Materials Science · Cross-listed from physics.soc-ph
The Physics of Sustainability: Material and Power Constraints for the Long Term
José Halloy, Petros Chatzimpiros, François Graner et al. (+1 more)
Much of today's sustainability discourse emphasizes efficiency, clean technologies, and smart systems, but largely underestimates fundamental physical constraints relating to energy-matter interactions. These constraints stem from the fact that Earth is a materially closed yet energetically open system, driven by the sustained but low power-density flux of
solar radiation. This Perspective reframes sustainability within these axiomatic limits, integrating relevant timescales and orders of magnitude. We argue that fossil-fueled industrial metabolism is inherently incompatible with long-term viability, while post-fossil systems are surface-, materials-, and power-intensive. Long-term sustainability must therefore be defined not only by how much energy or material is used, but also by how it is used: favoring organic, carbon-based chemistry with limited reliance on purified metals, operating at low power density, and maintaining low throughput rates. Achieving this requires radical technological shifts toward life-compatible systems and biogeochemical circular processes, and, likely as a consequence, a paradigm change toward degrowth to a steady-state. These two shifts are mutually reinforcing and together provide the necessary foundation for any viable future.
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All authors José Halloy, Petros Chatzimpiros, François Graner, Thomas Gregor
Materials Science
Ferroelectric metal-organic frameworks as wide band gap materials
Monirul Shaikh, Sathiyamoorthy Buvaneswaran, Asif Latief Bhat et al. (+2 more)
Wide band gap materials are particularly relevant at high temperatures. The band gap shrinkage at higher temperatures prevents device applications with narrow band gap
semiconductors. Considering $\alpha$-phase strontium cyanurate as a prototype structure, we identify a group of metal-organic frameworks (MOFs) that exhibit ultra-wide band gaps ranging from 5.5 to 5.7 eV. Recently, a strontium cyanurate compound was found to undergo a phase transition from a high-
symmetry $\beta$-phase to a low-
symmetry ferroelectric $\alpha$-phase when the temperature was reduced. In the present study, utilizing group theory techniques, we unravel that a zone-center $\Gamma_2^-$
phonon mode modifies our structures from high-
symmetry $\beta$-phase to a low-
symmetry $\alpha$-phase for A$_3$(O$_3$C$_3$N$_3$)$_2$ MOFs with A = Mg, Ca, Sr, and Ba. We implement first-principles calculations to investigate structural, ferroelectric, and optical properties of these compounds in $\alpha$-phase. The switching barriers between bistable polar states are also estimated. Further, to realize their feasibility, we examine the dynamical and thermal stabilities for all of these MOFs.
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All authors Monirul Shaikh, Sathiyamoorthy Buvaneswaran, Asif Latief Bhat, Trilochan Sahoo, Saurabh Ghosh
Materials Science
Thermal and Size Effects in Ferroelastic Domains by Machine Learning
Luka Geddis Zellmann, Sumner B. Harris, John R. R. Scott et al. (+4 more)
Ferroelastic domain walls (DWs) underpin key functionalities in complex
oxides. In free-standing ferroic thin films, where elastic interactions are highly thickness dependent, understanding DW behaviour across length scales and external stimuli is crucial. A thickness-dependent monopolar-to-dipolar crossover in elastic DW behaviour has been reported; however, how temperature influences this regime remains unexplored. Here, LaAlO3 thin films spanning the dipolar ($<200$ nm) and crossover (200-300 nm) regimes are investigated using in situ heating scanning transmission electron microscopy (STEM) and a machine-learning-driven image analysis approach. By tracking DW
curvature and density from above $T_C$ (approximately $550,^\circ$C) to room temperature (RT), a distinct interplay between temperature and thickness is identified. In the dipolar regime, DWs are mobile and curved near $T_C$ and gradually freeze upon cooling, consistent with the well-known temperature freezing regime. In contrast, within the crossover regime, DWs are nearly static, with minimal reconfiguration through cooling and
curvature an order of magnitude lower at RT. These results map the
evolution of DWs across the thermally driven super-elastic to freezing regimes, revealing how thickness and temperature govern DW morphology and dynamics, and providing insight relevant for domain engineering in free-standing
oxide thin films.
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All authors Luka Geddis Zellmann, Sumner B. Harris, John R. R. Scott, Yi-Chieh Yang, Joerg Jinschek, Rama Vasudevan, Miryam Arredondo
Materials Science · Cross-listed from cond-mat.mes-hall
Edge states of a Bi$_2$Se$_3$ nanosheet in a perpendicular magnetic field
Stan P. J. Koenis, Lucas Maisel Licerán and Henk T. C. Stoof
Conventional wisdom dictates that the conducting edge states of two-dimensional topological
insulators of the Bi$_2$Se$_3$ family are protected by time-reversal
symmetry. However, theoretical bulk calculations and a recent experiment show that the edge states persist in the presence of large external
magnetic fields. To address this apparent contradiction, we have developed an analytical description for the edge-state wave function of a semi-infinite sample in a perpendicular
magnetic field. Our description relies on the usual bulk Landau levels, together with additional states arising due to the presence of the hard wall, which are unnormalizable in the infinite system. The analytical wave functions agree extremely well with numerical calculations and can be used to directly analyze the behavior of the edge states in a
magnetic field.
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Materials Science
Epitaxial Sr(Sn, Ge)$_{x}$Ti$_{1-x}$O$_{3}$ buffer layers for continuous strain engineering on SrTiO$_{3}$ substrates
Ruben Hamming-Green, Ewout van der Veer and Beatriz Noheda
Epitaxial strain plays a key role in determining the structure and functionality of thin films, with the choice of substrate being traditionally used to control the magnitude of the applied strain. However, even in the large family of perovskite materials, this allows for only a limited, discrete set of strain states to be achieved. Here we report on an approach to controlling epitaxial strain for the growth of perovskite materials by involving a single SrTiO$_{3}$ substrate (the most available perovskite in single
crystal form) and a buffer layer that consists of the solid solution Sr(Sn, Ge)$_{x}$Ti$_{1-x}$O$_{3}$, of which the
lattice parameter can be tuned in a continuous fashion, from 3.880 Å up to 4.007 Å, while maintaining coherent epitaxial growth on SrTiO$_{3}$ with high quality interfaces. Using a BaTiO$_{3}$ overlayer as a model system, we show that changes to the buffer layer composition, i.e. increase of in-plane
lattice parameter, change the strain state of BaTiO$_{3}$ from fully relaxed, through highly compressively strained, to an exotic state showing 'inverted' epitaxy in which the buffer layer is relaxed from the substrate but
lattice matched to the overlayer.
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Materials Science
An intermediately-homogenized peridynamics approach to failure of microstructually disordered materials
Shucheta Shegufta and Michael Zaiser
Peridynamics provides a versatile tool for fracture modelling in materials where fracture pathways cannot be predicted beforehand, but must be envisaged as an emergent features of the deformation process. One class of materials where this is surely the case are materials with strong microstructural disorder such as random composites, random porous materials or disordered metamaterials. For this class of materials we propose an intermediately-homogenized peridynamic modelling approach where the disordered microstructure is not resolved in full spatial detail but described in terms of random order parameter fields which retain essential information about the local heterogeneity and spatial correlations of material properties.
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Materials Science · Cross-listed from physics.med-ph
Event-sparse stack denoising for 4D-STEM applications
Gregory Nordahl, Rebekka Klemmt and Espen Drath Bøjesen
We introduce a denoising method for four-dimensional scanning transmission electron microscopy (4D-STEM) that relies on processing local, scan position-independent electron event-sparse data stacks, called event-sparse stack denoising. This method adds an extra time dimension during data collection by recording multiple electron event-sparse diffraction patterns. The resulting
datasets are effectively five-dimensional, referred to as locally time-resolved STEM (LTR-STEM). Diffraction data stacks at each scan position are processed using one of two sparsity denoising pipelines: 1) the density-based spatial clustering of applications with noise (DBSCAN)
algorithm followed by multi-step persistence thresholding, or 2) sparse principal component analysis (sparse PCA), followed by single-step thresholding. Both methods perform well for diffraction data denoising, as shown by simulated peak signal-to-noise ratio (PSNR) curves, denoised experimental data for virtual imaging, and application-specific denoising for defect detection. PSNR analysis indicates that sparsity-denoised 4D-STEM data reaches the same PSNR as raw data at approximately 16% of the exposure time, demonstrating comparable image quality with a lower dose. In defect detection, a 4.1x increase in sensitivity to relative radial disk shift is observed in the denoised data. Moreover, the LTR-STEM technique may be used to inspect material degradation by tracking changes in diffraction disk intensity, allowing for critical dose estimation and exposure-selective imaging.
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Materials Science · Cross-listed from cond-mat.soft
A molecular dynamics study of surface-directed spinodal decomposition on a chemically patterned amorphous substrate
Syed Shuja Hasan Zaidi, Hema Teherpuria, Santosh Mogurampelly et al. (+1 more)
We employ a molecular dynamics (MD) study to explore pattern selection in binary fluid mixtures ($AB$) undergoing surface-directed spinodal decomposition on a chemically patterned amorphous substrate. We chose a checkerboard pattern with chemically distinct square patches of a side $M$, with neighboring patches preferring different particle types. We report the efficient transposition of the substrate's pattern as a registry to the fluid cross sections in its vicinity when the pattern's periodicity $\lambda/\sigma \simeq 2M$ ($\sigma$ being the fluid particle size) is larger than the mixture's spinodal length scale $\lambda_c/\sigma \simeq 2\pi/\xi_B$ ($\xi_B$ being the bulk correlation length). Our correlation analysis between the surface field and the surface-registries in the substrate's normal direction shows that the associated decay length, $L_{\perp}(t)$, increases with decreasing pattern periodicity ($\lambda$). $L_{\perp}(t)$ also exhibits diffusive growth with time $\sim t^{1/3}$, similar to wetting-layer growth for chemically homogeneous walls. Our MD results also show the emergence of composition waves parallel to the substrate, whose wavelength exhibits dynamical scaling with a power-law growth in time $L_{||}(z,t)\sim t^{\alpha}$. $L_{||}(z,t)$ shows dynamical crossovers from a transient surface-registry regime to universal phase-separation regimes for cross-sections with registries. We also give an account of the scaling of registry's formation and melting times with patch sizes.
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All authors Syed Shuja Hasan Zaidi, Hema Teherpuria, Santosh Mogurampelly, Prabhat K. Jaiswal
Materials Science
Bio-Organic Materials Based Resistive Switching Memories
Rahul Deb, Debajyoti Bhattacharjee and Syed Arshad Hussain
Resistive switching (RS) devices, based on soft materials such as organic, biomolecules as well as natural plant extracts etc., has emerged as a promising alternative to the conventional
memory technologies. They offer simple device structures, low power requirements, rapid switching and compatibility with high-density device integration. Over the last two decades, these classes of materials have been explored for both non-volatile
memory and artificial synapse functions. This chapter provides a brief overview of RS fundamentals, their major classifications, key applications, and recent trends in the use of organic and bio-derived materials.
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Materials Science
Interfacial effect on the optoelectronic and piezoelectric properties of Ge-Sn terminated Halide Perovskite heterostructure from first-principles study
L. Celestine, R. Zosiamliana, H. Laltlanmawii et al. (+6 more)
Since the very early stages of research on sustainable technologies, green energy conversion has always been a
prime focus. With the discoveries of countless functional materials in recent years, significant progress has been made to meet the global energy demand for sustainable development. Among them, halide perovskites have emerged as one of the most promising and reliable materials. In this work, we have investigated the lead-free halide perovskites, vis CsGeCl3 and RbSnBr3, within a framework of density functional theory (DFT) to explore their potential applicability in harvesting clean and renewable energy. This study gives a comprehensive analysis of the bulk, surface (001), and Ge-Sn-terminated interfaces within GGA and mGGA functionals. Interestingly, the inherent asymmetric arrangements of the systems exhibit remarkable optoelectronic and piezoelectric properties. The piezoelectric performance of each surface cut has been validated through the electromechanical coupling calculation.
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All authors L. Celestine, R. Zosiamliana, H. Laltlanmawii, B. Chettri, Lalhum Hima, Lalhriat Zuala, S. Gurung, A. Laref, D. P. Rai
Materials Science
Atomistic understanding of two-dimensional monatomic phase-change material for non-volatile optical applications
Hanyi Zhang, Xueqi Xing, Jiang-Jing Wang et al. (+8 more)
Elemental antimony (Sb) is a promising material for phase-change
memory, neuromorphic computing and nanophotonic applications, because its compositional simplicity can prevent phase segregation upon extensive programming. Scaling down the film thickness is a necessary step to prolong the lifetime of amorphous Sb, but the optical properties of Sb are also significantly altered as the thickness is reduced to a few nanometers, adding complexity to device optimization. In this work, we aim to provide atomistic understanding of the thickness-dependent optical responses in Sb thin films. As thickness decreases, both the extinction coefficient and optical contrast reduce in the near-infrared spectrum, consistent with previous optical measurements. Such thickness dependence gives rise to a bottom thickness limit of 2 nm in photonic applications, as predicted by coarse-grained device simulations. Further bonding analysis reveals a fundamentally different behavior for amorphous and crystalline Sb upon downscaling, resulting in the reduction of optical contrast. Thin film experiments are also carried out to validate our predictions. The thickness-dependent optical trend is fully demonstrated by our ellipsometric spectroscopy experiments, and the bottom thickness limit of 2 nm is confirmed by structural characterization experiments. Finally, we show that the greatly improved amorphous-phase stability of the 2 nm Sb thin film enables robust and reversible optical switching in a silicon-based waveguide device.
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All authors Hanyi Zhang, Xueqi Xing, Jiang-Jing Wang, Chao Nie, Yuxin Du, Junying Zhang, Xueyang Shen, Wen Zhou, Matthias Wuttig, Riccardo Mazzarello, Wei Zhang
Materials Science
Engineering Multifunctional Response in Monolayer Fe3O4 via Zr Adsorption: From Half-Metallicity to Enhanced Piezoelectricity
Sikander Azam, Qaiser Rafiq, Rajwali Khan et al. (+1 more)
Two-dimensional (2D)
magnetic oxides are increasingly studied for their multifunctional potential in fields like spintronics, optoelectronics, and energy conversion. In this research, we conduct a detailed first-principles study of pure monolayer Fe3O4 and its modification through Zr adsorption at two sites: on top of an Fe atom and at the bridge between Fe atoms. Using
spin-polarized density functional theory with the GGA plus U method, we examine how adsorption affects structure, electronic,
magnetic, optical, elastic, and piezoelectric properties. The original monolayer shows half-
metallicity, strong
spin polarization, and a moderate in-plane piezoelectric effect. Zr adsorption causes local
lattice distortions and orbital hybridization, resulting in intermediate electronic states, a reduced bandgap, and increased optical absorption in both
spin channels. Notably, Zr at the bridge site greatly enhances dielectric response, optical conductivity, and piezoelectric coefficients, tripling e11 compared to the pristine layer. Elastic constants indicate mechanical softening after functionalization, and energy loss spectra display shifts in plasmon resonance. These findings suggest Zr adsorption offers a controllable, non-destructive way to tune
spin, charge, and
lattice interactions in Fe4O4 monolayers, connecting
magnetic, optical, and piezoelectric functionalities within a single 2D material platform.
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All authors Sikander Azam, Qaiser Rafiq, Rajwali Khan, Hamdy Khamees Thabet
Materials Science
Electric-Field-Controlled Altermagnetic Transition for Neuromorphic Computing
Zhiyuan Duan, Peixin Qin, Chengyan Zhong et al. (+12 more)
Altermagnets represent a novel
magnetic phase with transformative potential for ultrafast spintronics, yet efficient control of their
magnetic states remains challenging. We demonstrate an ultra-low-power electric-field control of altermagnetism in MnTe through strain-mediated coupling in MnTe/PMN-PT
heterostructures with negligible Joule heating. Application of +6 kV/cm electric fields induces piezoelectric strain in PMN-PT, modulating the Néel temperature from 310 to 328 K. As a result, around the
magnetic phase transition, the altermagnetic
spin splitting of MnTe is reversibly switched "on" and "off" by the electric fields. Meanwhile, the piezoelectric strain generates
lattice distortions and
magnetic structure changes in MnTe, enabling up to 9.7% resistance modulation around the
magnetic phase transition temperature. Leveraging this effect, we implement programmable resistance states in a Hopfield neuromorphic network, achieving 100% pattern recognition accuracy at <=40% noise levels. This approach establishes the electric-field control as a low-power strategy for altermagnetic manipulation while demonstrating the viability of altermagnetic materials for energy-efficient neuromorphic computing beyond conventional charge-based architectures.
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All authors Zhiyuan Duan, Peixin Qin, Chengyan Zhong, Shaoxuan Zhang, Li Liu, Guojian Zhao, Xiaoning Wang, Hongyu Chen, Ziang Meng, Jingyu Li, Sixu Jiang, Xiaoyang Tan, Qiong Wu, Yu Liu, Zhiqi Liu
Materials Science
First-principles study of the phase competition, mechanical and piezoelectric properties of pseudo-binary (SiC)(AlN) alloy
Laszlo Wolf, Geoff L. Brennecka and Vladan Stevanović
The ongoing search for new piezoelectric materials offering adequate balance between piezoelectric response and other application-relevant properties has lead to the investigation of various
alloy systems. In this work we study the
alloy of the widely used AlN with SiC for their relative abundance, current use in other electronics applications and expected phase competition between wurtzite and other polymorphs, the kind of which has lead to some of the most interesting results notably between AlN and ScN. Here the pseudo-binary (SiC)(AlN)
alloy is studied from first-principles over the entire composition range. Relevant crystalline phases are identified using the First-Principles Random Structure Sampling approach which, in accordance with previous bulk experiments, finds wurtzite, zincblende and rhombohedral phases to be the only statistically relevant phases of the
alloy. Further study of these phases is done through Special Quasi-random Structures (SQS) and, in the case of the wurtzite phase, predictions of the stiffness, piezoelectric and dielectric tensors. Analysis of these tensors is done through the scope of a Bulk AcousticWave (BAW) filter application, where trends and trade-offs between the c-axis acoustic velocity and piezoelectric response enable identification of relevant compositions.
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Materials Science
Structure Prediction of Ionic Epitaxial Interfaces with Ogre Demonstrated for Colloidal Heterostructures of Lead Halide Perovskites
Stefano Toso, Derek Dardzinski, Liberato Manna et al. (+1 more)
Colloidal epitaxial
heterostructures are nanoparticles composed of two different materials connected at an interface, which can exhibit properties different from those of their individual components. Combining dissimilar materials offers opportunities to create several functional
heterostructures. Yet, assessing structural compatibility (the main prerequisite for epitaxial growth) is challenging when pairing complex materials with different
lattice parameters/
crystal structures. This complicates both the selection of target
heterostructures for synthesis and the assignment of interface models when new
heterostructures are obtained. Here, we demonstrate Ogre as a powerful tool to accelerate the design and characterization of colloidal
heterostructures. To this end we implemented developments tailored for the efficient prediction of epitaxial interfaces between ionic/polar materials, which encompass most colloidal
semiconductors. These include pre-screening candidate models based on charge balance at the interface and using a classical potential for fast energy evaluations, with parameters automatically extracted from the input bulk structures. These developments are validated for CsPbBr3/Pb4S3Br2
heterostructures, where Ogre produces interface models in agreement with density functional theory and experiments. Furthermore, we use Ogre to rationalize the templating effect of CsPbCl3 on the growth of lead sulfochlorides, where perovskite seeds induce the formation of Pb4S3Cl2 rather than Pb3S2Cl2 due to better epitaxial compatibility. Combining Ogre simulations with experimental data enables us to unravel the structure and composition of the hitherto unsolved CsPbBr3/BixPbySz interface and assign a structure to many other reported metal halide/
oxide based interfaces. The Ogre package is available on GitHub or via the OgreInterface desktop application, available for Windows, Linux and Mac.
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All authors Stefano Toso, Derek Dardzinski, Liberato Manna, Noa Marom
Materials Science · Cross-listed from cs.LG
Fitting magnetization data using continued fraction of straight lines
Vijay Prakash S
Magnetization of a
ferromagnetic substance in response to an externally applied
magnetic field increases with the strength of the field. This is because at the microscopic level,
magnetic moments in certain regions or domains of the substance increasingly align with the applied field, while the amount of misaligned domains decreases. The
alignment of such
magnetic domains with an applied
magnetic field forms the physical basis for the nonlinearity of magnetization. In this paper, the nonlinear function is approximated as a combination of continued fraction of straight lines. The resulting fit is used to interpret the nonlinear behavior in both growing and shrinking
magnetic domains. The continued fraction of straight lines used here is an algebraic expression which can be used to estimate parameters using nonlinear regression.
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Materials Science
Spin-orbit torques in bulk collinear antiferromagnets:complete classifications and the induced spin dynamics
Yizhuo Song, Jianting Dong, Jiahao Shentu et al. (+1 more)
Electric field induced
spin-orbit torques are the crucial mechanism for electric regulations of
antiferromagnetic order. However, the
spin-orbit torques in antiferromagnets and the induced
spin dynamics remain largely unexplored. In this work, the full classifications of SOTs in bulk collinear AFMs have been achieved based on
magnetic point group. Dependent on the
symmetries connecting the opposite
spin sublattices, the SOTs are classified into six distinct types. Among them, the SOTs and the induced Neel vector dynamics in three representative AFMs have been investigated, where the
spin sublattices are connected by fractional translation, spatial inversion, and neither by translation nor inversion
symmetry respectively. The SOTs on
spin sublattices have been calculated by first-principles calculations based on Kubo linear response theory, and then the induced
spin dynamics are simulated by LLG equations. In typical PT symmetric AFM and the inversion
symmetry breaking altermagnet, the simulations indicate that the deterministic switching of Neel vectors can be driven by field like torques. What's more, the fully electric writing of multiple
antiferromagnetic domains into single domain state with preset Neel vector direction and 180 deterministic switching may also be realized. Our work may shed light on the current control of
antiferromagnetic orders in collinear AFMs. Especially, for inversion
symmetry breaking altermagnet, the electric writing and reading of Neel vector are highly desirable for
antiferromagnetic memory applications.
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All authors Yizhuo Song, Jianting Dong, Jiahao Shentu, Jia Zhang
Materials Science
Spin Orientation Driven Polarization in Collinear Magnets
Yixun Zhang, Longju Yu, Yizhou Tong et al. (+4 more)
In a collinear magnet, the predominant
magnetic moments are collectively aligned along a specific spatial orientation, and this
alignment may yield intriguing phenomena such as
spin orientation driven polarization. It is well known that
spin orientation driven polarization is a relativistic effect that widely occurs in various type-II multiferroics. However, a universal theory that describes such a phenomenon and directs the corresponding materials discovery is lacking. Here, we revisit the
magnetic structures of collinear magnets and explore the
spin-orientation-dependent phenomena therein. Based on
symmetry principles, we analyze the
spin point groups (SPGs) that are associated with collinear magnets in the non-relativistic regime, demonstrate how relativistic
spin-orbit interaction reduces each SPG to various
magnetic point groups that are associated with different
magnetic alignments, and classify the SPGs with respect to
spin orientation driven polarization. We employ our theory to elucidate the mechanisms of
spin orientation driven polarization in a variety of type-II multiferroics. Combined with first-principles simulations, we further show that polarization may be driven in nonpolar collinear antiferromagnets (e.g., CuFeS$_2$) by reorienting their
magnetic alignments. Our theory provides guidelines for designing and discovering materials with
spin orientation driven polarization, which will benefit the development of spintronics based on type-II multiferroics and related materials.
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All authors Yixun Zhang, Longju Yu, Yizhou Tong, Ying Sun, Xu Li, Hong Jian Zhao, Yanming Ma
Materials Science
Fresnel Magnetic Imaging of Ultrasmall Skyrmion Lattices
Yongsen Zhang, Wei Liu, Meng Shi et al. (+9 more)
Magnetic skyrmions with ultrasmall nanometric dimensions hold significant promise for next-generation high-density spintronic devices. Direct real-space imaging of these topological
spin textures is critical for elucidating their emergent properties at the nanoscale. Here, we present Lorentz transmission electron microscopy studies of nanometric skyrmion
lattices in B20-structured Mn0.5Fe0.5Ge
crystals using Fresnel mode. According to conventional
chiral discrimination methods relying on static bright-dark contrast, we demonstrate an abnormal periodic
chiral-reversal phenomenon retrieved through the transport of intensity equation analysis of defocus-dependent Fresnel images. Through systematic off-axis electron holography experiments and numerical simulations, we attribute these
chiral misinterpretations to the sinusoidal modulation mechanism of the contrast transfer functionthat correlates with both defocus values and skyrmion dimensions. Our findings establish quantitative limitations of conventional Fresnel contrast analysis for ultrasmall skyrmions while revealing fundamental insights into defocus-mediated phase-to-intensity conversion processes in nanoscale
magnetic imaging.
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All authors Yongsen Zhang, Wei Liu, Meng Shi, Yaodong Wu, Jialiang Jiang, Sheng Qiu, Huanhuan Zhang, Hui Han, Mingliang Tian, Haifeng Du, Shouguo Wang, Jin Tang
Materials Science
Infusing Experimental Reality into Complex Many-Body Hamiltonians: The Observable-Constrained Variational Framework (OCVF)
Shaoliang Guo and Ziping Yang
Deep learning potentials for complex many-body systems often face challenges of insufficient accuracy and a lack of physical realism. This paper proposes an "Observable-Constrained Variational Framework" (OCVF), a general top-down correction paradigm designed to infuse physical realism into theoretical "skeleton" models (H_o) by imposing constraints from macroscopic experimental observables (\mathfrak{O}_{\text{exp},s}). We theoretically derive OCVF as a numerically tractable extension of the "Constrained-Ensemble Variational Method" (CEVM), wherein a neural network (\Delta H_\theta) learns the correction functional required to match the experimental data. We apply OCVF to BaTiO3 (BTO) to validate the framework: a neural network potential trained on DFT data serves as H_o, and experimental PDF data at various temperatures are used as constraints (\mathfrak{O}{\text{exp},s}). The final model, H_o + \Delta H_\theta, successfully predicts the complete phase transition sequence accurately (s', s \neq s'). Compared to the prior model, the accuracy of the Cubic-Tetragonal (C-T) phase transition temperature is improved by 95.8% , and the Orthorhombic-Rhombohedral (O-R) T_c accuracy is improved by 36.1%. Furthermore, the
lattice structure accuracy in the Rhombohedral (R) phase is improved by 55.6%, validating the efficacy of the OCVF framework in calibrating theoretical models via observational constraints.
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Materials Science
Development of a Ferromagnetic Resonance Measurement System Using NanoVNA
Reo Fukunaga, Ryunosuke Takahashi, Tetsuro Ueno et al. (+3 more)
Ferromagnetic resonance (FMR) is a fundamental technique for probing magnetization dynamics in spintronic and
magnetic materials. However, conventional FMR measurements rely on broadband vector network analyzers (VNAs), whose high cost limits accessibility for small laboratories and educational environments. To overcome this barrier, we have developed a compact and low-cost FMR measurement platform - the NanoVNA-FMR system-based on a commercially available NanoVNA. The setup integrates an electromagnet and a coplanar waveguide (CPW) and is fully automated using Python scripts. This enables synchronized
magnetic-field sweeping, S-parameter acquisition, and real-time visualization. The system successfully captures clear FMR spectra that exhibit systematic shifts in resonance frequency with increasing
magnetic field. The results are in excellent agreement with those obtained using a conventional VNA-based FMR system, confirming the quantitative reliability of the NanoVNA approach. Additionally, a 3D-printed sample holder further reduces overall system cost. These results demonstrate that the NanoVNA-FMR system provides a practical, accurate, and accessible alternative for quantitative
magnetic characterization and educational applications.
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All authors Reo Fukunaga, Ryunosuke Takahashi, Tetsuro Ueno, Hiroki Shoji, Yoshihiko Togawa, Hiroki Wadati
Materials Science · Cross-listed from cond-mat.str-el
Anomalous Hall effect and rich magnetic phase diagram of Mn$_{100-x}$Rh$_{x}$ epitaxial films
Cong Wang, Zheng Li, Jing Meng et al. (+7 more)
A series of Mn$_{100-x}$Rh$_x$ ($20 \le x \le 50$) thin films were epitaxially grown on the MgO substrate using magnetron sputtering technique, and were systematically investigated by magnetization, longitudinal electrical resistivity, and transverse
Hall resistivity. After optimizing the growth conditions, phase-pure Mn$_{100-x}$Rh$_x$ films with a cubic CsCl-type structure were obtained, and their
magnetic phase diagram was built. The manipulation of Rh content leads to a rich
magnetic phase diagram, where three different regimes can be identified: for $x < 40$, Mn$_{100-x}$Rh$_x$ films undergo a
ferromagnetic (FM) transition below $T_\mathrm{C} \approx$ 330-350 K; for $40 \le x \le 45$, in addition to the FM transition at $T_\mathrm{C} \approx$ 200 K, Mn$_{100-x}$Rh$_x$ films undergo a FM-to-
antiferromagnetic (AFM) transition at $T_\mathrm{N} \approx$ 120 K; finally for $x > 45$, only one AFM transition at $T_\mathrm{N} \approx$ 150 K can be tracked. All the Mn$_{100-x}$Rh$_x$ films exhibit distinct anomalous
Hall effect in their magnetically ordered state, which is most likely due to the intrinsic Berry-
curvature mechanism. In addition, all the anomalous
Hall transport properties, including the resistivity, conductivity, and angle exhibit a strong correlation with the
magnetic properties of Mn$_{100-x}$Rh$_x$ films, which become most evident for $x$ = 35. Our systematic investigations suggest a strong correlation between
magnetic properties and electronic band
topology in Mn$_{100-x}$Rh$_x$ films, highlighting their great potential for AFM spintronics.
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All authors Cong Wang, Zheng Li, Jing Meng, Hui Zhang, Haoyu Lin, Jiyuan Li, Kun Zheng, Yang Xu, Tian Shang, Qingfeng Zhan
Materials Science · Cross-listed from cond-mat.str-el
Investigating the origin of topological-Hall-like resistivity in Zn-doped Mn2Sb ferrimagnet
BoCheng Yu, JiaLiang Jiang, Jing Meng et al. (+7 more)
Skyrmions and other
chiral spin textures have been extensively studied as potential building blocks for novel spintronic devices.
Hall-resistivity anomalies that deviate from magnetization scaling, known as the topological
Hall effect, have been widely employed as evidence for the presence of
chiral spin textures in
magnetic materials. However, recent studies on
magnetic thin films have revealed a drawback of this approach, as the presumed topological
Hall contribution may in fact originate from trivial mechanisms. Here, we investigate the
magnetic and transport properties of a Zn-doped Mn2Sb ferrimagnet, whose related compounds have previously been suggested to exhibit a topological
Hall effect arising from
chiral spin textures.
Hall-resistivity anomalies are also observed in our sample, yet they show little correlation with the
magnetic or metamagnetic transitions and are therefore clearly distinct from those in
magnetic compounds hosting
chiral spin textures. Most importantly, additional Lorentz transmission electron microscopy measurements rule out the existence of
chiral spin textures in this ferrimagnet. Therefore, instead of a nontrivial origin, we attribute the
Hall-resistivity anomalies to the combined effect of multiple anomalous
Hall channels resulting from sample inhomogeneity. Our work shows that the difficulties of identifying
chiral spin textures through transport measurements also apply to bulk systems, prompting some existing results to be revisited.
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All authors BoCheng Yu, JiaLiang Jiang, Jing Meng, XiaoYan Zhu, Jie Ma, HaiFeng Du, QingFeng Zhan, Jin Tang, Yang Xu, Tian Shang
Materials Science
Defects Engineering of ZrTe5 for Stabilizing Ideal Topological States
Chia-Hsiu Hsu, Zezhi Wang, Sen Shao et al. (+6 more)
ZrTe5 is a highly tunable, high-mobility topological material that hosts a rich variety of
quantum phenomena, making it a promising platform for next-generation
quantum technologies. Despite intensive research efforts, experimental studies have reported inconsistent and sometimes conflicting results for its electronic and topological states, largely due to variations in sample quality. Here, through systematic frst-principles investigations of all intrinsic point defects, we identify a practical route to achieving stable and ideal topological characteristics in ZrTe5. We show that the competition between two dominant charged defects, donor-like Zr interstitials and acceptor-like Te vacancies, governs the
Fermi-level position. Furthermore, variations in defect density determine the topological phases of the samples. We theoretically propose and experimentally confrm that increasing the Te/Zr ratio during
crystal growth effectively suppresses intrinsic defects and stabilizes ZrTe5 in a nearly ideal weak topological
insulator state. These fndings provide clear guidance for defect control and sample optimization, paving the way toward robust and reproducible realization of topological
quantum states in ZrTe5 for future
quantum applications.
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All authors Chia-Hsiu Hsu, Zezhi Wang, Sen Shao, Yoshinori Okada, Feng-Chuan Chuang, Dong Xing, Ilya Belopolski, Cheng-Long Zhang, Guoqing Chang
Materials Science · Cross-listed from cond-mat.mes-hall
Stable skyrmion bundles at room temperature and zero magnetic field in a chiral magnet
Yongsen Zhang, Jin Tang, Yaodong Wu et al. (+5 more)
Topological
spin textures are characterized by topological
magnetic charges, Q, which govern their electromagnetic properties. Recent studies have achieved skyrmion bundles with arbitrary integer values of Q, opening possibilities for exploring topological spintronics based on Q. However, the realization of stable skyrmion bundles in
chiral magnets at room temperature and zero
magnetic field - the prerequisite for realistic device applications - has remained elusive. Here, through the combination of pulsed currents and reversed
magnetic fields, we experimentally achieve skyrmion bundles with different integer Q values - reaching a maximum of 24 at above room temperature and zero
magnetic field - in the
chiral magnet Co8Zn10Mn2. We demonstrate the field-driven annihilation of high-Q bundles and present a phase diagram as a function of temperature and field. Our experimental findings are consistently corroborated by micromagnetic simulations, which reveal the nature of the skyrmion bundle as that of skyrmion tubes encircled by a fractional Hopfion.
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All authors Yongsen Zhang, Jin Tang, Yaodong Wu, Meng Shi, Xitong Xu, Shouguo Wang, Mingliang Tian, Haifeng Du
Materials Science · Cross-listed from cond-mat.mes-hall
Deterministic Electrical Control of Single Magnetic Bubbles in Nanostructured Cells
Jialiang Jiang, Yaodong Wu, Lingyao Kong et al. (+10 more)
Localized particle-like
spin textures have been found to exhibit emergent electromagnetic properties, which hold promise for the development of intriguing spintronic devices. Among these textures,
magnetic bubbles represent localized
spin configurations that could serve as data bits. However, the precise methods for their electrical manipulation remain uncertain. Here, we demonstrate the deterministic electrical manipulations and detections of single
magnetic bubbles in kagome-latticed Fe3Sn2
magnetic nanostructured
cells. The current-induced dynamics of
magnetic bubbles were explored using nanosecond pulsed currents. We show single pulsed currents with low and high densities can be applied for the creation and deletion of a single bubble, respectively. The mutual writing-deleting operations on single bubbles are attributed to the thermal heating and non-thermal
spin-transfer torque effects in combination with micromagnetic simulations. We also realized the in-situ detection of a single bubble using the anisotropic magnetoresistance effect through a standard four-probe method. Our results could propel the development of bubble-based spintronic devices.
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All authors Jialiang Jiang, Yaodong Wu, Lingyao Kong, Yongsen Zhang, Sheng Qiu, Huanhuan Zhang, Yihao Wang, Junbo Li, Yimin Xiong, Shouguo Wang, Mingliang Tian, Haifeng Du, Jin Tang
Materials Science
Switching of topological phase transition from semiconductor to ideal Weyl states in Cu$_2$SnSe$_3$ family of materials
Huan Li
The exploration of topological phase transition (TPT) mechanisms constitutes a central theme in
quantum materials research. Conventionally, transitions between Weyl semimetals (WSMs) and other topological states rely on the breaking of time-reversal
symmetry (TRS) or precise manipulation of
lattice symmetry, thus constraints the available control strategies and restrict the scope of viable material systems. In this work, we propose a novel mechanism for TPT that operates without TRS breaking or
lattice symmetry modification: a class of
semiconductors can be directly transformed into an ideal WSM via bandgap closure. This transition is driven by chemical doping, which simultaneously modulates the band gap and enhances
spin-orbit coupling (SOC), leading to band inversion between the valence and conduction bands and thereby triggering the TPT. Using first-principles calculations, we demonstrate the feasibility of this mechanism in the Cu$_2$SnSe$_3$ family of materials, where two pairs of Weyl points emerge with energies extremely close to the
Fermi level. The bulk
Fermi surface becomes nearly point-like, while the surface
Fermi surface consists exclusively of
Fermi arcs. This
symmetry-independent mechanism bypasses the constraints of conventional
symmetry-based engineering, and also offers an ideal platform for probing the anomalous transport properties of WSMs.
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