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Physics Condensed Matter Materials Science

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Sunday 14 December

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

Singlet Fission among two Single Molecules

Sumanta Paul, Oleksandr Yampolskyy, Zehua Wu et al. (+2 more)

Singlet fission (SF) is a photophysical process where a singlet excitation generates two triplet excited states, enhancing exciton multiplication potentially useful for solar energy conversion. Since SF typically outcompetes radiative decay, single molecule studies of SF have remained elusive. Here, we present single molecule spectroscopy of a terrylenediimide (TDI) dimer at room and cryogenic temperatures. By analysing the stream of photons emitted by single dimers, the rates of formation and decay of SF-born triplet states were determined. We report considerable static and dynamic heterogeneities of the SF process which are reflected in broad rate distributions as well as the occasional occurrence of delayed fluorescence and rate fluctuations during spin evolution. Cryogenic experiments point to the formation of a coherent multiexciton superposition state which decays into the singlet exciton from which a correlated triplet pair evolves. Our results establish single molecule spectroscopy as a new avenue into mechanistic details of the SF process which often are drowned by ensemble av-eraging.
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All authors Sumanta Paul, Oleksandr Yampolskyy, Zehua Wu, Klaus Müllen, Thomas Basché

Materials Science · Cross-listed from cond-mat.soft

On the problem of simple shear of an incompressible viscoelastic solid under finite deformations

Vladislav V. Kozhukhov

In the framework of a viscoelastic material model, whose constitutive relation is given by a one-parameter family of Gordon-Schowalter derivatives, the problem of simple shear under acceleration and random velocity motion is considered. For motion with acceleration, the presence of non-zero normal stresses is discovered, which corresponds to the Poynting effect previously discovered for this material. A problem in which the shear rate was determined as a linear function of a random variable given from a normal distribution was studied. Within the framework of the methodology proposed by V.A. Lomakin, an analytical solution of the problem is constructed. A significant dependence of the dispersion of the stress tensor components on the choice of the objective derivative was found.
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Materials Science · Cross-listed from cond-mat.mes-hall

Magnetic topological textures in nonorientable surfaces

Carlos Saji, Mario A. Castro, Vagson L. Carvalho-Santos et al. (+3 more)

Topological magnetic textures confined to two-dimensional (2D) non-orientable manifolds exhibit behaviors absent in planar systems. We investigate bimerons on Möbius surfaces and show that the lack of global orientation alters conservation laws, yielding geometry-dependent topology and dynamics. Micromagnetic simulations reveal that the helical twist and non-orientable geometry reshape the effective topological charge and stabilize chiral configurations imposed by the surface. Under spin-polarized currents, bimerons display unconventional transport: the transverse response is locally reversed or globally suppressed due to charge inversion along the manifold. Moreover, we establish an Aharonov-Bohm effect associated with the magnonic modes of the texture; in particular, the translational Goldstone mode implies that a bimeron on a Möbius strip should exhibit path-dependent quantum interference. These results identify a geometry-driven regime of magnetization dynamics and provide a route to curvature-engineered spintronic functionalities.
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All authors Carlos Saji, Mario A. Castro, Vagson L. Carvalho-Santos, Eduardo Saavedra, Alvaro S. Nunez, Roberto E. Troncoso

Materials Science

Crossover Dynamics of Non-Fickian Ionic Diffusion in Solids

Gangbin Yan, Pierfrancesco Ombrini, Zhichu Tang et al. (+14 more)

Ionic diffusion in solids is central to energy storage, electronics, and catalysis, yet its chemical origins are difficult to resolve because conventional diffusion models struggle with effects of confinement, crystallographic disorder, lattice distortions, and coupling to electronic or phononic carriers. These challenges are especially pronounced in battery materials, where ionic and electronic motion occur together, complicating interpretation of electrochemical measurements. Here we use tracer exchange as a direct, non-electrochemical probe to reveal distinct ion-transport regimes in the one-dimensional conductor olivine Li_xFePO4 (0 <= x <= 1). Lithium isotope exchange validates single-file diffusion governed by strong ion-ion correlations, where 1D confinement suppresses bypassing and preserves spatial order. Kinetic Monte Carlo simulations and chronoamperometry quantify both Faradaic and non-Faradaic surface exchange, identifying electron transport, rather than Li+ mobility, as the rate-limiting step for electrochemical reaction. In addition, Li-Na exchange exhibits apparent superdiffusion, with rates that increase with Na content. Simulations attribute this behavior to surface-exchange limitations and Na-induced lattice strain that enhances cross-channel Li+ hopping and drives a crossover from 1D to quasi-2D transport. Four-dimensional STEM, in situ synchrotron XRD, X-ray absorption spectroscopy, and Mossbauer spectroscopy confirm that lattice softening and concerted polaron motion contribute to the observed dynamics. These results establish tracer exchange as a powerful tool for probing coupled ion-electron transport and provide chemical insight into how lattice mechanics and multicomponent exchange shape ionic diffusion in solids.
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All authors Gangbin Yan, Pierfrancesco Ombrini, Zhichu Tang, Shakul Pathak, Maoyu Wang, Barbara Lavina, Alexandros Vasileiadis, Suin Choi, Mingzhan Wang, Dongchen Ying, Qizhang Li, Esen E. Alp, Hua Zhou, Martin Z. Bazant, Qian Chen, Marnix Wagemaker, Chong Liu

Materials Science

To crack, or not to crack: How hydrogen favors crack propagation in iron at the atomic scale

Aleksei Egorov, Lei Zhang, Erik van der Giessen et al. (+1 more)

Steel is a key structural material because of its considerable strength and ductility. However, when exposed to hydrogen, it is prone to embrittlement. Mechanistic understanding of the origin of hydrogen embrittlement is hampered by the lack of reliable interatomic potentials. Here, we perform large-scale molecular dynamics simulations of crack propagation after having developed and validated an efficient yet density-functional-theory-accurate machine-learning potential for hydrogen in iron. Simulations based on our potential reveal that in the absence of H, iron is intrinsically ductile at finite temperatures with crack-tip blunting assisted by dislocation emission. By contrast, minute (part-per-million) hydrogen concentrations can switch the crack-tip behavior from ductile blunting to brittle propagation. Detailed analysis of our molecular dynamics results reveals that the combination of fast hydrogen diffusion and diminished surface energy is at the origin of embrittlement. Our results set the stage for a modified Griffith's criterion for hydrogen-induced brittle fracture, which closely captures the simulations and that can be used to assess embrittlement in iron-based alloys.
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All authors Aleksei Egorov, Lei Zhang, Erik van der Giessen, Francesco Maresca

Materials Science · Cross-listed from eess.SY

Sensitivity increase of 3D printed, self-sensing, carbon fibers structures with conductive filament matrix due to flexural loading

Matei Drilea, Alexander Dijkshoorn, Gusthavo Ribeiro Salomão et al. (+2 more)

The excellent structural and piezoresistive properties of continuous carbon fiber make it suitable for both structural and sensing applications. This work studies the use of 3D printed, continuous carbon fiber reinforced beams as self-sensing structures. It is demonstrated how the sensitivity of these carbon fiber strain gauges can be increased irreversibly by means of a pretreatment by pre-stressing the sensors with a large compressive bending load. The increase in the gauge factor is attributed to local progressive fiber failure, due to the combination of the thermal residual stress from the printing process and external loading. The coextrusion of conductive filament around the carbon fibers is demonstrated as a means of improving the reliability, noise and electrical connection of the sensors. A micrograph of the sensor cross section shows that the conductive filament contacts the various carbon fiber bundles. All-in-all, the use of pre-stressing carbon fiber strain gauges in combination with coextrusion of conductive filament hold promises for 3D printed structural sensors with a high sensitivity.
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All authors Matei Drilea, Alexander Dijkshoorn, Gusthavo Ribeiro Salomão, Stefano Stramigioli, Gijs Krijnen

Materials Science

Observation of magnetically coupled electro-optic effect in LiNbO3/LiTaO3 at room temperature

Yalong Yu, Hengwei Zhang, Xiaoyan Liu et al. (+1 more)

The magnetoelectric coupling effect serves as a crucial bridge between electrical and magnetic order parameters in condensed matter physics, forming the physical basis for the development of next-generation low-power information storage and sensing technologies. However, material systems exhibiting this effect at room temperature are extremely rare, and the coupling strength is typically very weak, which has long hindered the practical application of such phenomena despite their rich tunability. Here, we break this by reporting a pronounced magnetoelectric phenomenon,the magnetically coupled EO effect in the classic ferroelectric optical materials LiNbO3 and LiTaO3. We trace its origin to an unexpected source,the problematic direct current drift,a major reliability issue in photonic integrated circuits. We unambiguously demonstrate that this drift stems not from mobile ions but from defect-bound unpaired electrons, whose slow polarization relaxation is quenched upon the magnetic-field-induced formation of a room-temperature skyrmion states, as directly visualized by Lorentz transmission electron microscopy. This collective spin ordering not only solves the decades-old drift problem but also transforms the defect states into a magnetically responsive platform, exhibiting an efficiency up to 34 pm/V in LiNbO3 and 15 pm/V in LiTaO3-an orders-of-magnitude enhancement over conventional room-temperature magnetoelectric responses and even surpassing the materials' intrinsic Pockels coefficients. We also measured the magnetic response of this additional electro-optical effect and found that under the condition of applying a magnetic field of 0.1 T, an electro-optical coefficient adjustment of about 8 pm/V can be achieved (0.008 pm/V/Oe), which is equivalent to 30% of the electro-optical coefficient of LiNbO3 itself.
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All authors Yalong Yu, Hengwei Zhang, Xiaoyan Liu, Tao Chu

Materials Science

Plasma engineered Hydroxyl Defects in NiO a DFTSupported-Spectroscopic Analysis of Oxygen Hole States and Implications for Water Oxidation

Harol Moreno Fernandez, Mohammad Amirabbasi, Crizaldo Jr. Mempin et al. (+8 more)

Controlling lattice oxygen reactivity in earth abundant OER catalysts requires precise tuning of defect chemistry in the oxide lattice. Here, we combine DFT+U calculations with plasma assisted synthesis to show how O2 and H2O in the discharge govern vacancy formation, electronic structure, and catalytic predisposition in NiO thin films. Oxygen rich plasmas generate isolated and clustered Ni vacancies that stabilize oxygen ligand hole states and produce shallow O 2p Ni 3d hybrid levels, enhancing Ni O covalency. In contrast, introducing H2O during growth drives local hydroxylation that compensates vacancy induced Ni3+ centers, restoring Ni2+ like coordination, suppressing deep divacancy derived in gap states, and introducing shallow Ni O H derived valence-band tails. EXAFS confirms that hydroxylation perturbs only the local environment while preserving the medium-range NiO lattice, and Ni L-edge spectroscopy shows a persistent but redistributed ligand-hole population. These complementary vacancy and hydroxylation driven pathways provide a plasma controlled route to pre define electronic defect landscapes in NiO and to tune its activation toward OER relevant NiOOH formation.
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All authors Harol Moreno Fernandez, Mohammad Amirabbasi, Crizaldo Jr. Mempin, Andrea Trapletti, Garlef Wartner, Marc F. Tesh, Esmaeil Adabifiroozjaei, Thokozile A. Kathyola, Carlo Castellano, Leopoldo Molina Luna, Jan P. Hofmann

Materials Science

Thermoelectric properties of SbXY (X = Se, Te; Y = Br, I) Janus layers

M. Vallinayagam, A. E. Sudheer, A. Kumar et al. (+5 more)

We report a comprehensive investigation of the thermoelectric properties of SbXY (X = Se, Te; Y = Br, I) Janus layers (JL) using spin-polarized first-principles calculations. Ab initio molecular dynamics confirm that the 1T phase ($Pm31$) remains stable up to 1000 K, excluding any phase transitions. The calculated mean-square displacement further evidences the structural robustness. The thermal conductivity is strongly suppressed in Br-containing layers due to enhanced Froehlich interactions between optical and acoustic phonons. Electronic structure calculations reveal indirect band gaps of 1.1 to 1.3 eV, with valence and conduction bands dominated by the $p$-orbitals of halogen/chalcogen and of Sb, respectively. The carrier effective mass highlights anisotropic transport with lighter electrons being more mobile, while holes dominate the power factor, which attains values on the order of mW/mK$^2$. Direction-dependent transport indicates superior thermoelectric performance along the $xx$ direction, with negligible contribution along $yy$. The Figure of Merit reaches 0.6 at 1000 K in hole-doped SbSeBr, demonstrating strong potential for high-temperature applications. Our results reveal that the SbXY JLs, particularly SbSeBr, emerge as promising candidates for next-generation thermoelectric devices at elevated temperatures.
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All authors M. Vallinayagam, A. E. Sudheer, A. Kumar, G. Tejaswini, M. Posselt, C. Kamal, D. Murali, M. Zschornak

Materials Science

Extreme disorder in crystalline perovskite oxide: a new paradigm in quantum materials research

Srimanta Middey, Nandana Bhattacharya, Rukma Nevgi et al. (+2 more)

Perovskite oxides ($AB$O$_3$) have long been central to the advancement of modern condensed matter physics, owing to their rich and tunable electronic and magnetic properties. The quest to understand their various entangled phases has spurred the development of both cutting-edge experimental tools and innovative theoretical frameworks. In recent times, the emergence of high entropy oxides - materials in which five or more elements share a single crystallographic site - has introduced a powerful new paradigm in materials design. Embedding such extreme chemical disorder within the perovskite framework has opened vast opportunities for realizing novel physical phenomena inaccessible in conventional oxides. This review surveys the rapid advances in the synthesis, characterization, and exploration of the electronic and magnetic properties of compositionally complex perovskite oxides, offering key insights and highlighting promising avenues for future research.
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All authors Srimanta Middey, Nandana Bhattacharya, Rukma Nevgi, Suresh Chandra Joshi, Subha Dey

Materials Science

Probing Topological Surface States and Conduction via Extended Defects in (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ Films

Abby Liu, Armando Gil, Moon-ki Choi et al. (+10 more)

(Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ alloys are non-degenerate topological insulators (TIs) whose Dirac point (DP) can be tuned within the bulk bandgap by varying the composition, effectively reducing bulk conduction while allowing surface carrier conduction. Magnetotransport measurements of a series of (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ thin films indicate electron-dominated conduction, with weak anti-localization attributed to topological surface states (TSSs). Due to the similarity of phase coherence lengths and twin boundary spacings ($\sim$100 nm), we consider the role of twin boundaries as additional conducting paths. Density functional theory calculations reveal an enhanced density of states near the Fermi level at $60^\circ$ twin boundaries, with 2D carrier concentration in excess of $3 \times 10^{13}$ cm$^{-2}$. Furthermore, an analysis of the longitudinal magnetoconductivity yields an upper bound of $7.3 \times 10^{-4}$ S for twin boundary conductivity, resulting in a carrier mobility as high as $142$ cm$^2$/(V$\cdot$s). We discuss the role of twin boundaries in facilitating a transition from a massive Dirac cone dispersion to gapless, topologically protected surface states. Understanding the role of twin boundaries on carrier conduction in non-degenerate TIs is critical for the development of novel TI-based electronic devices.
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All authors Abby Liu, Armando Gil, Moon-ki Choi, Berna Akgenc Hanedar, Zecheng You, Shriya Sinha, Tahsin Hakioglu, Harley T. Johnson, Kai Sun, Roy Clarke, Ctirad Uher, Cagliyan Kurdak, Rachel S. Goldman

Saturday 13 December

Materials Science

Unveiling the amorphous ice layer during premelting using AFM integrating machine learning

Binze Tang, Chon-Hei Lo, Tiancheng Liang et al. (+6 more)

Premelting plays a key role across physics, chemistry, materials and biology sciences but remains poorly understood at the atomic level due to surface characterization limitations. We report the discovery of a novel amorphous ice layer (AIL) preceding the quasi-liquid layer (QLL) during ice premelting, enabled by a machine learning framework integrating atomic force microscopy (AFM) with molecular dynamics simulations. This approach overcomes AFM's depth and signal limitations, allowing for three-dimensional surface structure reconstruction from AFM images. It further enables structural exploration of premelting interfaces across a wide temperature range that are experimentally inaccessible. We identify the AIL, present between 121-180K, displaying disordered two-dimensional hydrogen-bond network with solid-like dynamics. Our findings refine the ice premelting phase diagram and offering new insights into the surface growth dynamic, dissolution and interfacial chemical reactivity. Methodologically, this work establishes a novel framework for AFM-based 3D structural discovery, marking a significant leap in our ability to probe complex disordered interfaces with unprecedented precision and paving the way for future disciplinary research, including surface reconstruction, crystallization, ion solvation, and biomolecular recognition.
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All authors Binze Tang, Chon-Hei Lo, Tiancheng Liang, Jiani Hong, Mian Qin, Yizhi Song, Duanyun Cao, Ying Jiang, Limei Xu

Materials Science

Many-Body Correlation Effects in Fröhlich Electron-Phonon Coupling

Zien Zhu, Chih-En Hsu, Benran Zhang et al. (+5 more)

In compound semiconductors and insulators, the polar electron-phonon coupling diverges at long range, known as the Fröhlich interaction. Modern first-principles electron-phonon calculations treat the Fröhlich interaction in a semiclassical electrostatic formalism based on density-functional perturbation theory. Here, using many-body $GW$ perturbation theory, we reveal important electron correlation effects in the Fröhlich-type electron-phonon coupling, which are missed by the prevailing approaches and rooted in the fundamentally distinct behavior between quasiparticle self-energy and semi-local exchange-correlation functionals in the long-range limit. Going beyond the electrostatic treatment, we derive and implement the $GW$ self-energy contribution to the long-range polar electron-phonon coupling, and demonstrate its critical role and nontrivial behaviors in properties such as electron linewidth and polaron formation in several prototype semiconductors. Remarkably, calculations on photoemission kink in electron-doped TiO$_2$ achieve excellent agreement with experiment. Our work establishes the many-body generalization of the Fröhlich interaction that is essential for accurate electron-phonon calculations at the full $GW$ level combined with Wannier interpolation techniques.
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All authors Zien Zhu, Chih-En Hsu, Benran Zhang, Zhenfa Zheng, Mauro Del Ben, Antonios M. Alvertis, Hung-Chung Hsueh, Zhenglu Li

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

A Software Package for Generating Robust and Accurate Potentials using the Moment Tensor Potential Framework

Josiah Roberts, Biswas Rijal, Simon Divilov et al. (+6 more)

We present the Plan for Robust and Accurate Potentials (PRAPs), a software package for training and using moment tensor potentials (MTPs) in concert with the Machine Learned Interatomic Potentials (MLIP) software package. PRAPs provides an automated workflow to train MTPs using active learning procedures, and a variety of utilities to ease and improve workflows when utilizing the MLIP software. PRAPs was originally developed in the context of crystal structure prediction, in which one calculates convex hulls and predicts low energy metastable and thermodynamically stable structures, but the potentials PRAPs develops are not limited to such applications. PRAPs produces two potentials, one capable of rough estimates of the energies, forces and stresses of almost any chemical structure in the specified compositional space – the Robust Potential – and a second potential intended to provide more accurate descriptions of ground state and metastable structures – the Accurate Potential. We also present a Python library, mliputils, designed to assist users in working with the chemical structural files used by the MLIP package.
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All authors Josiah Roberts, Biswas Rijal, Simon Divilov, Jon-Paul Maria, William G. Fahrenholtz, Douglas E. Wolfe, Donald W. Brenner, Stefano Curtarolo, Eva Zurek

Materials Science

Rational Design Principles for Na- and Li-ion Carbon Anodes from Interlayer Spacing Control

Ihor Radchenko and Oleksandr I. Malyi

Graphite, the standard commercial anode for Li-ion batteries, is thermodynamically incompatible with Na-ion batteries, leading researchers to search for alternative C-based structures (e.g., hard carbon, expanded graphite). In a simplified picture, the main idea of such search relies on identifying disordered C structures with a large interlayer spacing and distribution of local structural motifs (e.g., pores) with target electrochemical properties. Such exploration is typically done via trial-and-error experimentation, which often does not allow precise understanding of the role of interlayer distance and even Na/Li-ion intercalation in the electrochemical performance. Motivated by this, using density-functional theory and cluster expansion, we establish a structure-property relationship for Li- and Na-intercalation across a range of graphite interlayer spacings and stacking arrangements. We show that Na intercalation becomes thermodynamically possible in large concentrations above 4.21 Å even without a change in interlayer spacing. Conversely, Li intercalation has a narrow optimal window, with maximum capacity (close to the commercial limit) at approximately 3.75 Å, while larger spacings (e.g., 4.58 Å) quickly reduce Li storage capacity. We also find that AA-stacked domains consistently offer stronger ion bonding and higher voltages than AB-stacked domains for both ions. Our results, thus, not only explain the role of metal ion intercalation in the electrochemical performance, but also clarify the fundamental design trade-offs for expanded C anodes, offering practical targets and interlayer distance ranges for the independent optimization of the next generation of negative electrodes for metal-ion batteries.
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Materials Science · Cross-listed from cond-mat.soft

Morphogenesis of bacterial colonies in liquid crystalline environments

Sebastian Gonzalez La Corte, Thomas G. J. Chandler, Saverio E. Spagnolie et al. (+2 more)

Natural bacterial habitats are often complex fluids with viscoelastic and anisotropic responses to stress; for example, they can take the form of liquid crystals (LCs), with elongated microscopic constituents that collectively align while still retaining the ability to flow. However, laboratory studies typically focus on cells in simple liquids or complex fluids with randomly-oriented constituents. Here, we show how interactions with LCs shape bacterial proliferation in multicellular colonies. Using experiments, we find that in a nematic LC, cells generically form aligned single-cell-wide "chains" as they reproduce. As these chains lengthen, they eventually buckle in a highly localized manner. By combining our measurements with a continuum mechanical theory, we demonstrate that this distinctive morphogenetic program emerges because cells are kept in alignment due to the LC's elasticity; as each chain lengthens, growth-induced viscous stresses along its contour eventually overcome the elasticity of the surrounding nematic, leading to buckling. Our work thus reveals and provides mechanistic insight into the previously-overlooked role of LCs in sculpting bacterial life in complex environments.
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All authors Sebastian Gonzalez La Corte, Thomas G. J. Chandler, Saverio E. Spagnolie, Ned S. Wingreen, Sujit S. Datta

Materials Science

Shape descriptors of equilibrium states in a quantum lattice model with local multi-well potentials: A geometric analysis near the phase transitions in Sn$_2$P$_2$S$_6$ ferroelectric crystals

S. Özüm, T. Akkurt, R. Erdem et al. (+1 more)

We analyze the equilibrium states of quantum lattice model with local multi-well potentials for Sn$_2$P$_2$S$_6$ ferroelectric crystals using the mean and Gaussian curvatures ($H$, $K$), curvedness ($C$) and shape index ($S$). From the energy gap, pressure and temperature variations of $H$, $K$, $C$ and $S$, we have reported the geometric construction of the free energy surfaces for the ferroelectric and paraelectric phases. Their behaviors are explicitly observed near the ferroelectric-paraelectric phase transitions. It is found that $H$, $C$ and $S$ display a cusp singularity at the criticality while $K$ converges to zero on both sides of the critical and tricritical points.
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All authors S. Özüm, T. Akkurt, R. Erdem, N. Güçlü

Materials Science

Active learning potentials for first-principles phase diagrams using replica-exchange nested sampling

Nico Unglert, Michael Ketter and Georg K. H. Madsen

Accurate prediction of materials phase diagrams from first principles remains a central challenge in computational materials science. Machine-learning interatomic potentials can provide near-DFT accuracy at a fraction of the cost, but their reliability crucially depends on the availability of representative training data that span all relevant regions of the potential-energy surface. Here, we present a fully automated active-learning (AL) strategy based on replica-exchange nested sampling (RENS) for the generation of training data and the computation of complete pressure-temperature phase diagrams. In our framework, RENS acts as both the exploration engine and the acquisition mechanism: its intrinsic diversity and likelihood-constrained sampling ensure that the configurations selected for DFT labeling are both informative and thermodynamically representative. We apply the approach to silicon, germanium, and titanium using potentials trained at the r2SCAN level of theory. For all systems, the AL process converges within 10-15 iterations, yielding transferable potentials that reproduce known phase transitions and thermodynamic trends. These results demonstrate that RENS-based AL provides a general and autonomous route to constructing machine-learning interatomic potentials and predicting first-principles phase diagrams across broad thermodynamic conditions.
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Materials Science

Diamond crystal with Y-defects: spectroscopy and transmission electron microscopy

A.A. Shiryaev, E.A. Vasilev, A.L. Vasilev et al. (+3 more)

The paper presents results of investigation of a natural Ib-IaA diamond containing Y-defects from Yubileinaya kimberlite pipe, Yakutia. Analysis of spatial distribution of nitrogen-related A and C centers and intensity of Infra-red absorption at Raman frequency (1332 cm-1) reveals anticorrelation between these defects. Transmission electron microscopy of a zone with abundant Y-defects shows presence of dislocations in various configurations and numerous clusters of point defects generated by non-conservative dislocation motion. Extended defects with shape resembling thin (1-3 nm) rhombic plates with the largest dimension up to 20 nm are observed. Analysis of contrast of these defects shows that they represent nanosized voids (vacancy clusters). It is suggested that the defects were formed by annihilation of dislocation dipoles with subsequent growth by consumption of vacancies produced by non-conservative motion of dislocations. Upon excitation by 787 nm laser, numerous narrow photoluminescecne lines are observed between 800-900 nm; their intensity and position show pronounced spatial heterogeneity on scale of few microns. Qualitatively similar behaviour of photoluminescence was earlier noted for hydrogenated nanodiamonds. It is suggested that unusual behaviour of the luminescence lines may be explained by recombination processes at internal walls of the discovered nanovoids.
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All authors A.A. Shiryaev, E.A. Vasilev, A.L. Vasilev, V.V. Artemov, N.V. Gubanov, D.A. Zedgenizov

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

Experimental benchmark of the quantum-classical crossover in a spin ladder

Hironori Yamaguchi, Itsuki Shimamura, Akira Matsuo et al. (+4 more)

We report a spin-(1/2, 5/2) three-leg ladder realized in a radical-Mn polymer, exhibiting an antiferromagnetic transition and magnetization curves accurately described by classical mean-field theory. Although the underlying spin model intrinsically supports strong quantum fluctuations, as confirmed by quantum Monte Carlo simulations, the real system shows an anomalously complete suppression of quantum behavior. These findings provide a key experimental benchmark for the quantum-classical crossover and suggest that lattice topology can play a crucial role in tuning the balance between quantum and classical physics in strongly correlated systems.
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All authors Hironori Yamaguchi, Itsuki Shimamura, Akira Matsuo, Koichi Kindo, Koji Araki, Yoshiki Iwasaki, Masayuki Hagiwara

Materials Science

Anion correlation induced nonrelativistic spin splitting in rutile antiferromagnets

Siddhartha S. Nathan, Danilo Puggioni, Linding Yuan et al. (+1 more)

Many studies of non-relativistic spin-splitting (NRSS), or altermagnetism, have focused on idealized, perfectly ordered crystals, relying on symmetry-based approaches to identify candidate materials. Here, we theoretically investigate how local short-range ordering (SRO) influences NRSS of energy bands in partially ordered collinear antiferromagnetic iron oxyfluoride (FeOF). Using the cluster expansion method, we identify four nearly degenerate structures (energy difference $\leq 8$ meV per formula unit) that represent distinct snapshots of local plane-to-plane O/F correlations. Our density functional theory (DFT) results show robust NRSS along the $\Gamma$-M direction in all four structures, despite the absence of long-range order. The magnitude and character of the splitting depend sensitively on the specific direction of anion correlations, effects that are not fully captured in high-symmetry average structures. Notably, two configurations ($Pmc2_1$ and $Pm$) exhibit $\Gamma$-point spin splitting absent in ordered FeF$_2$ and a virtual crystal approximation model of FeOF. We further predict distinct magneto-optical Kerr effect (MOKE) signatures, enabling experimental detection of SRO-driven electronic structure changes. These results highlight heteroanionic compounds as a promising design space for NRSS antiferromagnets, with experimentally synthesized FeOF already exhibiting a substantially higher Néel temperature (315\,K) than FeF$_2$ (79\,K).
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All authors Siddhartha S. Nathan, Danilo Puggioni, Linding Yuan, James M. Rondinelli

Materials Science

Random Combinatorial Libraries and Automated Nanoindentation for High-Throughput Structural Materials Discovery

Vivek Chawla, Dayakar Penumadu and Sergei Kalinin

Accelerating the discovery of structural materials is essential for applications in hard and refractory alloys, hypersonic platforms, nuclear systems, and other extreme environment technologies. Progress is often constrained by slow synthesis and characterization cycles and the need for extensive mechanical testing across large compositional spaces. Here, we propose a rapid screening strategy based on random material libraries, in which thousands of distinct compositions are embedded within a single specimen, mapped by EDS, and subsequently characterized. Using nanoindentation as a representative case, we show that such libraries enable dense composition property mapping while reducing the number of samples required to explore high dimensional composition spaces compared to traditional synthesis and test workflows. An experimentally calibrated Monte Carlo framework is developed to quantify practical limits, including particle size, EDS noise and resolution, positional accuracy, and nanoindenter motion costs. The simulations identify regimes where random libraries provide orders of magnitude acceleration over classical workflows. Finally, we demonstrate experimental navigation of these libraries using automated indentation. Together, these results establish random libraries as a general route to high throughput characterization in structurally critical material systems.
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Materials Science

Epitaxial Recovery of beta-Ga2O3 after High Dose Implantation

Tianhai Luo, Katie R. Gann, Cameron A. Gorsak et al. (+3 more)

As an ultrawide bandgap semiconductor, beta-Ga2O3 has been attractive for its strong tolerance to irradiation damage and high n-type conductivity through ion implantation. Homoepitaxial (010) e̱ta}-Ga2O3 films grown by MOCVD were implanted with Ge to study the post-implantation damage and lattice recovery after thermal annealing. Box profiles of 100 or 50 nm at concentration of 5*10^19 or 3*10^19 cm^-3 were formed, with maximum displacement per atom (DPA) of 1.2 or 2.0. Lattice recovery was investigated using X-ray diffraction (XRD) for anneals from 100 C to 1050 C. A gamma-phase related peak was observed for all implant conditions. All samples showed strain relaxation of beta-phase peak at temperature below 500 C, with no significant change for the gamma-phase related peak. For lower damage implants, films recovered fully to epitaxial beta-phase after sequential annealing to 900 C. For the higher damage implant, the gamma-phase associated peak annealed out with increasing temperature, but a new diffraction peak formed at slightly smaller lattice spacing; full recovery of the lattice was not observed until annealing at 1050 C. The newly formed diffraction peak is identified as beta-(20-4), beta-(512), or beta-(71-2), each potentially arising from the conversion of gamma-phase to beta-phase via a common oxygen sub-lattice.
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All authors Tianhai Luo, Katie R. Gann, Cameron A. Gorsak, Hari P. Nair, R. B. van Dover, Michal O. Thompson

Materials Science

Simultaneous power generation and cooling using semiconductor-sensitized thermal cells

Atsushi Hayashida, Hitoshi Saito, Yang Chunxiang et al. (+5 more)

This manuscript reports a semiconductor-sensitized thermal cell (STC) that converts ambient heat into electrical power while simultaneously reducing its own temperature under isothermal conditions. Using a printable semiconductor–electrolyte architecture, we fabricate $4\,\mathrm{cm} \times 4\,\mathrm{cm}$ devices that generate up to approximately $0.2\,\mathrm{mW}$ at temperatures of $40$–$55\,^\circ\mathrm{C}$. During continuous discharge, the STC exhibits a transient temperature decrease followed by thermal equilibration with the environment. In contrast, periodic on–off discharge produces sustained cooling of approximately $1\,^\circ\mathrm{C}$ relative to a non-discharging reference. Notably, parallel integration of four STCs yields a nonlinear enhancement of cooling (approximately $5\,^\circ\mathrm{C}$) without a corresponding increase in electrical output. The observed behavior can be understood within a macroscopic energy-balance framework, in which time modulation of electrochemical heat consumption prevents the establishment of thermal steady state. These results demonstrate sustained isothermal cooling induced by heat-to-electricity conversion at practical device scales, and highlight semiconductor-sensitized thermal cells as a platform for coupled energy harvesting and thermal management.
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All authors Atsushi Hayashida, Hitoshi Saito, Yang Chunxiang, Taiga Nishii, Motokazu Ishihara, Yuta Nakamura, Kento Sunaga, Sachiko Matsushita

Friday 12 December

Materials Science

Perturbative second-order optical susceptibility of bulk materials: a symmetry-enforced return to non-orthogonal localized basis sets

Angiolo Huaman, Luis Enrique Rosas-Hernandez and Salvador Barraza-Lopez

The second-order optical susceptibility of semiconductors $\chi_{ijk}^{(2)}(-2\omega;\omega,\omega)$ finds application in metrology, spectroscopy, telecommunications, material characterization, and quantum information. Pioneering calculations of $\chi_{ijk}^{(2)}(-2\omega;\omega,\omega)$ utilized non-orthogonal Gaussian orbitals centered at atoms. That formulation transitioned into plane-wave-based algorithms as time went by. As of late, nevertheless, multiple tools for calculating optical susceptibilities have recast the problem using Wannier (i.e., localized) orbitals, making a comeback onto frameworks based on localized basis sets. Here, we present an approach for calculating $\chi_{ijk}^{(2)}(-2\omega;\omega,\omega)$ reliant on numerical pseudoatomic orbitals (PAOs) within perturbation theory in the velocity gauge. Its salient feature is a calculation of `Slater-Koster-like' two-center integrals of the momentum operator in between PAOs identified by symmetry. The approach was successfully tested on paradigmatic cubic silicon carbide (3C-SiC) and gallium arsenide, for which linear responses are contributed as well.
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Materials Science

In situ Study of p-NiO Film Quality at High Temperatures up to 1100 deg C

Hunter Ellis, Bobby G. Duersch, Botong Li et al. (+4 more)

NiO is a promising p-type material for photovoltaics and power electronics, but its temperature limits remain unclear. Using in situ high-temperature X-ray diffraction (HT-XRD) from 30 to 1100 C, we track the structural evolution of NiO thin films in air. The film crystallizes from an amorphous phase to cubic NiO between 300 and 400 C, where the emergence and growth of the (111) diffraction peak correlate with an increase in electrical resistivity. Further increases in temperature lead to improved crystallinity and higher resistivity. At 1100 C, the formation of Ni2O3 is observed, resulting in a highly resistive film. This study establishes a clear correlation between phase evolution, crystallinity, and resistive behavior in NiO thin films.
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All authors Hunter Ellis, Bobby G. Duersch, Botong Li, Imteaz Rahaman, Jim Pierce, Michael A. Scarpulla, Kai Fu

Materials Science

van der Waals Nanoreactors

Zhaoyi Joy Zheng, Haosen Guan, Danrui Ni et al. (+11 more)

Advancing the chemical synthesis of crystals is important for both fundamental research and practical applications of quantum materials. While established bulk-phase and thin-film growth methods have enabled enormous progress, synthesizing single crystals suitable for quantum electronic discoveries remains challenging for many emerging materials. Here, we introduce van der Waals (vdW) stacks as nanochemical reactors for single-crystal synthesis and demonstrate their broad applicability in growing both elemental and compound crystals at the micrometer scale. By encapsulating atomically thin reactants that are stacked compactly with inert vdW layers such as hexagonal boron nitride (hBN), we achieve nanoconfined synthesis with the resulting crystals remaining encapsulated. As proof of concept, we synthesized isolated single crystals of elemental tellurium and distinct types of Pd-Te compounds. Structural characterization, including atomic-resolution scanning transmission electron microscopy, confirms the high crystalline quality of the products. We confirm the intrinsic semiconducting gap of tellurium and observe that non-stoichiometric PdTe1-x with a significantly reduced Te content (x ~ 0.18, a regime not previously achieved) retains uniform crystallinity and exhibits superconductivity below a critical temperature of 3.8 K. This nanochemical synthesis is broadly generalizable, chip-integrable, well-suited to a wide range of processing conditions, and compatible with nanofabrication routines for constructing devices. The concept of vdW nanoreactors offers a powerful and versatile pathway to expand the accessible landscape of quantum materials.
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All authors Zhaoyi Joy Zheng, Haosen Guan, Danrui Ni, Guangming Cheng, Yanyu Jia, Ipsita Das, Yue Tang, Ayelet July Uzan-Narovlansky, Lihan Shi, Kenji Watanabe, Takashi Taniguchi, Nan Yao, Robert J Cava, Sanfeng Wu

Materials Science · Cross-listed from cs.AI

AGAPI-Agents: An Open-Access Agentic AI Platform for Accelerated Materials Design on AtomGPT.org

Jaehyung Lee, Justin Ely, Kent Zhang et al. (+3 more)

Agentic AI systems increasingly connect large language models (LLMs) to external scientific tools, yet whether and when tool access improves prediction accuracy remains uncharacterized. We present AGAPI (AtomGPT.org API), an open access platform integrating eight open-source LLMs with 18 REST endpoints (28 agent tools, 50 web apps) spanning materials databases, force fields, tight-binding band structures, X-ray diffraction, and protein structure. A three-evaluation residual decomposition on JARVIS-Leaderboard electronic-structure test sets separates agent pipeline fidelity from inherited density functional theory (DFT) functional bias. For bulk modulus and bandgap the agent reproduces JARVIS-DFT entries to numerical precision, so the experimental-reference degradation is functional bias, not agentic malfunction. On memorization-resistant test sets (57 defective supercells, 60 hypothetical compositions), tool-augmented mean absolute error (MAE) is below 0.005 eV versus 1.25 to 1.86 eV tool-free, confirming tools are indispensable where parametric knowledge is unavailable. We further demonstrate autonomous multi-step workflows including 10-operation defect-engineering pipelines. AGAPI is available at https://github.com/atomgptlab/agapi.
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All authors Jaehyung Lee, Justin Ely, Kent Zhang, Akshaya Ajith, Charles Rhys Campbell, Kamal Choudhary

Materials Science · Cross-listed from cond-mat.soft

Elastocapillary adhesion of soft gel microspheres

Joseph N. Headley, Edgar W. Lyons, Mathew Q. Giso et al. (+6 more)

Softer means stickier for solid adhesives, because material compliance facilitates close contact between non-conformal surfaces. Recent discoveries have revealed that soft materials can exhibit a rich array of new physics arising from competing effects of continuum elasticity, fluid-like surface mechanics, and internal poroelastic flows, all of which can directly impact interfacial interactions. In this work, we investigate this complex interplay across several orders of magnitude of elastic stiffness by measuring the complete adhesive contact geometry between compliant silicone gel microspheres and flat, rigid substrates. We observe a continuous elastocapillary transition in adhesion mechanics, with novel features revealed by both the breadth of data and the detailed contact geometries. Importantly, soft gel spheres exhibit a remarkably broad range of near-equilibrium contact morphologies and their contact line deformation is always mediated by a fluid contact zone that phase separates from the gel. To explain this, we develop a new model incorporating elastocapillary and poroelastic mechanics that predicts the complete range of adhesive behavior and elucidates energetic tradeoffs. The data and model together reveal a shallow energy landscape that may contribute to the robustness of everyday adhesives.
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All authors Joseph N. Headley, Edgar W. Lyons, Mathew Q. Giso, Emily P. Kuwaye, Caroline D. Tally, Aidan J. Duncan, Chaitanya Joshi, Timothy J. Atherton, Katharine E. Jensen

Materials Science

Valley-dependent electronic properties in two-dimensional altermagnetic iron-based transition metal chalcogenides

An-Dong Fan, Yong-Kun Wang, Jin-Yang Li et al. (+1 more)

Altermagnets represent a newly identified third class of collinear magnets and have recently emerged as a focal point in condensed matter physics. In this work, through first-principles calculations and theoretical analysis, we identify monolayer Fe$_2$MoX$_4$ (X = S, Se, Te) and Fe$_2$WTe$_4$, a class of iron-based transition metal chalcogenides, as promising altermagnetic materials. These systems are found to be semiconductors exhibiting spin splitting in their nonrelativistic band structures, indicative of intrinsic altermagnetic ordering. Remarkably, their valence bands feature a pair of valleys at the time-reversal-invariant momenta X and Y points. Unlike conventional valley systems, these valleys are related by crystal symmetries rather than time-reversal symmetry. We investigate valley-dependent physical phenomena in these materials, including Berry curvature and optical circular dichroism, revealing strong valley-contrasting behavior. Furthermore, we investigate the effect of uniaxial strain and show that it effectively lifts the valley degeneracy, resulting in pronounced valley polarization. Under hole doping, this strain-induced asymmetry gives rise to a piezomagnetic response. We also explore the generation of anisotropic noncollinear spin currents in these systems, expanding the scope of their spin-related functionalities. Our findings unveil rich valley physics in monolayer Fe$_2$MoX$_4$ (X = S, Se, Te) and Fe$_2$WTe$_4$, highlighting their significant potential for applications in valleytronics, spintronics, and multifunctional nanoelectronic devices.
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All authors An-Dong Fan, Yong-Kun Wang, Jin-Yang Li, Si Li