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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Thursday 9 July

Materials Science

A crystal-field route to THz-driven magnetization

T. Zalewski, M.S. Mrudul, Y. Lee et al. (+5 more)

Light carries angular momentum, but the microscopic pathways that transform it into magnetization remain elusive. Here we establish that crystal-field excitations, historically viewed primarily as equilibrium spectroscopic fingerprints of localized 4$f$ electrons, constitute an active microscopic route through which circularly-polarized terahertz (THz) light creates magnetic polarization. Using wavelength-selective ultrafast Faraday spectroscopy on the paramagnetic insulator CeF$_3$, we show that resonant excitation of localized 4$f$ crystal-field transitions generates a helicity-dependent magnetization that survives for up to about 100 ps. Most strikingly, while the optical helicity is held fixed, the THz-driven response reverses sign as the excitation wavelength is tuned across the crystal-field resonance. The resulting dispersive spectral response follows the crystal-field excitation spectrum rather than that of optical phonons, and is captured by resonant electronic theory of the inverse Faraday effect. Our results identify crystal-field excitations as a previously unrecognized dynamical reservoir for optical angular momentum and broaden the microscopic pathways through which THz light can create and manipulate magnetic states.
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All authors T. Zalewski, M.S. Mrudul, Y. Lee, M. Weissenhofer, A.V. Boris, P.M. Oppeneer, A. Kirilyuk, C.S. Davies

Materials Science

PhononScore: a phonon-aware scoring function for dynamical stability

Xiao-Qi Han, Ze-Feng Gao and Zhong-Yi Lu

In recent years, crystal generation models have enabled the design of massive numbers of candidate materials. However, the lack of dynamical stability among generated structures has become a major bottleneck preventing their translation into practical materials discovery. To address this challenge, we propose PhononScore, a phonon-aware scoring function for crystal generation. Unlike computationally expensive explicit phonon calculations, PhononScore predicts a unified stability score from crystal structures, enabling ranking of candidate materials dynamical stability with second-level computational cost. We construct a multi-fidelity phonon dataset containing 157,463 crystal structures. On the PhononBench benchmark, PhononScore improves the average dynamical stability rate of candidate pools generated by nine crystal generation models from 30.7% to 83.7%, achieving a 2.72-fold enrichment of stable structures, while the average stability rate of the Top-10 candidates reaches 97.5%. On a high-fidelity DFT-PBE phonon benchmark, the DFT-finetuned PhononScore-DFT increases the Top-100 stability rate to 93.0% and achieves 5-6-fold enrichment of dynamically stable structures under an extremely imbalanced hard-screening scenario. As a materials-screening tool analogous to scoring functions in drug discovery, PhononScore can serve directly as a dynamical-stability feedback signal for crystal generation, active learning, and reinforcement learning, enabling second-level stability-aware reranking without explicit phonon calculations and providing a unified and efficient dynamical stability evaluator for high-throughput materials discovery, active learning, reinforcement learning, and closed-loop inverse design. The online PhononScore platform is available at: http://phononbench.cn/phononscore/
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Materials Science

Exciton valley depolarization in monolayer MoS2: non-Markovian quantum dynamics, intervalley scattering, and the breakdown of the Dyakonov-Perel mechanism

Yang-hao Chan, Jonah B. Haber, Mit H. Naik et al. (+2 more)

In monolayer transition metal dichalcogenides, exciton valley relaxation is typically attributed to the Dyakonov-Perel (DP) mechanism, where frequent intravalley scattering with phonons or defects suppresses the intervalley exchange-induced precession and the role of intervalley scattering is considered secondary. Employing a first-principles nonequilibrium exciton Green's function (NEGF) approach with the generalized Kadanoff-Baym ansatz (GKBA), which treats exchange-driven precession and exciton-phonon scattering on an equal footing across the full Brillouin zone, we demonstrate that even in the small momentum regime most favorable to DP physics, realistic exciton-phonon scattering is too weak to induce the motional narrowing that defines the DP regime. Upon accounting for excitons across the entire Brillouin zone, large momentum intervalley scattering becomes the dominant pathway for valley relaxation, shortening the depolarization by a factor of 3-4 relative to intravalley-only models. We find that valley depolarization and decoherence time are approximately 50 fs at 300 K and lengthen to 130 fs at 10 K. By comparing our results with a Lindblad-type collision framework, we explicitly demonstrate the role of non-Markovian effects and reveal that the Markovian Lindblad framework is highly basis dependent. In the valley-pseudospin basis underlying prior analyses, the Lindblad approach artificially amplifies scattering-induced equilibration, biasing the dynamics toward a DP interpretation. Our study provides a comprehensive picture of valley relaxation, and establishes the exciton density matrix approach derived from NEGF+GKBA as a powerful tool for investigating ultrafast exciton dynamics.
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All authors Yang-hao Chan, Jonah B. Haber, Mit H. Naik, Felipe H. da Jornada, Diana Y. Qiu

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

Layer-resolved Electronic Structure and Correlation of Low-$n$ Square-planar Nickelates: A DFT+DMFT Prediction of Superconducting Candidates

Jian-Hong She, Rong-Qiang He and Zhong-Yi Lu

Multi-layer square-planar nickelates provide a rare platform in which the nominal Ni valence, dimensionality, and layer-resolved electronic structure can be tuned within the same structural family. Recent experiments have found superconductivity in $n=4$–8 $R_{n+1}Ni_nO_{2n+2}$ compounds, with the highest $T_c$ near $n=6$, whereas the more heavily hole-doped $n=3$ member remains nonsuperconducting. Here we propose spacer-layer Cl doping as a route to convert low-$n$ nickelates into superconducting candidates. Compared with changing the layer number $n$, Cl substitution on the spacer-layer oxygen sites offers a chemically natural way to continuously tune the Ni valence while leaving the NiO$_2$ planes largely intact; the lower-$n$ compounds may also be more accessible for synthesis. Using density functional theory combined with dynamical mean-field theory, we show that electron-compensated $n=2$ and $n=3$ La-based nickelates, targeted to the nominal Ni valence of superconducting $n=6$, develop Ni-$d$ correlations comparable to those of superconducting higher-$n$ compounds while preserving the characteristic low-energy Ni-$d$ electronic structure. These results suggest spacer-layer Cl doping as a promising strategy for designing low-$n$ square-planar nickelate superconductors.
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Materials Science · Cross-listed from cond-mat.mes-hall

Charge carrier flow through trimmed graphene nanoribbon junctions

Julien Leuenberger, Kristiāns Čerņevičs and Oleg V. Yazyev

As Moore's law approaches its fundamental limits, the development of nanoelectronic devices using low-dimension materials has become a promising avenue for further miniaturization and performance improvements. Among the various novel materials, graphene nanoribbons (GNRs) have emerged as particularly attractive candidates due to their unique electronic properties, opening up a whole new nanoelectronics paradigm consisting of circuits made entirely of graphene. However, due to the technical constraints that naturally arise when working on a two-dimensional plane, the design of efficient nanoelectronic components with a minimal spatial footprint remains a significant challenge. In particular, connecting various components can be a real architectural challenge, comparable to that of the first printed circuit boards. This paper investigates strategies for designing optimal-sized nanoribbon junctions which allow connecting GNRs at an angle, by trimming the junction edge while maintaining favorable electronic properties. Specifically, we show that the probability density current at the tip of junctions is negligible, implying that a selection of atoms can safely be removed without significantly altering the conductance. More generally, we demonstrate that larger trimmings have impacts on the conductance channels, resulting in a conductance that is mainly dictated by the ratio of armchair and zigzag edges. Finally, we propose a simple model relating this ratio to the conductance.
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Materials Science

Quantum weight and low-loss EELS signatures of Wannier quantum geometry in black phosphorus

Vinayak M. Kulkarni and Sharona Horta

Quantum geometry is now experimentally accessible in crystalline solids, with black phosphorus providing a key platform through polarization-resolved angle-resolved photoemission spectroscopy. We develop a first-principles framework that connects the momentum-resolved quantum metric of black phosphorus to a complementary bulk observable: the direction-resolved quantum weight measurable through low-loss electron energy-loss spectroscopy (EELS). A 32-band DFT–Wannier Hamiltonian is used to compute both single-band and occupied-manifold geometric quantities from analytic momentum derivatives. We show that the raw single-band quantum metric of the top valence band is not globally meaningful in the conventional cell because folding degeneracies and intra-valence near degeneracies produce true isolated-band singularities; masked maps and occupied-manifold projectors are therefore essential. Because semilocal PBE produces near-gap semimetallic pockets and spurious subgap interpolation features, we introduce an experimentally motivated restricted quantum weight $K_{ii}(\omega_c)$, which obeys the corresponding restricted Souza–Wilkens–Martin sum rule and is the appropriate quantity for low-loss EELS once the zero-loss region is excluded. The restricted in-plane quantum weight is nearly isotropic, $K_{zz}/K_{xx}=0.972\pm0.005$ (armchair/zigzag), despite the strong band-mass anisotropy and armchair-only absorption onset of black phosphorus. Orbital-resolved Hubbard–Hartree corrections leave the absolute quantum weights rigid at the sub-percent level while producing a small but resolved armchair-directed drift of $K_{zz}/K_{xx}$, approximately $+0.46\%$ per eV of $U$. These results identify low-loss EELS spectral moments as a practical probe of integrated quantum geometry in an anisotropic layered material.
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Materials Science · Cross-listed from cond-mat.supr-con

Theoretical exploration of Be Ag(II) F phases and their magnetic properties using learning algorithms

Katarzyna Kuder and Wojciech Grochala

The search for novel silver(II) fluorides is driven by their potential as electronic and magnetic analogues to high temperature cuprate(II) superconductor precursors. Here, we explore the previously uncharted Be Ag(II) F chemical space using global structure prediction algorithms combined with first principles calculations. Focusing on the AgBeF4 stoichiometry, we identify the five lowest enthalpy polymorphs crystallizing in the C2, P minus 1, and P 21/c space groups. All polymorphs show an antiferromagnetic ground state, with AgBeF4_4 and AgBeF4_5 exhibiting unprecedented strong superexchange interactions of J equal circa to minus 460meV and J equal circa to minus 359meV respectively. Those high J values are due to the presence of either [Ag2F7] for AgBeF4_4, or related infinite [AgF2/2+2/1]2 minus chains for AgBeF4_5. Although the phases are found to be metastable with respect to binary difluorides, the thermodynamic analysis suggests that they could be targeted via synthetic routes employing fluorine radicals, with reaction enthalpies reaching minus 370 kJ/mol.
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Materials Science

Polycrystalline ferroelectric croconic acid for multisource environmental energy harvesting

Gloria P. Moreno-Martínez, Hari K. Mishra, Xabier García-Casas et al. (+5 more)

The development of organic ferroelectric materials through scalable and simplified fabrication routes remains a major challenge for next-generation energy-harvesting technologies. Here, polycrystalline croconic acid (CA) thin films are fabricated by vacuum sublimation onto Ar plasma-treated flexible substrates and stabilized by in situ encapsulation with an adamantane-based remote plasma polymer. This solvent-free strategy effectively suppresses surface degradation under ambient conditions, providing long-term stability. Piezoresponse force microscopy confirms robust ferroelectricity with an oblique polarization orientation, well-defined domains, and low nanoscale coercive fields. The films were integrated into multilayer piezoelectric and pyroelectric devices. The piezoelectric performance strongly depends on film thickness, while embedding the CA layer between dielectric polymeric films significantly improves the macroscopic response, reaching power densities of up to 37 microW m-2 for ca. 2 micrometer CA films. Despite the common assumption that high crystallinity is required to sustain ferro-, piezo-, and pyroelectricity, these polycrystalline CA films exhibit remarkable RT pyroelectricity, a property not previously demonstrated in CA-based devices. A pyroelectric coefficient of ca. 10 microC m-2 K-1 highlights a functional response comparable to that of well-established organic and inorganic pyroelectric materials, demonstrating the potential of CA thin films for thermal energy harvesting. Beyond their functional performance, the proposed low-T fabrication route combines deposition and encapsulation in a single in situ process, simplifying device fabrication. Its compatibility with scalable vacuum technologies, flexible substrates, and further process optimization makes this approach highly promising for developing low-cost, lead-free, multisource energy-harvesting systems.
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All authors Gloria P. Moreno-Martínez, Hari K. Mishra, Xabier García-Casas, María Alcaire, Vanda Godinho, Juan R. Sanchez-Valencia, Ana Borras, Angel Barranco

Materials Science

Bright and Dark Excitons in CrSBr: Local Ligand-Field Character and Band-Coherent Optical Selection Rules

Swagata Acharya, Jessica McDivitt, Dimitar Pashov et al. (+3 more)

Magnetic van der Waals semiconductors such as CrSBr host an intricate exciton landscape whose physical interpretation has converged only recently. A many-body Feynman diagrammatic approach based on quasiparticle self-consistent GW with electron-hole ladder vertex corrections to the screened Coulomb interaction has established the electronic band gap, excitonic orbital character, real-space extent, binding energies, and bosonic-coupling signatures of the bright XA exciton near 1.34 eV and the higher XB manifold near 1.8 eV. These results agree well with ARPES and magneto-optical experiments and supersede the early Rydberg-like assignment of the excitons. What has remained unresolved is why these intense bright excitons coexist, within a few tens of meV, with companion states that are several orders of magnitude darker despite drawing from essentially the same single-particle transition manifold. Here we show that brightness is a band-coherent property of the excitonic eigenfunctions: bright and dark partners are sublattice-symmetric and sublattice-antisymmetric superpositions of the same ligand-field-like Bloch transitions across the two Cr atoms of the orthorhombic primitive cell. The commonly used Frenkel and Wannier-Mott labels describe what an exciton is made of, but brightness requires a symmetry-adapted interference rule between transition dipoles. Disentangling this bare excitonic structure is a prerequisite for interpreting the optical response of CrSBr once magnon, phonon, and photon couplings are included.
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All authors Swagata Acharya, Jessica McDivitt, Dimitar Pashov, Mark van Schilfgaarde, Justin C. Johnson, Jeffrey L. Blackburn

Materials Science

Bond, orbital and spin order in d4/d6/d7 perovskite oxides: successes and limitations of foundation interatomic potentials

Swagata Acharya, Dimitar Pashov, Mark van Schilfgaarde et al. (+1 more)

Foundation machine-learning interatomic potentials (MLIPs) are rapidly replacing density-functional theory (DFT) for modeling structure and nuclear dynamics, making their fidelity in strongly correlated systems an urgent question. We test three foundation potentials on the low-temperature order of three correlated, isostructural ABO3 perovskite oxides: LaMnO3 (d4), LaCoO3 (d6), and NdNiO3 (d7). We run molecular dynamics for 1 ns on 80- and 160-atom supercells from 50 to 300 K with no system-specific training. These oxides expose three distinct classes of low-temperature order that define a hierarchy of difficulty for the potentials. The scalar class, represented by NdNiO3, has a simple geometric fingerprint and is captured. The vector class, represented by LaMnO3, requires identifying which Cartesian axis carries the long bond at each site, and is captured in magnitude but not in symmetry. The on-site class, represented by the low-spin to high-spin crossover in LaCoO3, is a purely local multiplet population shift with no spatial order parameter and remains inaccessible to present-day MLIPs.
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All authors Swagata Acharya, Dimitar Pashov, Mark van Schilfgaarde, Alin M. Elena

Materials Science

Interplay between Electronic Structure, Chemical Bonding, and Lattice Symmetry in Bismuth Vanadate

Philip Schwinghammer, Franziska S. Hegner, Frederico P. Delgado et al. (+5 more)

Bismuth vanadate (BiVO$_4$) is a prototypical oxide photocatalyst that occurs in both tetragonal and monoclinic scheelite phases with markedly different photocatalytic and photoelectrochemical activities. Accurately identifying the monoclinic phase as the ground state and explaining the origin of its symmetry-breaking distortion are unusually challenging from a theoretical perspective, with various levels of theory and associated physical interpretations for this behaviour reported in the literature. Here, we resolve these discrepancies by systematically assessing the role of exact exchange with and without spin-orbit coupling, demonstrating that an accurate treatment of electronic localization is essential to stabilize the monoclinic scheelite structure. Using this framework, we compute the electronic band structure through dense sampling of the Brillouin zone and show that the band edges in monoclinic and tetragonal BiVO$_4$ lie far from conventional high-symmetry paths, leading to substantial differences in band gaps and carrier effective masses. Choosing the exchange-correlation functional that best reproduces the crystal structure leads to excellent predictions of the band gap once excitonic and thermal effects are taken into account. In addition, we show that the monoclinic distortion is driven by charge transfer between non-equivalent oxygen sites, which breaks the lattice symmetry and is suppressed by self-interaction errors when using semi-local DFT. These results establish a direct connection between the exchange-correlation functional, electronic localization, chemical bonding, and structural stability in BiVO$_4$, providing a foundation for robust ab initio descriptions of phase stability and optoelectronic properties in such complex oxides.
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All authors Philip Schwinghammer, Franziska S. Hegner, Frederico P. Delgado, Michel Panhans, Konrad Merkel, Frank Ortmann, Ian D. Sharp, David A. Egger

Materials Science

Nonlocal Electrostatic Origin of Schottky-Barrier Variability in 2D Contacts

Hangbo Zhou and Yong-Wei Zhang

Electrical contacts often limit the performance of atomically thin semiconductor devices. The Schottky barrier height (SBH) is conventionally treated as a local interface property, yet reported values for the same metal/2D-semiconductor contact vary by hundreds of meV. Here we show that, in top contacts, the effective SBH exhibits a pronounced nonlocal electrostatic dependence on defects near the contact edge, beyond the conventional local interface framework. A nonlocal electrostatic model, supported by density-functional-theory-based transport calculations for Ti–MoS$_2$ and Au–MoS$_2$, captures the large, metal-dependent variations in SBH as a function of defect position relative to the contact edge. These results provide a unified explanation for the longstanding variability in experimentally extracted SBHs and establish nonlocal electrostatics, mediated by edge-proximal defects, as a key mechanism governing carrier injection in 2D contacts.
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Materials Science

Phase stability and ionic transport in post-spinel CaV$_2$O$_4$ cathode

Dereje Bekele Tekliye, Javeed Ahmad Dar and Gopalakrishnan Sai Gautam

Calcium-ion batteries (CBs) represent an alternative to lithium-ion technology but their advancement is limited by the lack of high-performance intercalation cathodes. Identified via computational screening, post-spinel CaV$_2$O$_4$ has emerged as a promising candidate, though its practical application is hindered by limited electrochemical capacity. Hence, we investigate the thermodynamic and ionic transport characteristics of Ca$_x$V$_2$O$_4$ ($0 \leq x \leq 1$) in this work, by integrating the cluster expansion formalism with Monte Carlo simulations and density functional theory based calculations. We construct the temperature-composition phase diagram of Ca$_x$V$_2$O$_4$ revealing several stable phases ($\alpha$ through $\zeta$) that can appear during electrochemical operations at different voltages. Importantly, we observe the formation of the $\varepsilon$ phase at $x \sim 0.83$ across a 370-590~K temperature window via invariant reactions, which agrees with observations in the experimental voltage profiles. Further, migration barrier calculations confirm that Ca mobility is severely impeded within the $\alpha$ ($x \sim 0$) and $\gamma$ ($x \sim 0.5$) phases. With the strong Ca-vacancy ordering contributing to the high barrier in $\gamma$ and the persistent two-phase region stretching across the $\delta$ ($x \sim 0.67$) and the $\gamma$ phases, we expect the accessible electrochemical capacity in the CaV$_2$O$_4$ system to be kinetically limited to at most half the theoretical capacity at 298~K, in agreement with experiments. Strategies including cation doping and particle size reduction can be considered to flatten the potential energy landscape of $\gamma$ and improve Ca mobility. Our computational findings highlight the interplay between stability and transport and provide design strategies that can enable the practical use of CaV$_2$O$_4$ as a CB cathode.
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Materials Science

Perpendicular magnetic anisotropy tuning of macrospin-to-vortex transitions in Co-based artificial spin-vortex ice

Yu Maruyama, Amrit Kumar Mondal, Bijaya Kharel et al. (+4 more)

We investigate the macrospin-to-vortex (MS-to-V) transition in Co-based artificial spin-vortex ice (ASVI) in the presence of perpendicular magnetic anisotropy (PMA) by spin-wave spectroscopy. Detailed micromagnetic simulations using mumax3 reveal that the PMA modifies the magnetic energy landscape and facilitates vortex formation, suggesting that PMA can enhance the transition probability. To seek experimental validation of this hypothesis, we prepared Ti (3 nm)/Co (10 nm)/Ti (3 nm)/Pt (2 nm) (TCT) and Ti (3 nm)/Co (10 nm)/Pt (2 nm) (TCP) multilayer stacks. Vibrating sample magnetometry measurements confirm that the TCP film exhibits a larger PMA than the TCT film. Using these stacks, we then investigate the MS-to-V transition probability in ASVIs and found that TCP ASVIs exhibit a higher transition probability than TCT ASVIs, in agreement with the simulation prediction. These findings identify PMA as an effective design parameter for controlling vortex formation in ASVIs and provide a promising route toward task-dependent tuning of fading-memory properties for physical reservoir computing based on artificial spin lattices.
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All authors Yu Maruyama, Amrit Kumar Mondal, Bijaya Kharel, Ryo Ohshima, Jorge Puebla, M. Benjamin Jungfleisch, Masashi Shiraishi

Materials Science

Helically Enhanced Chiroptical Response and Symmetry Breaking in Conjugated Polymers

Aaron Forde, Braden M. Weight, Prashanna Poudel et al. (+5 more)

Chiral $\pi$-conjugated polymers are an attractive material platform for spin polarized carrier-transport and spectroscopy, but fundamental considerations for how torsional disorder influences the response properties of the material have not been considered. Here we combine atomistic electronic structure modeling with with experimental spectroscopic measurements to examine symmetry breaking in the prototypical $\pi$-conjugated polymer polyacetylene, (CH)$_x$. Chiral (CH)$_x$ oligomers are generated in distinct conformations which differ in their out-of-plane tonsorial ordering. We find that a helical conformation introduces orders of magnitude enhanced chiroptical activity due to a solenoid effect. This effect is visualized by the Transition Chiral Tensor analysis which shows signatures of domain ordering which eliminates destructive interference between electric and magnetic contributions. These findings highlight the capability to develop a hierarchical interpretation relating local, fragment symmetry breaking to global, nonlocal interactions governing chiroptical response in emerging chiral materials.
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All authors Aaron Forde, Braden M. Weight, Prashanna Poudel, Avadh Saxena, Zeev Valy Vardeny, Christoph Boehme, Alan Bishop, Sergei Tretiak

Materials Science

Interfacial chirality-induced magnetic-field-free switching with high energy efficiency in all-vdW heterostructures

Kai-Xuan Zhang, Suik Cheon, Seungbok Lee et al. (+12 more)

Chirality, a central concept across many scientific disciplines, continues to inspire the discovery of novel physical phenomena. In condensed matter physics, structural chirality - defined by the absence of mirror plane symmetries - has primarily been explored in bulk materials. However, new chiral phenomena can emerge uniquely at the interface, distinct from their bulk counterparts, when a chiral material forms a heterostructure. Here, we demonstrate that all van-der-Waals (vdW) heterostructure composed of the chiral Co1/3TaS2 and the achiral vdW ferromagnet Fe3GeTe2 exhibits two distinct and unconventional spin-orbit torques originating from the interfacial chirality. These torques enable magnetic-field-free switching of perpendicular magnetization with ultralow current density ~ 10^6 A/cm^2 and minimal power dissipation < 10^15 W/m^3. Moreover, by replacing Fe3GeTe2 with a similar vdW ferromagnet, Fe3GaTe2, but of higher Curie temperature, we achieved the magnetic-field-free switching at room temperature in the Fe3GaTe2/Co1/3TaS2 vdW heterostructure. Our findings establish interfacial chirality as a powerful new handle for spintronic control, opening a new pathway to explore chirality-induced phenomena beyond the bulk symmetry constraints - and paving the way toward highly efficient, low-power spintronic devices based on all-vdW heterostructures.
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All authors Kai-Xuan Zhang, Suik Cheon, Seungbok Lee, Joonyoung Choi, Jihoon Keum, Hyuncheol Kim, Yeochan An, Woonghee Cho, Suhan Son, Jingyuan Cui, Pyeongjae Park, Younjung Jo, Jun Sung Kim, Hyun-Woo Lee, Je-Geun Park

Wednesday 8 July

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

Observability of Finite-Depth Double-Diffusive Exchange from Sparse Temperature-Salinity Measurements

Sriram P. Kalathoor

Double-diffusive interfaces can support exchange histories that are spatially organized but only sparsely observed. A resolved three-dimensional calculation contains the route by which scalar gradients broaden, remain compact, connect with remote parts of a finite-depth layer, or organize horizontally, whereas field products usually provide profiles, repeated casts, autonomous-float records, or hydrographic sections. We ask which route-relevant features of finite-depth double-diffusive exchange remain observable after that measurement reduction. Four controlled finite-depth exchange histories are treated as known truth fields and sampled with vertical-profile, profile-bundle, vertical-coarsening, Argo-style, and section-like observing formats. The resulting observables are compared with selected Ice-Tethered Profiler, Argo, and CCHDO/GO-SHIP products to place the synthetic measurements in realistic observing contexts. Isolated profiles are weak route identifiers: at the final comparison time, strict case accuracy remains below 0.48, route-family accuracy is about 0.53–0.56 in leave-one-out profile classification, and 22 of 36 profiles are closer to a different-route profile than to a same-route profile under the current feature set. Profile bundles are substantially more informative. In the bundle-enumeration framework, the one-profile late-time route-family baseline is 0.694, while two-, three-, and four-profile bundles reach route-family accuracies of 0.917, 0.961, and 0.994. Coarse vertical sampling can preserve broad route separation while distorting local interface-width estimates, and section-like sampling adds horizontal-scale information only when station spacing resolves the relevant mode. The useful observing unit for hidden finite-depth double-diffusive exchange is therefore an ensemble or section, not an isolated cast.
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Materials Science · Cross-listed from cs.AI

PHITSBench: an execution-scored benchmark for AI-assisted PHITS radiation-transport input generation using natural language

Xianglin Ji and Svetlana V. Boriskina

We introduce PHITSBench, an execution-scored benchmark for the Monte Carlo Particle and Heavy Ion Transport code System (PHITS). PHITSBench comprises 282 transport-scorable tasks spanning three common workflow categories: parameter editing (Edit), syntax repair (Repair ), and complete simulation generation from natural-language descriptions (Reproduce). Each task is evaluated using a Composite Metric Score that combines execution success with agreement between generated and reference transport observables. Using PHITSBench, we evaluate five GPT-5.4-based configurations ranging from zero-shot prompting to knowledge-augmented and agentic workflows. Without domain-specific knowledge, the model performs well on editing and repair tasks (95% and 70% success, respectively) but fails to generate correct simulations from scratch (0% success on the Reproduce track). A structured, machine-readable PHITS knowledge catalog, supplied alongside the user manual, raises single-shot Reproduce-task success to 57%. Agentic execution provides a further improvement to 66-73%, but at increased computational cost. Failure analysis shows that the remaining errors are dominated by incorrect selection and configuration of physical observables rather than syntax generation. These results suggest that future progress in AI-assisted radiation-transport modeling will depend as much on machine-readable knowledge bases, curated domain-training datasets, and execution-grounded evaluation environments as on advances in foundation models themselves.
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Materials Science

Bulk Boundary Condition for Surface Calculations in Density Functional Theory

Sayan Bhowmik, Andrew J Medford and Phanish Suryanarayana

We present a bulk boundary condition formalism for surface calculations in Kohn–Sham density functional theory. The approach exploits the nearsightedness of electronic interactions in real space to restrict the calculation to a localized surface region. Within this region, the electron density is evaluated by leveraging the decay of the density matrix, with bulk values imposed on the density and electrostatic potential in the interior, and the electrostatic potential solved subject to bulk boundary conditions. The energy and atomic forces are computed using density-matrix-based expressions. Through representative calculations of surface and adsorption energies, we demonstrate the accuracy and efficiency of the proposed formalism.
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Materials Science · Cross-listed from cond-mat.soft

Directed assembly of tetrahedral patchy particles

Xin Yin, Ekaterina Kostyurina, Bert Nickel et al. (+2 more)

Colloidal particles with prescribed valency such as the tetrahedral patchy particles have long been seen as a viable route to technologically relevant open lattice structures on the scale of hundreds of nanometers. However, conceptual limitations and resulting competing local bonding configurations often lead to mixed lattice phases. Here, we present a DNA-origami enabled approach to controlling the attachment of tetrapod building blocks in predictable ways. By varying the relative strength of two designed binding configurations we are able to direct the assembly of tetrapod particles into diamond cubic, twinned diamonds, stacking-disordered mixtures, hexagonal diamonds, and sII clathrates. Under specific conditions, the diamond structures are interpenetrated by additional networks, resulting in triple cubic and triple hexagonal diamond structures. The 440 nm large unit cell of the clathrates shifts structural reflections into the visible range, giving these rationally designed, self-assembled crystals structural color.
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All authors Xin Yin, Ekaterina Kostyurina, Bert Nickel, Tim Liedl, Gregor Posnjak

Materials Science

Quantum Dot Moiré from Crossed MoS2 Nanoribbons

Xinting Shuai, Hao Zhang, Wenjing Wu et al. (+22 more)

Twisted atomically thin layers have attracted much attention for Moiré potential and correlated quantum phenomena. However, existing Moiré superlattices have largely been limited to extensive wavefunction without lateral confinement. Here we introduce a new platform where 1D nanoribbons of 2D MoS2 grown by vapor deposition can be easily superposed at various angles from stacking and transferring, to form Moiré quantum dots at their intersections with unique exciton physics. Angle-dependent Moiré intersections show enhanced exciton emission at commensurate angle 22 deg, which demonstrates faster relaxation at the cryogenic temperature. A size-dependent study further exhibits a reduced exciton energy and soften out-of-plane interlayer coupling for smaller Moiré areas. Our results reveal exciton physics turnability via precise overlapping of 1D nanoribbons.
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All authors Xinting Shuai, Hao Zhang, Wenjing Wu, Chongning Wu, Maryam Amiri, T. A. M. Ragib Shahriar, Dian Pan, Zhi Kai Ng, Tymofii Pieshkov, Leeza Dutta, Yijun Zhou, Rohith Narra, Luke Van Leeuwen, Jishnu Murukeshan, Luyao Shi, Jiawei Lai, Atin Pramanik, Bipin Kumar Gupta, Edwin Hang Tong Teo, Robert Vajtai, Xiang Zhang, Hanyu Zhu, Shengxi Huang, Aditya D. Mohite, Pulickel M. Ajayan

Materials Science · Cross-listed from quant-ph

Quantum Sensors for Chemistry and Materials Science

Piotr Put, Arjun Pillai, Xuan Hoang Le et al. (+2 more)

The advancement of chemistry and materials science relies on transformative analytical tools which can overcome the sensitivity, spatial resolution, and throughput limitations of conventional techniques. This review explores the application of quantum sensors - specifically optically pumped magnetometers (OPMs) and nitrogen-vacancy (NV) centers in diamond - as robust platforms for molecular and materials analysis. We contrast the extreme magnetic sensitivity of macroscopic OPM ensembles with the atomic-scale resolution and multimodal capabilities of solid-state NV centers. We highlight their deployment in zero- to ultralow-field and nanoscale NMR spectroscopy, real-time reaction monitoring, and transient radical and pH detection. Furthermore, we discuss their integration into high-throughput chemical assays and non-destructive materials diagnostics, such as operando battery monitoring. With the ongoing commercialization of these technologies and advances in quantum-enhanced sensitivities, quantum sensors are poised to routinely address complex real-world analytical challenges.
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All authors Piotr Put, Arjun Pillai, Xuan Hoang Le, Mikhail D. Lukin, Hongkun Park

Materials Science · Cross-listed from cond-mat.str-el

Electron-Phonon Functional Renormalization Group of Fermi Liquid Instabilities

C. Alexander Baum, Matteo Dürrnagel, Ronny Thomale et al. (+1 more)

We formulate a functional renormalization group (FRG) ansatz for correlated electron models that incorporates electronic interactions as well as electron-phonon coupling (EPC) stemming from dispersive phonon bands. Particularizing to the RG flow of the electron-electron interaction vertex, we treat phonon- and electron-mediated Fermi liquid instabilities on equal footing as we analyze tentative electronic order parameters related to charge, spin, nematicity, and superconducting pairing. We illustrate the approach at the example of Peierls-type transitions we find for the Hubbard model on the square lattice coupled to acoustic phonon bands. Our method allows to incorporate full electronic and phononic ab initio input, and thus lends itself to the analysis of electronic order from intertwined electronic interactions and EPC at a microscopically most substantiated level.
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All authors C. Alexander Baum, Matteo Dürrnagel, Ronny Thomale, Lennart Klebl

Materials Science · Cross-listed from cond-mat.str-el

Anisotropic vacancy-induced magnetization textures in altermagnets

Ruben Burkard, Mathias S. Scheurer and Urban F. P. Seifert

We study magnetic textures induced by vacancies in altermagnets using microscopic simulations and low-energy field theory. We show that a vacancy generically produces a real-space anisotropic distortion of the magnetic order, whose structure encodes the symmetry of the underlying altermagnetic state. This impurity response offers a direct route to detecting altermagnetic order with locally resolved probes. We demonstrate this for both classical altermagnets, where vacancies generate anisotropic magnetization textures in a transverse magnetic field, and quantum models, where fluctuations induce longitudinal power-law decaying magnetic distortions even at zero field.
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Materials Science

Second-harmonic signal in electric-field-modulated EPR spectra of Fe3 spin triangles

Jason S. R. McCoombs, Jorge I. Hilari, Jérôme Robert et al. (+4 more)

We present electric-field-modulated electron paramagnetic resonance (EFM-EPR) measurements on centrosymmetric single crystals of the molecular spin triangle $\mathrm{[{Fe_3}O({O_2}CPh){_6}(py){_3}]ClO{_4}{\cdot}py}$ ($\bf{Fe_3}$). We provide the first observation of second harmonic EFM-EPR signal in polynuclear magnetic molecules. This signal is simulated and explained in terms of an electric-field induced modulation of the isotropic exchange in the molecule, and of their symmetry lowering resulting from a Jahn-Teller effect. Additionally, an unexpected first harmonic EFM-EPR signal is observed. Various plausible symmetry-breaking mechanisms are discussed in an attempt to explain this feature, whose observation is unexpected in a nominally centrosymmetric crystal.
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All authors Jason S. R. McCoombs, Jorge I. Hilari, Jérôme Robert, Balwant Singh Chauhan, Ratnamala Chatterjee, Filippo Troiani, Athanassios K. Boudalis

Materials Science

Decoding magnetic texture

Michael P. Path, Jeffrey McCord and Michael Vogel

In magnetically ordered materials, magnetic field and temperature variations modify the magnetic texture through their coupling to the local energy landscape, imprinting distinct fingerprints in the resulting magnetic domain patterns. Retrieving these conditions from the pattern remains challenging, as stochastic nucleation and hysteresis produce a nonlinear, multivariate, and ambiguous relationship between magnetic domain morphology and external stimuli. To decode these fingerprints, we designed a controlled magneto-optical inference experiment that reconstructs magnetic field, temperature, and magnetic history from a single fine-scale, high-contrast, pixel-resolved optical polarization map of feature-rich magnetic domain textures in a bismuth-substituted yttrium iron garnet film. Deep convolutional neural networks are complemented by feature-based neural-network inference using hand-crafted, physically interpretable descriptors of measured magneto-optical image data, linking the decoded information to material-dependent features and exploring their contributions. Together, these results establish magnetic texture as a high-fidelity record of external conditions enabling accurate single image multiparametric sensing and paving the way for data-driven explorations of complex magnetic states. Uncovering the physically interpretable features that encode this record sheds new light on the physics of magnetic domain formation.
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Materials Science · Cross-listed from physics.comp-ph

Semilocal exchange functionals from the exact-exchange condition for the hydrogen atom: Hydrogenic exactness and recovery of Rydberg-like bound states

Fumihiro Imoto

In semilocal density functionals the exchange potential decays too rapidly outside atoms and molecules and lacks the correct $-1/r$ tail; as a consequence, functionals from PBE to modern meta-GGAs such as SCAN support no bound Rydberg-like state of an atom. We revisit the gradient-corrected exchange functional that Gill and Pople (GP93) constructed to reproduce the exact exchange potential of the hydrogen atom, solve their equation as an inverse problem, and use the resulting enhancement factor – the GP93 factor – as a tail-generating ingredient of a switched semilocal functional. The GP93 factor is exact on the hydrogen $1s$ density and, by uniform coordinate scaling, on hydrogenic $1s$ ions, where it yields the eigenvalue $-Z^2/2$ exactly (hydrogenic exactness). Its large-gradient growth has the hydrogen-exact form $O[s(\ln s)^{2/3}]$, distinct from the $s\ln s$ form of Armiento and Kümmel. The factor is combined with a kinetic-energy-density indicator so that its divergent branch acts only in one-electron-like regions; the GP93 ingredient is nonempirical, while a few switching parameters are calibrated to balance tail recovery against self-consistent-field stability. The resulting functional produces Rydberg-like series of bound virtual Kohn–Sham states in systems whose outermost shell is a one-electron-like $s$ shell – all-electron H and He, and Li, Na, and K with large-core pseudopotentials – and moves the highest-occupied eigenvalue toward the experimental ionization energy. For $p$-shell atoms (Ne, Ar) the switch closes, so the domain of applicability is fixed by design. Fixed-density tests indicate that a reduced-Laplacian switch distinguishes atomic tails from covalent bond centers, and that a density-only kinetic-energy functional renders the entire switch orbital-independent, so that no generalized Kohn–Sham solver is required.
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Materials Science

Are Machine Learning Interatomic Potentials Truly Practical? A Benchmark of 23 Mainstream Models

Hanwen Kang, Tenglong Lu, Sheng Meng et al. (+1 more)

Most MLIP benchmarks reward static accuracy while ignoring inference efficiency and hardware scalability – driving model bloat with unclear real-world value. We benchmark 23 mainstream open-source MLIPs on a low-cost NVIDIA DGX Spark (128 GB native memory, capped at 80 GB to mimic ordinary lab hardware), using a fixed 192-atom system under a unified ASE-based pipeline. We evaluate three dimensions: predictive accuracy, MD simulation throughput, and atomic scalability. Our results expose a sharp accuracy-efficiency trade-off: large SOTA models deliver only 3-5 meV/atom more accuracy than lightweight ones, but lose orders of magnitude in throughput – in the worst case, becoming only marginally faster than DFT itself. Lightweight MLIPs, by contrast, sit on the Pareto frontier and run on modest hardware. The lesson is that single-dimensional benchmarks mislead the field, and that future MLIP development should value efficiency and scalability alongside accuracy.
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All authors Hanwen Kang, Tenglong Lu, Sheng Meng, Miao Liu

Materials Science

Acoustic-phonon-driven spin-lattice relaxation of the hBN boron vacancy in the sub-THz regime

Priyo Adhikary and Pramey Upadhyaya

The negatively charged boron vacancy center in hexagonal boron nitride is a premier candidate for quantum sensing, yet its performance is critically limited by longitudinal spin-lattice relaxation time ($T_1$). A microscopic understanding of spin relaxation in the high magnetic field regime remains elusive, as the relevant Zeeman transitions lie far below the optical phonon energies typically invoked to describe the relaxation process. Here, we apply an ab initio acoustic mode spin-phonon relaxation theory to this problem and quantitatively reproduce the experimental magnetic field and temperature dependence of $T_1$ without empirical fitting parameters. We demonstrate that the relaxation dynamics are driven by a direct one-phonon emission and absorption process resonant with the Zeeman splitting. Furthermore, we identify the out-of-plane flexural phonon branch which is unique to two-dimensional hosts, as the primary source of decoherence, creating a distinct low-energy spectral function that facilitates spin relaxation. Our results provide a microscopic interpretation of the experimentally observed non-monotonic field and temperature dependence in two-dimensional quantum defect centers.
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Materials Science

MLIP Studio: An Open Platform for Interactive Benchmarking and Atomistic Simulations Using Machine Learning Interatomic Potentials

Manas Sharma, Sudeep Punnathanam and Ananth Govind Rajan

Universal machine learning interatomic potentials (MLIPs) are foundation AI models transforming atomistic simulations, but their practical use remains hindered by fragmented software ecosystems, dependency conflicts, and the lack of accessible benchmarking tools. These models approach first-principles density functional theory (DFT) accuracy at a fraction of the computational cost. We introduce MLIP Studio (available at https://mlipstudio.iisc.ac.in), an open and free platform that brings more than 60 universal MLIPs into a unified interactive interface for molecules and materials. The platform enables end-to-end MLIP-driven workflows, including property prediction, geometry optimization, vibrational and equation-of-state analysis, spin-state determination, custom model deployment, and high-throughput benchmarking against reference data. Automated parity plots and sortable error tables facilitate rapid identification of element-wise outliers and problematic data points. We demonstrate that MLIP-based pre-optimization can reduce subsequent DFT optimization effort by ~33$\times$. Additionally, the application enables benchmarking of computational performance. Through a comprehensive case study involving the 2D magnetic material CrCl$_3$ on a sapphire substrate, we show how cross-model comparisons of various properties and potential-energy landscapes can guide task-specific MLIP selection. Overall, MLIP Studio lowers the barrier to the reliable use of foundation models in end-to-end research workflows, benchmarking, and education in computational chemistry and materials science.
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