Materials Science · Cross-listed from physics.app-ph
Solar photocatalytic disinfection of well water using immobilized TiO$_2$: A comparative field study with SODIS in Antananarivo
Jean Odilon Andrianirina, Philippe Manjakasoa Randriantsoa, Georgette Ramanantsizehena et al. (+2 more)
Access to safe drinking water remains a major challenge in rural areas of developing countries. This study investigates the feasibility of a simple, low-cost
solar photocatalytic reactor coated with a commercial titanium dioxide (TiO$_2$) pigment for the disinfection of well water contaminated with fecal coliforms. A TiO$_2$ film was deposited on a glass plate using a straightforward acetone slurry method and exposed to natural sunlight in Antananarivo, Madagascar. The efficiency was compared with the conventional SODIS method (
solar disinfection without catalyst). Water samples from ten different wells were characterized for physicochemical and bacteriological quality. After 10 minutes of
solar exposure, the photocatalytic reactor reduced presumptive fecal coliform counts below the method detection limit ($<$1~CFU/100~mL) in all ten samples tested, whereas the SODIS control reduced the initial count by approximately 51% in a representative sample. While disinfection kinetics varied slightly with water turbidity and pH, inactivation below the detection limit was consistently achieved. Pearson correlation analysis showed no statistically significant linear correlation between the inactivation rate constant and any measured water-quality parameter (all $p > 0.4$). The results demonstrate that even a non-uniform, low-purity TiO$_2$ coating significantly accelerates bacterial inactivation under
solar radiation, offering a promising and affordable household-scale treatment technology for low-resource settings. However, longer-term validation, catalyst stability, dark-control assessment, and leaching studies are still required before widespread implementation can be recommended.
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All authors Jean Odilon Andrianirina, Philippe Manjakasoa Randriantsoa, Georgette Ramanantsizehena, Domohina Raharinirina, Malik Maaza
Materials Science
Dynamical stability and multifunctional properties of Ni2+/Pr3+ co-doped CsPbCl3 perovskite: insights from first-principles lattice dynamics and carrier transport
Sikander Azam, Asif Zaman, Qaiser Rafiq et al. (+2 more)
All inorganic halide perovskites offer promising optoelectronic properties at low cost, but their structural softness and thermal instability limit applications. Density functional theory using the FP-LAPW method (WIEN2k) was used to study Ni2+/Pr3+ co-doping in CsPbCl3. Results show Ni2+ substitutes for Pb2+ at the B-site and Pr3+ for Cs at the A-site, keeping charge balance. Co-doping stabilizes the
lattice, raises formation energies of halogen and metal vacancies, and reduces deep defect levels in the band gap.
Phonon dispersion confirms that both pristine and co-doped CsPbCl3 are dynamically stable. Ni2+/Pr3+ co-doping suppresses low-energy vibrations and causes mode splitting in the 3 to 5 THz range, increasing
phonon scattering and lowering
lattice thermal conductivity. Mechanical analysis reveals higher elastic constants and bulk modulus, while ductility remains unchanged. Electronic structure calculations reveal Ni-3d and Pr-4f states at the band edges, reducing effective carrier mass and passivating vacancy states. Optical absorption is red-shifted, and the high-frequency ({\epsilon} = 2.4) and low-frequency ({\epsilon} = 7.4) dielectric constants are distinct. Transport analysis finds higher carrier mobility due to lighter effective masses. Altogether, Ni2+/Pr3+ co-doping reduces defect concentrations and improves the optoelectronic properties of CsPbCl3.
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All authors Sikander Azam, Asif Zaman, Qaiser Rafiq, Amin Ur Rahman, Saleem Ayaz Khan
Materials Science
Enhanced Tantalum Superconducting Resonator Performance via All-Surface Organic Monolayer Passivation
Harsh Gupta, Moritz Singer, Benedikt Schoof et al. (+4 more)
Tantalum is a promising platform for superconducting
quantum circuits, yet coherence times remain limited by dielectric losses from interfacial two-level systems (TLS), exacerbated by native
oxide regrowth. Here, we implement molecular surface passivation using self-assembled organic monolayers on freshly etched tantalum and silicon in coplanar waveguide resonators. Surface characterization by contact angle, XPS, FTIR and TEM confirm the formation of ordered, nanometer-thick films that suppress
oxide formation. Microwave measurements in the ~5-9 GHz range reveal internal quality factors up to 1.8x10^6 in the single-
photon regime at 100 mK, representing a ~140% improvement over untreated devices with native
oxide. Power and temperature dependent measurements attribute this enhancement to reduced TLS-induced losses. These results demonstrate that molecular passivation effectively engineers low-loss interfaces and provides a scalable route toward high-coherence superconducting
quantum devices.
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All authors Harsh Gupta, Moritz Singer, Benedikt Schoof, Anna Cattani-Scholz, Shreya Sharma, Luca Rommeis, Marc Tornow
Materials Science · Cross-listed from quant-ph
Tantalum Damascene Coplanar Waveguide Resonators Fabricated Using 300 mm Scale Processes
Ekta Bhatia, Yingge Du, Krishna P Koirala et al. (+12 more)
Surface
oxides contribute to losses in superconducting transmon devices resulting in degraded performance. We explore the use of the damascene process to replace the sidewall native
oxide of a device with a metal/substrate interface. We simulate sidewall oxidation by burying an
oxide layer during fabrication. We observe a modest improvement between the two types of devices, which is suggestive of a reduction in the surface participation ratio.
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All authors Ekta Bhatia, Yingge Du, Krishna P Koirala, Chung Kow, Mingzhao Liu, Juan Macy, Tharanga R. Nanayakkara, Francisco Ponce, Satyavolu S. Papa Rao, Drew J. Rebar, Peter V. Sushko, Brent A VanDevender, Chongmin Wang, Marvin G. Warner, Zhihao Xiao
Materials Science
Spin-polarized Energy Density Method from Spin-Density Functional Theory
Yang Dan and Dallas R. Trinkle
The energy density method is generalized to include
spin polarization with the full formalism derived based on
spin-density functional theory, which aims at decomposing the total energy into well-defined atomic energies. The method involves two steps: (1) decomposing the total energy into
spin-polarized energy density functions in real space, and (2) integrating these energy densities over chosen gauge-invariant volumes for uniquely defined atomic energies, whose summation over all the atoms restores the DFT total energy up to a constant difference. This method is numerically implemented into the Vienna ab initio simulation package for the projector augmented-wave method, and is showcased with two applications. In the first application, we model the paramagnetic face-centered cubic Fe using
spin special quasirandom structures; the
spin energies are fit to
spin cluster expansions and a deep neural network. In the second application, we calculate the atomic energy distributions of dilute
magnetic semiconductor Ni-doped GaN with different dopant distances and
spin configurations. This method extracts additional useful information for the study of
magnetic systems with density functional theory.
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Materials Science
Carrier scattering considerations and thermoelectric power factors of half-Heuslers
Rajeev Dutt, Bhawna Sahni, Yao Zhao et al. (+7 more)
The electronic and thermoelectric (TE) transport properties of 13 n-type and p-type half-Heusler
alloys are computationally examined using Boltzmann transport. The electronic scattering times resulting from all relevant
phonon interactions and ionized
impurity scattering (IIS) are fully accounted for using ab initio extracted parameters. We find that at room temperature the average peak TE power factors (PF) of all materials we examine reside between 5 and 10 mW/mK$^2$. We also find that IIS in combination with the long range polar optical
phonon (POP) scattering are more influential in determining the electronic transport and PF over all other non-polar
phonon interactions (acoustic and optical
phonon transport). In fact, the combination of POP and IIS determines the thermoelectric power factor of the half-Heuslers examined on average by about 65%. The results highlight the crucial impact of Coulombic scattering process (POP and IIS) on the TE properties of half-Heusler
alloys and provide profound insight for understanding transport, which can be applied widely in other complex bandstructure materials. In terms of computation expense, the computationally cheaper POP and IIS provide an acceptable first-order estimate of the power factor of these materials, while the non-polar contributions, which require more expensive ab initio calculations, could be of secondary importance.
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All authors Rajeev Dutt, Bhawna Sahni, Yao Zhao, Yuji Go, Saff E Awal Akhtar, Ankit Kumar, Sumit Kukreti, Patrizio Graziosi, Zhen Li, Neophytos Neophytou
Materials Science
How Electrons Become Mobile in a Colossal Dielectric – Fe$_2$TiO$_5$
M. L. McLanahan and A. P. Ramirez
We measure the colossal permittivity in single
crystal Fe$_2$TiO$_5$ using broadband spectroscopy in the frequency range 20 Hz - 1 MHz. The relaxation response is analyzed using a Debye-like model with Arrhenius activation in two different ways and yields an energy barrier of 286.1 $\pm$ 2.8 meV. DC transport yields an activation energy of 288.8 $\pm$ 2.8 meV. These results strongly imply that the energy barrier for localized dipole motion and itinerant charge transport originate from the same atom-level forces. A further implication is that colossal dielectric behavior is a microscopic bulk phenomenon arising from a system on brink of
metallicity.
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Materials Science · Cross-listed from cond-mat.mes-hall
Cryogenic shock exfoliation for ultrahigh mobility rhombohedral graphite nanoelectronics
Ludwig Holleis, Youngjoon Choi, Canxun Zhang et al. (+16 more)
Rhombohedral multilayer
graphene (RMG) offers a highly tunable platform for correlated electron physics, featuring field-effect control of
magnetic, superconducting, and topological phases[1-24]. The promise of these materials has been held back by the limited abundance of rhombohedral stacking in natural graphite, which constrains both sample yield and useful area. Here we introduce 'cryogenic shock exfoliation' to produce large area rhombohedral
graphene flakes which, combined with a low-pressure van der Waals assembly technique that preserves stacking order, enable highly uniform devices exceeding 1300 $\mu m^2$ with fabrication yields of 90%. Using scanning nanoSQUID-on-tip imaging, we demonstrate uniform
spin magnetism over the full central 10 times 10 $\mu m^2$ area of our devices. Transverse
magnetic focusing reveals a disorder mean free path exceeding 200 $\mu m$ at low temperatures. Within the flat surface bands of RMG[20], we observe a size-driven crossover from Poiseuille to porous electron flow in the intermediate-temperature regime of strong electron-electron hydrodynamics[16, 25], providing a further signature of ultrahigh device quality. Our approach overcomes a key materials bottleneck in the fabrication of mesoscopic rhombohedral
graphene devices, paving the way for incorporating strongly correlated phases into two-dimensional nanoelectronics.
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All authors Ludwig Holleis, Youngjoon Choi, Canxun Zhang, Jack H. Farrell, Gabriel Bargas, Audrey Hsu, Zexing Chen, Ian Sackin, Wenjie Zhou, Yi Guo, Thibault Charpentier, Yifan Jiang, Benjamin A. Foutty, Aidan Keough, Martin E. Huber, Takashi Taniguchi, Kenji Watanabe, Andrew Lucas, Andrea F. Young
Materials Science
Extending Hamiltonian-Adaptive Resolution Simulation to Interfaces: An Updated LAMMPS Implementation and Application to Porous Solids
Hari Haran Sudhakar, Alessandra Serva and Rocio Semino
Many natural phenomena involve processes that happen simultaneously at different characteristic length- and timescales. Typically, the region where the process of interest happens is affected by fluctuations in its surroundings. Modeling these systems requires an effective combination of simulation resolutions. The
Hamiltonian-Adaptive Resolution Simulation (H-AdResS) method allows to model dual-resolution systems in length- and time-scales compatible with molecular
diffusion, by combining atomistic and particle-based coarse graining models in the same simulation box. In this work, a new implementation of H-AdResS is provided in LAMMPS 2023. New features extend the usage to more diverse interaction potentials and simplify the preparation of input files via dedicated lammps input commands, while keeping the efficiency gain of the basis method. The implementation is benchmarked by reproducing water properties from a reference atomistic simulation. Importantly, the new implementation includes changes in compensation routines allowing to simulate systems with fluctuating density. As an example, the method in its new implementation is applied to modeling a porous metal-organic framework and its gas adsorption structure and transport properties. We demonstrate that structural and dynamic properties in the atomistic region of the dual-resolution scheme are unaffected and remain those of the fully atomistic system, while increasing simulation efficiency. This paves the way for using H-AdResS to simulate complex interfaces across applications in energy storage, electrocatalysis, and membrane technologies.
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Materials Science · Cross-listed from cond-mat.mes-hall
Bismuth Films on EuO(111) as a Platform for Proximity-Induced Topological States
Subham Naskar and Sujit Manna
Interfacing two-dimensional bismuth with a
magnetic layer provides a promising route towards realizing higher-order topological phases. In particular, bismuthene on a
ferromagnetic insulator substrate has been theoretically proposed by \citet{Chen2020} as a universal platform for
magnetic second-order topological
insulators. Here, we report the experimental realization of epitaxial bismuth films grown on the
ferromagnetic insulator EuO(111). Using high-resolution scanning tunneling microscopy, we observe atomically ordered bi-layer bismuth with a (012)-oriented quasi-square
lattice, corresponding to a stabilized $\alpha$-phase bismuthene. The resulting film is exceptionally flat compared to conventional metallic films, reflecting the intrinsic two-dimensional nature of the Bi(012) phase. Tunneling spectroscopy(STS) reveals a robust energy gap of about 400 meV in the local density of states, consistent with a
quantum spin Hall insulating phase persisting up to room temperature. Spatially resolved STS further identifies enhanced edge-localised states at the island boundaries. Complementary low-temperature magnetotransport measurements on proximity-coupled ultrathin Bi films exhibit linear magnetoresistance and a
Hall sign reversal, indicative of
quantum-confinement-driven surface-dominated transport. Our results establish bismuthene-
magnetic-
insulator heterostructures as a viable experimental platform for realizing magnetically tunable topological phases, providing a critical step toward the observation of higher-order
topology in two dimensions.
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Materials Science
OptiMat Alloys: a FAIR, living database of multi-principal element alloys enabled by a conversational agent
Yang Hu and Vladyslav Turlo
The FAIR principles have transformed how computational data and workflows are shared in materials research, yet existing repositories can only serve pre-computed entries – broad coverage is perpetually incomplete and cannot adapt to new questions on demand. To address these challenges, we present OptiMat
Alloys, a large
language model-powered conversational
agent for multi-principal element
alloy exploration built on three pillars: a living database that stores every calculation with provenance, low-barrier accessibility through a web interface requiring zero programming expertise, and built-in uncertainty quantification via cross-potential and cross-configuration validation. Coupling foundational machine learning interatomic potentials covering near-all periodic table of elements with natural-
language interaction, OptiMat
Alloys enables targeted, on-demand computation guided by the user's domain knowledge-extending FAIR from pre-computed repositories to on-demand knowledge generation and making computational
alloy screening accessible to any materials scientist.
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Materials Science
Critical role of phase-dependent properties in modeling photothermal sintering of LiCoO2 cathodes
Yang Hu, Benoit Sklénard, Wouter Vels et al. (+2 more)
Photothermal (photonic) sintering crystallizes as-deposited amorphous LiCoO2 (LCO) cathodes for solid-state thin-film batteries using millisecond, surface-localized heating. However, process design often relies on 1D models with phase-averaged, temperature-independent properties, which can mispredict peak temperatures and thermal damage margins. Here we develop a multiscale, data-driven framework that provides phase- and grain size-resolved thermophysical inputs for stoichiometric LCO. We train an Allegro neural network potential with near-ab initio accuracy, enabling Green-Kubo calculations of thermal conductivity for crystalline and amorphous phases. The low, weakly density-dependent conductivity of amorphous LCO motivates its use as an effective intergranular phase in a thin-interface model that reproduces observed grain-size-dependent thermal transport. Combined with measured wavelength-resolved optical properties in 1D multiphysics simulations, we show amorphous LCO absorbs more strongly and reaches higher peak temperatures than crystalline LCO; thus crystalline, constant-property models systematically overestimate safe operating windows.
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All authors Yang Hu, Benoit Sklénard, Wouter Vels, Yaroslav E. Romanyuk, Vladyslav Turlo
Materials Science
Modeling High Entropy Alloys' Mechanical Property through Natural Language-Derived Descriptors
Li-Cheng Hsiao, Zi-Kui Liu and Wesley Reinhart
Processing treatments of
alloys, despite being influential to
alloy properties, are often neglected in machine-learning aided
alloy designs due to the difficulties in expressing this information. We investigated the expressiveness of
transformer embeddings through synthesized annealing processing treatment text and verified that
embeddings could be utilized to reconstruct the processing parameters of
alloys effectively with an R2>0.99. We then utilized the vector representations of
alloys' processing treatment descriptions as descriptors to model high-
entropy alloys' hardness and achieved a 20% improvement in prediction, verifying that natural
language-derived descriptors of processing treatment information could be utilized to improve prediction of
alloy properties.
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Materials Science
Sign-resolved nanoscale readout and control of hidden antiferromagnetic spin order
A. Schmid, D. Siebenkotten, D. Dai et al. (+16 more)
Antiferromagnetic memories promise ultrafast, stray-field-free information storage. Yet perfect
magnetic compensation conceals the information carrier itself: the sign of the Néel vector distinguishing two time-reversed states. Moreover, in future dense
memories, the local polarity of Néel domains would need to be read out on the nanoscale. We make this hidden polarity visible in a fully-compensated, high-Néel-temperature, PT-symmetric antiferromagnet by driving interband electric-dipole transitions by mid-infrared near-fields confined at a scanning probe. The excitation generates a Néel-order-dependent
quantum-metric photocurrent, a
Hall-like signal reversing with Néel order, which we term the optical nonlinear anomalous
Hall effect. This optically induced electrical readout maps opposite Néel polarities with sub-100-nm resolution at room temperature and, combined with
spin-orbit-torque writing, reveals Néel-texture polarization and reversible domain-wall motion, establishing electrical-write/optoelectronic-read
antiferromagnetic functionality.
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All authors A. Schmid, D. Siebenkotten, D. Dai, J. Godinho, T. Ostatnický, N. Zou, Y. Zhang, J. Železný, Z. Šobáň, F. Křížek, V. Novák, S. Fairman, A. Hoehl, A. Hertwig, T. Janda, M. A. Huber, R. Huber, B. Kästner, J. Wunderlich
Materials Science
Electronic and Vibrational Properties of On-Surface Synthesized Gulf-Edged Chiral Graphene Nanoribbons
Xuanchen Li, Amogh Kinikar, Vikas Sharma et al. (+8 more)
On-surface synthesis enables
graphene nanoribbons (GNRs) with atomic precision, but the structural diversity of
chiral GNRs remains constrained by the limited range of precursor architectures. Here, we design a trisnaphthalene-based diiodo precursor and use it to synthesize a gulf-edged (4,2,7)-chGNR on Au(111). Scanning tunneling microscopy and bond-resolved non-contact atomic force microscopy establish the atomically precise ribbon structure, while scanning tunneling spectroscopy and periodic density functional theory calculations identify a closed-shell semiconducting state with an experimental band gap of 1.8 eV. Raman spectroscopy, supported by vibrational calculations, resolves a mode localized predominantly at the gulf-edge C-H groups and reveals rapid spectral degradation following air exposure. These results demonstrate a precursor-design concept for a distinct chGNR architecture and correlate its atomic structure with its electronic, vibrational, and environmental-response properties.
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All authors Xuanchen Li, Amogh Kinikar, Vikas Sharma, Andres Ortega Guerrero, Riya Sebait, George F. S. Whitehead, Mickael Lucien Perrin, Carlo A. Pignedoli, Roman Fasel, Ashok Keerthi, Gabriela Borin Barin
Materials Science
Direct observation of surface bandgap shrinkage and negative electronic compressibility in SrTiO3
Warakorn Jindata, Trung-Phuc Vo, Chutchawan Jaisuk et al. (+4 more)
In this work, we investigate and compare the electronic structures of SrTiO3 and KTaO3 under ultraviolet (UV) light induced electron doping. Using angle-resolved photoemission spectroscopy (ARPES), the
evolution of the surface electronic structures of SrTiO3 and KTaO3 is systematically examined as a function of electron density. In contrast to KTaO3, SrTiO3 exhibits a pronounced shrinking of its surface bandgap by approximately 390 meV, accompanied by a counterintuitive shift of the valence band peak toward lower binding energies of up to 200 meV with increasing electron density. This anomalous behavior constitutes a spectroscopic signature of negative electronic compressibility (NEC). Density-functional-theory calculations provide qualitative support for the experimental observations. The calculations show that surface formation already reduces the apparent near-gap separation in SrTiO3, while additional electron accumulation further drives the slab toward a more metallic state; oxygen-vacancy models likewise produce strong bandgap reduction, identifying plausible mechanisms contributing to the observed surface bandgap shrinkage. These findings establish a direct spectroscopic link between bandgap engineering and the NEC effect at the SrTiO3 surface, highlighting the potential of SrTiO3 for next-generation
oxide electronic, optoelectronic, and high-performance capacitive energy storage devices applications.
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All authors Warakorn Jindata, Trung-Phuc Vo, Chutchawan Jaisuk, Sung-Kwan Mo, Thanh-Tien Nguyen, Ján Minár, Worawat Meevasana
Materials Science
Nearly Complete Charge–Spin Conversion via Strain-Eliminated Fermi Pockets in $d$-Wave Altermagnets
Wancheng Zhang, Fangqi Liu, Yong Liu et al. (+4 more)
Ideal $d$-wave altermagnets with nearly orthogonal flat
Fermi surfaces enable complete
spin-channel separation and 100% theoretical charge–
spin conversion efficiency (CSE). The metallic altermagnet $\mathrm{KV_2Se_2O}$ exemplifies this, but realistic samples host residual elliptical
Fermi pockets that enhance charge conductivity while suppressing
spin conductivity, drastically reducing CSE. Here we show that in-plane equibiaxial tensile strain systematically eliminates these parasitic pockets, restoring the flat-band geometry. Our first-principles calculations reveal that CSE increases monotonically with strain, reaching a record $\sim$96% at 4% strain. An effective tight-binding model confirms that pocket suppression, governed by reduced next-nearest-neighbor hoppings, is the dominant mechanism. We further identify an unconventional out-of-plane
spin current component with CSE $\sim$55% at optimal orientations, enabling field-free perpendicular magnetization switching. Moreover, the same strain-driven removal of parasitic pockets yields
giant TMR enhancement in $\mathrm{KV_2Se_2O}$-based
magnetic tunnel junctions, from $10^{5}%$ to $10^{9}%$, and the
giant TMR persists over a wide energy window near the
Fermi level. These findings establish strain engineering as a clean, widely applicable strategy to maximize CSE and magnetoresistance in $d$-wave altermagnets, and provide predictive descriptors for screening high-efficiency spintronic materials.
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All authors Wancheng Zhang, Fangqi Liu, Yong Liu, Jingguo Hu, Zhihong Lu, Rui Xiong, Zhenhua Zhang
Materials Science
Amorphous Nanoconfinement Enables Self-sustaining Sabatier Reaction at Ambient Conditions
Zhiyong Qiu, Cheng Li, Jinzhen Yang et al. (+9 more)
The Sabatier reaction, the catalytic hydrogenation of CO2 into CH4, offers a cornerstone for carbon capture and utilization, and in-situ resource utilization during space exploration; however, it faces a fundamental thermodynamic-kinetic paradox: although highly exothermic, conventional catalysts still require continuous external heating to activate CO2 and maintain stable operation. Here we report an amorphous silica-embedded ruthenium catalyst that enables a long-term self-sustaining autothermal Sabatier reaction dispensing with external energy supply. Operating under ambient conditions, this system achieves a record-high CH4 yield of 0.50 mol gcat-1 h-1 with 100% selectivity, stable operation for over 2,000 hours, and a record-low catalyst bed temperature down to 100 oC. This exceptional self-sustaining behavior stems from the synergistic effect of the catalyst's ultralow effective thermal conductivity (0.27 W m-1 K-1), induced by amorphous nanoconfinement, and its superior intrinsic activity. This synergy generates localized hot spots at Ru sites while suppressing macroscopic heat loss. In situ measurements further reveal CH4 formation even at 54 oC and identify a *CO-mediated pathway for CO2 methanation. The reaction ignites readily with a lighter or focused sunlight and persists even under forced convection from an electric fan, demonstrating strong environmental tolerance. By removing the need for constant energy input, this "ignite-and-forget" system paves the way for decentralized Power-to-Gas systems and autonomous fuel production in resource-constrained environments like Mars.
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All authors Zhiyong Qiu, Cheng Li, Jinzhen Yang, Fangkun Sun, Zheng Zhang, Canwen Yu, Weizheng Cai, Liang Guo, Yutong Gong, Junjie Wang, Meng Danny Gu, Jiazhen Wu
Materials Science
Neural surrogates for crystal growth dynamics with variable supersaturation: explicit vs. implicit conditioning
Matteo Rigoni, Daniele Lanzoni, Francesco Montalenti et al. (+1 more)
Simulations of
crystal growth are performed by using Convolutional Recurrent Neural Network surrogate models, trained on a
dataset of time sequences computed by numerical integration of Allen-Cahn dynamics including faceting via kinetic anisotropy. Two network architectures are developed to take into account the effects of a variable supersaturation value. The first infers it implicitly by processing an input mini-sequence of a few
evolution frames and then returns a consistent continuation of the
evolution. The second takes the supersaturation parameter as an explicit input along with a single initial frame and predicts the entire sequence. The two models are systematically tested to establish strengths and weaknesses, comparing the prediction performance for models trained on
datasets of different size and, in the first architecture, different lengths of input mini-sequence. The analysis of point-wise and mean absolute errors shows how the explicit parameter conditioning guarantees the best results, reproducing with high-fidelity the ground-truth profiles. Comparable results are achievable by the mini-sequence approach only when using larger training
datasets. The trained models show strong conditioning by the supersaturation parameter, consistently reproducing its overall impact on growth rates as well as its local effect on the faceted morphology. Moreover, they are perfectly scalable even on 256 times larger domains and can be successfully extended to more than 10 times longer sequences with limited error accumulation. The analysis highlights the potential and limits of these approaches in view of their general exploitation for
crystal growth simulations.
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All authors Matteo Rigoni, Daniele Lanzoni, Francesco Montalenti, Roberto Bergamaschini
Materials Science
Nickel intercalation in epitaxial graphene on SiC(0001): a novel platform for engineering two-dimensional heterostructures
Ylea Vlamidis, Stiven Forti, Antonio Rossi et al. (+5 more)
Two-dimensional (2D)
magnetic materials integrated with
graphene offer a compelling platform for next-generation spintronic devices, yet nickel in its 2D form remains largely unexplored, due to fundamental synthesis limitations. Here, we report the controlled intercalation of Ni beneath epitaxial
graphene on the Si-face of SiC(0001), achieved through a scalable colloidal nanoparticle deposition route. Chemically synthesized Ni nanoparticles (~10 nm diameter) are uniformly deposited onto
graphene via immersion in colloidal solution at room temperature; subsequent thermal annealing at 650 {\deg}C drives intercalation, yielding well-ordered Ni islands at the
graphene/buffer-layer interface with morphology dictated by annealing conditions. Scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), supported by density functional theory (DFT) calculations, elucidate the atomic and electronic structure of the intercalated layers. DFT simulations further confirm the thermodynamic stability of the 2D nanostructures as a function of shape and lateral size, predicting a robust average
magnetic moment of 0.9 $\mu_B$ per atom. The resulting Ni-intercalated
graphene on SiC constitutes a well-defined 2D
heterostructure combining preserved
graphene band structure with robust interfacial magnetism, stable under ambient conditions. These findings establish a reproducible, scalable pathway to engineer
magnetic graphene-based
heterostructures and open new avenues for their integration into spintronic architectures.
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All authors Ylea Vlamidis, Stiven Forti, Antonio Rossi, Arrigo Calzolari, Carmela Marinelli, Camilla Coletti, Stefan Heun, Stefano Veronesi
Materials Science · Cross-listed from cond-mat.supr-con
Effect of Mn Substitution on Superconductivity in PrFeAs(O,F): Role of Magnetic Impurities
Priya Singh, Konrad Kwatek, Tatiana Zajarniuk et al. (+5 more)
We investigate Mn substitution at the Fe site in PrFe1-xMnxAsO0.7F0.3 (0 to 0.1) using structural, Raman, density functional theory (DFT), transport, and
magnetic measurements. X-ray diffraction and Raman analyses confirm preferential Mn incorporation into the FeAs planes, accompanied by
lattice expansion and suppression of Fe-related vibrational modes. Electrical transport reveals a systematic decrease of the superconducting transition temperature from 48 K (x = 0) to complete suppression at x = 0.1, together with low-temperature resistivity upturns evolving toward insulating-like behavior. Magnetization and magnetotransport measurements show degradation of superconducting coherence, critical current density, upper critical field, and
vortex activation energy with increasing Mn content. The results demonstrate that Mn acts as an efficient
magnetic impurity, strongly perturbing the electronic and
magnetic environment of the FeAs layers. Comparative analysis indicates relatively enhanced robustness of superconductivity in the Pr-based system, highlighting the role of rare-earth-dependent electronic correlations in
impurity effects.
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All authors Priya Singh, Konrad Kwatek, Tatiana Zajarniuk, Taras Palasyuk, Cezariusz Jastrzębski, A. Szewczyk, Michał Wierzbicki, Shiv J. Singh
Materials Science
Self-consistent evaluation of the Berry connection for Wannier functions
Martin Thümmler, Thomas Lettau, Alexander Croy et al. (+2 more)
The Berry connection is a gauge-dependent quantity frequently used to describe the optical response of solids. Its evaluation requires a k-derivative with respect to the
cell periodic-part of the Bloch-functions and is commonly calculated in the Wannier basis by using overlap
matrices of
cell-periodic parts of Bloch-functions at neighboring k-points. So far, all proposed interpolation schemes for the Berry connection do not account for the
matrix structure of the overlap
matrices explicitly but treat the
matrix elements as independent, or only distinguish between diagonal and off-diagonal entries. In this work, we propose a self-consistent interpolation scheme based on the
matrix logarithm resulting in a strongly improved accuracy. Furthermore, we discuss how the basis set incompleteness of the bands used in the ab-initio calculation imposes constraints on the accuracy. We quantify the basis incompleteness based on the singular values of the overlap
matrices and relate it to the invariant part of the spread functional $\Omega_\mathrm{I}$ of the Wannier functions. Numerical calculations for monolayer MoS$_2$ and bulk Si demonstrate that the proposed interpolation scheme is much less sensitive to the Wannierization details and leads to an improved quality of the velocity
matrix and the optical conductivity.
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All authors Martin Thümmler, Thomas Lettau, Alexander Croy, Ulf Peschel, Stefanie Gräfe
Materials Science · Cross-listed from cond-mat.supr-con
Two-gap to Single-gap Transition and Two-dome-like Superconductivity in Alkali-Metal Intercalated Bilayer PdTe2
Yu-Lin Han, Shu-Xiang Qiao, Kai-Yue Jiang et al. (+5 more)
PdTe2 has been synthesized with controllable thickness down to the monolayer limit. Based on first-principles calculations within the fully anisotropic Migdal-Eliashberg framework, this work reveals that alkali-metal intercalation markedly enhances the weak superconductivity of
bilayer PdTe2, boosting the transition temperature from 1.4 K to 5.0 -13.5 K and yielding a two-dome-like
evolution of Tc. Rubidium intercalation induces the highest Tc of 13.5 K, which can be further increased to 14.5 K under biaxial tensile strain. The strain-dependent
evolution of Tc also exhibits a two-dome-like behavior, reflecting the interplay between strain-induced band structure modifications and electron-
phonon coupling (EPC). Moreover, a systematic correlation is identified between interlayer interaction and superconducting gap. Lithium intercalation induces a distinct two-gap state, whereas intercalants with larger atomic radii (Na, K, Rb, and Cs) drive the system into a single-gap character. The two-gap to single-gap transition originates from the modulation of interlayer coupling through intercalation-induced interlayer expansion. In addition, pristine and Li/Na-intercalated
bilayers exhibit nontrivial band
topology, suggesting that layered PdTe2 provides a promising platform for realizing the coexistence of superconductivity and nontrivial
topology. These results provide detailed anisotropic insights into EPC and offer viable pathways for enhancing Tc and achieving diverse properties in layered PdTe2 systems.
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All authors Yu-Lin Han, Shu-Xiang Qiao, Kai-Yue Jiang, Jie Zhang, Bao-Tian Wang, Ping Zhang, C. S. Ting, Hong-Yan Lu
Materials Science
Emergence of a non-bulk hexagonal Fe$_2$S$_2$ single layer via phase transformation
Affan Safeer, Wejdan Beida, Felix Oberbauer et al. (+8 more)
Two-dimensional materials can stabilize
crystal structures that are absent from their bulk counterparts, offering opportunities for materials design. Here, we report the synthesis of a previously unknown hexagonal Fe$_2$S$_2$ single layer with $\beta$-CuI structure, a buckled layer of two vertically stacked FeS honeycomb
lattices, realized by thermally induced transformation of single layer mackinawite grown on
graphene/Ir(111). In situ scanning tunneling microscopy and low-energy electron diffraction reveal a transition from a tetragonal to a hexagonal
lattice accompanied by distinct morphological and electronic signatures. The hexagonal Fe$_2$S$_2$ forms reproducibly upon annealing and represents a new structural motif within the Fe-S material family. First-principles calculations identify the $\beta$-CuI structure as most consistent with experiment. The calculations suggest that on-site Coulomb interactions and
magnetic order are relevant to understanding the stability of the new 2D Fe-S compound. The preferred nucleation of single-layer mackinawite, despite being energetically disfavored, is speculated to result from its low edge energy, analogous to the 3D case. Our results establish Fe$_2$S$_2$ as a platform for exploring structural polymorphism in two dimensions and demonstrate that reduced dimensionality can stabilize
crystal structures not accessible in bulk materials.
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All authors Affan Safeer, Wejdan Beida, Felix Oberbauer, Nicolae Atodiresei, Gustav Bihlmayer, Max Wolfertz, Chiara Schlichte, Wouter Jolie, Stefan Blügel, Jeison Fischer, Thomas Michely
Materials Science · Cross-listed from cond-mat.mes-hall
Nihad Abuawwad and Samir Lounis
Chiral spin textures such as skyrmions have attracted considerable
attention due to their nontrivial
topology, chirality, stability at the nanoscale, and potential for low-power spintronic devices. The recent discovery of intrinsic magnetism in van der Waals (vdW) materials and the ability to engineer their
heterostructures has opened a new platform to study and manipulate such textures. In these layered systems, atomically sharp interfaces, strong
spin-orbit coupling, and tunable
symmetry breaking provide unique opportunities to stabilize and control
chiral magnetic states. This review summarizes the fundamental mechanisms underlying the formation of
chiral spin textures in vdW
heterostructures, including the roles of exchange interactions,
magnetic anisotropy, Dzyaloshinskii-Moriya interaction, and dipolar effects. We highlight key experimental advances in the observation and manipulation of
chiral textures, discuss their dynamical properties and transport signatures, while overviewing selected theoretical investigations. Finally, we outline current challenges and future directions toward realizing robust, room-temperature
chiral spin textures for practical spintronic technologies.
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Materials Science · Cross-listed from cond-mat.supr-con
Pairing mechanism and superconductivity in 1313 phase La$_3$Ni$_2$O$_7$
Cui-Qun Chen, Ming Zhang, Fan Yang et al. (+1 more)
Recently, the observation of superconductivity (SC) with $T_c$ $\approx$ 3.6 K in the pressurized 1313 La$_3$Ni$_2$O$_7$ has attracted considerable interest. Here, we systematically investigate the electronic properties and superconducting mechanism of 1313 La$_3$Ni$_2$O$_7$ using density functional theory plus dynamical mean-field theory (DFT+DMFT) and random phase approximation (RPA). Our DFT+DMFT calculations reveal that the single-layer (SL) subsystem exhibits nearly insulating behavior, with the $d_{z^2}$ orbital showing Mott physics, while the trilayer (TL) subsystem remains metallic. This indicates that SC primarily resides in the TL subsystem, whose Ni-$e_g$ orbitals are found to be hole-doped relative to bulk La$_4$Ni$_3$O$_{10}$. Based on DFT+DMFT-derived low-energy
Hamiltonian, RPA-based analysis yields an $s^{\pm}$-wave pairing
symmetry within the TL subsystem. Importantly, we identify two key factors that contribute to the significant suppression of $T_c$ in 1313 La$_3$Ni$_2$O$_7$ compared to bulk La$_4$Ni$_3$O$_{10}$. First, the hole doping in the TL subsystem, as established by DMFT, leads to a decreased pairing strength, as confirmed by RPA calculations – a trend resembling that in bulk La$_4$Ni$_3$O$_{10}$. Second, the SL subsystem acts as a bridge connecting adjacent superconducting TL subsystems, thereby forming an S-N-S Josephson junction. The resulting interlayer Josephson coupling governs the phase coherence between TL subsystems and further suppresses the global $T_c$. Combinedly, our findings suggest that the high-$T_c$ phase in the RP La$_3$Ni$_2$O$_7$ family should be attributed to the 2222 La$_3$Ni$_2$O$_7$ rather than the 1313 La$_3$Ni$_2$O$_7$.
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All authors Cui-Qun Chen, Ming Zhang, Fan Yang, Dao-Xin Yao
Materials Science · Cross-listed from cond-mat.stat-mech
How to quantify long-time rotational motion in molecular systems
Romain Simon, Hadrien Bobas, François Villemot et al. (+2 more)
We show that all existing methods quantifying rotational motion in molecular fluids eventually have severe limitations in systems undergoing complex rotational motion characterized by slow, heterogeneous, or intermittent dynamics. This impacts in particular the study of rotational dynamics in molecular supercooled
liquids near their glass transition, as well as discussions of the decoupling between rotational and translational motion and violations of the Debye-Stokes-Einstein relation. We present a brief overview of existing methods and explain why none of them can accurately capture the
evolution of rotational dynamics from a diffusive fluid to an arrested solid, thus resolving inconsistent literature results. We then introduce an empirical method that efficiently solves all issues. We
benchmark our method devising a family of continuous time random walk models for rotational dynamics. Our method correctly quantifies the statistics of free and caged rotational motion, as well as non-Gaussian and non-Fickian rotational dynamics, and should allow a better characterization of dynamic heterogeneity in the rotational motion of supercooled molecular fluids.
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All authors Romain Simon, Hadrien Bobas, François Villemot, Jean-Louis Barrat, Ludovic Berthier
Materials Science · Cross-listed from cond-mat.mes-hall
Design optimization of flux concentrators for magnetic tunnel junctions-based sensors
Thomas Brun, Javier Rial, Lucia Risoli et al. (+6 more)
Miniaturized, ultra-sensitive and easily integrable magnetometers are needed for many applications, like space exploration or health monitoring. Achieving this goal requires a
magnetic sensor with high sensitivity and low noise. High sensitivity (>1000 %/mT) can be obtained by integrating high gain permalloy flux concentrators (FC). And reducing the
magnetic 1/f noise can be realized by increasing the number of
magnetic tunnel junctions (MTJs) in the air-gap of the FC. However, this is obtained at the expense of a wider air-gap and consequently a decrease of the
magnetic gain and thus of the sensitivity. In this paper, we explore a design optimization scheme in order to find the best trade-off between high FC gain and low
magnetic noise. To model the gain of the flux concentrator, we propose two complementary approaches; one is based on finite elements simulations of the FC gain where the influence of geometrical parameters of the air-gap is investigated. Then, in a second step, we propose an analytical formula consistent with all our simulations results and based on
magnetic reluctance. Finally, we derive an analytical model of the sensor detectivity from which we can extract the optimal sensor design which allows an improvement by three orders of magnitude of the performances compared to a single junction.
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All authors Thomas Brun, Javier Rial, Lucia Risoli, Johanna Fischer, Philippe Sabon, Guillaume Jannet, Matthieu Kretzschmar, Helene Bea, Claire Baraduc
Materials Science
Data-Driven Thermal and Mechanical Modeling of Defective Covalent Organic Frameworks
Aleksander Szewczyk, Leonardo Medrano Sandonas, David Bodesheim et al. (+2 more)
Covalent Organic Frameworks (COFs) are versatile two-dimensional (2D) materials for flexible electronics, catalysis, and sensing, owing to their tunable architectures and large surface areas. However, like most materials, COFs inevitably contain synthesis-induced defects, which-similar to
graphene-can strongly influence intrinsic properties, such as thermal transport and mechanical strength. To address this challenge, we have assessed the performance of a set of machine learning interatomic potentials (MLIP) capable of efficient large-scale simulations of COFs with
quantum accuracy. In doing so, QCOF models (
Quantum COF) were developed by tuning the state-of-the-art MACE architecture on an extensive
dataset of non-
equilibrium COF conformations generated from high-fidelity density functional theory calculations. The accuracy, computational efficiency,
memory footprint, and transferability to unseen chemical environments of these models were benchmarked against general-purpose MACE models and their fine-tuned variants. Our results show that an invariant QCOF model with a small descriptor dimensionality and cutoff outperforms all other models in most validation tasks, including scalability to large systems, force prediction in defective COFs, and
phonon dispersion calculations. The best-performing QCOF model was then used to run large-scale simulations of thermal conductivity for defective CTF-1 and COF-LZU1 systems via non-
equilibrium MD, revealing a more pronounced sensitivity of CTF-1 to structural defects. Stress-strain curves were also investigated, showing that the mechanical response remains nearly invariant at low defect densities, while asymmetric behaviour emerges at large strains. This work thus provides a foundation for the design of robust
quantum-informed MLIP for large-scale property simulations of defective of extended network materials.
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All authors Aleksander Szewczyk, Leonardo Medrano Sandonas, David Bodesheim, Bohayra Mortazavi, Gianaurelio Cuniberti