simultaneous lower-mantle pressures and temperatures. A marked reduction in conductivity between 60 and 100~GPa at $\sim1700$~K is consistent with the iron spin crossover. Combined with our previous results for Fe- and Fe,Al-bearing bridgmanite, the data define a lower-mantle conductivity profile that increases with pressure to $\sim10$~W\,m$^{-1}$\,K$^{-1}$ near the CMB, constraining mantle heat flux, plume buoyancy, and long-term geodynamic evolution.
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All authors Alexander F. Goncharov, Irina Chuvashova, Eric Edmund, JungFu Lin, Zena Younes, Nicolas Jaisle, Axel Phelipeau, Carmen Sanchez-Valle, Christoph Otzen, Clemens Prescher, Hanns-Peter Liermann, Nico Giordano, James McHardy, Karen Appel, Michal Andrzejewski, S. V. Rahul, Minxue Tang, Jolanta Sztuk-Dambietz, Thomas Michelat, Torsten Laurus, Malcolm McMahon, Mark Robertson, Rachel Husband, Efim Kolesnikov, Sebastien Merkel, Silvia Boccato, Carsten Baehtz, Guillaume Morard, Emma S. Bullock, Cornelius Strohm, Zuzana Konopkova, Ryan Stewart McWilliams

Materials Science · Cross-listed from cs.DB

Ontology-based knowledge graph infrastructure for interoperable atomistic simulation data

Abril Azocar Guzman, Sarath Menon, Tilmann Hickel et al. (+1 more)

The reuse of atomistic simulation data is often limited by heterogeneous formats, incomplete metadata, and a lack of standardized representations of workflows and provenance. Here we present an ontology-based infrastructure for representing and integrating atomistic simulation data as a knowledge graph. The approach combines domain ontologies with a software framework that enables data capture both from existing datasets and directly from simulation workflows at the point of generation. Heterogeneous data from multiple sources are normalized into a common, ontology-aligned representation, enabling consistent querying and analysis across datasets. We demonstrate these capabilities through the integration of grain boundary data, cross-dataset analysis of material properties, and extraction of derived thermodynamic quantities from existing simulations. In addition, workflows are represented in a machine-readable form, enabling both forward provenance tracking and partial reconstruction of computational procedures. The resulting knowledge graph contains over 750,000 triples describing nearly 8,000 computational samples. This work provides a practical framework for improving the findability, interoperability, and reuse of atomistic simulation data.
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All authors Abril Azocar Guzman, Sarath Menon, Tilmann Hickel, Stefan Sandfeld

Materials Science

Metallic d-wave altermagnetism in WFeB: a platform for electrically switchable perpendicular spin-splitter response

Eranga H. Gamage, Zhen Zhang, Subhadip Pradhan et al. (+9 more)

We report the synthesis and magnetic characterization of WFeB and identify it as a metallic d-wave altermagnet representative of a broader TiNiSi-type family. Neutron diffraction, Mössbauer spectroscopy, and magnetometry establish a collinear altermagnetic ordering confirmed by first-principles calculations. The electronic structure shows a nonrelativistic spin splitting of approximately 100 meV, but it also supports a strong spin-splitter transport response. This demonstrates that efficient spin-current generation can occur even with such modest band splitting. Symmetry analysis shows that selected film orientations permit deterministic switching of the Néel vector by current-induced staggered torques, enabling electrical control of a perpendicular spin-splitter response. These results establish WFeB and related TiNiSi-type antiferromagnets as a platform for electrically switchable charge-to-spin conversion driven by altermagnetic symmetry.
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All authors Eranga H. Gamage, Zhen Zhang, Subhadip Pradhan, Ajay Kumar, David R. Ramgern, V. Ovidiu Garlea, Yaroslav Mudryk, Saeed Kamali, Douglas Warnberg, Kirill D. Belashchenko, Vladimir Antropov, Kirill Kovnir

Materials Science

Spatially modulated morphotropic phase boundaries in a compressively strained multiferroic thin film

Ting-Ran Liu, Xiangwei Guo, Sajid Husain et al. (+5 more)

The coexisting rhombohedral-like (R', MA) and tetragonal-like (T', MC) monoclinic phases in compressively strained bismuth ferrite thin films exhibit exceptional piezoelectric and magnetic properties. While previous studies have largely focused on probing the morphotropic phase boundaries (MPBs) comprising ordered R'/T' twins, their self-organizing structures remain not fully explored. Here, we observed two types of interphase boundaries in a 60 nm-thick BiFeO3 film epitaxially grown on a LaAlO3 substrate by employing multi-modal diffraction-based electron microscopy. First, the flat MPBs form lines extending >1 mm, and repeat almost every ~20 um. Additionally, we uncover a new type of phase boundary with zig-zag regions of alternating R'/R' and T'/T' twin domains. Cross-sectional multislice electron ptychography confirms the atomic-scale polarization rotation across the MPB, with out-of-plane strain varying >15%. Plan-view electron backscatter diffraction reveals the lattice disclination of ~1.5-degrees across the zig-zag interphase boundaries, while having >2.5 degrees within the MPB. Phase-field modeling suggests that the formation of zig-zag phase boundaries arises from balancing between Landau and elastic energies. We speculate that such well-ordered interphase boundaries are associated with mesoscale in-plane strain modulations, thus providing a way to engineer and harness their properties for potential device applications.
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All authors Ting-Ran Liu, Xiangwei Guo, Sajid Husain, Maya Ramesh, Pushpendra Gupta, Darrell Schlom, Ramamoorthy Ramesh, Yu-Tsun Shao

Materials Science

Stress Asymmetry in Hard Magnetic Soft Materials

H. Gökçen Güner, Francois Barthelat, John D. Clayton et al. (+3 more)

Hard magnetic soft materials – soft polymers embedded with hard magnetic particles – are modeled using continuum magnetomechanical formulations in which the deformation and the magnetization field are the primary kinematic variables. A recent question in such formulations is whether the Cauchy stress is symmetric, which is directly related to frame invariance and angular momentum balance. This note discusses energetically equivalent formulations, related by a change of variables between referential and current descriptions of the magnetization, and shows that they generally yield different Cauchy stresses, including a change in their symmetry. Specifically, the formulation based on a referential magnetization produces a symmetric Cauchy stress, while that based on a current magnetization generally yields an asymmetric Cauchy stress. We highlight that when the internal variable (magnetization field) is at the energy-minimizing equilibrium configuration, the divergences of these stresses are the same, and both stresses are symmetric.
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All authors H. Gökçen Güner, Francois Barthelat, John D. Clayton, Carlos Mora-Corral, Noel Walkington, Kaushik Dayal

Materials Science

Propagation-mediated amplification of \{11\={2}0\}-biased inversion domain boundary alignment in polarity-mixed GaN lateral overgrowth

Harim Song, Donghoi Kim and Chinkyo Kim

GaN polarity inversion and the associated inversion domain boundaries (IDBs) are frequently observed during lateral overgrowth and are often discussed in terms of the small energetic spread among competing IDB structures predicted by first-principles calculations. In circular mask openings, \(\{11\bar{2}0\}\)-aligned IDBs have previously been explained by geometric closure of a single-polarity hexagonal domain at the circular boundary. Here we examine an experimentally distinct regime in which opposite-polarity domains already coexist within the opening before the later development of long, straight IDB traces. In this mixed-polarity regime, the final trace orientation cannot be attributed solely to the macroscopic circular boundary. Nevertheless, plan-view SEM line-trace statistics show that IDB orientations remain biased toward the \(\{11\bar{2}0\}\) family. To quantify how this bias develops during propagation, we perform distance-resolved, length-weighted orientation analysis in concentric annular regions defined from the opening center. The resulting metrics show that \(\{11\bar{2}0\}\)-biased alignment is progressively amplified with propagation distance, while the orientation distribution becomes narrower, indicating systematic sharpening of the preferred alignment state. We further apply the same ring-resolved statistical operators to minimal two-domain propagation simulations in a circular opening and find that a propagation-mediated anisotropy reproduces the observed radial amplification under fixed circular geometry. Together, these results establish a quantitative phenomenology of \(\{11\bar{2}0\}\)-biased IDB alignment in polarity-mixed GaN lateral overgrowth on patterned sapphire and indicate that, although mask-boundary-imposed selection may describe single-polarity closure cases, the present mixed-polarity regime is better explained by propagation-mediated amplification.
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Materials Science · Cross-listed from cond-mat.mes-hall

A footprint of zero-point entropy in higher-temperature magnetic thermodynamics

Sergey Syzranov and Arthur P. Ramirez

Identifying extensively degenerate zero-temperature states is key in characterizing spin-liquid-candidate materials and spin ices. In experiments, finding zero-point entropy (ZPE) is often attempted by measuring the entropy released by a material when cooled down from very high to very low temperatures. Such investigations are often unreliable and lead to controversial results because accessible temperatures may be insufficient to accurately capture essential low- and high-temperature features of magnetic materials. The purpose of this paper is to point out a simple, easily accessible signature of nonzero ZPE: the Maxwell's relation $\left(\partial S/\partial H\right)_T = \left(\partial M/\partial T\right)_H$ can appear violated if a vanishing ZPE is assumed incorrectly. This relation can further be used for estimating the ZPE. In many materials below characteristic temperatures, the criterion of non-vanishing ZPE has a particularly simple form: $\left(\frac{\partial C}{\partial H}\right)_T\left(\frac{\partial M}{\partial T}\right)_H<0$. We discuss these effects and the ZPE signature in the benchmark test case of the well-studied spin ice $Dy_2Ti_2O_7$.
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Materials Science · Cross-listed from cs.LG

Perspective: Towards sustainable exploration of chemical spaces with machine learning

Leonardo Medrano Sandonas, David Balcells, Anton Bochkarev et al. (+20 more)

Artificial intelligence is transforming molecular and materials science, but its growing computational and data demands raise critical sustainability challenges. In this Perspective, we examine resource considerations across the AI-driven discovery pipeline–from quantum-mechanical (QM) data generation and model training to automated, self-driving research workflows–building on discussions from the “SusML workshop: Towards sustainable exploration of chemical spaces with machine learning” held in Dresden, Germany. In this context, the availability of large quantum datasets has enabled rigorous benchmarking and rapid methodological progress, while also incurring substantial energy and infrastructure costs. We highlight emerging strategies to enhance efficiency, including general-purpose machine learning (ML) models, multi-fidelity approaches, model distillation, and active learning. Moreover, incorporating physics-based constraints within hierarchical workflows, where fast ML surrogates are applied broadly and high-accuracy QM methods are used selectively, can further optimize resource use without compromising reliability. Equally important is bridging the gap between idealized computational predictions and real-world conditions by accounting for synthesizability and multi-objective design criteria, which is essential for practical impact. Finally, we argue that sustainable progress will rely on open data and models, reusable workflows, and domain-specific AI systems that maximize scientific value per unit of computation, enabling efficient and responsible discovery of technological materials and therapeutics.
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All authors Leonardo Medrano Sandonas, David Balcells, Anton Bochkarev, Jacqueline M. Cole, Volker L. Deringer, Werner Dobrautz, Adrian Ehrenhofer, Thorben Frank, Pascal Friederich, Rico Friedrich, Janine George, Luca Ghiringhelli, Alejandra Hinostroza Caldas, Veronika Juraskova, Hannes Kneiding, Yury Lysogorskiy, Johannes T. Margraf, Hanna Türk, Anatole von Lilienfeld, Milica Todorović, Alexandre Tkatchenko, Mariana Rossi, Gianaurelio Cuniberti

Materials Science

NLSTEM: Non-local denoising for enhanced 4D-STEM pattern indexing

Yichen Yang, Olivier Pierron, Josh Kacher et al. (+1 more)

4D-STEM-based orientation and phase mapping has enabled rapid microstructure quantification that can be directly combined with standard TEM- and STEM-based imaging modes. Typically, orientation mapping is coupled with beam precession (i.e. precession electron diffraction) to achieve high indexing rates, adding to the cost and often decreasing the spatial resolution of the approach. This paper introduces a new post processing approach modeled after the non-local pattern averaging and reindexing algorithm developed for the electron backscatter diffraction community, wherein post-collection, patterns are averaged using a distance similarity parameter. Results from Ni and Au thin films show that indexing rates can be significantly improved using this post-processing technique due to improved signal-to-noise ratios in the diffraction patterns. Interestingly, the highest indexing rates are achieved in samples heavily damaged via ion irradiation, suggesting that averaging over curved lattices further improves indexing rates.
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All authors Yichen Yang, Olivier Pierron, Josh Kacher, David Rowenhorst

Materials Science

Molecular beam epitaxy of wafer-scale O-band InAs/InGaAs quantum dots on GaAs for quantum photonics

Pavel S. Avdienko, Lukas Hanschke, Quirin Buchinger et al. (+13 more)

We report a scalable molecular beam epitaxy strategy to achieve a low density of O-band electrically tunable InAs/InGaAs quantum dots (QDs) on GaAs(001) substrates. Our approach is based on a gradient deposition of InAs in the sub-ML regime and subsequent capping with an InGaA strain-reducing layer to redshift the emission wavelength. For different growth conditions, we investigate the optical properties of the dots using photoluminescence mapping and correlate with structural properties determined by scanning transmission electron microscopy. Using a surface roughness modulation technique and synchronizing InAs sub-monolayer deposition cycles with substrate rotation, we control the dot density and position low-density regions (< 1 QD per um^2) on the substrate. Hyperspectral imaging is used to map the spatial and spectral characteristics of many individual dots in the low-density region, confirming that our approach is universally applicable to conventional MBE growth on (001) surfaces. Finally, we tune the QD emission wavelength within the O-band using electric fields and demonstrate single-photon emission with g(2)(0) = 0.020(14).
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All authors Pavel S. Avdienko, Lukas Hanschke, Quirin Buchinger, Nikolai Bart, Hubert Riedl, Bianca Scaparra, Yu Xia, Ziria Herdegen, Knut Müller-Caspary, Gregor Koblmüller, Tobias Huber-Loyola, Arne Ludwig, Andreas Pfenning, Sven Höfling, Kai Müller, Jonathan J. Finley