Materials Science · Cross-listed from cond-mat.mes-hall
Spontaneous Polarization Suppression of Exciton-Exciton Annihilation in 3R-Stacked MoS$_2$ Bilayers
Tae Gwan Park, Xufan Li, Kyungnam Kang et al. (+4 more)
Rapid
exciton-
exciton annihilation (EEA) in two-dimensional
semiconductors limits access to high-density excitonic regimes essential for efficient optoelectronic operation under strong excitation. Here, we show that EEA is suppressed by repulsive dipole-dipole interactions between interlayer
excitons polarized by the spontaneous polarization intrinsic to rhombohedral (3R)-stacked MoS$_2$
bilayers. Using ultrafast pump-probe spectroscopy, we measure an EEA rate of $\gamma_{\rm EEA}=(5.03\pm0.99)\times10^{-3}$ cm$^2$ s$^{-1}$ in 3R
bilayers, which is approximately 18.2-fold smaller than that in monolayers and 2.9-fold smaller than that in nonpolar 2H
bilayers. Despite the higher
exciton diffusivity recently reported for 3R relative to 2H
bilayers, the reduced EEA rate in 3R indicates a rate-limited regime governed by the close-encounter annihilation probability rather than
diffusion. A rate-limited annihilation model incorporating a dipole-dipole repulsive potential captures the observed ratio $\gamma_{{\rm EEA},3{\rm R}}/\gamma_{{\rm EEA},2{\rm H}}\approx0.35$ for an
exciton-
exciton encounter distance of $\sim$1.3 nm, consistent with the
bilayer exciton Bohr radius. These results show that spontaneous polarization in 3R-stacked
bilayers suppresses nonlinear excitonic losses and provides a route toward high-density excitonics.
Read the full abstract ▾
All authors Tae Gwan Park, Xufan Li, Kyungnam Kang, David B. Geohegan, Christopher M. Rouleau, Alexander A. Puretzky, Kai Xiao
Materials Science · Cross-listed from quant-ph
Die to wafer direct bonding of (100) single-crystal diamond thin films for quantum optoelectronics
Dominic Lepage, Amin Yaghoobi, Heidi Tremblay et al. (+1 more)
This work unlocks the manufacturing of nanophotonic
quantum systems that exploit the unique material properties of single-
crystal diamond (SCD). We achieve this by introducing a
semiconductor-compatible process for the direct bonding of multiple high-quality, ultrathin diamond films onto a carrier wafer, enabling the subsequent parallel nanofabrication of optoelectronic integrated
circuits. Central to this approach is a new diamond surface-preparation method that avoids boiling tri-acid mixtures while producing exceptionally clean 20 um thin single
crystals. These platelets are bonded side-by-side to 100 mm silica wafers and exhibit a record shear strength of 45.1 MPa for (100)-oriented diamond, surpassing all previously reported bonding attempts. Evidence indicates that the bonding is dominated by van der Waals interactions, likely arising from mismatched protonation mechanisms between Si-OH and C-OH surface terminations, rather than from covalent-bond-driven mechanisms. Despite this non-molecular nature, the
heterostructures remain stable through
liquid immersions and standard nanofabrication steps. Because the method depends primarily on surface cleanliness and roughness rather than specific chemistries, it is broadly transferable across wafer materials. This capability to parallel-bond ultrathin SCD films onto large-area substrates provides a scalable route to high-performance platforms spanning nanophotonic
quantum technologies, high-power electronics, MEMS, and biotechnology.
Read the full abstract ▾
All authors Dominic Lepage, Amin Yaghoobi, Heidi Tremblay, Dominique Drouin
Materials Science
Spin crossover in FeO under shock compression
Lélia Libon, Alessandra Ravasio, Silvia Pandolfi et al. (+17 more)
FeO (wüstite), which exhibits complex electronic and structural properties with increasing pressure and temperature, is a key mineralogical phase for understanding deep planetary interiors. However, direct measurements of its
spin state at high-pressure and temperature remain challenging in static compression experiments. Here, we employ
laser-driven shock compression to extend the FeO principal Hugoniot up to $\sim$900 GPa and perform in situ X-ray diffraction and X-ray emission spectroscopy up to 250 GPa, probing FeO's
crystal structure and
spin state. We demonstrate a continuous
spin crossover of iron in FeO over a broad pressure range, with the high-
spin state persisting beyond Earth's core-mantle boundary (CMB) conditions. These observations provide new experimental constraints on iron
spin state at extreme conditions essential for geophysical models of (exo)planetary interiors.
Read the full abstract ▾
All authors Lélia Libon, Alessandra Ravasio, Silvia Pandolfi, Yanyao Zhang, Xuehui Wei, Jean-Alexis Hernandez, Hong Yang, Amanda J. Chen, Tommaso Vinci, Alessandra Benuzzi-Mounaix, Clemens Prescher, François Soubiran, Hae Ja Lee, Eric Galtier, Nick Czapla, Wendy L. Mao, Arianna E. Gleason, Sang Heon Shim, Roberto Alonso-Mori, Guillaume Morard
Materials Science
Engineering Quantum Phases in Two Dimensions via Vacancy-Induced Electronic Reconstruction
Emmanuel V. C. Lopes, Felipe Crasto de Lima, Caio Lewenkopf et al. (+1 more)
Topological phases of matter are commonly understood as emerging either from crystalline
symmetry and intrinsic
spin-orbit coupling or from disorder-driven electronic renormalization. In realistic materials, however, structural defects naturally combine both ingredients. Here, we demonstrate a general and material-independent mechanism by which atomic vacancies can induce topological phase transitions in two-dimensional
semiconductors that are otherwise topologically trivial. Vacancies generate locally ordered dangling-bond states governed by well-defined hopping and
spin-orbit interactions, while their spatial distribution and mutual coupling introduce long-range disorder. As vacancy concentration increases, the hybridization of these defect states forms an emergent electronic subspace that undergoes a topological transition. Using a tight-binding framework supported by large-scale density functional theory calculations, we show that this vacancy-induced electronic reconstruction can robustly stabilize
quantum spin Hall,
quantum anomalous
Hall, and Weyl semimetal phases, depending on
symmetry breaking and
spin polarization. Our results establish vacancies not merely as perturbations, but as active design elements capable of transforming trivial
insulators into topological
quantum matter, opening realistic routes for defect-engineered topological devices.
Read the full abstract ▾
All authors Emmanuel V. C. Lopes, Felipe Crasto de Lima, Caio Lewenkopf, Adalberto Fazzio
Materials Science · Cross-listed from cond-mat.soft
Breakloose suppression in minimal friction models
Shubham Agarwal
Breakloose friction, the transient force peak at the onset of sliding, is often pronounced in nanoscale contacts but weak or absent in macroscopic systems. Although this behavior is commonly associated with rupture fronts and process-zone effects, how the stiction peak is controlled by system size, temperature, driving rate, and loading geometry, and what mechanisms underlie its emergence or suppression, remains incompletely understood. Here we investigate this problem using three minimal friction models with distinct loading geometries: a multi-particle Prandtl-Tomlinson system with independently driven particles, an end-driven Frenkel-Kontorova chain with elastic stress transmission along the interface, and a uniformly driven FK chain in which each site is coupled locally to the driving stage. We show that similar macroscopic suppression of breakloose friction can arise from fundamentally different mechanisms. In multi-particle PT systems, increasing system size or temperature promotes statistical dephasing of local depinning events, smoothing the global response. In end-driven FK chains, internal elasticity redistributes stress along the interface, delaying sliding onset and, together with higher temperature or slower driving, enabling progressive relaxation during loading. In uniformly-driven FK chains, the stiffness of the driving springs controls the synchronization of slip events and thereby the character of the sliding response. These results demonstrate that the presence or absence of a breakloose peak does not uniquely identify a single physical mechanism, but instead reflects the interplay of local pinning, elastic coupling, and contact architecture.
Read the full abstract ▾
Materials Science
Accelerating Structure-Property Relationship Discovery with Multimodal Machine Learning and Self-Driving Microscopy
Jiawei Gong, Danqing Ma, Ralph Bulanadi et al. (+4 more)
Microscopy combined with local spectroscopy is widely used to correlate nanoscale structure with functional properties in materials, but conventional measurements rely heavily on human-selected sampling locations and predefined targets, limiting
dataset diversity and the potential for discovery. Here, we present a framework that integrates autonomous microscopy with a dual-novelty deep kernel learning (DN-DKL) for adaptive data acquisition and a dual variational autoencoder (VAE) for representation learning. DN-DKL actively guides the microscopy toward structurally and spectroscopically novel regions, enabling efficient collection of large spectral
datasets. Dual-VAE embeds local structure and spectroscopic responses into a shared latent
manifold that serves as a structure-property relationship map. We applied this framework for the investigation of halide perovskite films using conductive atomic force microscopy. The results reveal distinct hysteresis behaviors that are linked to specific nanoscale structural motifs, including grain boundary junction points that show hysteresis under different bias conditions and asymmetric grain boundaries that suppress charge transport. This framework establishes a general strategy that leverages the complementary strengths of self-driving microscopy, machine learning, and human expertise to accelerate scientific discovery in functional materials.
Read the full abstract ▾
All authors Jiawei Gong, Danqing Ma, Ralph Bulanadi, Robert Moore, Rama Vasudevan, Lianfeng Zhao, Yongtao Liu
Materials Science · Cross-listed from cond-mat.mes-hall
Maxim Trushin
Field emission from metals underpinned early
vacuum-tube technology, and recent nanoscale engineering made field-emission devices compatible with modern silicon platforms. However, the limited tunability of electron transport in metals has restricted their applicability. Here, we show that noble metals coated with
graphene exhibit clean non-monotonic $I-V$ characteristics arising from resonant tunneling through
graphene's electronic states, enabled by
graphene's atomic thinness and weak electronic hybridization with noble metals. Our approach combines ab-initio interface parameters with exact solutions of the Schrödinger equation for electron transmission across the interface. We analyze two experimentally relevant geometries: a vertical configuration with a flat suspended emitter and a coplanar configuration with sharp electrodes allowing for strong field enhancement and gating. These results establish a practical route to tunable electron transport in metal
heterostructures, positioning them as competitive components for air-channel field-emission nanoelectronics.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.soft
Hydrodynamic Modeling of Odd Nematic Elasticity in Liquid Crystals
Zeyang Mou, Haijie Ren, Ding Xu et al. (+2 more)
There is a recent interest in studying odd elasticity in soft solids. Current focus has been on simple solids. However, many soft solids are structured and can exhibit nematic elasticity or viscoelasticity. Here we generalize the concept of odd elasticity to nematic elasticity. By rewriting the governing equation for two-dimensional nematic
liquid crystals (LCs) in terms of complex Ginzburg–Landau equation, we propose an odd nematic elastic term and its stress term in the hydrodynamic model of nematic LCs. The odd nematic elasticity can be physically interpreted as non-reciprocal interactions between neighboring directors. In odd nematics we find that domain walls become self-propelled and are accompanied by a bidirectional flow, and point defects can self-
spin, develop a spiral pattern, and induce a vortical flow. Interactions of a pair of defects show rich dynamics that are distinct from those in active nematics. As such, we have developed an odd general elasticity, which can be further generalized to other viscoelastic materials, and proposed a novel way to manipulate topological defects in nematic LCs.
Read the full abstract ▾
All authors Zeyang Mou, Haijie Ren, Ding Xu, Igor S. Aranson, Rui Zhang
Materials Science
From pore collapse to crystal growth: ultrafast laser-induced stishovite formation in nanoporous silica
Aram Yedigaryan, Mohamed Yaseen Noor, Elena Kachan et al. (+4 more)
The crystallization of amorphous solids under ultrafast
laser irradiation represents a paradigm of non-
equilibrium phase transitions, where the interplay between electromagnetic energy localization and atomic-scale dynamics remains largely uncharted. By using a multiscale framework that couples finite-difference time-domain simulations of nonlinear femtosecond
laser pulse propagation with molecular dynamics of the atomic response, we demonstrate that field enhancement around the pores of nanoporous amorphous silica confines
laser energy and drives rapid pore collapse. In nanoporous silica, the enhanced local electromagnetic field leads to stronger energy absorption compared with smaller-pore and homogeneous systems. This heterogeneous energy localization provides preferential nucleation sites within the dense glass network, leading to ultrafast formation of stishovite on a sub-nanosecond timescale, faster than in homogeneous silica. This accelerated crystallization can outpace pressure relaxation making the transition to a high-pressure phase possible. These results are confirmed by experimental observations of femtosecond-
laser-induced crystallization in confined geometries, and show that electromagnetic hotspots in nanoporous glass structures can be tailored to control solid-state transformations.
Read the full abstract ▾
All authors Aram Yedigaryan, Mohamed Yaseen Noor, Elena Kachan, Gabriel Calderon, Jinwoo Hwang, Enam Chowdhury, Jean-Philippe Colombier
Materials Science
Data-knowledge dual-driven intelligent framework for full-chain, experiment-efficient synthesis of 2D dendrites
Wenqiang Huang, Xuhang Gu, Susu Fang et al. (+9 more)
Exemplified by the chemical vapor deposition growth of two-dimensional dendrites, which has potential applications in catalysis and presents a parameter-intensive, data-scarce and reaction process-complex model problem, we devise a machine intelligence-empowered framework for the full chain support of material synthesis, encompassing rapid process optimization, accurate customized synthesis, and comprehensive mechanism deciphering.First, active learning is integrated into the experimental workflow, identifying an optimal recipe for the growth of highly-branched, electrocatalytically-active ReSe2 dendrites through 60 experiments (4 iterations), which account for less than 1.3% of the numerous possible parameter combinations.Then, a prediction accuracy-guided data augmentation strategy is developed combined with a tree-based machine learning (ML)
algorithm, unveiling a non-linear correlation between 5 process variables and fractal dimension (DF) of ReSe2 dendrites with only 9 experiment additions, which guides the synthesis of various user-defined DF. Finally, we construct a data-knowledge dual-driven mechanism model by integration of cross-scale characterizations, interpretable ML models, and domain knowledge in thermodynamics and kinetics, unraveling synergistic contributions of multiple process parameters to the product morphology. This work demonstrates the ML potential to transform the research paradigm and is adaptable to broader material synthesis.
Read the full abstract ▾
All authors Wenqiang Huang, Xuhang Gu, Susu Fang, Shen'ao Xue, Huanhuan Xing, Junjie Jiang, Junying Zhang, Shen Zhou, Zheng Luo, Jin Zhang, Fangping Ouyang, Shanshan Wang
Materials Science · Cross-listed from cs.CV
What DINO saw: ALiBi positional encoding reduces positional bias in Vision Transformers
Moritz Pawlowsky, Antonis Vamvakeros, Alexander Weiss et al. (+3 more)
Vision transformers (ViTs) - especially feature foundation models like DINOv2 - learn rich representations useful for many downstream tasks. However, architectural choices (such as positional encoding) can lead to these models displaying positional biases and artefacts independent of semantic content. This makes zero-shot adaption difficult in fields like material science, where images are often cross-sections of homogeneous microstructure (i.e. having no preferred direction). In this work, we investigate the positional bias in ViTs via linear probing, finding it present across a range of objectives and positional encodings, and subsequently reduce it by finetuning models to use ALiBi relative positional encoding. We demonstrate that these models retain desirable general semantics and their unbiased features can be used successfully in trainable
segmentation of complex microscopy images.
Read the full abstract ▾
All authors Moritz Pawlowsky, Antonis Vamvakeros, Alexander Weiss, Anja Bielefeld, Samuel J. Cooper, Ronan Docherty
Materials Science
Phonon collisional broadening and heat transport beyond the Boltzmann equation
Enrico Di Lucente, Nicola Marzari and Michele Simoncelli
In
crystals, macroscopic technological properties such as thermal conductivity originate from the microscopic drift and scattering of
phonons, commonly described by the Boltzmann Transport Equation (BTE). Despite its widespread use, the most general space-time nonlocal form of the BTE still lacks a rigorous derivation of its collisional part based on
Fermi's Golden Rule (FGR), and becomes inadequate in several regimes, including when the energy-variation scale set by
phonon dispersion approaches that of collisional broadening. A hallmark of this issue is the poor numerical convergence of conductivity with respect to the smearing used to evaluate FGR rates. This is often circumvented using adaptive schemes, which however violate detailed balance and allow unphysical negative
eigenvalues in the collision operator. Here, we overcome these limitations by rigorously deriving the space-time-dependent BTE from the Kadanoff-Baym Equations (KBE), and introduce a linearized generalized BTE (LGBTE) that goes beyond the FGR framework, incorporating self-consistent, physically derived, fully anharmonic, and mode-resolved collisional broadening and energy-nonconserving scattering. More generally, we establish a hierarchy of ansätze on Green's functions, enabling controlled extensions of the semiclassical BTE and a roadmap toward
quantum KBE accuracy. Finally, using first-principles simulations complemented by analytical arguments, we show that this approach addresses two long-standing problems of the FGR-based linearized BTE across
crystal dimensionalities: (i) the lack of conductivity convergence, common to heat conductors like diamond; and (ii) its universal failure in all 2D systems, rooted in FGR predicting an unphysical overdamping for scattering channels involving flexural vibrations, as shown in the insulating {\alpha}-GeSe monolayer.
Read the full abstract ▾
Materials Science
Low bending rigidity and large Young's modulus drive strong flexural phonon renormalization in two-dimensional monolayers
Navaneetha K Ravichandran
Many intriguing phenomena such as the wave-like hydrodynamic heat flow, the logarithmic divergence of electrical resistivity at low temperatures and microscale kirigami are driven by flexural acoustic (ZA)
phonons in two-dimensional (2D) materials. Yet, a definitive first-principles description of their dispersion, with explicit consideration of the
crystal anharmonicity and the stability of large 2D monolayers against thermal fluctuations, is lacking in the literature. Using first-principles calculations, we show that the bending
rigidity ($\kappa$) controls the anharmonic renormalization of the ZA
phonons throughout the Brillouin zone in 2D monolayers, with stronger renormalization in low-$\kappa$ materials like germanene and weaker effects in high-$\kappa$ materials like molybdenum disulphide. Furthermore, the ZA
phonons at long wavelengths undergo an additional renormalization to stabilize the flat phase of the 2D monolayers against thermal fluctuations, which is modulated by the competing influence of the bending
rigidity and the in-plane Young's modulus in all materials. The resulting renormalized ZA
phonon dispersions are qualitatively and quantitatively different from those commonly used by the first-principles community, thus motivating a re-examination of the ZA
phonon-driven unconventional thermal and electronic phenomena in 2D as well as lower-dimensional systems. Our work provides new insights into the role of nanoscale
crystal anharmonicity and macroscale elasticity in shaping the vibrational properties of 2D materials and will inform novel engineering applications that are exclusive to low dimensions such as kirigami, with materials beyond
graphene.
Read the full abstract ▾
Materials Science · Cross-listed from cs.LG
Novelty-Driven Target-Space Discovery in Automated Electron and Scanning Probe Microscopy
Utkarsh Pratiush, Kamyar Barakati, Boris N. Slautin et al. (+4 more)
Modern automated microscopy faces a fundamental discovery challenge: in many systems, the most important scientific information does not reside in the immediately visible image features, but in the target space of sequentially acquired spectra or functional responses, making it essential to develop strategies that can actively search for new behaviors rather than simply optimize known objectives. Here, we developed a deep-kernel-learning BEACON framework that is explicitly designed to guide discovery in the target space by learning structure-property relationships during the experiment and using that evolving model to seek diverse response regimes. We first established the method through demonstration workflows built on pre-acquired ground-truth
datasets, which enabled direct benchmarking against classical acquisition strategies and allowed us to define a set of monitoring functions for comparing exploration quality, target-space coverage, and surrogate-model behavior in a transparent and reproducible manner. This benchmarking framework provides a practical basis for evaluating discovery-driven
algorithms, not just optimization performance. We then operationalized and deployed the workflow on STEM, showing that the approach can transition from offline validation to real experimental implementation. To support adoption and extension by the broader community, the associated notebooks are available, allowing users to reproduce the workflows, test the
benchmarks, and adapt the method to their own instruments and
datasets.
Read the full abstract ▾
All authors Utkarsh Pratiush, Kamyar Barakati, Boris N. Slautin, Catherine C. Bodinger, Christopher D. Lowe, Brandi M. Cossairt, Sergei V. Kalinin
Materials Science
Ligand-Controlled Phonon Dynamics in CsPbBr3 Nanocrystals Revealed by Machine-Learned Interatomic Potentials
Seungjun Cha, Chen Wang, Victor Fung et al. (+1 more)
Halide perovskite nanocrystals are leading candidates for next-generation optoelectronics, yet the role of surface ligands in controlling their
phonon dynamics remains poorly understood. These dynamics critically govern nonradiative relaxation, energy up-conversion, and
phonon-assisted anti-Stokes emission. Conventional ab initio methods, while accurate, are computationally infeasible for experimentally relevant nanocrystal sizes that require thousands of atoms to capture realistic ligand shells and dynamic disorder at finite temperatures. Here, we introduce a machine- learned interatomic potential fine-tuned on small CsPbBr3 nanocrystals with diverse ligands, enabling accurate prediction of ligand-induced
phonon properties far beyond the spatial and temporal scales of ab initio methods. We find that both cationic and anionic ligands systematically
redshift Pb-Br-Pb stretching modes while blueshifting the PbBr64- octahedral rotation mode, with stronger overall effects for anionic passivation. Notably, anionic ligands stiffen the rotation mode non-monotonically with respect to the ligand binding energy. Our findings reveal important roles of cationic and anionic ligands in modulating key dynamic modes of halide perovskite nanocrystals associated with detrimental nonradiative losses, offering mechanistic insights and design principles for high-performance perovskite nanocrystal optoelectronics.
Read the full abstract ▾
All authors Seungjun Cha, Chen Wang, Victor Fung, Guoxiang Hu
Materials Science · Cross-listed from physics.ins-det
Advances in the Fabrication of On-chip Superconducting Integral Field Units for CMB and Line-Intensity Astronomy
L. G. G. Olde Scholtenhuis, D. Perez Capelo, K. Karatsu et al. (+7 more)
Studying the polarization and spectral distortion of the
Cosmic Microwave Background (CMB) in tandem with intensity fluctuations of the
Cosmic Infrared Background (CIB) allows us to verify our assumptions on
cosmic inflation and investigate the dynamics and
evolution of
galaxy clusters in the last 10 billion years. Because of its broadband emission and being an all-sky extended source, observing the entire CMB in detail is a very time-consuming and expensive exercise. Fortunately, in the last few years, the on-chip superconducting spectrometer technology has moved out of the lab and into the
telescope. With its compact size and background-limited sensitivity, this family of instruments is particularly well-suited for fast and large area observations in a relatively unexplored range of the electromagnetic spectrum. However, recent examples of this technology do not yet reach the requirements needed for large spectroscopic and polarimetric surveys of the CMB. We formulate several of these requirements and introduce novel on-chip components and fabrication techniques. We introduce a cross-over to enable distinguishing signal polarization, minimize signal loss by locally optimized lithography of a coplanar-waveguide (CPW), lower the spectral resolution of microstrip filters by deposition of a dielectric layer, and increase the yield of the spectrometer array by removing individual line shorts. These together have culminated in the successful fabrication of a fourteen-spaxel IFU.
Read the full abstract ▾
All authors L. G. G. Olde Scholtenhuis, D. Perez Capelo, K. Karatsu, D. J. Thoen, A. J. van der Linden, S. O. Dabironezare, L. H. Marting, J. J. A. Baselmans, S. Vollebregt, A. Endo
Materials Science
$\mathrm{Cs_3V_9Te_{13}}$: A New Vanadium-Based Material with a Reuleaux-Triangle-Like Lattice and a Possible Phase Transition near 48 K
Zhen Zhao, Jianping Sun, Xin-Wei Yi et al. (+10 more)
Exploring and synthesizing materials with new
crystal structures provides an important route to discovering exotic
quantum phenomena. However, materials with unconventional
lattice geometries remain largely unexplored. Here, we report the discovery of a new vanadium-based material, $\mathrm{Cs_3V_9Te_{13}}$, featuring a Reuleaux-triangle-like
lattice. Electrical transport and
magnetic measurements consistently reveal an anomaly near 48 K, and this feature shows little sensitivity to the applied
magnetic field. A corresponding anomaly is also observed in the
Hall coefficient near 48 K, indicating a marked change in the carrier response. In addition, temperature-dependent x-ray diffraction results indicate no obvious structural change across 48 K. Taken together, these results suggest that the anomaly is not induced by the structural transition, but associated to a possible electronic and/or
magnetic phase transition. High-pressure transport measurements and first-principles calculations further reveal a highly tunable electronic state in $\mathrm{Cs_3V_9Te_{13}}$, with the kagome-like electronic feature and pressure-suppressed antiferromagnetism. These results demonstrate this material, with its structurally novel Reuleaux-triangle-like
lattice, as a new platform for exploring the interplay between nontrivial
lattice geometry and emergent physical phenomena.
Read the full abstract ▾
All authors Zhen Zhao, Jianping Sun, Xin-Wei Yi, Ruwen Wang, Lin Zhu, Tong Liu, Haisen Liu, Hui Guo, Wu Zhou, Jinguang Cheng, Gang Su, Haitao Yang, Hong-Jun Gao
Materials Science
Plasticity from Symmetry: A Gauge-Theoretic Framework
Kevin T. Grosvenor, Mario Solís and Piotr Surówka
Plastic deformation is widely regarded as an intrinsically dissipative phenomenon and its theoretical description is largely phenomenological. We argue instead that plasticity possesses a non-dissipative,
symmetry determined backbone: defect kinematics are fixed by
symmetry prior to dissipation and separate from constitutive assumptions. Starting from the spontaneous breaking of spacetime
symmetries in a crystalline phase, we construct an effective field theory in which elasticity and geometry reorganize into a coupled higher-rank tensor vector gauge structure. The gauge fields are not postulated, rather they emerge naturally from stress and defect conservation laws. Dislocations, disclinations, and torsional defects appear as gauge charges of non-integrable geometry whose continuity equations and mobility constraints follow directly from Gauss laws. This clarifies the long-standing ambiguity over which variables are fundamental in the gauge theory of defects and shows that plasticity admits an ideal gauge-theoretic formulation, with dissipative flow arising as a controlled deformation of this conservative theory.
Read the full abstract ▾
Materials Science
Fully anharmonic calculations of the free energy of migration of point defects in UO2 and PuO2
Dillon G. Frost, Johann Bouchet, Mihai-Cosmin Marinica et al. (+3 more)
Calculating
diffusion rates of point defects in materials typically relies on the harmonic approximation to estimate migration free energies. However, anharmonic effects can have a large impact on
diffusion properties, and explicitly accounting for them is usually computationally demanding and difficult to achieve in practice. In this work, we investigate the role of anharmonic effects on defect migration in UO2 and PuO2 using the potential of average force integration (PAFI) method. Fully anharmonic migration free energies are computed for several cation and anion defect types, using the Cooper-Rushton-Grimes (CRG) potential and a recently developed machine learning spectral neighbour analysis potential (SNAP) for UO2. Results are systematically compared to harmonic estimates based on attempt frequencies and the Debye approximation. Our results reveal that the validity of the harmonic approximation strongly depends on the defect type and the underlying potential, with significant deviations observed in several cases. In particular, defect migration barriers are found to decrease strongly with increasing temperature (up to 1 eV between 0 and 1200 K), and anharmonic contributions can substantially modify migration
entropies and, consequently,
diffusion coefficients. Comparing defect migration in UO2 and PuO2 using the CRG potential reveals that PuO2 has lower migration enthalpies at 0~K for all considered defects, but this is compensated by higher attempt frequencies, resulting in similar overall jump frequencies in UO2 and PuO2. These findings provide insight into the limitations of commonly used approximations and highlight the importance of anharmonic effects for predictive modeling of
diffusion in
nuclear fuels as well as in other classes of materials.
Read the full abstract ▾
All authors Dillon G. Frost, Johann Bouchet, Mihai-Cosmin Marinica, Clovis Lapointe, Jean-Bernard Maillet, Luca Messina
Materials Science
Anharmonicity Driven by Vacancy Ordering Unlocks High-performance Thermoelectric Conversion in Defective Chalcopyrites II-III$_2$-VI$_4$
Hui Zhang, Jincheng Yue, Jiongzhi Zheng et al. (+8 more)
Defective chalcopyrites have recently emerged as promising thermoelectric materials because their ordered intrinsic vacancies can profoundly reshape both
lattice dynamics and electronic structure. Here, we present a comprehensive theoretical investigation of the
lattice thermal and carrier transport properties of II-III$_2$-VI$_4$ defective chalcopyrites by combining first-principles calculations with machine-learning interatomic potentials. We show that vacancy ordering enhances
lattice distortion, leading to strong anharmonicity and metavalent bonding. The interplay of soft low-frequency
phonons, strongly negative Grüneisen parameters, and a substantially enlarged four-
phonon scattering phase space results in four-
phonon-scattering-dominated heat transport, yielding ultralow
lattice thermal conductivity. Meanwhile, systematic anion substitution at the VI-site provides an effective route to tune the electronic structure: reduced anion electronegativity weakens metal-anion hybridization, shifts anion $p$ states upward, narrows the band gap, and thereby improves electrical transport. Benefiting from this synergy between vacancy-induced
phonon suppression and anion-regulated electronic optimization, CdGa$_2$Te$_4$ exhibits an ultralow
lattice thermal conductivity of 0.19 W$\cdot$m$^{-1}$K$^{-1}$ and a high room-temperature $ZT$ of 0.957. This work not only predicts defective chalcopyrites as a promising platform for high-performance thermoelectrics but also provides a practical design strategy by integrating vacancy ordering, higher-order
phonon scattering, and anion-dependent band engineering.
Read the full abstract ▾
All authors Hui Zhang, Jincheng Yue, Jiongzhi Zheng, Ning Wang, Wenling Ren, Shuyao Lin, Chen Shen, Hao Gao, Yanhui Liu, Yue-Wen Fang, Tian Cui
Materials Science
Tritium for Nanoscale Hydrogen Analysis by Atom Probe Tomography
Maria Vrellou, Alexander Welle, Stefan Wagner et al. (+6 more)
Accurate nanoscale detection of hydrogen is essential for understanding hydrogen-related phenomena in materials, yet conventional tracing with deuterium is often complicated by residual background hydrogen. This study evaluates tritium as a highly resolvable isotopic marker for nanoscale hydrogen analysis in metals using atom probe
tomography. Titanium was selected for its ability to incorporate hydrogen isotopes, providing a suitable platform for tritium detection. Time of flight secondary ion mass spectrometry and electron backscatter diffraction were performed prior to tritium charging to characterize the initial composition and microstructure. Atom probe
tomography in
laser mode before and after tritium charging, at three post-charging time intervals, enables tracking of tritium incorporation over time. Thermal desorption analysis confirmed the presence of tritium and complemented the secondary ion mass spectrometry measurements, highlighting the role of the surface
oxide layer in modulating tritium release. While tritium, deuterium, and protium differ in their
diffusion and trapping behavior, the distinct mass signal associated with tritium provides a practical advantage for resolving hydrogen at very low concentrations. This work serves as a fundamental benchmarking study for leveraging tritium and atom probe
tomography as a combined tool for understanding hydrogen in materials, relevant for interpreting local processes such as hydrogen embrittlement.
Read the full abstract ▾
All authors Maria Vrellou, Alexander Welle, Stefan Wagner, Marco Weber, Rolf Rolli, Hans-Christian Schneider, Astrid Pundt, Xufei Fang, Christoph Kirchlechner
Materials Science
Early Prediction of Creep Failure via Bayesian Inference of Evolving Barriers
Juan Carlos Verano-Espitia, Tero Mäkinen, Mikko J. Alava et al. (+1 more)
Creep under a sustained load can persist for long times yet culminate in abrupt yielding or rupture, implying a finite lifetime even when the material appears solid. Here, we formulate lifetime prediction as
Bayesian inference over an evolving activation-energy landscape. A time-dependent distribution of activation barriers controls deformation: stress lowers barriers, while irreversible rearrangements deplete the weakest sites and reshape the low-barrier tail. Using early-time acoustic emission data,
Bayesian inference estimates the evolving barrier statistics in each sample and yields posterior predictive distributions for the time-to-failure. This approach provides online uncertainty-aware lifetime forecasts – already at around 10~% of the sample lifetime – that link microscopic barrier
evolution to macroscopic creep dynamics.
Read the full abstract ▾
All authors Juan Carlos Verano-Espitia, Tero Mäkinen, Mikko J. Alava, Jérôme Weiss
Materials Science
First-Principles Investigation of the Pressure Dependent Physical Properties of Intermetallic Kagome ZrRe2
Mst. Irin Naher, A. F. M. Yusuf Haider, Dholon Kumar Paul et al. (+3 more)
We present a density functional theory investigation of the pressure dependent structural, electronic, mechanical, thermophysical, vibrational, and optical properties of the intermetallic Kagome compound ZrRe2. The calculated ground-state structural parameters are in excellent agreement with available experimental results. The estimated structural parameters, elastic constants, and
phonon dispersion confirm the structural, chemical, mechanical, and dynamical stability of ZrRe2 up to 25 GPa. The Kagome feature in the material has been identified from the electronic band structure for the first time. ZrRe2 exhibits topological feature at 0 GPa, which vanishes under 25 GPa.
Fermi surface (FS) analysis predicts that ZrRe2 could potentially host a charge density wave (CDW) phase. The electronic and optical studies confirmed its metallic nature. The Debye temperature and
phonon thermal conductivity are moderate, while the melting point is relatively high. Furthermore, ZrRe2 possesses moderate electron-
phonon coupling, which weakens under pressure as the
phonon modes harden. Consequently, the superconducting transition temperature decreases with increasing pressure. Most of the properties studied and analyses performed in this paper are novel in nature.
Read the full abstract ▾
All authors Mst. Irin Naher, A. F. M. Yusuf Haider, Dholon Kumar Paul, Md Lutfor Rahman, Firoze H. Haque, Saleh Hasan Naqib
Materials Science · Cross-listed from physics.comp-ph
Tuning Cu/Diamond Interfacial Thermal Conductance via Nitrogen-Termination Engineering
Guang Yang, Xinling Tang, Zhongkang Lin et al. (+4 more)
Cu-diamond composites are recognized as promising high-thermal-conductivity candidates for electronic cooling, offering tunable properties and competitive cost. However, their performance is significantly limited by the poor Cu/diamond interfacial thermal conductance (ITC). Here, we propose a nitrogen-termination strategy to tune the ITC of Cu/diamond interfaces and unravel atomistic mechanisms by which nitride interlayers tailor
phonon transport. Based on the MACE machine-learning interatomic potential (MLIP) framework, we fine-tune the pre-trained MACE-MPA-0 foundation model by incorporating customized C-N-Cu training
datasets. Through MLIP-driven
lattice dynamics simulations, we demonstrate that an atomically flat N-termination on diamond enhances the ITC by 21% compared to the bare Cu/diamond interface. Mode-resolved
phonon spectroscopy reveals that the LA
phonons with frequency above 4 THz and wavevectors near {\Gamma}-X and {\Gamma}-U directions are selectively modulated by N-termination engineering. Analyses of local vibrational states and interfacial bonding further indicate that the N-termination on diamond tunes the interfacial heat conduction via surficial mass modification and bonding regulation, as evidenced by variations in LDOS overlap and COHP spectra. These findings open venues for tuning heat transfer across Cu/diamond interfaces via non-metallic modification, which avoids the graphitization issues associated with metallic coatings, and provide novel guidelines for upgrading the
phonon-mediated heat transfer in Cu-diamond composites.
Read the full abstract ▾
All authors Guang Yang, Xinling Tang, Zhongkang Lin, Yulin Gu, Wei Hao, Yujie Du, Xiaoguang Wei