Materials Science · Cross-listed from physics.comp-ph
DISCOVER: A Physics-Informed, GPU-Accelerated Symbolic Regression Framework
Udaykumar Gajera, Mohsen Sotoudeh, Kanchan Sarkar et al. (+1 more)
Symbolic Regression (SR) enables the discovery of interpretable mathematical relationships from experimental and simulation data. These relationships are often coined descriptors which are defined as a fundamental materials property that is directly correlated to a desired or undesired functional property of the material. Although established approaches such as Sure Independence Screening and Sparsifying Operator (SISSO) have successfully identified low-dimensional descriptors within large feature spaces many existing SR tools integrate poorly with modern Python workflows, offer limited control over the symbolic search space, or struggle with the computational demands of large-scale studies. This paper introduces DISCOVER (Data-Informed Symbolic Combination of Operators for Variable Equation Regression), an open-source symbolic regression package developed to address these challenges through a modular, physics-motivated design. DISCOVER allows users to guide the symbolic search using domain knowledge, constrain the feature space explicitly, and take advantage of optional GPU acceleration to improve computational efficiency in data-intensive workflows, enabling reproducible and scalable SR workflows. The software is intended for applications in computational physics, computational chemistry, and materials science, where interpretability, physical consistency, and execution time are especially important, and it complements general-purpose SR frameworks by emphasizing the discovery of physically meaningful models.
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All authors Udaykumar Gajera, Mohsen Sotoudeh, Kanchan Sarkar, Axel Groß
Materials Science · Cross-listed from cond-mat.str-el
D. R. Baykusheva, D. P. Carmichael, C. S. Weber et al. (+12 more)
Quantum control of the many-body wavefunction is a central challenge in
quantum materials research, as it could yield a precise control knob to manipulate emergent phenomena. Floquet engineering, the coherent dressing of
quantum states with periodic non-resonant optical fields, has become an important strategy for
quantum control. Most applications to solid-state systems have targeted weakly interacting or single-ion states, leaving the manipulation of many-body wavefunctions largely unexplored. Here, we use Floquet engineering to achieve
quantum control of a strongly correlated Hubbard
exciton in the one-dimensional Mott
insulator Sr$_2$CuO$_3$. A nonresonant midinfrared optical field coherently dresses the
exciton wavefunction, driving its rotation between bright and dark states. We use resonant third-harmonic generation to quantify ultrafast $\pi/2$ rotations on the Bloch sphere spanned by these
exciton states. Our work advances the quest towards programmable control of correlated states and
exciton-based
quantum sensing.
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All authors D. R. Baykusheva, D. P. Carmichael, C. S. Weber, I-T. Lu, F. Glerean, T. Meng, P. B. M. De Oliveira, C. C. Homes, I. A. Zaliznyak, G. D. Gu, M. P. M. Dean, A. Rubio, D. M. Kennes, M. Claassen, M. Mitrano
Materials Science
Establishing Atomic Coherence in Twisted Oxide Membranes Containing Volatile Elements
Young-Hoon Kim, Reza Ghanbari, Min-Hyoung Jung et al. (+3 more)
Twisted
oxide membranes represent a promising platform for exploring moire physics and emergent
quantum phenomena. However, the presence of amorphous interfacial dead layers in conventional
oxide heterostructures impedes coherent coupling and suppresses moire-induced interactions. While high-temperature thermal treatments can facilitate interfacial bonding, additional care is needed for materials containing volatile elements, where elevated temperatures may cause elemental loss. This study demonstrates the realization of atomically coherent, chemically bonded interface in twisted NaNbO3
heterostructures through controlled oxygen-annealing treatment. Atomic-resolution imaging and spectroscopy reveal ordered perovskite registry accompanied by systematic
lattice contraction and modified electronic structure at the twisted interface, providing signatures of chemical reconstruction rather than physical adhesion. This reconstructed interface mediates highly asymmetric strain propagation in which the bottom membrane remains nearly relaxed while the top membrane accommodates substantial shear strain, thereby establishing a strain gradient that enables long-range electromechanical coupling throughout the twisted
oxide membranes. By resolving the nature of the reconstructed interface, these findings establish a robust pathway for achieving coherent and strain-tunable
oxide moire superlattices, opening pathways to engineer emergent ferroic and electronic functionalities.
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All authors Young-Hoon Kim, Reza Ghanbari, Min-Hyoung Jung, Young-Min Kim, Ruijuan Xu, Miaofang Chi
Materials Science
Kolmogorov-Arnold Networks Applied to Materials Property Prediction
Ryan Jacobs, Lane E. Schultz and Dane Morgan
Kolmogorov-Arnold Networks (KANs) were proposed as an alternative to traditional neural network architectures based on multilayer perceptrons (MLP-NNs). The potential advantages of KANs over MLP-NNs, including significantly enhanced parameter efficiency and increased interpretability, make them a promising new regression model in supervised machine learning problems. We apply KANs to prediction of materials properties, focusing on a diverse set of 33 properties consisting of both experimental and calculated data. We compare the KAN results to random forest, a method that generally gives excellent performance on a wide range of properties predictions with very little optimization. The KANs were worse, on par, or better than random forest about 35%, 60%, and 5% of the time, respectively, and KANs are in practice more difficult to fit than random forest. By tuning the network architecture, we found property fits often resulted in 10-20% lower errors compared to the standard KAN, and typically gave results comparable to random forest. In the specific context of predicting reactor pressure vessel transition temperature shifts, we explored the parameter efficiency and the interpretable power of KANs by comparing predictions of simple KAN models (e.g., < 50 parameters) and closed-form expressions suggested by the KAN fits to previously published deep MLP-NNs and hand-tuned models created using domain expertise of embrittlement physics. We found that simple KAN models and the resulting closed-form expressions produce prediction errors on par with established hand-tuned models with a comparable number of parameters, and required essentially no domain expertise to produce. These findings reinforce the potential applicability of KANs for machine learning in materials science and suggest that KANs should be explored as a regression model for prediction of materials properties.
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Materials Science · Cross-listed from quant-ph
Krypton-sputtered tantalum films for scalable high-performance quantum devices
Maciej W. Olszewski, Lingda Kong, Simon Reinhardt et al. (+9 more)
Superconducting
qubits based on tantalum (Ta) thin films have demonstrated the highest-performing microwave resonators and
qubits. This makes Ta an attractive material for superconducting
quantum computing applications, but, so far, direct deposition has largely relied on high substrate temperatures exceeding \SI{400}{\celsius} to achieve the body-centered cubic phase, BCC (\textalpha-Ta). This leads to compatibility issues for scalable fabrication leveraging standard
semiconductor fabrication lines. Here, we show that changing the sputter gas from argon (Ar) to krypton (Kr) promotes BCC Ta synthesis on silicon (Si) at temperatures as low as \SI{200}{\celsius}, providing a wide process window compatible with back-end-of-the-line fabrication standards. Furthermore, we find these films to have substantially higher electronic conductivity, consistent with clean-limit superconductivity. We validated the microwave performance through coplanar waveguide resonator measurements, finding that films deposited at \SI{250}{\celsius} and \SI{350}{\celsius} exhibit a tight performance distribution at the state of the art. Higher temperature-grown films exhibit higher losses, in correlation with the degree of Ta/Si intermixing revealed by cross-sectional transmission electron microscopy. Finally, with these films, we demonstrate transmon
qubits with a relatively compact, \SI{20}{\micro\meter} capacitor gap, achieving a median quality factor up to 14 million.
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All authors Maciej W. Olszewski, Lingda Kong, Simon Reinhardt, Daniel Tong, Xinyi Du, Gabriele Di Gianluca, Haoran Lu, Saswata Roy, Luojia Zhang, Aleksandra B. Biedron, David A. Muller, Valla Fatemi
Materials Science · Cross-listed from cond-mat.soft
Deep Learning the Small-Angle Scattering of Polydisperse Hard Rods
Lijie Ding and Changwoo Do
We present a deep learning framework for modeling and analyzing the small-angle scattering data of polydisperse hard-rod systems, a widely used models for anisotropic colloidal particles. We use a variational autoencoder-based neural network to learn the mapping from the system parameters such as the volume fraction, rod length, and polydispersity, to the scattering function. The
dataset for training and testing such neural network model is obtained from Markov chain Monte Carlo simulation of 20,000 hard spherocylinders using the hard particle Monte Carlo package from the HOOMD-blue. Four
datasets were generated, each with 5,500 pairs of system parameters and corresponding scattering functions. We use one of the
dataset to investigate the feasibility of the learning, and three additional
datasets with different polydisperse distribution to demonstrate the generality of our approach. The neural network model transcends the fundamental limitations of the Percus-Yevick approximation by accurately capturing anisotropic interactions and high-concentration effects that analytical models often fail to resolve. This framework achieves significantly higher accuracy in reproducing scattering functions and enables a least-square fitting routine for quantitative data analysis.
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Materials Science · Cross-listed from quant-ph
Optically Addressable Molecular Spins at 2D Surfaces
Xuankai Zhou, Yan-Tung Kong, Cheuk Kit Cheung et al. (+18 more)
Optically addressable
spins at material surfaces have represented a long-standing ambition in
quantum sensing, providing atomic resolution and
quantum-limited sensitivity. However, they are constrained by a finite depth at which the
quantum spins can be stabilized. Here, we demonstrate a hybrid molecular-2D architecture that realizes
quantum spin sensors directly on top of the surface. By anchoring
spin-active molecules onto hexagonal boron nitride (hBN), we eliminate the depth of the
quantum sensor while also exhibiting robust
spin properties from 4~K to room temperature (RT). The Hahn-echo
spin coherence time exceeds \(T_2 = 3.4~\upmu\text{s}\) at 4~K, outperforming values in bulk organic
crystals and overturning the prevailing expectation that
spin inevitably deteriorates upon approaching the surface. By chemically tuning the molecule through deuteration, \(T_2\) improves by more than 10-fold, and under dynamic decoupling, coherence is prolonged to the intrinsic lifetime limit, exceeding 300~\(\upmu\text{s}\). Proximal
proton spins and the
magnetic response of two-dimensional magnets beneath the hBN layer have been detected at RT. These molecular
spins form surface
quantum sensors with long coherence, optical addressability, and interfacial versatility, enabling a scalable, adaptable architecture beyond what conventional solid-state platforms offer.
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All authors Xuankai Zhou, Yan-Tung Kong, Cheuk Kit Cheung, Guodong Bian, Reda Moukaouine, King Cho Wong, Yumeng Sun, Cheng-I Ho, Vladislav Bushmakin, Nils Gross, Chun-Chieh Yen, Tim Priessnitz, Malik Lenger, Sreehari Jayaram, Takashi Taniguchi, Kenji Watanabe, Anton Pershin, Ruoming Peng, Ádám Gali, Jurgen Smet, Jörg Wrachtrup
Materials Science · Cross-listed from quant-ph
A Surface-Scaffolded Molecular Qubit
Tian-Xing Zheng, M. Iqbal Bakti Utama, Xingyu Gao et al. (+24 more)
Fluorescent
spin qubits are central building blocks of
quantum technologies. Placing these
qubits at surfaces maximizes coupling to nearby
spins and fields, enabling nanoscale sensing and facilitating integration with photonic and superconducting devices. However, reducing the dimensions or size of established
qubit systems without sacrificing the
qubit performance or degrading the coherence lifetime remains challenging. Here, we introduce a surface molecular
qubit formed by pentacene molecules scaffolded on a two-dimensional (2D) material, hexagonal boron nitride (hBN). The
qubit exhibits stable fluorescence and optically detected
magnetic resonance (ODMR) from cryogenic to ambient conditions. With fully deuterated pentacene, the Hahn-echo coherence reaches 22 $\mu$s and further extends to 214 $\mu$s under dynamical decoupling, outperforming state-of-the-art shallow NV centers in diamond, despite being positioned directly on the surface. We map the local
spin environment, resolving couplings to nearby
nuclear and electron
spins that can serve as auxiliary
quantum resources. This platform combines true surface integration, long
qubit coherence, and scalable fabrication, opening routes to
quantum sensing,
quantum simulation, and hybrid
quantum devices. It also paves the way for a broader family of 2D material-supported molecular
qubits.
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All authors Tian-Xing Zheng, M. Iqbal Bakti Utama, Xingyu Gao, Moumita Kar, Xiaofei Yu, Sungsu Kang, Hanyan Cai, Tengyang Ruan, David Ovetsky, Uri Zvi, Guanming Lao, Yu-Xin Wang, Omri Raz, Sanskriti Chitransh, Grant T. Smith, Leah R. Weiss, Magdalena H. Czyz, Shengsong Yang, Alex J. Fairhall, Kenji Watanabe, Takashi Taniguchi, David D. Awschalom, A. Paul Alivisatos, Randall H. Goldsmith, George C. Schatz, Mark C. Hersam, Peter C. Maurer
Materials Science
Global Plane Waves From Local Gaussians: Periodic Charge Densities in a Blink
Jonas Elsborg, Felix Ærtebjerg, Luca Thiede et al. (+3 more)
We introduce ELECTRAFI, a fast, end-to-end differentiable model for predicting periodic charge densities in crystalline materials. ELECTRAFI constructs anisotropic Gaussians in real space and exploits their closed-form
Fourier transforms to analytically evaluate plane-wave coefficients via the Poisson summation formula. This formulation delegates non-local and periodic behavior to analytic transforms, enabling reconstruction of the full periodic charge density with a single inverse FFT. By avoiding explicit real-space grid probing, periodic image summation, and spherical harmonic expansions, ELECTRAFI matches or exceeds state-of-the-art accuracy across periodic
benchmarks while being up to $633 \times$ faster than the strongest competing method, reconstructing
crystal charge densities in a fraction of a second. When used to initialize DFT calculations, ELECTRAFI reduces total DFT compute cost by up to ~20%, whereas slower charge density models negate savings due to high inference times. Our results show that accuracy and inference cost jointly determine end-to-end DFT speedups, and motivate our focus on efficiency.
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All authors Jonas Elsborg, Felix Ærtebjerg, Luca Thiede, Alán Aspuru-Guzik, Tejs Vegge, Arghya Bhowmik
Materials Science · Cross-listed from physics.bio-ph
Controlled drug delivery from chitosan-coated heparin-loaded nanopores anodically grown on nitinol shape-memory alloy
M. Moradi, E. Salahinejad, E. Sharifi et al. (+1 more)
Nitinol (NiTi shape-
memory alloy) is an interesting candidate in various medical applications like dental, orthopedic, and cardiovascular devices, owing to its unique mechanical behaviors and proper biocompatibility. The aim of this work is the local controlled delivery of a cardiovascular drug, heparin, loaded onto nitinol treated by electrochemical anodizing and chitosan coating. In this regard, the structure, wettability, drug release kinetics, and
cell cytocompatibility of the specimens were analyzed in vitro. The two-stage anodizing process successfully developed a regular nanoporous layer of Ni-Ti-O on nitinol, which considerably decreased the sessile water contact angle and induced hydrophilicity. The application of the chitosan coatings controlled the release of heparin mainly by a diffusional mechanism, where the drug release mechanisms were evaluated by the Higuchi, first-order, zero-order, and Korsmeyer-Pepass models. Human umbilical cord endothelial
cells (HUVECs) viability assay also showed the non-cytotoxicity of the samples, so that the best performance was found for the chitosan-coated samples. It is concluded that the designed drug delivery systems are promising for cardiovascular, particularly stent applications.
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All authors M. Moradi, E. Salahinejad, E. Sharifi, L. Tayebi
Materials Science · Cross-listed from cond-mat.str-el
Real-Time Iteration Scheme for Dynamical Mean-Field Theory: A Framework for Near-Term Quantum Simulation
Chakradhar Rangi, Aadi Singh and Ka-Ming Tam
We present a time-domain iteration scheme for solving the Dynamical Mean-Field Theory (DMFT) self-consistent equations using retarded Green's functions in real time. Unlike conventional DMFT approaches that operate in imaginary time or frequency space, our scheme operates directly with real-time quantities. This makes it particularly suitable for near-term
quantum computing hardware with limited
Hilbert spaces, where real-time propagation can be efficiently implemented via Trotterization or variational
quantum algorithms. We map the effective
impurity problem to a finite one-dimensional chain with a small number of bath sites, solved via exact diagonalization as a proof-of-concept. The hybridization function is iteratively updated through time-domain fitting until self-consistency. We demonstrate stable convergence across a wide range of interaction strengths for the half-filled Hubbard model on a Bethe
lattice, successfully capturing the metal-to-
insulator transition. Despite using limited time resolution and a minimal bath discretization, the spectral functions clearly exhibit the emergence of Hubbard bands and the suppression of spectral weight at the
Fermi level as interaction strength increases. This overcomes major limitations of two-site DMFT approximations by delivering detailed spectral features while preserving efficiency and compatibility with
quantum computing platforms through real-time dynamics.
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Materials Science · Cross-listed from cond-mat.str-el
Magnetization Plateaus in the Spin-Orbit Coupled Bilayer Triangular Lattice Antiferromagnet Rb2Co2(SeO3)3
Shengzhi Zhang, Gabriel Silva Freitas, Vivien S. Zapf et al. (+8 more)
Geometric frustration among competing
spin exchanges can give rise to novel
quantum phases by enhancing fluctuations that drive
magnetic systems beyond the classical regime. We investigate the frustrated array of strongly correlated
spin dimers in the
bilayer triangular
lattice antiferromagnet \rcs{} under applied
magnetic fields. A cascade of magnetization plateaus appears at \(M/M_s = 1/3, 1/2, 2/3,\) and \(5/6\), together with a weak anomalous feature near \(M/M_s = 1/6\), in fields up to 60 T. Concurrent changes in magneto-dielectric response follows the plateau boundaries. The finite slope of each plateau and the absence of a zero-field gap in our ultralow-temperature ac susceptibility down to 20 mK indicate broken \(U(1)\)
spin-rotation
symmetry. A minimal
bilayer-dimer model treated with bond operator representation reproduces the low-field sequence only when \(U(1)\)
symmetry is explicitly lifted by
spin-orbit-driven, bond-dependent anisotropy. Near saturation, a projected triangular pseudospin model accounts for the high-field plateaus with modest further-neighbor interactions. These results demonstrate that anisotropic exchange arising from
spin-orbit-coupled moments is essential for stabilizing the full plateau hierarchy in \rcs{}, a mechanism overlooked in previous interpretations of Co-based triangular
bilayers.
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All authors Shengzhi Zhang, Gabriel Silva Freitas, Vivien S. Zapf, Minseong Lee, Wonjune Choi, Shi-Zeng Lin, Tong Chen, Collin Broholm, Xianghan Xu, Robert J. Cava, Eun Sang Choi
Materials Science
Atomic imaging of 2D transition metal dihalides
Wendong Wang, Gareth R.M Tainton, Nick Clark et al. (+14 more)
Transition metal di-iodides such as FeI2, NiI2 and CoI2 are an emerging class of 2D magnets exhibiting rich and diverse
magnetic behaviour, but their study at the monolayer limit has been severely hindered by fabrication challenges due to their air-sensitivity. Here, we introduce a
polymer-free method for clean, rapid, and high-yield assembly of hermetically encapsulated suspended samples of air-sensitive monolayers. Applying it to di-iodides enables atomic resolution characterisation of thin samples - down to the monolayer limit - for the first time. Our imaging, combined with complementary first-principles calculations, reveals an unusually small energy barrier between alternate stable stacking polytypes in few-layer films, enabling extrinsic control of the stacking phase. We also observe stable isolated iodine vacancies that do not aggregate to form extended structures, and identify and verify the stability of the various edge configurations of thin samples. These results establish the unique structural characteristics of these materials in the thin limit, and more broadly demonstrate the utility of our transfer platform for creating atomically clean suspended vdW
heterostructures.
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All authors Wendong Wang, Gareth R.M Tainton, Nick Clark, James G. McHugh, Xue Li, Sam Sullivan-Allsop, David G. Hopkinson, Oldrich Cicvarek, Francisco Selles, Rui Zhang, Joshua D. Swindell, Alex Summerfield, David J. Lewis, Vladimir I Falko, Zdenek Sofer, Sarah J. Haigh, Roman Gorbachev
Materials Science
Comparative Analysis of Plasticity-based GND Density Estimation Methods in Crystal Plasticity Finite Element Models
Michael Pilipchuk, Chaitali Patil and Veera Sundararaghavan
In
crystal plasticity finite element (CPFE) simulations, accurately quantifying geometrically necessary dislocations (GNDs) is critical for capturing strain gradients in polycrystals. We compare different methods for quantifying GNDs, all of which originate from the Nye tensor, which is computed as the curl of the plastic deformation gradient. The projection technique directly decomposes the Nye tensor onto individual screw and edge dislocation components to compute GNDs. This approach requires converting a nine-component Nye tensor into densities for a larger number of dislocation systems, a fundamentally underdetermined (non-unique) process, which is resolved using $L2$ minimization. In contrast, when employing CPFE analysis, one could directly compute dislocation densities on each slip system using shear gradients. Projection and slip gradient methods are compared with respect to their prediction of GNDs with changing grain size, strain, and grain neighborhoods, including multigrain junctions. Although these techniques match analytical GND densities for single slip, single
crystal deformation, and are consistent with anticipated overall GND trends, we find that the GND densities from projection techniques are significantly lower than those predicted from CPFE-based slip gradients in polycrystals. A suggested improvement of only using the active dislocation systems in the projection technique almost entirely resolved this mismatch.
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Materials Science · Cross-listed from physics.chem-ph
Locally Scaled Self-Interaction Corrected Energy Functionals with Complex Optimal Orbitals
Jukka John, Hlynur Gu{\dh}mundsson, I{\dh}unn Björg Arnaldsdóttir et al. (+2 more)
We present a fully variational locally scaled self-interaction corrected (SIC) energy functional using complex optimal orbitals. This represents an important milestone for fully variational SIC energy functionals, which have been shown to improve the prediction of the properties of atomic, molecular and solid state systems in general, in both ground and excited states. However, it depends on the system and property of the system whether it is beneficial to scale the SIC correction by a factor of one-half, which makes the application of SIC inconsistent. In the limit of a single electron the SIC exactly cancels the self interaction error, but overcorrects the error in regions of high density where there is large overlap between occupied orbitals. The newly implemented local scaling function, $z(\mathbf{r})$, which is based on an iso-orbital indicator derived from considering the kinetic energy density in the iso-electron and many electron case, and takes into account that the orbitals are complex, naturally scales the SIC correction from $0\leq z(\mathbf{r}) \leq 1$ in regions of high and low (isolated orbital) electron density. The locally scaled and fully variational SIC framework is general and applicable to atomic, molecular and solid-state systems.
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All authors Jukka John, Hlynur Gu{\dh}mundsson, I{\dh}unn Björg Arnaldsdóttir, Hannes Jónsson, Elvar Örn Jónsson
Materials Science
Revealing the (111) surface electronic structure of epitaxially grown Na$_2$KSb photocathode
N.Yu. Solovova, V.A. Golyashov, S.V. Eremeev et al. (+5 more)
A recent study has established the Na$_2$KSb(Cs) photocathode as a highly efficient emitter of
spin-polarized electrons. However, the electronic structure of alkali antimonides remains poorly understood. In this work, we report the first crystalline epitaxial growth of Na$_2$KSb films, achieved via chemical vapor deposition (CVD) on a
graphene-coated SiC(0001) substrate. The high crystalline quality of these films enabled a direct investigation of the material's electronic structure using angle-resolved photoemission spectroscopy (ARPES). By comparing the experimental results with density functional theory (DFT) calculations, we have identified dispersive surface states originating from different terminations of the Na$_2$KSb(111) surface. Furthermore, we demonstrate that the crystalline order of the film is preserved following its activation via the deposition of Cs and Sb. This finding opens a pathway for investigating the electronic structure of multialkali Na$_2$KSb(Cs) photocathodes and for rationally improving their properties.
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All authors N.Yu. Solovova, V.A. Golyashov, S.V. Eremeev, S.Yu. Priobrazhenskii, S.P. Lebedev, A.A. Lebedev, V.S. Rusetsky, O.E. Tereshchenko
Materials Science
Lanthanide-Dependent Clustering in Yb$^{3+}$/Ln$^{3+}$ Co-Doped CaF$_2$ Nanocrystals: Correlating Spectroscopic Signatures with DFT Insights
Sangeetha Balabhadra, Haoming Xu, Jiajia Cai et al. (+3 more)
The formation of heterogeneous lanthanide-ion clusters in CaF$_2$ was investigated experimentally and computationally. CaF$_2$ nanoparticles co-doped with 20~mol% Yb$^{3+}$ and 2~mol% Ln$^{3+}$ (Ln$^{3+}$ = Ce$^{3+}$, Pr$^{3+}$, Nd$^{3+}$, Sm$^{3+}$, Eu$^{3+}$, Gd$^{3+}$, Ho$^{3+}$, Er$^{3+}$, and Tm$^{3+}$) were synthesized via a hydrothermal method. The structural and morphological properties were characterized using powder X-ray diffraction, dynamic light scattering, and transmission electron microscopy techniques. High-resolution
Fourier transform infra-red spectroscopy revealed the presence of Yb$^{3+}$ isolated cubic centers and various cluster sites. The relative concentration of the clusters varied with the choice of the co-doping ion. Calculations based on density functional theory were used to estimate the formation energies and local coordination structures of different clusters. The calculations indicate that the neutral $C_{4v}$ aggregations containing Ln$^{3+}$ tend to decrease across the lanthanide series, while the negatively charged derivatives of hexameric clusters are relatively constant. This variation matches the experimental results. This study advances understanding of the clustering mechanisms in lanthanide-doped CaF$_2$ nanoparticles and has implications for luminescence optimization in advanced nanomaterials.
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All authors Sangeetha Balabhadra, Haoming Xu, Jiajia Cai, Chang-Kui Duan, Michael F. Reid, Jon-Paul R. Wells
Materials Science
All-electrical switching of spin texture in a strain-tunable 2D Janus ferroelectric altermagnet
Tao Yao, Quan Shen, Wenhu Liao et al. (+2 more)
Altermagnetism (AM), a collinear
magnetic phase with momentum-dependent
spin splitting, is a promising candidate for strong magnetoelectric coupling. However, realizing direct and tunable coupling between ferroelectricity (FE) and AM within a single two-dimensional (2D) material remains an outstanding challenge. Here, based on first-principles calculations, we identify the distorted phase of monolayer Janus VOClBr as an intrinsic 2D FE-AM. This phase demonstrates robust magnetoelectric coupling, as evidenced by a complete reversal of momentum-space
spin polarization upon FE switching, and further supported by
spin texture analysis and the magneto-optical Kerr effect. Notably, the FE properties are highly strain-tunable: biaxial compression strain of -4% reduces the FE polarization switching barrier by approximately 87%, whereas a tensile strain of +3% induces a phase transition to an antiferromagnet. Leveraging the lock-in between the electrically controlled
spin texture and the magneto-optical Kerr effect signal, we propose a non-volatile, polymorphic spintronic
memory device featuring all-electrical writing and optical readout. This work establishes 2D FE-AMs as a versatile platform for coupled ferroic orders and paves the way for voltage-controlled, multifunctional
spin-logic devices.
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All authors Tao Yao, Quan Shen, Wenhu Liao, Jianing Tan, Jiansheng Dong
Materials Science · Cross-listed from cond-mat.mes-hall
Dual-Switch Control of a Layer-Locked Anomalous Valley Hall Effect in a Sliding Ferroelectric Antiferromagnet
Quan Shen, Wenhu Liao, Degao Xu et al. (+2 more)
The integration of ferroelectric (FE) and
antiferromagnetic (AFM) orders in twodimensional (2D) materials provides a promising avenue for the nonvolatile control of coupled
spin and valley degrees of freedom, a capability central to advancing spinvalleytronics. However, realizing a single material system where these
quantum states can be independently and reversibly manipulated by distinct stimuli, a prerequisite for multifunctional devices, has remained elusive. Here, we demonstrate a dual-switch mechanism in
bilayer VS2, a room-temperature FE-AFM system, that enables electrical and
magnetic control of a layer-locked anomalous valley
Hall effect (AVHE). First-principles calculations reveal that interlayer sliding breaks spatial inversion
symmetry, inducing a switchable out-of-plane FE polarization that coexists with interlayer AFM. The
spin-orbit coupled valley polarization can be reversibly switched either by FE polarization reversal or by a
magnetic-field-induced
spin-flip transition, confirming the existence of electrically and magnetically addressable valley states. The Berry
curvature exhibits both valley-contrasting and layer-locked characteristics, which underpin a switchable
Hall response. Notably, electric and
magnetic switching are functionally equivalent in modulating valley, layer, and
spin indices, revealing strong magnetoelectric coupling. This work establishes a multidegree-of-freedom operational paradigm in 2D multiferroics and opens a viable design pathway toward multi-state
memory and
spin-valleytronic logic devices.
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All authors Quan Shen, Wenhu Liao, Degao Xu, Jiansheng Dong, Jianing Tan
Materials Science
Discrete Dislocation Dynamics Modeling of Nanotwinned Materials: Orientation Effects in a Multilayer Twinned Structure of Copper
DeAn Wei, Michael Zaiser, Jing Tang et al. (+1 more)
The impact of twin boundaries (TBs) on the microstructure
evolution and plastic deformation mechanisms of face-centered cubic (FCC) metals has been extensively studied since the discovery that nanotwinned materials exhibit a favorable combination of high strength and ductility. In this work, a dislocation-twin boundary interaction model for copper is incorporated into a three-dimensional discrete dislocation dynamics (DDD) framework. This approach is applied to systematically investigate the orientation effects on the deformation of nanotwinned copper, utilizing a multilayer twinned structure (MTS) with a twin thickness of 160 nm. The simulation results show that the stress-strain response of MTSs under uniaxial loading depends significant on the orientation of the loading axis. Dislocations inclined to TBs are confined to slip in single- or multi-layer twin lamellae; when the loading axis is oriented perpendicular or parallel to TBs, such whereas when loading axis inclined to TBs, the dislocations with glide plane parallel to TBs are easily activated (mainly twinning dislocations) and the TBs do not hinder the dislocations and behave in soft modes. If the hard mode dominates the deformation mechanism, microstructures with single-layer confined slip lead to significant hardening behavior, while microstructures with multilayer confined slip maintain stable plastic flow and do not lead to hardening. Finally, through the introduction of critical resolved shear stresses (CRSSs) specific to various deformation modes and the adaptation of Schmid's law, we have effectively projected the additional anisotropic characteristics induced by TBs in MTSs.
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All authors DeAn Wei, Michael Zaiser, Jing Tang, Xu Zhang
Materials Science
Near-field effects on cathodoluminescence outcoupling in perovskite thin films
Robin Schot, Imme Schuringa, Álvaro Rodríguez Echarri et al. (+7 more)
Halide perovskite
semiconductors are a promising material for high-efficiency
solar cells. Their optical properties can vary within and between crystallographic grains. We present spatially-resolved cathodoluminescence (CL) spectroscopy at 2 keV and 5 keV on polycrystalline CsPbBr3 perovskite films to study these variations at the nanoscale. The CL maps show a strongly reduced intensity near the polycrystalline grain boundaries. We perform numerical simulations of the far-field emission of the electron beam-generated optical near fields using the surface profiles from AFM as input. We find that near grain boundaries the light outcoupling is strongly reduced due to enhanced internal reflection and light trapping at the curved surfaces. Lateral variations in CL intensity inside grains are due to Fabry-Perot-like resonances in the film, with the substrate acting as a back reflector. Our results show that near-field coupling and interference effects can dominate nanoscale luminescence maps of halide perovskite films. The results are broadly relevant for the analysis of cathodoluminescence and photoluminescence of corrugated thin films.
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All authors Robin Schot, Imme Schuringa, Álvaro Rodríguez Echarri, Lars Sonneveld, Tom Veeken, Yang Lu, Samuel D. Stranks, Albert Polman, Bruno Ehrler, Saskia Fiedler
Materials Science
Si-Ga2O3/p-GaN epitaxial heterostructure based self-powered and visible-blind UV photodetectors with fast and electrically tuneable response time
Ajoy Biswas, Amandeep Kaur, Bhabani Prasad Sahu et al. (+5 more)
n-Ga2O3/p-GaN heterojunction based photodetector devices are fabricated on Si-doped (-201) \beta-Ga2O3 epitaxial layers grown by pulsed
laser deposition (PLD) technique on p-type c-GaN/sapphire templates. These devices demonstrate the ability to act as highly efficient self-powered visible blind UV-photodetectors with fast response time. It has been found that the optimum performance of the detector in terms of its responsivity, detectivity and response time could be achieved by adjusting the Si doping level and the thickness of the Ga2O3 layer. Our best performing device showing the peak responsivity and detectivity of 56.8 mA/W and 3*10^12 Jones, respectively, is achieved for 660 nm thick Ga2O3 layer with Si-concentration of 8*10^18 cm^-3. Moreover, as low as a few nW of optical signal can be sensed by the detector. The response time of the detector is found to be only a few tens of nanoseconds, which highlights their potential for application in ultrafast detection of UV light. These devices also exhibit a slower component of photoresponse with a timescale of a few tens of milliseconds. Interestingly, the time-scale of the slower response can be prolongated by several orders of magnitude through enhancing the applied reverse bias. Such an electrical tuneability of the response time is highly desirable for neuromorphic device applications.
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All authors Ajoy Biswas, Amandeep Kaur, Bhabani Prasad Sahu, Sushantika Saha, Umakanta Patra, Rupa Jeena, Pradeep Sarin, Subhabrata Dhar
Materials Science
2D abrupt nano-junctions blending sp-sp2 bonds on atomically precise heterostructures
Alice Cartoceti, Simona Achilli, Masoumeh Alihosseini et al. (+8 more)
Two-dimensional
heterostructures combining sp-sp2 hybridization,blending
graphene with graphyne-based allotropes, offer substantial potential for enhancing the tunability of electronic and transport properties while providing significant structural flexibility. These attributes are desirable for next generation nanoscale electronic applications. Despite such potential, their experimental realization remains elusive, as synthesized carbon
heterostructures are limited to doped,
graphene-based systems exhibiting exclusively sp2 hybridization. Here, we demonstrate the on-surface synthesis of covalently bonded sp-sp2 lateral
heterostructures between
graphene nanoribbons and graphdiyne networks on Au(111). Atomic-resolution scanning tunnelling microscopy, combined with density functional theory, reveals the formation mechanism of the covalent interfacial bonds between nanoribbons and graphdiynes, also highlighting the key role of surface chemistry. Bromine atoms deriving from the molecules dehalogenation and chemisorbed along the nanoribbon inhibit the junction formation, but bonding efficiency can be boosted up to 71% by controlled removal of these by-products. Electronic structure and transport calculations show that the 2D
heterostructure by itself is characterized by disentangled properties for the two subsystems, forming an atomically narrow junction enabling voltage-tunable spatial current separation in two dimensions. There results define a viable strategy for engineering
graphene-based sp-sp2
heterostructures, paving the way for the design and synthesis of all-carbon nanoscale electronic architectures.
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All authors Alice Cartoceti, Simona Achilli, Masoumeh Alihosseini, Adriana E. Candia, Enrico Beltrami, Paolo D'Agosta, Alessio Orbelli Biroli, Francesco Sedona, Andrea Li Bassi, Jorge Lobo Checa, Carlo S. Casari
Materials Science
Charge redistribution at metal-ZrO2 interfaces: A combined DFT and continuum electrostatic study
Ximeng Wang, Yongfeng Zhang, Dmitry Skachkov et al. (+5 more)
Nanoscale metallic inclusions (NMIs) are commonly observed within
oxide scales formed during high-temperature oxidation, revealing the existence of chemical and electronic heterogeneity beyond conventional corrosion theories that assume homogeneous, fully oxidized films. Using tetragonal zirconia (tZrO2) facing a series of face-centered cubic (fcc) metals as the model system, this work investigates the short-range and long-range charge redistributions across metal-
oxide interfaces by coupling density functional theory (DFT) calculations with continuum modeling. We show that metal-
oxide contact induces a short-range charge redistribution confined to a few atomic layers and a long-range redistribution of space charge that can extend over macroscopic distances within weakly doped
oxides. DFT calculations show that the short-range redistribution is dominated by metal induced gap states (MIGS) in tZrO2 facing noble metals like Au and Ag, and by chemical bonding in tZrO2 facing active metals like Al. DFT-informed continuum theoretical analysis shows that the range of space-charge redistribution is governed by the doping level of tZrO2, and that the Schottky barrier height (SBH) exhibits a stronger dependence on the metal work function than the doping level. Both the short-range and long-range charge redistributions can alter the transport of charge carriers via their associated electric fields, extending several nm to hundreds of nm from the interface, depending on the doping concentrations, suggesting possible heterogeneous
oxide growth caused by NMIs.
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All authors Ximeng Wang, Yongfeng Zhang, Dmitry Skachkov, Arnab Das, Junliang Liu, Alexander Kvit, Jennifer T. Choy, Adrien Couet
Materials Science
Mapping optical, chemical, structural features in ZrO2 via cross-sectional SEM-Cathodoluminescence correlation microscopy
Ricardo Vidrio, Yuhan Tong, Junliang Liu et al. (+11 more)
Understanding how nanoscale heterogeneities influence charge transport and mass transfer in
oxides is critical for developing advanced materials for energy and electronic uses. In high-temperature applications, the formation of thermal
oxides with complex chemical and structural features plays a central role in material lifetime. While thermally grown zirconia (ZrO2) on zirconium
alloys exhibits strong chemical and microstructural gradients across the
oxide thickness, linking these heterogeneities to electronic-defect landscapes remains challenging. We demonstrate cross-sectional scanning electron microscope-cathodoluminescence (SEM-CL) as a mesoscale probe of spatial variations in luminescence in zirconia and establish correlations with co-registered electron backscatter diffraction (EBSD) and electron probe micro-analysis (EPMA) on the same region. The SEM-CL signal is dominated by the ~2.7 eV defect band, but its intensity varies strongly across the
oxide cross section. Correlative EBSD-CL analysis reveals that CL intensity increases with grain area and decreases at the grain boundaries, consistent with enhanced non-radiative recombination associated with microstructural disorder. EPMA mapping shows that a substantial fraction of CL-dark features co-localize with secondary phase precipitates enriched in iron. These results show that SEM-CL contrast in corrosion-grown ZrO2 is controlled by both chemical heterogeneity and microstructural disorder, underscoring the need for correlative registration to interpret CL images. This multi-modal approach provides an efficient route to connect electronic properties and luminescence signatures across complex
oxide cross sections to underlying chemistry and microstructure, thereby providing a pathway to relate local defect landscapes to regions likely to bias electronic/ionic transport during oxidation.
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All authors Ricardo Vidrio, Yuhan Tong, Junliang Liu, Bil Schneider, William O. Nachlas, Nathan Curtis, Maryam Zahedian, Alexander Kvit, Hongliang Zhang, Zefeng Yu, Ximeng Wang, Yongfeng Zhang, Adrien Couet, Jennifer T. Choy
Materials Science · Cross-listed from cond-mat.str-el
Probing multipolar order in the candidate altermagnet MnF$_2$ through the elastocaloric effect under strain
Rahel Ohlendorf, Luca Buiarelli, Hilary M. L. Noad et al. (+5 more)
Altermagnets break a combination of time-reversal and rotational
symmetries without generating a net magnetization. As such, the order parameter of $d$-wave altermagnets has the same
symmetry as
magnetic multipoles, and couples to the product of a
magnetic field and uniaxial strain. We combine elastocaloric experiments, free-energy modeling, and first-principles calculations on MnF$_2$ to establish a thermodynamic probe of the predicted finite-temperature altermagnetic critical point. These results pave the way to explore altermagnetic
quantum criticality in $d$-wave materials and beyond.
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All authors Rahel Ohlendorf, Luca Buiarelli, Hilary M. L. Noad, Andrew P. Mackenzie, Rafael M. Fernandes, Turan Birol, Jörg Schmalian, Elena Gati
Materials Science
Symmetry Adapted Analysis of Screw Dislocation: Electronic Structure and Carrier Recombination Mechanisms in GaN
Yuncheng Xie, Haozhe Shi, Menglin Huang et al. (+3 more)
As fundamental one-dimensional defects, screw dislocations profoundly reshape the energy landscape and carrier dynamics of crystalline materials. By restoring the exact
algebra of the screw dislocation group, we unveil the latent
symmetry constraints that govern the electronic structure, providing a more rigorous physical picture than the conventional treatments. When applied to GaN, the method yields a band-connectivity constraint and rigorous dipole selection rules for polarization-resolved transitions. Combined with computed
Hamiltonian matrix, the approach gives
symmetry-filtered radiative and dielectric calculations and reveals a piezoelectrical effect at the dislocation core that strongly suppresses radiative recombination. The pronounced dominance of non-radiative capture over radiative recombination highlights the detrimental impact of screw dislocations on the luminous efficiency of GaN, providing a theoretical foundation for optimizing dislocation-limited optoelectronic devices.
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All authors Yuncheng Xie, Haozhe Shi, Menglin Huang, Weibin Chu, Shiyou Chen, Xin-Gao Gong
Materials Science
Site preference of chalcogen atoms in 1T$^\prime$ $MX_{2(1-x)}Y_{2x}$ ($M=$ Mo and W; $X, Y=$ S, Se, and Te)
Shota Ono and Ryotaro Ohse
The
insulator-metal transition, accompanying the structural phase transition from 2H to 1T$^\prime$ structure, has been reported in two-dimensional W-S-Te and W-Se-Te systems. It is also reported that Te atoms tend to occupy a specific site of the 1T$^\prime$ structure. Here, we study the site preference of chalcogen atoms in $MX_{2(1-x)}Y_{2x}$ ($M=$ Mo and W; $X, Y=$ S, Se, and Te; $0\le x \le 1$) using first-principles approach. We demonstrate that the site preference of chalcogen atoms explains the universal correlation between the formation energy and the Peierls-like distortion amplitude in the 1T$^\prime$ phase. The impact of the site preference on the linear elastic properties is strong, whereas its impact is weak in the non-linear regime. This establishes the structure-property relationships in $MX_{2(1-x)}Y_{2x}$ systems.
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Materials Science
Mapping Metastable Magnetic Textures in (Fe0.5Co0.5)5GeTe2 with in-situ Lorentz Transmission Electron Microscopy
Reed Yalisove, Hongrui Zhang, Xiang Chen et al. (+5 more)
Topologically protected
magnetic textures are a promising route to low-energy control of magnetism, but they are most often studied away from ambient conditions, typically at low temperatures and high
magnetic fields. Here we use in-situ Lorentz transmission electron microscopy with control of temperature and
magnetic field to investigate the skyrmion metastability in (Fe0.5Co0.5)5GeTe2 (FCGT). By field-cooling FCGT in
magnetic fields of different magnitude to different base temperatures and then removing the applied field, we create meta(stable) zero-field
magnetic states. We use this method to build a phase diagram of the zero-field metastable
spin structures in FCGT, which will be critical for selecting the desired topologically-protected
spin state for future studies to manipulate magnetism with stimuli such as electric current, electric field, mechanical strain, and more.
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All authors Reed Yalisove, Hongrui Zhang, Xiang Chen, Fanhao Meng, Jie Yao, Robert Birgeneau, Ramamoorthy Ramesh, Mary C. Scott
Materials Science
Atomic and Electronic Structure of Strongly Charged Domain Walls in van der Waals {\alpha}-In$_2$Se$_3$
Gillian Nolan, Edmund Han, Shahriar Muhammad Nahid et al. (+4 more)
Here, we use atomic resolution scanning transmission electron microscopy (STEM) and first principles calculations to study the atomic and electronic structure of strongly charged domain walls in $\alpha$-In$_2$Se$_3$. STEM imaging and density functional theory (DFT) show that head-to-head (HH) domain walls contain a layer of nonpolar $\beta$-In$_2$Se$_3$, whereas tail-to-tail (TT) domain walls are atomically abrupt. We apply 4D STEM and multislice electron ptychography to map ferroelectric domains in 2D and 3D, showing that nearly $180^\circ$ domain walls exhibit complex, curved 3D structures that differ from ideal $180^\circ$ structures. Band structure calculations show localized conducting states within a $\sim$ 1 nm thick layer at both HH and TT domain walls, such as a midgap state at the $\beta$ layer of the HH domain wall. These properties make strongly charged domain walls in $\alpha$-In$_2$Se$_3$ excellent candidates for realizing 2D electron or hole gases and domain wall engineering in van der Waals ferroelectrics.
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All authors Gillian Nolan, Edmund Han, Shahriar Muhammad Nahid, Patrick Carmichael, Arend M. van der Zande, André Schleife, Pinshane Y. Huang