Materials Science · Cross-listed from cs.LG
A Conformation-Centric Generative Foundation Model for Linear Polymer Modeling and Design
Fanmeng Wang, Ruochao Wang, Shan Mei et al. (+5 more)
Linear
polymers, macromolecules formed from monomers covalently bonded into continuous chains, underpin countless technologies and are indispensable to modern life. While deep learning is advancing
polymer science, existing methods typically represent the whole linear
polymer solely through monomer-level descriptors, overlooking the global structural information inherent in
polymer conformations, which ultimately limits their practical performance. Moreover, this important field still lacks a dedicated foundation model that can effectively support diverse downstream tasks, thereby severely constraining progress. To address these challenges, we introduce PolyConFM, a foundation model tailored for modeling and designing linear
polymers through conformation-centric generative pretraining. Recognizing that each linear
polymer is essentially a continuous chain whose conformation can be naturally decomposed into a sequence of local conformations (i.e., those of its repeating units), we pretrain PolyConFM under the conditional generation paradigm, reconstructing these local conformations via masked autoregressive (MAR) modeling and further generating their orientation transformations to recover the corresponding
polymer conformation. Meanwhile, we construct a linear
polymer conformation
dataset via molecular dynamics simulations to mitigate data sparsity, thereby enabling conformation-centric pretraining. Experiments demonstrate that PolyConFM consistently outperforms representative task-specific methods across diverse downstream tasks, thereby equipping
polymer science with a powerful tool targeting linear
polymers.
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All authors Fanmeng Wang, Ruochao Wang, Shan Mei, Wentao Guo, Hongshuai Wang, Qi Ou, Zhifeng Gao, Hongteng Xu
Materials Science · Cross-listed from physics.chem-ph
Nano-electronvolt Fourier-limited transition of a single surface-adsorbed molecule
Masoud Mirzaei, Alexey Shkarin, Burak Gurlek et al. (+7 more)
High-resolution spectroscopy allows one to probe weak interactions and to detect subtle phenomena. While such measurements are routinely performed on atoms and molecules in the gas phase, spectroscopy of adsorbed species on surfaces is faced with challenges. As a result, previous studies of surface-adsorbed molecules have fallen short of the ultimate resolution, where the transition linewidth is determined by the lifetime of the excited state. In this work, we conceive a new approach to surface deposition and report on
Fourier-limited electronic transitions in single dibenzoterrylenes adsorbed onto the surface of an anthracene
crystal. By performing spectroscopy and super-resolution microscopy at
liquid helium temperature, we shed light on various properties of the adsorbed molecules. Our experimental results pave the way for a new class of experiments in surface science, where high spatial and spectral resolution can be combined.
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All authors Masoud Mirzaei, Alexey Shkarin, Burak Gurlek, Johannes Zirkelbach, Ashley J. Shin, Irena Deperasińska, Boleslaw Kozankiewicz, Tobias Utikal, Stephan Götzinger, Vahid Sandoghdar
Materials Science
Turn-on of Current-Induced Spin Torque upon Noncollinear Antiferromagnetic Ordering in Delafossite PdCrO2
Xiaoxi Huang, Qi Song, Gautam Gurung et al. (+10 more)
We report measurements of the current-induced
spin torque produced by the delafossite antiferromagnet PdCrO2 and acting on an adjacent
ferromagnetic permalloy layer. The
spin torque increases strongly as the temperature is reduced through the Neel temperature, when the PdCrO2 transitions from a paramagnetic phase to a noncollinear
antiferromagnetic state. This result is qualitatively consistent with density functional theory calculations regarding how
spin-current generation changes upon
antiferromagnetic ordering in PdCrO2.
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All authors Xiaoxi Huang, Qi Song, Gautam Gurung, Daniel A. Pharis, Thow Min Jerald Cham, Yulan Chen, Rakshit Jain, Maciej Olszewski, Yufan Feng, Amal El-Ghazaly, Evgeny Y. Tsymbal, Darrell G. Schlom, Daniel C. Ralph
Materials Science · Cross-listed from cond-mat.mes-hall
Comparative study of phonon-limited carrier transport in the Weyl semimetal TaAs family
Shashi B. Mishra, Zhe Liu, Sabyasachi Tiwari et al. (+2 more)
We present a systematic first-principles study of
phonon-limited transport in the TaAs family of Weyl semimetals using the ab initio Boltzmann transport equation. The calculated electrical conductivities show excellent agreement with experimental data for high-quality samples, confirming that transport in these systems is predominantly limited by
phonon scattering. Among the four compounds, NbP achieves the highest conductivity, governed primarily by its large
Fermi velocities that offset its stronger scattering rates. In contrast, TaAs displays the lowest conductivity, linked to reduced carrier pockets and limited carrier velocities. Additionally, NbP conductivity remains largely unaffected by small hole or electron doping, whereas TaAs exhibits pronounced electron-hole asymmetry. NbAs and TaP show intermediate behavior, reflecting their
Fermi surface
topologies and scattering phase space. These findings provide microscopic insight into the transport mechanisms of the TaAs family and emphasize the critical role of
phonons, doping, and carrier dynamics in shaping their electronic response.
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All authors Shashi B. Mishra, Zhe Liu, Sabyasachi Tiwari, Feliciano Giustino, Elena R. Margine
Materials Science · Cross-listed from math.RT
Representation of tensor functions using lower-order structural tensor set: three-dimensional theory
Mohammad Madadi and Pu Zhang
The representation theory of tensor functions is a powerful mathematical tool for constitutive modeling of anisotropic materials. A major limitation of the traditional theory is that many point groups require fourth- or sixth-order structural tensors, which significantly impedes practical engineering applications. Recent advances have introduced a reformulated representation theory that enables the modeling of anisotropic materials using only lower-order structural tensors (i.e., second-order or lower). Building upon the reformulated theory, this work establishes the representations of tensor functions for three-dimensional centrosymmetric point groups. For each point group, we propose a lower-order structural tensor set and derive the representations of tensor functions explicitly. For scalar-valued and second-order symmetric tensor-valued functions, our theory is indeed applicable to all three-dimensional point groups because their representations are determined by the corresponding centrosymmetric groups. The representation theory presented here is broadly applicable for constitutive modeling of anisotropic materials.
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Materials Science
CBVB-nH complexes as prevalent defects in metal-organic vapor-phase epitaxy-grown hexagonal boron nitride
Marek Maciaszek and Bartłomiej Baur
Optically active defects in hexagonal boron nitride (hBN) are promising candidates for active components in emerging
quantum technologies, such as single-
photon emitters and
spin centers. However, further progress in hBN-based
quantum technologies requires a deeper understanding of the physics and chemistry of hBN defects. In this work, we employ ab initio calculations to investigate the thermodynamic stability and optical properties of defect complexes involving carbon, boron vacancies, and hydrogen. We demonstrate that the formation of CBVB-nH complexes (n from 0 to 3) is energetically favorable under nitrogen-rich conditions in the presence of carbon and hydrogen. The low formation energies and high binding energies of these complexes arise from the strong electrostatic attraction between the positively charged carbon substitutional defect (CB) and the negatively charged hydrogen-passivated boron vacancies (VB-nH). These complexes are particularly likely to form in metal-organic vapor-phase epitaxy (MOVPE)-grown samples, where growth occurs in the presence of carbon and hydrogen and is accompanied by a high density of boron vacancies. The optical properties of CBVB-nH complexes are analyzed and compared to recent photoluminescence measurements on MOVPE-grown hBN samples. In particular, we investigate the origin of the emission peaks at 1.90 eV and 2.24 eV and demonstrate that both the energies and lineshapes are consistent with hole capture by negatively charged CBVB and CBVB-H complexes.
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Materials Science
Structure and magnetism of MnGe thin films grown with a nonmagnetic CrSi template
B. D. MacNeil, J. S. R. McCoombs, D. Kalliecharan et al. (+7 more)
We report a method to grow B20 MnGe thin films using molecular-beam epitaxy, which employs an ultrathin CrSi template layer on Si(111). This layer is expected to be nonmagnetic, in contrast to MnSi and FeGe buffer layers that have been used previously. This template layer permits an investigation of the intrinsic properties of MnGe in the ultrathin-film limit without the influence of a neighboring
magnetic layer. Single-phase MnGe(111) films were grown with thicknesses between 2 and 40 nm, which exhibited low interfacial roughnesses on the order of 0.6 nm. The films crystallized in a B20 structure with a small rhombohedral distortion. Magnetometry measurements in out-of-plane fields are consistent with a cone phase derived from helimagnetic order propagating along the film normal. However, an unexpected remanent moment develops below 35K, concomitant with features in the field dependence of the transport data. This provides indirect evidence for the presence of a low-temperature phase which has been identified by others as either a triple-Q topological
spin-hedgehog
lattice, or a multidomain single-Q helical state.
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All authors B. D. MacNeil, J. S. R. McCoombs, D. Kalliecharan, J. Myra, M. Pula, J. F. Britten, G. B. G. Stenning, K. Gupta, G. M. Luke, T. L. Monchesky
Materials Science
Resonant diffraction and photoemission inconsistent with altermagnetism in epitaxial RuO$_2$ films
Benjamin Z. Gregory, Neha Wadehra, Shuyuan Zhang et al. (+15 more)
Excitement about the
magnetic and electronic properties of RuO$_2$ is growing, fueled by reports of antiferromagnetism, strain-induced superconductivity, and its recent classification as a member of a newly proposed
magnetic class, altermagnets, with RuO$_2$ widely regarded as the paradigmatic example. Nevertheless, the
magnetic ground state of RuO$_2$ remains contentious, as several recent experiments report no evidence of
magnetic order. To address this discrepancy, we performed resonant elastic scattering measurements on a series of epitaxial RuO$_2$ thin films grown on the (100)-plane of TiO$_2$ substrates across a range of strain states. Leveraging full polarization control and azimuthal scans of the structurally forbidden 100 Bragg reflection, we systematically tested for signatures of colinear
antiferromagnetic order. We found that the resonant elastic scattering signal in RuO$_2$ thin films likely originates from anisotropic charge scattering, not long-range
antiferromagnetic order. Using angle-resolved photoemission spectroscopy we uncover a band structure without altermagnetic band splitting that is consistent with a nonmagnetic phase. Similarly, anisotropic magnetoresistance results show no evidence of magnetism. The combination of three independent measurements suggests the absence of altermagnetism in RuO$_2$.
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All authors Benjamin Z. Gregory, Neha Wadehra, Shuyuan Zhang, Yi Wu, Samuel Poage, Jörg Strempfer, Asish K. Kundu, Anil Rajapitamahuni, Elio Vescovo, Anita Verma, Betül Pamuk, Jacob Ruf, Hari Nair, Nathaniel J. Schreiber, Kaveh Ahadi, Kyle M. Shen, Darrell G. Schlom, Andrej Singer
Materials Science · Cross-listed from math.MG
Continuous invariant-based asymmetries of periodic crystals quantify deviations from higher symmetry
Surya Majumder, Daniel Widdowson, Yury Elkin et al. (+4 more)
Ideal
symmetry is known to break down under almost any noise. One measure of asymmetry in a periodic
crystal is the relative multiplicity Z' of geometrically non-equivalent units. However, Z' discontinuously changes under almost any displacement of atoms, which can arbitrarily scale up a primitive
cell. This discontinuity was recently resolved by a hierarchy of invariant descriptors that continuously change under all small perturbations. We introduce a Continuous Invariant-based Asymmetry (CIA) to quantify (in physically meaningful Angstroms) the deviation of a periodic
crystal from a higher
symmetry form. Our experiments on several
Crystal Structure Prediction
datasets show that about a half of simulated
crystals have high values of CIA, while all experimental structures in these
datasets have CIA=0. On another hand, many
crystals with high values Z' in the Cambridge Structural Database (CSD) turned out to be close to more symmetric forms with Z'<=1 due to low values of CIAs.
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All authors Surya Majumder, Daniel Widdowson, Yury Elkin, Olga Anosova, Andrew I Cooper, Graeme M Day, Vitaliy Kurlin
Materials Science
Scalable and deterministic construction of moiré superlattice in 2D materials using stressor films
Yu-Mi Wu, Sihun Lee, Yufeng Xi et al. (+6 more)
Moiré superlattice in two-dimensional (2D) materials provides a powerful platform to engineer emergent electronic states, yet the construction of moiré superlattices remains lab-scale, involving much trial and error and with little control. Here, we demonstrate the construction of a heterostrain-induced moiré superlattice in transition metal dichalcogenides using a scalable process that deterministically induces strain to 2D materials. By applying patterned thin-film stressors and probing the resulting structures with scanning transmission electron microscopy, we directly resolve the induced heterostrain,
lattice deformations, and stacking variations that produce the moiré superlattice. We find that uniaxial and biaxial heterostrain give rise to distinct moiré patterns, including stripes and distorted hexagonal patterns. With this approach, we create in-plane polar distortions and thus in-plane polarization at the domain boundaries of the moiré superlattice in MoS$_2$. The deterministic and scalable construction of moiré patterns using a well-established scalable process opens opportunities to design new moiré geometries in 2D materials.
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All authors Yu-Mi Wu, Sihun Lee, Yufeng Xi, Stephen D. Funni, Saif Siddique, Natalie L. Williams, Giovanni Sartorello, Hesam Askari, Judy J. Cha
Materials Science
Strain-induced Moiré Reconstruction and Memorization in Two-Dimensional Materials without Twist
Nazmul Hasan, Tara Peña, Aditya Dey et al. (+7 more)
Two-dimensional (2D) materials with a twist between layers exhibit a moiré interference pattern with larger periodicity than any of the constituent layer unit
cells. In these systems, a wealth of exotic phases appear that result from moiré-dependent many-body electron correlation effects or non-trivial band
topology. One problem with using twist to generate moiré interference has been the difficulty in creating high-quality, uniform, and repeatable samples due to fabrication through mechanical stacking with viscoelastic stamps. Here we show, a new method to generate moiré interference through the controlled application of layer-by-layer strain (heterostrain) on non-twisted 2D materials, where moiré interference results from strain-induced
lattice mismatch without twisting or stacking. Heterostrain generation is achieved by depositing stressed thin films onto 2D materials to apply large strains to the top layers while leaving layers further down less strained. We achieve deterministic control of moiré periodicity and
symmetry in non-twisted 2D multilayers and
bilayers, with 97% yield, through varying stressor film force (film thickness X film stress) and geometry. Moiré reconstruction effects are memorized after the removal of the stressor layers. Control over the strain degree-of-freedom opens the door to a completely unexplored set of unrealized tunable moiré
geometric symmetries, which may now be achieved in a high-yield and user-skill independent process taking only hours. This technique solves a long-standing throughput bottleneck in new moiré
quantum materials discovery and opens the door to industrially-compatible manufacturing for 2D moiré-based electronic or optical devices.
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All authors Nazmul Hasan, Tara Peña, Aditya Dey, Dongyoung Yoon, Zakaria Islam, Yue Zhang, Maria Vitoria Guimaraes Leal, Arend M. van der Zande, Hesam Askari, Stephen M. Wu
Materials Science · Cross-listed from cond-mat.str-el
Evidence for a field-induced Lifshitz transition in the Weyl semimetal CeAlSi
M. M. Piva, T. Helm, J. C. Souza et al. (+4 more)
The Weyl semimetal CeAlSi crystallises in the noncentrosymmetric tetragonal space group $I4_1md$ and exhibits
ferromagnetic order below 8 K, thereby breaking both spatial inversion and time-reversal
symmetries. This unique combination of properties establishes CeAlSi as a model system for studying the interplay between non-trivial topological states and strong electron correlations. In this work, we report observations of Shubnikov-de Haas oscillations in the electrical resistivity under
magnetic fields up to 68 T applied parallel to the [001] crystallographic axis. Our measurements reveal an abrupt change in the oscillation frequencies near 14 T, which is indicative of a field-induced Lifshitz transition. Additionally, our results are consistent with the
ferromagnetic order bringing the Weyl nodes closer to the
Fermi level in CeAlSi. Furthermore, they suggest that the RKKY interaction plays an important role.
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All authors M. M. Piva, T. Helm, J. C. Souza, K. R. Pakuszewski, C. Adriano, P. G. Pagliuso, M. Nicklas
Materials Science · Cross-listed from cond-mat.str-el
First-order phase transition driven by competing charge-order fluctuations in 1T'-TaTe$_{2}$
S. K. Mahatha, A. Kar, J. Corral-Sertal et al. (+20 more)
First-order phase transitions, characterized by a discontinuous change in the order parameter, are intriguing phenomena in condensed matter physics. However, the underlying, material-specific, microscopic mechanisms often remain unclear. Here, we unveil a high-temperature incommensurate charge-order precursor with the wave vector $\mathbf{q}^* = (0, \frac{1}{4}+\delta, \frac{1}{2})$ in the 1T' phase of TaTe$_2$, which competes with fluctuating high-temperature Ta trimer bonding states at $\mathbf{q}_\mathrm{CO} =(0, \frac{1}{3}, 0)$. The precursor state follows the temperature dependence of the hidden incommensurability of the $\textit{quasi}$-1D nested
Fermi surface. In contrast, the low-temperature commensurate charge order at $\mathbf{q}_\mathrm{CO}$, characterized by a charge disproportionation of the inequivalent Ta sites, appears to be driven by local chemical bonding. Dynamical
lattice calculations identify an imaginary optical mode at $\mathbf{q}^*$, involving an in-plane vibration of the Ta atoms forming a chain-like structure that renormalizes below $T_\mathrm{CO}$. Our experimental and theoretical observations suggest that the controversial first-order phase transition, as captured by phenomenological Ginzburg-Landau theory, results from the competition between two order parameters: one involving
Fermi surface nesting and the other involving local chemical bonding.
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All authors S. K. Mahatha, A. Kar, J. Corral-Sertal, Josu Diego, A. Korshunov, C.-Y. Lim, F. K. Diekmann, D. Subires, J. Phillips, T. Kim, D. Ishikawa, G. Marini, I. Vobornik, Ion Errea, S. Rohlf, M. Kalläne, V. Bellini, A. Q. R. Baron, Adolfo O. Fumega, A. Bosak, V. Pardo, K. Rossnagel, S. Blanco-Canosa
Materials Science
Ultrafast exciton polaron dynamics in 2D Ruddlesden Popper lead halide perovskites
Anirban Mondal, Kwang Jin Lee, Seungmin Lee et al. (+5 more)
Two dimensional Ruddlesden Popper (2D) RP hybrid perovskites exhibit substantially higher chemical and structural stability than their three dimensional (3D) counterparts, positioning them as promising candidates for next generation optoelectronics. While quasiparticle dynamics in 3D perovskites are well studied, their 2D analogues remain comparatively underexplored. Here we systematically investigate the branching, dynamics, and interactions of free
excitons (FEs) and
exciton polarons EPs in monolayer 2D RP perovskites using visible range femtosecond transient absorption TA spectroscopy. We prepared monolayer 2D RP perovskite thin films with varied organic spacers and distinct fabrication routes for comparative analysis. We find that the EP binding energy is 50 65 meV in (BA)2PbI4 and 37 39 meV in (PEA)2PbI4, consistent with spacer layer dependent coupling as corroborated by FTIR. We reveal a dynamic
equilibrium between FEs and EPs that persists for tens of picoseconds. Notably, the TA signatures differ by fabrication route films from the newly developed process show weaker Auger annihilation and a reduced hot
phonon bottleneck than those from the conventional route trends consistent with fewer traps and
impurities in the former. Coupled rate equation modeling reproduces the transients and quantifies the processes of hot carrier relaxation,
exciton exciton annihilation,
exciton phonon coupling, and FE EP interconversion. These results demonstrate that the chemical synthetic process (fabrication route) and spacer choice significantly influence EP stability and population balance, offering practical levers for engineering ultrafast photophysics in 2D perovskites and guiding the design of advanced optoelectronic devices.
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All authors Anirban Mondal, Kwang Jin Lee, Seungmin Lee, Oui Jin Oh, Myeongsam Jen, Jun Hong Noh, Jong Min Lim, Minhaeng Cho
Materials Science
Unraveling the Corrosion Mechanism of Boro-Alumino-Phospho-Silicate Glass: Advanced Insights from Solid-State NMR Spectroscopy
Muhammad Amer Khan, Lili Hu, Shubin Chen et al. (+2 more)
Corrosion mechanism of minerals and glass is a critical study domain in geology and materials science, vital for comprehending material durability under various environmental conditions. Despite decades of extensive study, a core aspect of these mechanisms - specifically, the formation of amorphous alteration layers upon exposure to aqueous environments - remains controversial. In this study, the corrosion behavior of a boro-alumino-phospho-silicate glass (BAPS) was investigated using advanced solid-state
nuclear magnetic resonance (SSNMR) and SEM techniques. The results reveal a uniform nanoscale phase separation into Al-P-rich and Al-Si-rich domains. During corrosion, the Al-P-rich domain undergoes gelation, whereas the Al-Si-rich domain remains vitreous, forming a gel layer comprised of both phases. Although SEM images show a sharp gel/glass interface - suggestive of a dissolution-precipitation mechanism - the phase coexistence within the gel layer provides definitive evidence against such a mechanism. Instead, we propose an in situ transformation mechanism governed by chemical reactions, involving: (i) preferential hydrolysis of Al-P-rich domain leading to porous gel regions; (ii) retention of Al-Si glass domains within the gel layer, with water infiltrating inter-network spaces; and (iii) selective leaching of phosphorus over aluminum, leading to reorganization of the gel network.
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All authors Muhammad Amer Khan, Lili Hu, Shubin Chen, Yongchun Xu, Jinjun Ren
Materials Science · Cross-listed from cond-mat.mes-hall
Magnetically controllable nonlinear valley Hall effect in centrosymmetric ferromagnets
Ruijing Fang, Jie Zhang, Zhichao Zhou et al. (+1 more)
Valley
Hall effect is fundamental to valleytronics and provides a promising avenue for advancing information technology. While conventional valley
Hall effect requires the inversion
symmetry breaking, the recently proposed nonlinear valley
Hall (NVH) effect removes the
symmetry constraint, and broaden material choices. However, existing studies are limited to nonmagnetic materials without
spin involvement and rely on external strain to break rotational
symmetry. Here, to address these limitations, we design a magnetically controllable NVH effect in centrosymmetric ferromagnets, by the tight-binding model and first-principles calculations. The model calculations demonstrate nonvanishing NVH conductivities can emerge in pristine hexagonal
lattice without external strain, with the magnitude, sign, and
spin polarization of the conductivities being all dependent on the magnetization orientation. The effect thus generates various
spin-polarized valley
Hall currents, characterized by distinct combinations of current direction and
spin polarization. First-principle results on a
ferromagnetic VSi$_2$N$_4$
bilayer confirm considerable NVH conductivities and their dependence on the magnetization. The magnetically controllable NVH effect unlocks the potential of centrosymmetric magnets for valleytronics, and offer opportunities for novel spintronic and valleytronic devices.
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All authors Ruijing Fang, Jie Zhang, Zhichao Zhou, Xiao Li
Materials Science · Cross-listed from physics.comp-ph
GO-Diff: Data-free and amortized global structure optimization
Nikolaj Rønne, Tejs Vegge and Arghya Bhowmik
We introduce GO-Diff, a
diffusion-based method for global structure optimization that learns to directly sample low-energy atomic configurations without requiring prior data or explicit relaxation. GO-Diff is trained from scratch using a Boltzmann-weighted score-matching loss, leveraging only the known energy function to guide generation toward thermodynamically favorable regions. The method operates in a two-stage loop of self-sampling and model refinement, progressively improving its ability to target low-energy structures. Compared to traditional optimization pipelines, GO-Diff achieves competitive results with significantly fewer energy evaluations. Moreover, by reusing pretrained models across related systems, GO-Diff supports amortized optimization - enabling faster convergence on new tasks without retraining from scratch.
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Materials Science
Computational Insights into Defect Induced Modulation in Electronic Properties of 2D Nitride Monolayers
Shreya G. Sarkar, Kuneh Parag Shah and Brahmananda Chakraborty
Two-dimensional (2D) nitride materials such as hexagonal boron nitride (h-BN), graphitic carbon nitride (g-C$_3$N$_4$), and beryllonitrene (BeN$_4$) have emerged as promising candidates for next generation electronic, optoelectronic, and energy applications due to their unique structural and electronic properties. This study presents a systematic investigation of the effects of vacancy defect, specifically the role of nitrogen and constituent atom vacancies on the electronic properties of these materials. Our findings reveal that the introduction of nitrogen vacancies significantly alters the electronic characteristics of these materials. In h-BN, the presence of a nitrogen monovacancy significantly lowers the work function from 5.97 eV to 3.45 eV, one of the lowest values reported for any 2D material. Additionally, this defect reduces the band gap from 4.6 eV to 0.64 eV, driving the material toward half-metallic behavior. This is accompanied by the emergence of flat bands near the
Fermi level, indicative of strong electron-electron interactions. In g-C$_3$N$_4$, nitrogen vacancies lead to a decrease in work function and band gap, with double nitrogen vacancies rendering the material nearly metallic. In BeN$_4$, nitrogen vacancies result in minimal charge redistribution and a slight increase in work function, highlighting the material's unique electronic behavior. These results underscore the potential of vacancy engineering in tuning the electronic properties of 2D nitride materials, offering avenues for the design of materials with tailored work functions and band gaps for applications in optoelectronics, spintronics, and catalysis.
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Materials Science
Integration of imprint-free and low coercivity ferroelectric BaTiO3 thin films on silicon
Jingtian Zhao, Beatriz Noheda and Martin F. Sarott
Highly-crystalline ferroelectric
oxides integrated on Si hold great promise for energy-efficient
memory and logic technologies. Exploiting epitaxial strain engineering in these materials is, however, severely hampered on Si, where the large structural mismatch often results in an inferior interfacial quality and causes a degradation of the ferroelectric switching characteristics. In this work, we present the growth of single-crystalline BaTiO3 thin films on Si, exhibiting imprint-free switching, low coercivity, high remanent polarization, and no fatigue for over $10^{10}$ switching cycles. We accomplish this via the insertion of a SrSn1-xTixO3 layer on SrTiO3-buffered Si. This layer serves as a pseudo substrate that alleviates the thermal strain that the Si substrates imposes on the BaTiO3 layer, while simultaneously providing moderate compressive strain that stabilizes a pure out-of-plane polarization. Thus, our work paves the way toward the fabrication of Si-compatible, low-power-consuming ferroelectric devices for non-volatile
memory applications.
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Materials Science
Angular Emission Properties of Strained Transition-Metal Dichalcogenides
Lee Grimberg, Svyatoslav Kostyukovets and Moshe G. Harats
Monolayers of transition-metal dichalcogenides have shown that uniaxial strain changes both the photoluminescence emission energy and intensity. The changes are attributed to the band-structure
evolution under tensile strain where both the bandgap decreases and a direct-to-indirect transition occurs. This was shown for relatively high strains, whereas this is not the case at low strain values $<1\%$ in which in this work, we observe the erratic dependency of the photoluminescence intensity at low strain values as a function of strain. We find that the dominant physical property is the dependence of the optical-dipole emission on the
curvature of the substrate. We validate the behavior of the photoluminescence intensity with experimental angular emission spectroscopy (k-space imaging). These findings are supported by Finite-Difference Time-Domain simulations, in agreement with the experimental data. Our findings present the importance of choosing the right substrate for flexible devices based on transition-metal dichalcogenides.
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Materials Science · Cross-listed from cond-mat.mes-hall
Hybrid light-matter boundaries of graphene in a chiral cavity
Volker Karle, Oriana K. Diessel, Vasil Rokaj et al. (+1 more)
Recent advances in
chiral cavities that can couple coherently to two-dimensional materials have opened a powerful route to reshape electronic
topology without an external drive. Here we establish the bulk-boundary correspondence for
graphene embedded in a circularly polarized cavity. By combining exact diagonalization (ED) of zigzag ribbons, a semi-analytic T-
matrix for half-infinite
lattices, and analytical insights from a Dirac-Jaynes-Cummings model, we show that (i) every light-matter interaction-induced gap hosts pairs of unidirectional light-matter edge currents depending on the Chern number of the band while some of them are even bright; (ii) these
chiral states persist throughout the entire
photon ladder; and (iii) their dispersion, localization length and
photon distribution exhibit a universal scaling controlled by the light-matter interaction. Time-
evolution simulations further demonstrate that a dark electronic edge excitation can be converted into a bright and unidirectionally propagating current that remains coherent over long time scales. Our results predict an experimental signature of the hybrid band
topology and a blueprint for tunable
chiral channels in next generation
quantum optical solid-state devices.
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All authors Volker Karle, Oriana K. Diessel, Vasil Rokaj, Ceren B. Dağ
Materials Science · Cross-listed from cond-mat.mes-hall
Spin-Selective Second-Order Topological Insulators Enabling Cornertronics in 2D Altermagnets
Ning-Jing Yang, Zhigao Huang and Jian-Min Zhang
Recent progress in spintronics within the paradigm of altermagnets (AMs) opens new avenues for next-generation electronic device design. Here, we establish a
spin-corner locking mechanism that generates second-order topological states in two-dimensional (2D) altermagnetic systems, through effective model analysis. Remarkably, the breaking of Mxy
symmetry under uniaxial strain creates
spin-resolved corner modes, driving the system into a corner-polarized second-order topological
insulator (CPSOTI). Beyond critical strain, a topological phase transition to
quantum anomalous
Hall insulator occurs with quantized conductance. Through first-principles calculations, we identify two experimentally viable candidates for 2D intrinsic AM CrO and Cr$_2$Se$_2$O – which host robust CPSOTI. Moreover, we construct the topological phase diagram of CrO and predict the existence of an altermagnetic Weyl semimetal phase. Our findings open technological avenues in altermagnetism and higher-order
topology, while providing opportunities for coupling topological spintronics with cornertronics.
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Materials Science
Tuning the non-linear interactions of hybrid interlayer excitons in bilayer MoS2 via electric fields
Mathias Federolf, Alexander Steinhoff, Monika Emmerling et al. (+3 more)
Hybrid interlayer
excitons in
bilayer MoS2 are a promising platform for nonlinear optics due to their intrinsic dipolar character, which combines in-plane and out-ofplane dipole moments. In this work, we directly probe the nonlinear
exciton-
exciton interactions of hybrid interlayer
excitons. By applying an external out-of-plane electric field, we polarize the
excitons to enhance their mutual dipolar interactions, thereby deliberately favoring these repulsive contributions over competing attractive manybody corrections. We furthermore establish a fully microscopic theoretical description of these effects to explain the core experimental results. The tuning results in a significantly larger blueshift compared to the zero-field case and perspectively opens an avenue to even switch between repulsive and attractive interaction potentials. Our findings establish that strong nonlinearities can be tuned via an external electric field, providing a new degree of control over
exciton interactions beyond density tuning alone.
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All authors Mathias Federolf, Alexander Steinhoff, Monika Emmerling, Matthias Florian, Christian Schneider, Sven Höfling
Materials Science
Isothermal Annealing Effects on $\beta$-Relaxations and Crystallization Behaviors in Amorphous GeTe
Arune Makareviciute, Qun Yang, Tomoki Fujita et al. (+12 more)
A secondary $\beta$-relaxation process is often the dominant source of atomic dynamics below $T_\mathrm{g}$ in many glass forming systems. Recent studies reported the presence of $\beta$-relaxations in amorphous phase-change materials (PCMs) and showed that suppressing the $\beta$-relaxation via annealing in Ge$_{15}$Sb$_{85}$ can effectively slow down its crystallization kinetics. Yet, when Sb is replaced by Te, similar annealing protocol has little effect on the Te-rich
alloy Ge$_{15}$Te$_{85}$. Here, we investigate amorphous GeTe that is a Sb-free PCM, but with faster crystallization kinetics than Ge$_{15}$Te$_{85}$. Using powder mechanical dynamic spectroscopy, we observe a clear reduction of the excess-wing in the loss modulus upon isothermal annealing, indicating a suppression of its $\beta$-relaxation. Ultrafast calorimetric analysis and time-resolved optical reflectivity measurements show that, whereas as-deposited GeTe exhibit
stochastic crystallization behaviors, annealed samples crystallize more slowly with reduced stochasticity. Synchrotron X-ray scattering experiments reveal reinforced Peierls-like distortions in the amorphous structure after annealing, and demonstrate that, even if annealing introduces nucleation sites, it nonetheless slows down crystallization kinetics. These finding suggests that, in annealed GeTe, crystallization is limited by
crystal growth rate, which is retarded through the suppression of $\beta$-relaxation.
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All authors Arune Makareviciute, Qun Yang, Tomoki Fujita, Oliver Gross, Nico Neuber, Maximilian Frey, Jens Moesgaard, Cecile Chaxel, Julian Pries, Mads Ry Vogel Jørgensen, Frederik Holm Gjørup, Matthias Wuttig, Hai-bin Yu, Jiangjing Wang, Shuai Wei
Materials Science
Surface Properties of Ga-Cu Based Liquid-Metal Alloys: Impact of Cu Dilution Topography and Reaction Conditions
Tzung-En Hsieh, Michael S. Moritz, Andreas Mölkner et al. (+10 more)
We studied the surface properties of Ga-Cu based
liquid metal
alloys, a promising material system for supported catalytically active
liquid metal solutions (SCALMS). The impact of Cu dilution in the (
liquid) Ga
matrix is in-detail investigated by X-ray and UV photoelectron spectroscopy (XPS/UPS) and Machine-Learned-Force Field (ML-FF) calculations. With decreasing Cu content, microscopic and macroscopic Ga-Cu model samples exhibit a shift of the Cu 2p core level line to higher binding energies (Eb) as well as a correspondingly shifted and narrowed d-band with respect to pure Cu, which we ascribe to site isolation. To study the property
evolution of Ga-Cu at SCALMS reaction conditions, i.e., where Cu is present in
liquid Ga, additional XPS measurements were performed between 100 and 500 oC. The observed Cu 2p shift to lower Eb is tentatively ascribed to changes in the local environment with increasing temperature, i.e. bond elongation, which is corroborated by ML-FF simulations. The increased Cu surface content at low temperatures is attributed to the presence of crystallized Cu-rich intermetallic compounds, as evidenced by transmission electron microscopy images. In an attempt to generalize the findings for filled d-band transition metals (TMs) in
liquid Ga also Ga-Ag and Ga-Au model systems were investigated. The observed insights may be another step of paving the way for an insight-driven development of low-temperature melting
liquid metals for heterogeneous catalysis.
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All authors Tzung-En Hsieh, Michael S. Moritz, Andreas Mölkner, Christoph Wichmann, Johannes Frisch, Julien Steffen, Caiden J. Parker, Vaishnavi Krishnamurthi, Torben Daeneke, Hans-Peter Steinrück, Andreas Görling, Christian Papp, Marcus Bär
Materials Science
Colossal Cryogenic Electro-Optic Response Through Metastability in Strained BaTiO$_{3}$ Thin Films
Albert Suceava, Sankalpa Hazra, Aiden Ross et al. (+14 more)
The search for thin film electro-optic (EO) materials that can retain superior performance under cryogenic conditions has become critical for
quantum computing. Barium titanate thin films show large linear EO coefficients in the tetragonal phase at room temperature, which is severely degraded down to ~200 pm V$^{-1}$ in the rhombohedral phase at cryogenic temperatures. There is immense interest in manipulating these phase transformations and retaining superior EO properties down to
liquid helium temperature. Utilizing the thermodynamic theory of optical properties, a large low-temperature EO response is designed by engineering the energetic competition between different ferroelectric phases, leading to a low-
symmetry monoclinic phase with a massive EO response. The existence of this phase is demonstrated in a strain-tuned BaTiO$_{3}$ thin film that exhibits a linear EO coefficient of 2516 +/- 100 pm V$^{-1}$ at 5 K, which is an order of magnitude higher than the best reported performance thus far. Importantly, the EO coefficient increases by 100x during cooling, unlike the conventional films, where it degrades. Further, at the lowest temperature, significant higher order EO responses also emerge. These results represent a new framework for designing materials with property enhancements by stabilizing highly tunable metastable phases with strain. Copyright 2025 The Author(s). Advanced Materials published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. (A. Suceava, S. Hazra, A. Ross, et al. "Colossal Cryogenic Electro-Optic Response Through Metastability in Strained BaTiO3 Thin Films." Adv. Mater. (2025): e07564. https://doi.org/10.1002/adma.202507564)
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All authors Albert Suceava, Sankalpa Hazra, Aiden Ross, Ian Reed Philippi, Dylan Sotir, Brynn Brower, Lei Ding, Yingxin Zhu, Zhiyu Zhang, Himirkanti Sarkar, Saugata Sarker, Yang Yang, Suchismita Sarker, Vladimir A. Stoica, Darrell G. Schlom, Long-Qing Chen, Venkatraman Gopalan
Materials Science
Towards Universal Material Property Prediction with Deep Learning and Single-Descriptor electronic Density
Feng Chen, Shu Li, Xin Chen et al. (+3 more)
Owing to its high scalability and computational efficiency, machine learning methods have been increasingly integrated into various scientific research domains, including ab initio-based materials design. It has been demonstrated that, by incorporating modern machine learning
algorithms, one can predict material properties with practically acceptable accuracy. However, one of the most significant limitations that restrict the widespread application of machine learning is its lack of transferability, as a given framework is typically applicable only to a specific property. The origin of this limitation is rooted in the fact that a material's properties are determined by multiple degrees of freedom – and their complex interplay – associated with
nuclei and electrons, such as atomic type, structural
symmetry, and the number and
quantum states of the valence electrons, among others. The inherent complexity rules out the possibility of a single machine learning framework providing a full description of these critical quantities. In this paper, we develop a universal machine learning framework based solely on a physically grounded and theoretically rigorous descriptor – electronic charge density. Our framework not only enables accurate prediction of eight different material properties (with R$^2$ values up to 0.94), but also demonstrates outstanding multi-task learning capability, as prediction accuracy improves when more target properties are incorporated into a single training process, thereby indicating excellent transferability. These results represent a significant step toward realizing the long-standing goal of a universal machine learning framework for the unified prediction of all material properties.
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All authors Feng Chen, Shu Li, Xin Chen, Dennis Wong, Biplab Sanyal, Duo Wang
Materials Science
The nature of polar distortions in ferroelectrics
Hong Jian Zhao, Laurent Bellaiche and Yanming Ma
Polar distortion, the collective off-center displacements of atoms, is a fingerprint of a ferroelectric that governs its properties and functionalities. Since the 1970s, the concepts of proper, improper and triggered ferroelectrics have been established to shed light on a diversity of polar distortion mechanisms. Such concepts assign a single nature to polar distortion and are helpful to interpret how polar distortions occur in conventional ferroelectrics such as barium titanate. However, applying these concepts to complex ferroelectrics (e.g., polar orthorhombic hafnia) is notoriously challenging and can yield highly controversial arguments. Here we resolve this issue by developing a tailor-made graph theory for clarifying the nature of polar distortions in complex ferroelectrics, which emphasizes that polar distortions in such ferroelectrics usually exhibit multiple natures among proper, improper and triggered characteristics. We demonstrate the robustness of our theory by working with perovsktie superlattices and polar orthorhombic hafnia (i.e., two representative cases). We successfully identify the mixed proper-improper nature in perovsktite superlattices and reconcile the controversy on polar orthorhombic hafnia by confirming its mixed trigger-improper nature. Our work will definitely lead to a revisitation of concepts in ferroelectric physics and provide opportunities for discovering novel ferroelectrics and related phenomena.
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