Materials Science · Cross-listed from cond-mat.mes-hall
Machine learning assisted high throughput prediction of moiré materials
Daniel Kaplan, Alexander C. Tyner, Eva Y. Andrei et al. (+1 more)
The world of 2D materials is rapidly expanding with new discoveries of stackable and twistable layered systems composed of
lattices of different
symmetries, orbital character, and structural motifs. Often, however, it is not clear a priori whether a pair of monolayers twisted at a small angle will exhibit correlated or interaction-driven phenomena. The computational cost to make accurate predictions of the single particle states is significant, as small twists require very large unit
cells, easily encompassing 10,000 atoms, and therefore implementing a high throughput prediction has been out of reach. Here we show a path to overcome this challenge by introducing a machine learning (ML) based methodology that efficiently estimates the twisted interlayer tunneling at arbitrarily low twist angles through the local-configuration based approach that enables interpolating the local stacking for a range of twist angles using a random forest regression
algorithm. We leverage the kernel
polynomial method to compute the density of states (DOS) on large real space graphs by reconstructing a
lattice model of the twisted
bilayer with the ML fitted hoppings. For twisted
bilayer graphene (TBG), we show the ability of the method to resolve the magic angle DOS at a substantial improvement in computational time. We use this new technique to scan through the database of stable 2D monolayers (MC2D) and reveal new twistable candidates across the five possible points groups in two-dimensions with a large DOS near the
Fermi energy, with potentially exciting interacting physics to be probed in future experiments.
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All authors Daniel Kaplan, Alexander C. Tyner, Eva Y. Andrei, J. H. Pixley
Materials Science · Cross-listed from physics.chem-ph
A Cartesian-3j Framework for Machine Learning Interatomic Potentials
Zemin Xu, Chenyu Wu, Wenbo Xie et al. (+1 more)
Machine learning interatomic potentials (MLIPs) have brought substantial gains in the extrapolation capability in computational chemistry. However, most equivariant models are typically built with spherical tensors (STs), while Cartesian tensor formulations remain less developed despite their natural
alignment with atomic coordinates and tensorial targets. In this work, we develop a Cartesian framework for irreducible Cartesian tensors (ICTs) by introduce the Cartesian-3j symbol and Cartesian Generalized Clebsch-Gordan Coefficients, which serve as direct analogues of the Wigner-3j symbol and Generalized Clebsch-Gordan coefficients defined for ST coupling. We extend the e3nn library to support ICT product, and use this framework to build Cartesian counterparts of MACE, NequIP, and Allegro, allowing the first controlled comparison where architectures are held fixed and only the tensor basis is changed. Our experiments show that irreducible Cartesian models can achieve accuracy comparable to spherical counterparts, but direct Cartesianization incurs unfavorable compute and
memory scaling, motivating dedicated Cartesian architectural choices. Leveraging ICTs and our framework, we introduce TACE-v1-OAM-M and demonstrate that it achieves competitive performance on Matbench Discovery compared to state-of-the-art ST models.
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All authors Zemin Xu, Chenyu Wu, Wenbo Xie, P. Hu
Materials Science · Cross-listed from physics.chem-ph
Multimer Embedding for Molecular Crystals Utilizing up to Tetramer Interactions
Alexander List, A. Daniel Boese and Johannes Hoja
Molecular
crystals possess a highly complex crystallographic landscape which in many cases results in the experimental observation of multiple
crystal structures for the same compound. Accurate results can often be obtained for such systems by employing periodic density functional theory using hybrid functionals; however, this is not always computationally feasible. One possibility to circumvent these expensive periodic calculations is the utilization of multimer
embedding methods. Therein, the fully periodic
crystal is described at a lower level of theory, and subsequently monomer energies, dimer interaction energies, etc. are corrected via high-level calculations. In this paper, we further extend such a multimer
embedding approach by one multimer order for all investigated properties, allowing us to compute
lattice energies up to the tetramer
embedding level, and atomic forces, the stress tensor, and harmonic
phonons up to the trimer level. We test the significance of including these higher-order multimers by
embedding PBE0+MBD multimers into periodic PBE+MBD calculations utilizing the X23
benchmark set of molecular
crystals and comparing the results to explicit periodic PBE0+MBD calculations. We show that tetramer interactions systematically improve the
lattice energy approximation and explore multiple possibilities for multimer selection. Furthermore, we confirm that trimer interactions are crucial for the description of the stress tensor, yielding
cell volumes within 1 % of those of PBE0+MBD. Subsequently, this also results in an improvement of the description of vibrational properties, giving on average gamma point frequencies within 1.3 wave numbers and vibrational free energies within 0.3 kJ/mol of the PBE0+MBD results.
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Materials Science · Cross-listed from physics.ins-det
A MAPS Detector for High Resolution Low Dose EBSD
Barnaby D.A. Levin, Kalani Moore, Nicolò M. Della Ventura et al. (+3 more)
The use of highly sensitive pixelated direct detectors has dramatically improved the performance of high energy instrumentation such as transmission electron microscopy. Here, we describe a recently developed monolithic active pixel sensor designed for low energy scanning electron microscopy applications. This detector enables electron backscatter diffraction (EBSD) at lower energies and dose than are accessible with existing scintillator-coupled detectors, expanding grain orientation mapping capabilities to materials such as ceramics that are poor electron conductors. The high detector sensitivity allows collection of rich diffraction information - providing dislocation defect contrast that is otherwise not accessible via EBSD. Indeed, even the energy of single electron interaction events can be measured with this detector, which we demonstrate to energy filter diffraction patterns revealing details of how diffraction occurs at low energy.
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All authors Barnaby D.A. Levin, Kalani Moore, Nicolò M. Della Ventura, McLean P. Echlin, Tresa M. Pollock, Daniel S. Gianola
Materials Science
Thermodynamical study of N$_2$ clathrate hydrate from DFT calculations
L. Martin-Gondre, V. Meko Fotso, C. Métais et al. (+3 more)
Thermodynamic stability of N$_2$ clathrate hydrates in the sI and sII structures is investigated using density functional theory with several exchange-correlation functionals, explicitly accounting for composition (cage occupancies) and pressure at T = 0 K. Among the tested functionals, revPBE-D3(0) best reproduces experimental
lattice parameters and bulk
moduli B$_0$ . Energetic analyses confirm the strong impact of large cage double occupancy on sI, whereas the convex-hull results show that sI with single occupancy remains thermodynamically stable up to $\sim$ 0.8 GPa alongside sII with single occupancy. Increasing pressure then stabilizes sII with double occupancy, consistent with its larger large-cage volume and lower framework strain. These results provide a coherent, first-principles thermodynamic framework for N$_2$ hydrate stability and a baseline for finite-temperature extension.
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All authors L. Martin-Gondre, V. Meko Fotso, C. Métais, A. Patt, J. Ollivier, A. Desmedt
Materials Science
Comparing Hubbard parameters from linear-response theory and a Hartree-Fock-based approach
Wooil Yang, Iurii Timrov, Francesco Aquilante et al. (+1 more)
Density-functional theory with on-site $U$ and inter-site $V$ Hubbard corrections (DFT+$U$+$V$) is widely used to predict properties of transition-metal and rare-earth compounds, but its accuracy depends critically on how these parameters are obtained. While they can be determined empirically, first-principles approaches offer better consistency, though their results can differ and a systematic comparison is lacking. Here, we compare two widely used approaches, linear-response theory (LRT) and the Hartree–Fock-based pseudohybrid functional formalism, applied to representative
oxides (MnO, NiO, CoO, FeO, BaTiO$_3$, ZnO, and ZrO$_2$). For partially occupied transition-metal $d$ states, both methods yield comparable $U$ values, but they differ significantly for nearly empty or fully filled $d$ shells. For O-$2p$ states, LRT systematically predicts large $U$ values ($\sim 10~\mathrm{eV}$), whereas the pseudohybrid approach gives system-dependent values. Even larger differences appear for the inter-site $V$: the former yields small values ($<1~\mathrm{eV}$), while the latter gives larger values ($\sim 3~\mathrm{eV}$) due to its dependence on charge redistribution. We further show that the pseudopotential choice, which defines Hubbard projectors, affects the parameters and their agreement. Overall, while parallels between these two methods exist, they rely on different assumptions, leading to variations in predictions of material properties.
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All authors Wooil Yang, Iurii Timrov, Francesco Aquilante, Young-Woo Son
Materials Science
Spin-Dependent Nonorthogonal Generalized Wannier Functions and their Integration with PAW and Hubbard Corrections in Linear-Scaling DFT
Miguel Escobar Azor, David D. O'Regan, Ali Safavi et al. (+3 more)
We present a
spin-dependent extension of the non-orthogonal generalized Wannier function (NGWF) formalism within the framework of linear-scaling density functional theory (LS-DFT) as implemented in the ONETEP code. In traditional LS-DFT representations, both
spin channels are constrained to share a common variational basis, which limits the accuracy for systems that are
spin-polarized or exhibit
magnetic order. Our approach allows NGWFs to vary independently for each
spin channel, enabling a more accurate representation of
spin-polarization in the electronic density. We demonstrate the efficacy of this method through a series of test cases, including localized
magnetic defects in two-dimensional hBN, transition metal complexes, two-dimensional van der Waals
magnetic materials, and both bulk and nanocluster
ferromagnetic Co. In each scenario, the incorporation of
spin-dependent NGWFs results in enhanced accuracy for total energy calculations, improved localization of
spin density, and accurate predictions of
magnetic ground states. This improvement is particularly notable when combined with DFT+U and DFT+U+J corrections. In this work, we take the opportunity to describe the combination of DFT+U+J and the projector-augmented wave (PAW) formalism within the LS-DFT framework, including how PAW participates in the ionic Pulay force, and in the minimum-tracking linear response approach for computing parameters in situ. Our findings demonstrate that
spin-dependent NGWFs are a crucial and computationally efficient advancement in the linear-scaling DFT simulation of
spin-polarized materials.
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All authors Miguel Escobar Azor, David D. O'Regan, Ali Safavi, Jacek Dziedzic, Chris-Kriton Skylaris, Nicholas D. M. Hine
Materials Science
Self-supported bulk MXene electrodes for electrochemical hydrogen applications
Rebeca Miyar, Bar Favelukis, Eva B. Mayer et al. (+7 more)
MXenes are promising candidates for electrochemical applications due to their high conductivity, tunable surface chemistry, and catalytic potential. However, their use in bulk electrode form remains unexplored despite advantages such as higher current density and improved mechanical integrity. Herein, we present a methodology for the fabrication of self-supported vdW solid Ti3C2Tz MXene electrodes, produced by cold compaction followed by
vacuum heat treatment at 600 {\deg}C, which effectively removes interlayer confined water and stabilizes the bulk 3D structure. The resulting binder-free electrodes exhibit enhanced mechanical robustness along with structural and chemical stability in various electrolytes. The MXene electrodes demonstrate adequate HER activity while maintaining electrochemical stability over time, with minimal oxidation or changes in termination surface chemistry. This approach is scalable and cost-effective, overcoming limitations of nanoscale MXene architectures in electrochemical environments and offering a practical pathway toward MXene-based materials for sustainable hydrogen energy technologies.
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All authors Rebeca Miyar, Bar Favelukis, Eva B. Mayer, Manoj Prabhakar, Yug Joshi, Gerhard Dehm, Jochen M. Schneider, Maria Jazmin Duarte, Barak Ratzker, Maxim Sokol
Materials Science
High-Throughput Prediction of Exfoliable Non-van der Waals Materials from a Universal Potential
Tom Barnowsky, Carsten Timm and Rico Friedrich
Exfoliation and cleavage create two-dimensional (2D) materials and surfaces with physical and chemical properties distinct from their bulk parents. The rising class of non-van der Waals (non-vdW) 2D materials derived from non-layered
crystals provides a fascinating platform, expanding the landscape of low-dimensional materials. Current computational models, however, provide limited guidance: existing descriptors are largely tailored to vdW layered systems. Here, we introduce a general framework predicting
crystal cleavage and exfoliable 2D subunits directly from bulk structures. At its core is a universal eXfoliation and Cleavage Potential (XCP) enabling large-scale screening of diverse materials at negligible computational cost. Applying this approach, we obtain 44,030 cleavable surfaces and candidate non-vdW 2D materials from which we investigate - according to our criteria - 2,531 likely exfoliable ones using high-throughput density functional theory. A large fraction of these candidates is found to be dynamically and thermodynamically stable, while showing negligible overlap with existing 2D materials databases. Our study thus opens a systematic route to explore and design 2D materials with high chemical and structural diversity.
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Materials Science · Cross-listed from physics.optics
Intrinsic temporal and spectral mixing in time-resolved terahertz spectroscopy
Benjamin J. Dringoli and David G. Cooke
In an ultrafast optical-pump terahertz-probe measurement, the photoinduced material response can be modulated on a timescale shorter than the extent of the THz pulse. In this situation, the measured time-frequency response deviates from a simple time-dependent linear response. When full two-dimensional time-frequency maps are measured, this yields complex features that can be incorrectly assigned to a photoexcited coherent response. We investigate this experimentally via the measured response of photoexcited SnSe, whereby photoinduced phase change dynamics lead to ultrafast changes of the charge carrier and
lattice optical conductivity response. Two-dimensional time-frequency THz transmission maps subsequently show unexpected time-frequency features at early pump-probe delay times. These features are reproduced in both finite-difference time-domain simulations of the THz experiment and in an extension of non-
equilibrium response function theory, demonstrating their systematic origin. This work improves the understanding of systematic effects in high time resolution optical-pump THz-probe spectroscopy, and explores the conditions in which they are likely to appear.
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Materials Science
How accurate are foundational machine learning interatomic potentials for heterogeneous catalysis?
Luuk H. E. Kempen, Raffaele Cheula and Mie Andersen
Foundational machine learning interatomic potentials (MLIPs) are being developed at a rapid pace, promising closer and closer approximation to ab initio accuracy. This unlocks the possibility to simulate much larger length and time scales. However,
benchmarks for these MLIPs are usually limited to ordered, crystalline and bulk materials. Hence, reported performance does not necessarily accurately reflect MLIP performance in real applications such as heterogeneous catalysis. Here, we systematically analyze zero-shot performance of 80 different MLIPs, evaluating tasks typical for heterogeneous catalysis across a range of different data sets, including adsorption and reaction on surfaces of alloyed metals,
oxides, and metal-
oxide interfacial systems. We demonstrate that current-generation foundational MLIPs can already perform at high accuracy for applications such as predicting vacancy formation energies of perovskite
oxides or zero-point energies of supported nanoclusters. However, limitations also exist. We find that many MLIPs catastrophically fail when applied to
magnetic materials, and structure relaxation in the MLIP generally increases the energy prediction error compared to single-point evaluation of a previously optimized structure. Comparing low-cost task-specific models to foundational MLIPs, we highlight some core differences between these model approaches and show that – if considering only accuracy – these models can compete with the current generation of best-performing MLIPs. Furthermore, we show that no single MLIP universally performs best, requiring users to investigate MLIP suitability for their desired application.
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Materials Science
Structural transitions related to order-disorder and thermal desorption of D atoms in TbFe$_{2}$D$_{4.2}$
V. Paul-Boncour and O. Isnard
TbFe$_{2}$D$_{4.2}$ deuteride crystallizes in a monoclinic structure ($Pc$ space group) with deuterium inserted into 13 [Tb$_{2}$Fe$_{2}$] and 5 [TbFe$_{3}$] tetrahedral interstitial sites. Its structural
evolution versus temperature has been investigated by combining in-situ X-ray and
neutron diffraction (XRD and NPD) with differential scanning calorimetry (DSC) experiments.Upon heating, the deuteride undergoes a reversible order-disorder transition from an ordered monoclinic structure to a disordered cubic structure between 320 and 380 K. Then, a multipeak thermal desorption occurs between 400 and 550 K, which can be explained by the transitions between different cubic deuterides separated by two-phase ranges. After controlled partial D desorption of TbFe$_{2}$D$_{4.2}$,the XRD patterns of several TbFe$_{2}$D$_{x}$ deuterides were measured ex-situ using synchrotron radiation at room temperature, revealing the formation of different phases with cubic or monoclinic structures separated by two phase ranges.A tetragonal superstructure was observed for a phase with $x$ = 2. This work can explain previous results of the literature indicating the existence of cubic and or rhombohedral hydrides depending on the hydrogenation conditions and the H content. The monoclinic structures reported here correspond to a slight distortion of the previous rhombohedral structures described by other authors.
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Materials Science
Photoinduced phase heterogeneity and charge localization in SnSe
Benjamin J. Dringoli, Stefano Mocatti, Giovanni Marini et al. (+4 more)
Time-resolved multi-terahertz (THz) spectroscopy is used to observe pump fluence-dependent dynamics in the optical conductivity of photoexcited tin selenide (SnSe) over an ultrabroadband spectral range of 0.5 - 11 THz at fluences from 0.1 - 7.5 mJ/cm$^2$. A free carrier Drude spectrum is observed at pump fluences below 3 mJ/cm$^2$, with optical
phonons well described by the
equilibrium Pnma structural phase. With increasing fluence, a suppression of the DC photoconductivity is observed, indicating an interruption of long range transport due to phase disorder. Concomitantly, the optical
phonons exhibit features that can no longer be explained by a pure Pnma phase, with a frequency shift and narrowing of the $B^2_{1u}$ mode and a new mode appearing at $\sim$3.0 THz consistent with a transition to a higher-
symmetry structure. At an intermediate fluence of 3.1 mJ/cm$^2$, a high frequency Lorentzian component consistent with phase heterogeneity appears that rapidly
redshifts after 2 ps and whose amplitude exponentially decays on a 90 ps time scale. Our experimental measurements and theoretical calculations provide evidence for a non-thermal, photo-induced nucleation of higher
symmetry, semi-metallic phase domains in SnSe appearing within 200 fs.
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All authors Benjamin J. Dringoli, Stefano Mocatti, Giovanni Marini, Zhongzhen Luo, Matteo Calandra, Mercouri G. Kanatzidis, David G. Cooke
Materials Science · Cross-listed from cond-mat.mes-hall
Wigner polarons reveal Wigner crystal dynamics in a monolayer semiconductor
Lifu Zhang, Liuxin Gu, Haydn S. Adlong et al. (+12 more)
Wigner
crystals,
lattices made purely of electrons, are a quintessential paradigm of studying correlation-driven
quantum phase transitions. Despite decades of research, the internal dynamics of Wigner
crystals has remained extremely challenging to access, with most experiments probing only static order or collective motion. Here, we establish monolayer WSe2 as a new materials platform to host zero-field Wigner
crystals and then demonstrate that
exciton spectroscopy provides a direct means to probe both static and dynamic properties of these electron
lattices. We uncover striking optical resonances that we identify as Wigner polarons, quasiparticles formed when the electron
lattice is locally distorted by
exciton-Wigner
crystal coupling. We further achieve all-optical control of
spins in the Wigner
crystal, directly probing valley-dependent Wigner polaron scattering well above the
magnetic ordering temperature and in the absence of any external
magnetic field. Finally, we demonstrate optical melting of the Wigner
crystal and observe intriguingly different responses of the umklapp (static) and Wigner polaron (dynamic) resonances to optical excitation. Our results open up exciting new avenues for elucidating electron dynamics and achieving ultrafast optical control of interaction-driven
quantum phase transitions in strongly correlated electron systems.
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All authors Lifu Zhang, Liuxin Gu, Haydn S. Adlong, Arthur Christianen, Eugen Dizer, Ruihao Ni, Rundong Ma, Suji Park, Houk Jang, Takashi Taniguchi, Kenji Watanabe, Ilya Esterlis, Richard Schmidt, Atac Imamoglu, You Zhou
Materials Science
Recent Advances in Metallic Glasses
Silvia Bonfanti, Ralf Busch, Jesper Byggmästar et al. (+12 more)
This paper reviews recent advances in the field of metallic glasses, focusing on the development of novel experimental techniques and in silico models. We discuss progress in experimental characterization, additive manufacturing, multiscale modeling approaches, and the growing role of machine learning in understanding and designing these complex materials. On the experimental side, we highlight measurements of thermophysical properties of supercooled
liquids via fast chip calorimetry and enhancements in mechanical properties through rejuvenation treatments. This work underscores the crucial role of short-range order and medium-range order in controlling metallic glass mechanical properties. Recent progress in structural probes allows in situ observations of deformation mechanisms, positioning the field well to further advance our understanding of mechanical properties. Additive manufacturing of metallic glasses is discussed as one encouraging new manufacturing route for metallic glasses. We examine
laser powder-bed fusion process physics and the central trade-off between amorphicity and densification, including heat affected zone devitrification and defects formation, together with emerging mitigation strategies and applications. On the theoretical and simulation side, we review advances in nanoscale, mesoscale, and continuum modeling of metallic glasses that have led to promising approaches by which multiscale schemes can incorporate data sourced from atomic-scale simulations. These efforts have helped to elucidate the connection between the glass structure and mechanical and rheological responses. We also cover the development of machine learning interatomic potentials for metallic glasses, along with machine learning driven prediction of glass forming ability and inverse design methods. Finally, challenges and directions for future research are presented and discussed.
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All authors Silvia Bonfanti, Ralf Busch, Jesper Byggmästar, Jeppe C. Dyre, Jürgen Eckert, Spencer Fajardo, Michael L. Falk, Isabella Gallino, Jamie J. Kruzic, Jiayin Lu, Giulio Monaco, Misaki Ozawa, Anshul D. S. Parmar, Chris H. Rycroft, Srikanth Sastry
Materials Science
High-Temperature Activation of Single-Photon Emitters in monolayer WS2
Gyeongjun Lee, Antoine Borel, Takashi Taniguchi et al. (+3 more)
Controlled activation of defect-bound excitonic states in two-dimensional
semiconductors provides a route to isolated
quantum emitters and a sensitive probe of defect physics. Here we demonstrate that in situ high-temperature annealing of hBN-encapsulated monolayer WS$_2$ on a suspended microheater leads to the emergence of spectrally isolated single-
photon emitters at cryogenic temperatures. Annealing at temperatures around 1100 K produces a sharp emission line, $X_L$, red-shifted by approximately 80 meV from the neutral
exciton and exhibiting a linewidth below 200 $\mu$eV. Photoluminescence excitation spectroscopy and power-dependent measurements show that $X_L$ originates from annealing-induced defects in the WS$_2$ monolayer, while second-order
photon correlation measurements reveal clear antibunching with $g^{(2)}(0)<0.5$. These results establish high-temperature in situ annealing as a controlled means to access defect-bound excitonic states and single-
photon emission in van der Waals materials.
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All authors Gyeongjun Lee, Antoine Borel, Takashi Taniguchi, Kenji Watanabe, Fausto Sirotti, Fabian Cadiz
Materials Science
Predictive Inorganic Synthesis based on Machine Learning using Small Data sets: a case study of Hydrodynamic Diameter-controlled Cu Nanoparticles
Brent Motmans, Digvijay Ghogare, Thijs G.I. van Wijk et al. (+6 more)
Cu NPs have a broad applicability, yet their synthesis is sensitive to subtle changes in reaction parameters. This sensitivity, combined with the time- and resource-intensive nature of experimental optimization, poses a major challenge in achieving reproducible and size-controlled synthesis. While ML shows promise in materials research, its application is often limited by scarcity of large high-quality experimental data sets. This study explores ML to predict the DLS-derived hydrodynamic diameter of Cu NPs using a small data set of 25 syntheses. Latin Hypercube Sampling is used to efficiently cover the parameter space while creating the experimental data set. Ensemble regression models successfully predict hydrodynamic diameters with good predictive performance given the limited
dataset. Since quantitative regression requires a unique DLS-derived hydrodynamic diameter, the regression model is restricted to mono-modal DLS distributions, while a complementary classification model identifies synthesis conditions for which quantitative prediction is applicable. Using equivalent out-of-sample validation, the ML and DoE models showed comparable generalization. The final ensemble model achieved an R2=0.74 compared to 0.60 for the DoE model, while retaining the complete synthesis parameter space, making it better suited for synthesis guidance. Additionally, classification models using both random forests and LLMs are evaluated to distinguish between large and small particles. These classification models exhibited only modest predictive performance, indicating that this small
dataset is insufficient to fully exploit the capabilities of complex LLMs. Overall, this study demonstrates that carefully curated small data sets, paired with robust classical ML, can effectively support the synthesis of Cu NPs and highlights that for lab-scale studies, complex models like LLMs may offer limited benefits.
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All authors Brent Motmans, Digvijay Ghogare, Thijs G.I. van Wijk, Joren Van Herck, Saba Heidarian, Pieter De Meyer, Berend Smit, An Hardy, Danny E.P. Vanpoucke
Materials Science
Solid Oxide Electrolysis Cells: Bridging Materials Development and Process System Engineering for Gigawatt-Scale Applications
Matthias Riegraf, Marc Riedel, Soren Hojgaard Jensen et al. (+3 more)
High-temperature solid
oxide electrolysis
cells (SOECs) are a potential core power-to-X (P2X) technology due to their unparalleled system efficiencies, that can exceed 85 % when excess heat from exothermic downstream processes is available. Recent advancements in materials,
cell and stack design have enabled the deployment of megawatt (MW) scale demonstration plants and gigawatt (GW) scale manufacturing capacities. Consequently, key challenges to industrial-scale adoption scale now increasingly lie at the system level. Unlike previous SOEC reviews focused on materials and stack-level innovations, this work uniquely addresses emerging interdisciplinary system-level challenges and highlights the need for a paradigm shift. Several key insights are identified. Pressurized operation plays a crucial role in enhancing SOEC system performance and enabling better process integration. The dynamic capabilities of SOECs are better than often assumed and can further be improved via advanced operating strategies and modularization. Balance-of-plant (BoP) component costs rival stack capital expenditure, emphasizing the need for cost reductions through economies of scale via mass production and cross-industry synergies. Co-electrolysis remains at a lower technology readiness level and lacks MW scale demonstration. Furthermore, demonstrated integration with downstream processes across entire P2X chains remains scarce. Future research and development strategies are proposed, offering a roadmap to overcome these challenges and accelerate SOEC commercialization.
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All authors Matthias Riegraf, Marc Riedel, Soren Hojgaard Jensen, Srikanth Santhanam, S. Asif Ansar, Marc Heddrich
Materials Science
Probing formation and epitaxy of ultrathin Titanium Silicide using low and medium energy ion scattering
Philipp M. Wolf, Eduardo Pitthan, Zhen Zhang et al. (+3 more)
Titanium silicide is a key contact material in advanced three-dimensional
semiconductor device architectures. Here, we examine the formation of ultrathin Ti-silicide on Si(100) using a combination of non-destructive in-situ and ex-situ ion scattering techniques capable of resolving composition and structure at the nanoscale. In-situ Time-of-Flight Low-Energy Ion Scattering (ToF-LEIS) indicates intermixing after annealing at 350 {\deg}C, with further compositional changes after annealing at 500 {\deg}C, including the emergence of a Si terminating layer at the surface. Consecutive ex-situ Time-of-Flight Medium-Energy Ion Scattering (ToF-MEIS) reveals a Ti-rich polycrystalline surface layer and a Si-rich interface layer exhibiting strong ordering along the Si [100] axis. High-Resolution Transmission Electron Microscopy (HR-TEM) images confirm these findings, revealing a $\approx$1.5 nm thick epitaxial silicide layer at the interface. The presence of an epitaxial interface is particularly promising for minimizing contact resistivity in ultrathin contact layers, where interfacial order can dominate electronic performance. In addition, both ToF-MEIS and HR-TEM unveil significant variations in the thickness of the silicide layer, with a substantial interface roughness but no translation of this roughness to the surface.
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All authors Philipp M. Wolf, Eduardo Pitthan, Zhen Zhang, Tuan T. Tran, Radek Holeňák, Daniel Primetzhofer
Materials Science
Atomic forces from correlation energy functionals based on the adiabatic-connection fluctuation-dissipation theorem
Damian Contant and Maria Hellgren
We extend the capabilities of correlation energy functionals based on the adiabatic-connection fluctuation-dissipation
theorem by implementing the analytical atomic forces within the random phase approximation (RPA), in the context of plane waves and pseudopotentials. Forces are calculated at self-consistency through the optimized effective potential method and the Hellmann-Feynman
theorem. In addition, non-self-consistent RPA forces, starting from the PBE generalized gradient approximation, are evaluated using density functional perturbation theory. In both cases, we find forces of excellent numerical quality. Furthermore, for most molecules and solids studied, self-consistency is found to have a negligible impact on the computed geometries and vibrational frequencies. The RPA is shown to systematically improve over PBE and, by including the exact-exchange kernel within RPA + exchange (RPAx), through finite-difference total energy calculations, we obtain an accuracy comparable to advanced wavefunction methods. Finally, we estimate the anharmonic shift and provide accurate theoretical references based on RPA and RPAx for the zone-center optical
phonon of diamond, silicon, and germanium.
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Materials Science · Cross-listed from cond-mat.str-el
Interfacial Strain Modulated Correlated Plasmons in La1.85Sr0.15CuO4 and Their Role in High-temperature Superconductivity
Xiongfang Liu, Shengwei Zeng, Xun Liu et al. (+9 more)
High-temperature superconductivity in cuprate materials remains a major challenge in physics due to the complexity of their strongly correlated electronic states. Interfacial strain is a powerful lever for tuning electronic correlations in complex
oxides, offering new pathways to control emergent
quantum phases. Here, we report the discovery of interfacial strain modulated correlated plasmons observed exclusively in superconducting La1.85Sr0.15CuO4 (LSCO) through spectroscopic ellipsometry. This form of plasmons is absent in the non-superconducting LSCO counterparts. Detailed analysis reveals that these correlated plasmons, arising from the collective excitations within Mott-correlated bands, are driven by long-range electronic correlations in the Cu-O planes. Furthermore, long-range electronic correlations, intricately modulated by interfacial strain, may play a crucial role in the emergence of superconductivity and in tuning the transition temperature. Dynamical cluster approximation (DCA) with
quantum Monte Carlo (QMC) calculations of the extended Hubbard model suggest that long-range Coulomb interactions play an important role in LSCO, showing good agreement with our experimental findings. The collective evidence from both the experimental results and theoretical findings provides new insights into the nature of collective excitations and their pivotal role in the emergence of high-temperature superconductivity.
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All authors Xiongfang Liu, Shengwei Zeng, Xun Liu, Kun Han, Difan Zhou, Chi Sin Tang, Ping Yang, Mark B. H. Breese, Chuanbing Cai, Ariando Ariando, Mi Jiang, Xinmao Yin
Materials Science
Interplay of Crystallization and Amorphous Spinodal Decomposition during Thermal Annealing of Organic Photoactive Layers
Maxime Siber, Olivier J. J. Ronsin, Gitti L. Frey et al. (+1 more)
Tailoring the nanomorphology of organic photoactive layers through a specialized chain of processing steps is an imperative challenge on the path towards reliable and performant organic electronic manufacturing. This hurdle generally proves delicate to be overcome, as organic materials can be subject to many different phase transformation phenomena that are able to interfere with each other and produce a wide variety of morphological configurations with distinct structural, mechanical, and optoelectronic properties. A typical combination of such mechanisms, which the present systems are often prone to, and which is complex to investigate experimentally at the nanoscale, is the phase separation resulting from the interplay between amorphous demixing and crystallization. In this work, an in-house Phase-Field modeling framework is employed to simulate and, consequently, explain the phenomenological behavior of a photoactive bulk heterojunction during a thermal annealing treatment. The model predictions are validated against available electron microscopy imaging of the nanostructural
evolution during the process. It is demonstrated that the simulations can successfully provide a detailed comprehension of
crystal nucleation and growth shaped by amorphous spinodal decomposition, so as to yield valuable insights for physically-based morphology control. In addition, this study shows the relevance of extensive thermodynamic and kinetic characterizations of organic
semiconductor mixtures (e.g., phase diagram assessments, surface tension measurements, composition-dependent molecular diffusivity evaluations) for the associated field of research.
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All authors Maxime Siber, Olivier J. J. Ronsin, Gitti L. Frey, Jens Harting
Materials Science
Orbital-related gyrotropic responses in Cu$_2$WSe$_4$ and chirality indicator
Kazuki Nakazawa, Terufumi Yamaguchi and Ai Yamakage
In recent years, counterparts of phenomena studied in spintronics have been actively explored in the orbital sector. The relationship between orbital degrees of freedom and
crystal chirality has also been intensively investigated, although the distinction from gyrotropic properties has not been fully clarified. In this work, we investigate
spin and orbital Edelstein effects as well as the nonlinear responses in the ternary transition-metal chalcogenide Cu$_2$WSe$_4$, which has a gyrotropic but achiral
crystal structure. We find that in the Edelstein effect, magnetization is dominated by the orbital contribution rather than the
spin contribution. On the other hand, both the nonlinear
chiral thermoelectric (NCTE)
Hall effect–a response to the cross product of the electric field and the temperature gradient–and the nonlinear
Hall effect–conventional second-order response to the electric field–are found to be dominated by the Berry
curvature dipole. We further find that
spin-orbit coupling plays only a minor role in these effects, whereas the orbital degrees of freedom are essential. Finally, we demonstrate that the orbital
magnetic-moment contributions to both the Edelstein effect and the NCTE
Hall effect are closely linked to chirality, and we discuss the possibility of using them as a chirality indicator.
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Materials Science
Magnetic behavior and phase diagram of epitaxial Er3Fe5O12 thin films across the compensation temperature
Satakshi Pandey, Antoine Barbier, Anne Forget et al. (+6 more)
Rare-earth iron garnet (RE3Fe5O12) films are promising insulating ferrimagnets. They can show low
magnetic damping, perpendicular
magnetic anisotropy, and ultrafast
spin dynamics, which makes them ideal for
spin transport applications. In this work, we investigate the interaction between the
magnetic sublattices in Er3Fe5O12 thin films grown by pulsed
laser deposition on a Gd3Ga5O12 substrate. Structural and
magnetic characterization reveals high-quality single-
crystal growth, with compensation temperature close to the reported bulk value (~80 K).
Magnetic phase diagrams based on element-specific measurements map out the regions where ferrimagnetic, canted, and aligned phases are stable across the compensation temperature. The micromagnetic dynamics resulting from perpendicular
magnetic pulse perturbation of an in-plane magnetized layer was investigated at room temperature and reveals complex configurations. These results are a key feature for modulating magnetization dynamics through the compensation phenomenon, which is essential for
spin-based devices operating in a low-temperature regime.
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All authors Satakshi Pandey, Antoine Barbier, Anne Forget, Brice Sarpi, Francesco Maccherozzi, Roberto Sant, Nicholas B. Brookes, Jean-Baptiste Moussy, Pamella Vasconcelos Borges Pinho
Materials Science
Tight-binding and density-functional study of the Raman tensor in two-dimensional massive Dirac fermion systems
Selçuk Parlak, Abhishek Kumar, Runhan Li et al. (+2 more)
Recently, two unusual features were theoretically predicted for the Raman response of out-of-plane
phonons in
magnetic two-dimensional materials hosting massive Dirac
fermions. First, the phase difference between certain Raman tensor elements was found to be quantized to $\pm \pi/2$, sensitive only to the sign of the Dirac
fermion mass. Second, a selection rule was identified in the Raman intensity under circularly polarized light, which generalizes the well-known optical valley selection rule. These predictions were based on a low-energy effective model in the continuum approximation. Here, we test the robustness of those results for more realistic theoretical approaches. First, we calculate the Raman tensor for an electronic tight-binding model on a honeycomb
lattice with broken time-reversal and inversion
symmetries. Second, we compute the Raman tensor from density-functional theory for a monolayer of
ferromagnetic 2H-RuCl$_2$. Both calculations corroborate the analytical results found in the continuum model, thereby theoretically confirming the peculiar behavior of the Raman tensor for two dimensional massive Dirac
fermion systems.
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All authors Selçuk Parlak, Abhishek Kumar, Runhan Li, Maia G. Vergniory, Ion Garate
Materials Science
Extending the Flory-Huggins Theory for Crystalline Multicomponent Mixtures
Maxime Siber, Olivier J. J. Ronsin and Jens Harting
The Flory-Huggins theory is a well-established
lattice model that is commonly used to study the mixing of distinct chemical species. It can successfully predict phase separation phenomena in blends of incompatible materials. However, it is limited to amorphous mixtures, excluding systems where the phase segregation is shaped by the concurrent crystallization of one or several blend components. A generalization of the Flory-Huggins formalism is thus necessary to capture the coupling and the interplay of crystallization with amorphous demixing mechanisms, such as spinodal decomposition. This work therefore revolves around the derivation of a free energy model for multicomponent mixtures that encompasses the physics of both processes. It is detailed which concepts from the original Flory-Huggins theory are required to apprehend the presented developments and how the current framework is built upon them. Furthermore, additional discussion points address chemical potential calculations and selected examples of binary and ternary phase diagrams, thereby highlighting the variety of blend behaviors that can be represented.
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Materials Science · Cross-listed from cond-mat.supr-con
Entropy stabilization and effect of A-site ionic size in bilayer nickelates
Jia-Yi Lu, Jia-Xin Li, Xin-Yu Zhao et al. (+5 more)
The discovery of high-temperature superconductivity in La$_3$Ni$_2$O$_7$ under high pressure has sparked a surge of research into Ruddlesden-Popper (RP) nickelates. Currently, stabilizing the
bilayer RP phases with smaller $A$-site ions remains a significant challenge. In this work, we have successfully synthesized medium- and high-
entropy bilayer nickelates, La$_{1.2}$Pr$_{0.6}$Nd$_{0.6}$Sm$_{0.6}$Ni$_2$O$_{7-\delta}$ and La$_{0.67}$Pr$_{0.67}$Nd$_{0.67}$Sm$_{0.33}$Eu$_{0.33}$Gd$_{0.33}$Ni$_2$O$_{7-\delta}$, by utilizing the concept of configuration
entropy stabilization. The high-
entropy nickelate exhibits the smallest unit-
cell volume and the largest orthorhombic distortion reported to date. The chemical pressure induced by the smaller A-site ions significantly enhances the NiO$_6$ octahedral rotation/distortion and shortens the interlayer Ni-Ni interatomic spacing. Physical property measurements reveal bad electrical conductivity alongside a markedly elevated density-wave transition temperature. Notably, the superconducting transition temperature extrapolated from structural correlations is projected to exceed 100 K. Our work not only demonstrates
entropy stabilization of
bilayer nickelates, but also reveals the effect of $A$-site-ion size on the
crystal structure and physical properties, opening a new pathway for developing nickelate
superconductors and tuning their electronic properties.
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All authors Jia-Yi Lu, Jia-Xin Li, Xin-Yu Zhao, Ya-Nan Zhang, Yi-Qiang Lin, Kai-Xin Ye, Hui-Qiu Yuan, Guang-Han Cao
Materials Science · Cross-listed from cond-mat.str-el
Magnetic-field-induced insulating behavior in black phosphorus under pressure
Kazuto Akiba, Yuzuki Sega, Yuichi Akahama et al. (+3 more)
We investigated the out-of-plane magnetoresistance of pressurized black phosphorus (BP) with a longitudinal field configuration. Despite the absence of the Lorentz force in the present configuration, we observed a significant enhancement of magnetoresistance marked with a clear onset field in both the semiconducting (1.1 GPa) and semimetallic (1.3 GPa) phases. The insulating behavior observed near the
semiconductor-semimetal transitio pressure is possibly associated with emergence of an excitonic phase, which has been suggested in a recent theoretical study. BP under finely tuned pressure can be a candidate to realize the field-induced electronic phase transition in a moderate
magnetic field below 9 T.
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All authors Kazuto Akiba, Yuzuki Sega, Yuichi Akahama, Yuta Seo, Tomoki Machida, Masashi Tokunaga
Materials Science · Cross-listed from cond-mat.supr-con
Beyond dpa: an atomistic framework for a quantitative description of radiation damage in YBa2Cu3O7
Federico Ledda, Daniele Torsello, Davide Gambino et al. (+8 more)
Radiation damage in high-temperature cuprate
superconductors represents one of the main technological challenges for their deployment in harsh environments, such as fusion reactors and accelerator facilities. Their complex
crystal structure makes modeling irradiation effects in this class of materials a particularly demanding task, for which existing damage models remain inadequate. In this work, we develop an atomistic-based approach for describing primary radiation damage in YBa2Cu3O7, by coupling Molecular Dynamics and Binary Collision Approximation simulations in a way that makes them complementary. When integrated with Primary Knock-on Atom spectra obtained from Monte Carlo codes, our results establish a framework for multiscale modeling of radiation damage, enabling quantitative estimates of several damage descriptors, such as defect production, defect clustering, and the effective damaged volume for any specific irradiation conditions where collision cascades dominate. This computational approach is suitable for the prediction of irradiation effects in any complex functional
oxide, with applications ranging from aerospace to
nuclear fusion and high-energy physics.
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All authors Federico Ledda, Daniele Torsello, Davide Gambino, Flyura Djurabekova, Fabio Calzavara, Niccolò Di Eugenio, Ville Jantunen, Antonio Trotta, Erik Gallo, Kai Nordlund, Francesco Laviano
Materials Science · Cross-listed from cond-mat.supr-con
Visualizing Pair-breaking Scattering Interference in Bulk FeSe
Matthew Toole, Nileema Sharma, James McKenzie et al. (+3 more)
Spatially periodic modulations of the superconducting gap have been recently reported in diverse materials and are often attributed to pair density wave order. An alternative mechanism, termed pair-breaking scattering interference (PBSI), was proposed to produce gap modulations without finite-momentum pairing. Here we investigate signatures of PBSI in bulk FeSe using scanning tunneling microscopy with superconductive tips, enabling enhanced energy resolution and Josephson tunneling. Subsurface
magnetic scatterers with Yu-Shiba-Rusinov states are identified in FeSe, around which we observe particle-hole symmetric gap modulations accompanied by spatial modulation of the Josephson current. Those modulations have wavevectors consistent with intra-pocket PBSI. We further demonstrate that phase-referenced quasiparticle interference imaging offers an independent and direct probe of PBSI beyond gap mapping. These results establish PBSI as a viable origin of gap modulations in
superconductors lacking preexisting charge/
spin density wave orders, and motivate further investigation of the intriguing gap modulation phenomenology.
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All authors Matthew Toole, Nileema Sharma, James McKenzie, Fangjun Cheng, Sheng Ran, Xiaolong Liu