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Physics Condensed Matter Materials Science

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Friday 2 October

Materials Science

Floquet density response in laser-assisted fast-electron scattering from solids

Ferdinand Evers, Sascha Schäfer and Richard Korytár

We extend the Bethe–Floquet formalism of Joachain and coworkers, originally developed for laser-assisted electron–atom collisions, to inelastic scattering of fast electrons from a many-body condensed-matter target in a time-periodic light field. At first order in the projectile–target interaction, the general Floquet–Fourier cross section separates into exact laser-dressed projectile kernels and a matrix-valued Floquet density response of the target. For spatially structured or translationally non-invariant systems, the latter is the bi-momentum Floquet structure factor; its momentum diagonal defines the Floquet generalization of the dynamic structure factor, constrained by Hermiticity, positivity, and sum rules. As a controlled realization of the general projectile kernel, an eikonal–Volkov approximation for slowly varying inhomogeneous fields yields a finite-momentum-resolution convolution of the target response. In the homogeneous-field dipole limit, the projectile kernel reduces to Bessel-function sidebands and the cross section takes the familiar Bethe–Floquet form. The Floquet density correlator separates exactly into the outer product of the pump-induced coherent mean density and connected fluctuations. In the straight-trajectory nonrecoil limit, the coherent, target-elastic sector defines the weak-coupling PINEM amplitude; repeated coherent insertions generate the PINEM Bessel ladder, with an explicit no-double-counting prescription for combining this channel with connected losses. As worked examples, we evaluate the connected, target-changing cross section analytically for a metal in the Drude and diffusive limits, recovering Bessel-weighted plasmon-loss and diffusive combs, and for a driven two-level model that exhibits off-diagonal Floquet coherences through Bessel-channel interference.
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Materials Science · Cross-listed from cond-mat.other

Fracture under body forces: An accessible test and analysis

Farhad Kamarei, Sarah Bueno De Castro, Jeffery R. Roesler et al. (+1 more)

Fracture in large-scale structures — from failing concrete dams to calving glaciers — is dominated by self-weight. Yet, owing to their immense scale, directly studying when and where cracks nucleate and propagate in these systems under gravity is unfeasible. To date, experimental investigations have largely relied on mimicking self-weight in scaled-down specimens via centrifugal forces, necessitating specialized centrifuge facilities. In this Letter, we introduce a simple benchtop test that bypasses the need for this infrastructure. The method utilizes a cantilever beam containing a downward-pointing V-notch, loaded solely by its self-weight. Through appropriate selection of the notch geometry and placement and the beam dimensions, the setup forces a crack to nucleate at the notch tip and propagate through the specimen in a measurable manner. We demonstrate the utility of this self-weight fracture test on a 3D-printable mortar and analyze the results using the fracture theory recently introduced in (\citeauthor{LPKFG2026}, 2026). Inter alia, the findings provide a first validation of the theory for fracture driven by body forces.
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All authors Farhad Kamarei, Sarah Bueno De Castro, Jeffery R. Roesler, Oscar Lopez-Pamies

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

Bogoliubov self-consistent $GW$ and second-order Green's function methods for attractive fermionic interactions

Mauricio Rodríguez-Mayorga, Johannes Tölle and Pierre-François Loos

Describing fermionic systems with attractive interactions, such as superconductors and atomic nuclei, beyond the mean-field level remains a central challenge. In this work, we investigate the performance of Bogoliubov fully self-consistent $GW$ (Bog.~sc$GW$) and second-order Green's function (Bog.~scGF2) methods, implemented within a unified imaginary-time and imaginary-frequency framework. Using the attractive Hubbard model as a benchmark against full configuration interaction (FCI), we find that Bog. scGF2 provides a more accurate description than Bog.~sc$GW$. In particular, Bog.~sc$GW$ systematically overestimates the correlation energy, with errors increasing rapidly as the attractive interaction strength grows. These results highlight the importance of exchange contributions in strongly correlated fermionic systems, even when exchange effects are included only at low order in perturbation theory.
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Materials Science · Cross-listed from cs.CE

Reformulating plastic instabilities within a damage-like variational framework

Baptiste Reyne

Yield point phenomena in metals, anticracks in soils and snows, or planewise collapses in lattice metamaterials, are different manifestations of plastic instabilities characterized by stress softening and strain localization. Several independent constitutive descriptions exist and suffer from similar challenges: experimental difficulties to link local events to global measurements, and computational lack of convergence, spurious localization and mesh sensitivity. This work proposes a minimal field-agnostic constitutive framework where plastic softening is represented by a damage-like internal variable which explicitly separates stable hardening behavior from unstable softening. The resulting formulation admits a variational structure and can leverage regularization tools originally developed by the ductile fracture community. The framework aims at emphasizing similarities within plastic instability phenomena and establishing a bridge with continuum damage mechanics, to open a path towards regularized variational formulations of localized plastic flows.
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Materials Science · Cross-listed from cond-mat.mes-hall

Beyond Pure Dephasing: Quantum Error Correction in Single Molecules Requires Multiple Spins

Matteo Mezzadri, Silvia Macedonio, Luca Lepori et al. (+5 more)

We propose multi-spin molecules as a viable architecture for fault-tolerant quantum computing. To this aim, we introduce a correction protocol handling both diagonal and off-diagonal errors, typically associated with dephasing and relaxation. The scheme is based on a hybrid encoding which combines dephasing-tolerant units suppressing the leading pure dephasing error into a multi-spin molecule implementing a multi-qubit code for residual off-diagonal errors. Our proposal leverages peculiar properties of molecular spins, i.e. the strong hierarchy between different errors and the possibility to engineer multi-spin molecules at the synthetic level. Moreover, it addresses the important issue of the loss of coherences in anharmonic systems subject to off-diagonal errors, which hampers their correction at the single spin level. Thanks to the huge suppression of dephasing by the first-level code, we numerically demonstrate the potential performance of this strategy even with a limited number of spins per logical unit.
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All authors Matteo Mezzadri, Silvia Macedonio, Luca Lepori, Emilio Macaluso, Francesco Albarelli, Richard E.P. Winpenny, Alessandro Chiesa, Stefano Carretta

Materials Science

Illuminating early ZrC oxidation using ensemble small-cell DFT with dynamic gas management

Philip Wurzner, Boyang Chen, Matthias Möller et al. (+3 more)

During zirconium carbide oxidation, liberated carbon can remain beneath the oxide or escape as gas, complicating the interpretation of mass measurements. We adapt the small-cell ensemble method using sixteen 140 ps ab initio molecular dynamics trajectories at 873-1273 K under a sustained high oxygen flux with gas removal. The average rates of net mass gain and total carbon transfer into gas or retained chains follow Arrhenius trends. Above 973 K, gas evolution levels off while total carbon transfer increases. The fraction of transferred carbon retained in chains rises from 40 % at 973 K to 66 % at 1273 K. Fits after 40 ps suggest declining carbon transfer rates over time, although not in every trajectory. These results show that carbon partitioning during early oxidation depends on temperature, with increasing temperature above 973 K favouring chain formation over gasification.
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All authors Philip Wurzner, Boyang Chen, Matthias Möller, Sebastian Feld, Qi-Jun Hong, Yinglu Tang

Materials Science

Second-order Raman and anharmonic lattice dynamics in lead-halide perovskites

Chao Shen, Florian Kluibenschedl, Ayan A. Zhumekenov et al. (+4 more)

We explore the microscopic origin of THz-driven lattice dynamics in methylammonium lead bromide CH$_3$NH$_3$PbBr$_3$ using two-dimensional THz Kerr-effect spectroscopy. The analysis of the experiment enables discrimination between competing nonlinear excitation mechanisms and reveals that the dominant pathway is phonon-mediated rather than purely photonic. In particular, we argue that the commonly observed 1.15~THz Raman-active $A_g$ mode is not excited directly by the THz electric field. Instead, it emerges through cubic anharmonic coupling to an infrared-active phonon at 0.68~THz. Furthermore, a satellite feature at 1.36~THz is identified as a two-phonon Raman response of the same infrared-active mode. The observation of strong quadratic coupling involving the infrared-active phonon suggests an unconventional form of electron-phonon dressing present in lead-halide perovskites.
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All authors Chao Shen, Florian Kluibenschedl, Ayan A. Zhumekenov, Mikhail Lemeshko, Osman M. Bakr, Artem G. Volosniev, Zhanybek Alpichshev

Materials Science

Algebra of symmetry allowed physical properties of crystals

Piotr Fabrykiewicz

The symmetry of a physical system given by the 122 magnetic point groups (MPGs) leads to only 21 sets of restrictions on any physical tensors. Those, so called, tenor forms were labeled by letters from A to U by R. R. Birss (Symmetry and Magnetism, North Holland, Amsterdam, 1964). A new concept of property-related point groups (PRPGs) is proposed. It is shown that the 21 PRPGs isomorphic to the 21 non-centrosymmetric crystallographic point groups (CPGs) corresponds to the 21 tensor forms. Therefore instead of a symbols from A to U one can use PRPGs as mathematical objects corresponding to the tenor forms. From the Neumann's principle given multipole component is only allowed in a system when a group describing symmetry of the system is a subgroup of the multipole component symmetry. Each tensor can be expressed in the terms of the multipole degrees of freedom, i.e. it corresponds to a subset of all multipole components allowed by given PRPG. Those relations leads to the algebra of tensor forms, where space of allowed tensor components and space of PRPG operators are somehow dual to each other.
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Materials Science

Coercivity-Aware Machine Learning Discovery of Rare-Earth-Free Soft Magnetic Alloys with First-Principles Magnetic Benchmarks

Avik Mahata and David Priefer

Coercivity-aware machine learning is developed to screen rare-earth-free soft magnetic alloys using Curie temperature and coercivity as coupled design targets. A compiled experimental magnetic-material dataset is evaluated using composition-grouped partitioning to avoid overlap of identical compositions between training and testing, and elemental fractions and composition-weighted elemental descriptors are examined for prediction of the two magnetic properties. Residual-based prediction intervals and distance-to-training filters are then incorporated to screen Fe-Co-Ni-Mn-Al-Si compositions. Composition-grouped evaluation shows lower predictive accuracy than conventional random partitioning, demonstrating the importance of evaluating transfer to previously unseen compositions. Combining weighted elemental descriptors with elemental fractions improves Curie-temperature prediction, whereas the additional descriptors do not improve coercivity prediction, consistent with the strong dependence of coercivity on processing and microstructure. Uncertainty-aware screening substantially narrows the candidate space and identifies Fe-Co-rich compositions for further evaluation. First-principles calculations independently show strong magnetic polarization and magnetovolume effects in representative Fe-Co structures, while finite-temperature atomistic spin simulations place the Fe-Co benchmark systems on high magnetic-ordering-temperature scales. The combined approach provides a computational framework for prioritizing rare-earth-free soft-magnetic chemistries while distinguishing composition-level screening from candidate-specific physical validation.
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Materials Science · Cross-listed from quant-ph

Self-organized Layered Structures of Nitrogen-Vacancy Centers with Preferential Orientation in Heteroepitaxial Diamond Films

Vadim Lebedev, Alejandro Martínez-Méndez, Jesús Moreno-Meseguer et al. (+6 more)

Here, we report the fabrication and characterization of single crystal diamond films on a two-inch wafer-scale containing three-dimensional layered structures of negatively charged nitrogen-vacancy color centers (NV$^{-}$). The (100)-oriented layered diamond films were grown by chemical vapor deposition (CVD) to create spatially separated regions of enhanced emission associated with NV$^{-}$ centers. Such localized emission enhancement as well as 2D and 3D arrays of spins could enable close-packed architectures for emerging quantum devices, such as data processors, memory cells, and magnetic sensors. A cyclic sequence of CVD growth and oxygen-plasma etching is employed, resulting in the in-situ formation of layered inverted pyramidal structures with flat $\{$111$\}$ sidewalls. These pits are subsequently overgrown by nitrogen-doped diamond to achieve NV$^{-}$-rich facets with a uniform N-V bond arrangement and improved nitrogen incorporation efficiency.
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All authors Vadim Lebedev, Alejandro Martínez-Méndez, Jesús Moreno-Meseguer, Jan Engels, Jürgen Weippert, Jan Kustermann, Felix Hoffmann, Javier Prior, Jan Jeske

Materials Science

Ab initio design of enhanced and sign-reversible spin Hall and spin Nernst conductivity in skutterudite materials

Saikat Debnath, Babu Baijnath Prasad and Shishir Kumar Pandey

The search for novel materials capable of robust spin-current generation remains an active area of research. Here, we investigate the intrinsic spin Hall and spin Nernst effects in Co- and Rh-based skutterudites and explore their enhancement through heavy-metal substitution and site-selective doping. Using first-principles calculations and Wannier-based tight-binding models, we analyze the spin Berry curvature and spin-transport responses of pristine MX$_3$, where M = Co, Rh and X = As, Sb, as well as chemically modified systems. Despite sizable momentum-resolved spin Berry curvature, the pristine compounds exhibit relatively small net spin Hall responses due to substantial cancellation across the Brillouin zone. Isoelectronic Ir and Bi substitution at 8$c$ Wycoff M site produces little enhancement near the E$_F$, whereas non-isoelectronic Pt substitution yields a relatively better response. Most interestingly, the incorporation of Pt at the interstitial $2a$ Wycoff site of RhAs$_3$ nearly doubles the spin Hall conductivity to $\sim400~(\hbar/e)(\Omega,\mathrm{cm})^{-1}$ near the E$_F$ when compared to Pt substitution at 8$c$ position. At 300 K, the same interstitially filled system exhibits a spin Nernst conductivity of $\sim1.46~(\hbar/e),\mathrm{A,m^{-1}K^{-1}}$ at the E$_F$, nearly an order of magnitude larger than that of $M$-site Pt substitution. The enhanced responses arise from Pt $5d$ states, strong spin-orbit coupling, and avoided crossings that generate pronounced spin-Berry-curvature hot spots. These results demonstrate that site-selective chemical engineering can effectively overcome momentum-space cancellation resulting in enhanced spin Hall and spin Nernst responses in skutterudites. Our results provide a possible route towards robust spin-current generation in this class of materials.
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Materials Science

Optimizing the magnetic hyperthermia efficiency from the structural dependence of dipolar interactions in magnetic nanoparticles assemblies

Abdelhamid Morjane, François Vernay and Vincent Russier

Magnetic hyperthermia, based on the conversion of the magnetic energy of magnetic nanoparticles (MNP) under an alternating external field into heat, presents a great interest, especially because of important applications such as promising advances in cancer treatment. The underlying frequency-dependent response of the MNP assembly under the excitation field depends on the first hand on the individual properties of the MNP such as their size, shape and magnetocrystalline anisotropy and on the other hand on collective properties generated by interactions between MNP. Due to the long-range dipolar component of the latter, the first consequence is the so-called demagnetizing effects, making the response dependent on the external sample shape. This is the reason for studying the properties of MNP in assemblies of anisotropic external shapes such as films, chains, or elongated aggregates. In the present work, using a recently developed Time Quantified Monte Carlo (TQMC) framework for dynamic simulations, we focus more precisely on the importance of the local structure in such anisotropic aggregates to the dipolar interactions contribution of the response to the external field. Here the local structure is understood as both the location of the nanoparticles and the distribution of their easy axes. We show that the latter must be determined in a self-consistent way starting with the equilibrium structure of a ferrofluid modeled as the dipolar hard sphere fluid.
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Materials Science · Cross-listed from physics.chem-ph

Preparation sequence controls oxygen partitioning between boron and lithium on tungsten

Predrag S Krstic, Meral Sharkass, Swarit Dwivedi et al. (+3 more)

Classical reactive molecular dynamics of boron- and lithium-conditioned tungsten surfaces show that the order in which boron and oxygen are introduced - not the boron inventory - controls surface chemistry. On a thin engineered tungsten oxide, boron captures 81% of oxygen and consumes the oxide; on an engineered ~2 nm mixed WO3/WO2 film, boron captures only 20% and leaves 52% of reaction-zone tungsten in WO3-like coordination; and in a co-deposited W-B substrate later exposed to oxygen, boron captures only 28% despite a tenfold larger inventory. Adding lithium leaves the oxide-first cases unchanged but transforms the co-deposited case, where lithium becomes the dominant oxygen captor (58%) and a lithium-borate-glass-like network form. We outline the expected, divergent responses of the boron-only and boron-plus-lithium materials to deuterium irradiation.
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All authors Predrag S Krstic, Meral Sharkass, Swarit Dwivedi, Dalia Sayed Ahmed, Yun Kyung Shin, Adri CT van Duin

Materials Science

Orientation refinement for nanobeam precession electron diffraction patterns using spot intensity profiles

Arthur Després, Muriel Vérion and Edgar F. Rauch

We develop a method to measure crystallographic orientations with high angular resolution for nano-beam precession electron diffraction patterns, and applicable to 4D scanning precession electron diffraction. We show that internal variations of intensity in the diffraction spots can be simulated and correlated to experimental variations to measure the crystallographic orientation with a much better angular resolution that with the standard method of automated crystal orientation mapping (ACOM). In a tilt series carried out with long exposure time on a monocrystal of silicon around the main goniometer tilt axis, the imposed tilt angles are retrieved with a 0.044{\deg} to 0.054{\deg} precision with refinement, against 0.25{\deg} to 0.33{\deg} with the standard method. Shorter exposure times, introducing Poisson noise, marginally degrade the precision to a 0.054{\deg} to 0.066{\deg} range. The method also corrects a systematic error of ACOM near zone axis.
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Materials Science

Emergent Noncoplanar Spin Chirality through Magnetic and Nonmagnetic Substitution in the Kagome Antiferromagnet Mn$_3$Sn

Anupam Barik, Achintya Low, Susanta Ghosh et al. (+2 more)

Controlling noncoplanar spin textures in centrosymmetric magnets remains a central challenge for realizing emergent Berry-phase phenomena. Here, we demonstrate that magnetic (Cr) and nonmagnetic (Cu) substitution at the Mn site provide distinct routes to engineer spin chirality and topological transport in the kagome antiferromagnet Mn$_3$Sn. Cr substitution enhances low-temperature spin canting, stabilizing a dense noncoplanar texture that yields a pronounced topological Hall effect (THE) at low temperatures. In contrast, Cu substitution drives a spin-reorientation transition accompanied by an easy-axis rotation, creating a broad temperature window (150–208 K) where competing magnetic anisotropies stabilize noncoplanar spin textures and generate a large THE. A concurrent carrier-type crossover signals an underlying electronic-structure reconstruction. These results reveal that exchange enhancement and exchange dilution represent two fundamentally different pathways for tuning real-space Berry curvature, establishing chemical substitution as a powerful strategy for engineering topological transport in kagome antiferromagnets.
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All authors Anupam Barik, Achintya Low, Susanta Ghosh, Kapildeb Dolui, Setti Thirupathaiah

Materials Science

Temperature–Composition Mapping and Growth-History Dependence of rBN-Related Raman Responses in BN Grown on Fe–B under Flowing N$_2$

Donghoi Kim, Ayoung Cho, Kyeongho Park et al. (+2 more)

BN products formed on Fe–B sources under flowing N$_2$ were investigated primarily at 1250–1400~$^\circ$C over nominal B contents of 1–10~wt% to determine how rBN-related Raman character depends on growth condition and history. Spatially resolved Raman mapping across 44 growth conditions identified a restricted temperature–composition region in which the integrated rBN-related low-frequency response over 750–835~cm$^{-1}$, $A_{750-835}$, is strongly developed together with the integrated total response of the main $\sim$1367~cm$^{-1}$ BN band, $A_{1367}^{\rm{total}}$. In addition, the asymmetric high-wavenumber extension of the $\sim$1367~cm$^{-1}$ band was quantified by subtracting a symmetric fitted core and integrating the far high-wavenumber residual, $T_{\rm{high}}^{\rm{far}}$. The independently defined $A_{750-835}$ and $T_{\rm{high}}^{\rm{far}}$ responses exhibit a strong correspondence across the full dataset, supporting their use as complementary rBN-related Raman observables. In contrast, $A_{750-835}/A_{1367}^{\rm{total}}$ varies systematically among growth conditions, indicating that the relative prominence of the low-frequency response changes with temperature and composition rather than tracking the overall BN response through a fixed proportionality. Growth-duration experiments at 1350~$^\circ$C further show that this ratio also depends on high-temperature N$_2$ dwell time, establishing growth history as an additional kinetic variable. Powder X-ray diffraction on selected products independently confirms the presence of rBN-related stacking, while second-harmonic generation provides complementary symmetry-sensitive evidence. These results define a processing window favorable for strong rBN-related Raman response and introduce a quantitative framework for tracking both the low-frequency and band-asymmetry signatures associated with rBN-related BN structure.
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All authors Donghoi Kim, Ayoung Cho, Kyeongho Park, Young Duck Kim, Chinkyo Kim

Materials Science

LATHE: LAnguage-driven Toolkit for Hypothesis-based crystal Editing

Qianyu Zheng, Shuyi Jia and Victor Fung

Manipulating crystal structures towards targeted geometric properties or symmetry constraints is a longstanding challenge. Existing computational frameworks fall short: LLMs have poor spatial awareness and operate at coarse granularity in the token space, while diffusion- and gradient-based structure generation approaches generally produce complete structures de novo rather allowing for fine-grained editing of a given input under arbitrary constraints. We present LATHE, a geometric toolkit that closes this gap by expressing seven classes of crystallographic properties — bond length, bond angle, dihedral angle, coordination environment, lattice parameters, cell volume, and space group, as differentiable objectives to enable direct geometric editing of crystal structures. To demonstrate its usage in materials design, we further expose LATHE through a Model Context Protocol server and embed it in a closed-loop multi-agent system which translates hypotheses intogeometric modifications in natural language towards a given design objective. Across single-property benchmarks, LATHE attains near-perfect constraint satisfaction on all seven property types while keeping optimized structures close to local energy minima. The LATHE-equipped agent translates over 87.5% of natural-language prompts into valid executable configurations and faithfully completes them. In a band-gap inverse-design case study, the multi-agent loop reaches the target tolerance window in nine of ten independent runs at a typical cost of thirteen hypothesis-evaluation cycles. By bridging natural-language hypothesis generation and physically grounded gradient-based structural editing, this work establishes a paradigm for interpretable, closed-loop computational materials discovery that is immediately applicable to a broad class of functional material design tasks.
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Thursday 1 October

Materials Science · Cross-listed from cond-mat.mes-hall

Surface scalar plasmons on curved interfaces: a venue for analogue gravity

Matheus E. Pereira

We investigate whether the geometry of a curved conductor–dielectric interface can modify the effective mass and propagation of scalar surface plasmons (SSPs). In the hydrodynamic limit, we describe SSPs as density perturbations in a semiclassical jellium electron gas. Using a thin–layer dimensional reduction procedure, we derive a massive Klein–Gordon equation for SSPs on the curved interface with a geometric potential. We find that under specific conditions, the geometric potential allows SSP propagation with a vanishing effective mass. We then apply the formalism to a well known analogue black hole configuration, determining the corresponding quasinormal mode frequencies. Our results show that interface curvature provides a geometric handle on plasmon propagation and localization, suggesting new possibilities for plasmon transport and analogue gravity experiments with surface plasmons.
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Materials Science · Cross-listed from astro-ph.EP

Pressure-induced desalting of NaCl-bearing ice VII: A compositional filter in water-rich planets

Alasdair Nicholls, Tomasz Poreba, Xi Zhu et al. (+6 more)

Sodium chloride is a major component of extraterrestrial oceans, but it is generally assumed to be excluded from the high-pressure ice mantles of water-rich planets. Here we show that a concentrated NaCl solution, when quenched in an amorphous state before compression, crystallises in a metastable NaCl-bearing ice VII phase. Synchrotron x-ray diffraction and neutron diffraction reveals an expanded and strongly disordered ice VII lattice with no detectable crystalline NaCl. Ab initio calculations reproduce lattice expansion by substituting water molecules for Na$^+$ and Cl$^-$ ions and show that the structural response increases strongly with salt concentration. Upon decompression at 300 K, the phase expels crystalline NaCl at $5.1 \pm 0.3$ GPa and does not reform upon recompression, demonstrating that its formation is controlled by the thermodynamic pathway. Despite an 8.5% larger unit-cell volume, NaCl-bearing ice VII has a density close to that of pure ice VII and is substantially less dense than an equivalent mechanical mixture of ice and halite. These properties suggest that salty ice may be transported through deep convecting mantles but release salt near the 5 GPa boundary, where the denser products could inhibit further upward transport. Pathway-dependent salt trapping may therefore provide a previously unrecognised control on chemical exchange between rocky interiors and subsurface oceans.
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All authors Alasdair Nicholls, Tomasz Poreba, Xi Zhu, Richard Gaal, Stefan Klotz, Gabriel Tobie, Henrik M. Ronnow, Razvan Caracas, Livia Eleonora Bove

Materials Science · Cross-listed from cond-mat.dis-nn

Quantum transmission in 1D disordered stealthy hyperuniform Kronig–Penney-like models

Shaobing Yuan, Carlo Vanoni and Salvatore Torquato

Disordered stealthy hyperuniform (SHU) systems are emerging as platforms for controlling classical and quantum transport due to vanishing single-scattering contributions in the stealthy regime. Here, to our knowledge, we present the first perturbation theory of one-dimensional quantum transport through a continuum of identical point scatterers with SHU positional disorder. Our perturbation theory indicates the exact cancellation of all the lower-order terms due to the Fourier-space stealthy condition $S(q)=0$, and the further suppression of the lowest non-vanishing fourth order in the Lyapunov exponent $\lambda(k)$ due to the real-space hyperuniform constraint $\lim\limits_{D\to\infty}\sigma_D^2=c<\infty$. Our findings presents universal implications of the general wave-propagation phenomena in disordered SHU systems.
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Materials Science · Cross-listed from cond-mat.soft

How Does Hard Magnetic Soft Matter Deform?

Daniel Katusele, Carmel Majidi, Liping Liu et al. (+2 more)

Hard Magnetic Soft Materials, i.e., elastomers seeded with hard magnetic particles, convert magnetic energy into complex motion and have become central to the design of untethered soft robots, biomedical devices, and, in general, for enabling fast, wireless actuation. Their behavior depends critically on how the surrounding soft matrix deforms and transmits torque to each magnetized inclusion, yet there is no consensus on the correct mapping between macroscopic strain and microscopic motion. Competing models predict conflicting particle rotations and magnetic responses under identical loads. Here, we construct counterexamples that show the key shortcomings in these models, and then establish a first-principles framework that leads to an optimal deformation mapping. The resulting closed-form law unifies conflicting models and shows that they are, in fact, simply different limits of our general approach. Our work permits the rational design of magnetically actuated soft devices and a unified view of deformation in magnetic soft matter, and broadly, in similar architectured materials.
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All authors Daniel Katusele, Carmel Majidi, Liping Liu, Pradeep Sharma, Kaushik Dayal

Materials Science · Cross-listed from cond-mat.dis-nn

Universal energy barrier for plastic flow in a network glass

Ibrahim Ghanem, Richard Jana, Wolfram G. Nöhring et al. (+2 more)

Shear transformations are the elementary events of plasticity in glasses and underpin many mesoscopic models of plastic flow, yet their atomic origin and energetics remain difficult to establish. Here we use a machine-learned interatomic potential to show that, in amorphous carbon as a representative network glass, a shear transformation corresponds to the breaking or formation of a single covalent bond. The simplicity of the associated reaction coordinate, the bond length, enables us to extract energy landscapes and barriers. Despite the intrinsic structural disorder, we find that all energy landscapes collapse onto a universal barrier shape. What remains bond-specific is a single scale, the bond-jump distance, which fixes the barrier height through a cubic law. Combined with the activation statistics of shear transformations, this yields a model that predicts the plastic flow stress from independently determined bond-level quantities. Our results provide microscopic support for phenomenological models of plastic flow in glasses and suggest a route towards a quantitative description of amorphous plasticity.
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All authors Ibrahim Ghanem, Richard Jana, Wolfram G. Nöhring, Michael Moseler, Lars Pastewka

Materials Science · Cross-listed from cs.LG

The AI Theorist reveals excitonic structure in $\alpha$-RuCl$_3$

Hongjian Zhou, Xianfan Nie, Sean Wu et al. (+5 more)

Advances in experimental instrumentation and automation generate increasingly rich datasets, but turning experimental observations into microscopic understanding remains a bottleneck in scientific discovery. To accelerate this process, we introduce AI Theorist, a system of artificial intelligence (AI) agents for autonomous discovery of physical models through hypothesis generation, first-principles calculations and evidence-driven refinement. We apply the framework to $\alpha$-RuCl$_3$, a leading candidate material for realizing a Kitaev quantum spin liquid, to investigate its electronic structure through optical spectra. AI Theorist develops a new interpretation of the optical and photocurrent observations, identifying distinct excitonic states with contrasting optical selection rules and real-space distributions. To our knowledge, this is the first demonstration of an AI system autonomously developing a physical model to explain previously unpublished experimental observations in a quantum material, utilizing first-principles electronic-structure and many-body calculations. Our results establish a route to autonomous theoretical discovery in materials science, in which AI agents use first-principles calculations to turn experimental observations into physical models and testable predictions.
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All authors Hongjian Zhou, Xianfan Nie, Sean Wu, Tarun Patel, Jinge Wu, Andrew Liu, Adam Wei Tsen, David A. Clifton

Materials Science

Distinguishing sodium-ion penetration and sustained transport in realistic hard carbon nanostructures

Carolina Cruz-Cardona, Andreea Hedes, Patrick Rowe et al. (+7 more)

Hard carbons are promising anodes for sodium-ion energy storage, yet the relationship between their heterogeneous microstructure and sodium transport remains poorly understood. Here, we combine machine-learning-generated hard-carbon structures with molecular dynamics simulations of explicit 1 M NaPF6 in ethylene carbonate/dimethyl carbonate electrolyte to investigate sodium storage and transport across carbon structures with densities from 0.5 to 2.0 g cm-3. Increasing carbon density produces less accessible pore networks and greater graphitic local ordering, allowing the influence of microstructure on electrochemical response and Na+ transport to be examined systematically. Sodium uptake increases with applied potential but decreases strongly with carbon density, while electrode charging persists even in the densest structure, where Na+ uptake remains very small. Coordination analysis shows increasing interaction with the carbon framework under applied potential, while Na+ retains a partially solvated environment. Three-dimensional trajectory analysis reveals heterogeneous, predominantly tortuous transport pathways, with the more open HC-C1 structure supporting broader penetration and greater sustained displacement. Maximum penetration depth and retained displacement are not equivalent: ions can transiently reach deep regions of denser carbon structures before returning towards the electrolyte interface. Potential-of-mean-force analysis further shows that deep penetration occurs across a range of projected free-energy changes and cannot be described by a single energetic criterion. These results show that Na+ storage and transport are governed by the interplay between electrostatic driving force, electrolyte solvation, pore accessibility and confinement, highlighting carbon microstructure as a key determinant of sustained ionic penetration.
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All authors Carolina Cruz-Cardona, Andreea Hedes, Patrick Rowe, Anderson Arboleda-Lamus, Raul Arenal, Zhenyu Guo, Heather Au, Magda M. Titirici, Celine Merlet, Carla de Tomas

Materials Science

Thickness-Controlled Ferroelectric-to-Ionic Transport in CuCrP2S6 at Room Temperature

Subhashree Chatterjee, Abhishek Bajgain, Rabindra Basnet et al. (+1 more)

Ambient-temperature coexistence of ferroelectricity, photoconductivity, and ionic transport in ultra-thin van der Waals (vdW) compound CuCrP2S6 (CCPS) offers significant potential for multifunctional electronic, photonic, and neuromorphic applications. However, ferroelectricity and ionic transport can become antagonistic when sharing a common atomic origin, like the copper ions in CCPS. We address this fundamental dichotomy by systematically investigating the thickness-dependent evolution of ferroelectricity, ionic migration, and memristive behavior in CCPS diodes via electrostatic and photo-assisted interfacial band tuning. Using piezoresponse, Kelvin probe, and conductive atomic force microscopy, alongside photoexcited transport measurements, we identify distinct thickness regimes. CCPS flakes thinner than ~ 40 nm exhibit robust, reversible ferroelectric (FE) switching. Conversely, thicker samples display suppressed switchable polarization, with electrical conduction dominated by Cu+ migration, filamentary memristive switching, and rectification reversal. Optical illumination further enhances ionic mobility via photogenerated carriers, driving photo-assisted ionic transport in non-FE flakes and a coupled photoferroionic response in FE flakes. These findings clarify how ferroelectricity fundamentally alters ionic transport dynamics in vdW ferroionic systems.
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All authors Subhashree Chatterjee, Abhishek Bajgain, Rabindra Basnet, Ramesh C. Budhani

Materials Science · Cross-listed from physics.optics

Thin-capping layer epitaxial quantum dots for near-field quantum photonics

Yuting Guo, Jonathan Bar-David, Pasquale Cilibrizzi et al. (+3 more)

Epitaxial quantum dots (QDs) are widely recognised as one of the best quantum light sources, given their good stability, brightness, quantum efficiency and coherence. To reach such properties, QDs are protected from potentially detrimental surface states by a relatively thick capping layer, typically exceeding 50nm. This prevents the implementation of near-field effects, like plasmonic-based ones, that can dramatically increase the light-matter interaction, since the control of the spontaneous emission dynamics and directionality of the emission can only occur if the emitter is in close proximity (typically tens of nanometers or less) from the metallic structures. In this work, we report the growth and optical characterisation of InAs/GaAs QDs with GaAs capping layer thickness of 10nm, 20nm, and a more standard 95nm. Remarkably, we observe emission linewidths up to 5 times smaller than previously reported, with unperturbed excitonic lifetimes. These results demonstrate that the epitaxial QD's high optical quality can be maintained even when the emitters are at reduced distances from the surface, opening the path for the exploration of near-field light-matter interactions with coherent and stable emitters, suitable for quantum technology applications.
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All authors Yuting Guo, Jonathan Bar-David, Pasquale Cilibrizzi, Sung-Yul L. Park, Jin Dong Song, Luca Sapienza

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

Frustration-induced multiferroicity in hauerite MnS2

Vilmos Kocsis, Harish K. Singh, Kranthi K. Bestha et al. (+4 more)

Pyrite-type mineral hauerite MnS$_2$ is a magnetic insulator with localized $S=\frac52$ moments. Below 48 K, it develops a collinear antiferromagnetic order, accompanied by unit-cell doubling and breaking the inversion symmetry. We demonstrate that the latter gives rise to a ferroelectric polarization of up to 360 $\mu$C/m$^2$ rendering MnS$_2$ a type-II multiferroic. Microscopically, the electronic polarization originates from S$_2$ dimers that acquire a dipole moment induced by the frustrated magnetic ordering of neighboring Mn sites. We show that time-reversal symmetry leaves ferroelectric domains intact, and that domain switching necessitates overcoming a high energy barrier set by the magnetic exchange energy scale.
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All authors Vilmos Kocsis, Harish K. Singh, Kranthi K. Bestha, Yaqian Guo, Maxim Mostovoy, Jeroen van den Brink, Oleg Janson

Materials Science

GEODE: Symmetry-Preserving Cartesian Diffusion for Crystal Generation

Yuchen Lou and Alex M. Ganose

Most known inorganic crystals exhibit symmetric atomic arrangements, yet generative models often fail to reproduce them. Explicitly enforcing these symmetries has so far yielded fewer stable and novel structures than unconstrained generation. We introduce Generative Equivariant Orbit Diffusion Engine (GEODE), to our knowledge the first model to combine coordinate and lattice diffusion in Cartesian space. GEODE first samples symmetry templates, then jointly generates the lattice, atomic coordinates and atom types while preserving the specified symmetry with a novel Wyckoff-constrained loss. Cartesian diffusion gives coordinate noise a consistent physical scale that we empirically demonstrate improves performance. Unconditional generation achieves a metastable, unique and novel (mSUN) rate of 11.9%, compared with 7.7% for the next best symmetry-aware model. We also introduce sampling time template filtering, which increases mSUN by ~6% without retraining, making GEODE competitive with leading symmetry-agnostic models. Template selection also enables joint symmetry and property guidance, which we demonstrate through classifier-free guidance of permittivity.
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Materials Science · Cross-listed from physics.flu-dyn

Direct Modeling of Pore Size Evolution and Microcollapse in Lyophilization by Population Balance

Isaac Stonewall Wheeler, Vivek Narsimhan, Alina A. Alexeenko et al. (+1 more)

In the primary drying step of pharmaceutical freeze drying, it is well known that amorphous excipients are prone to "microcollapse" as they approach their glass transition temperature. Existing modeling approaches for this phenomenon generally entail either avoidance of this regime or an experimentally burdensome empirical assessment of the resulting drop in resistance to mass transfer. In this work, we approach the phenomenon head-on by developing a population balance model for the pore size distribution of a freeze-dried cake during microcollapse and relating the pore size to mass transfer resistance. By treating the population balance with the method of moments and an interpolative closure, we keep the model's computational burden on par with the literature-standard model for primary drying. For a literature example when mass transfer resistance clearly varies as a function of product temperature during drying, we fit the population balance model to cases with high and low product temperature and show that it can then simulate intermediate cases with equal accuracy. The validity of the expression for mass transfer resistance is demonstrated with another literature data set, where pore size distributions were measured after the fact for a formulation without microcollapse; only a single parameter from this model needs to be fit to those cases to yield predictive accuracy in product temperature on par with post-hoc empirical assessment. Finally, a sophisticated multi-experiment fit for one formulation across a range of conditions yields quantitative agreement in product temperatures, suggesting that the rate constant for microcollapse behavior may be a material parameter and independent of the precise porous geometry.
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All authors Isaac Stonewall Wheeler, Vivek Narsimhan, Alina A. Alexeenko, Davide Fissore

Materials Science

Weak non-Landau-type contributions to the diamagnetism of graphite

A. V. Nikolaev, A. V. Bibikov, M. Ye. Zhuravlev et al. (+1 more)

The exceptionally large diamagnetic susceptibility of a single-crystal graphite in the direction perpendicular to the graphene layers is caused by the Landau levels. However, there are also other contributions to the magnetic susceptibility. In particular, in metals the Pauli paramagnetism is leading, whereas in dielectrics the diamagnetic Langevin and paramagnetic Van Vleck terms are essential. These components of magnetic susceptibility are also present in graphite. In this work, we calculate the magnitudes of all these small contributions from first principles. It is found that the Pauli paramagnetism is negligible (2.3 x 10^{-9} emu/g), whereas the other diamagnetic contribution - arising from the Langevin and Van Vleck mechanisms - is comparable to the in-plane experimental diamagnetism of graphite and to the diamagnetic response of C60 and C70} fullerenes. This diamagnetic contribution proves to be slightly anisotropic (-2.93 x 10^{-7} emu/g along the x- or y-axes and -2.24 x 10^{-7} emu/g along the $z-$axis), with the averaged value -2.7 x 10^{-7} emu/g.
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All authors A. V. Nikolaev, A. V. Bibikov, M. Ye. Zhuravlev, L. L. Tao