Materials Science · Cross-listed from cond-mat.mes-hall
Resolution of Topology and Geometry from Momentum-Resolved Spectroscopies
Shaofeng Huang and Chen Fang
Extracting the complete
quantum geometric and topological character of Bloch wavefunctions from experiments remains a challenge in condensed matter physics. Here, we resolve this by introducing the "wavefunction form factor" (WFF)
matrix, a quantity directly constructible from intensities in momentum- and energy-resolved spectroscopies like ARPES and INS. We demonstrate that band
topology is encoded in "spectral nodes" – momentum-space points where the WFF determinant vanishes, providing a direct readout of topological invariants via a topological selection rule. Furthermore, when the number of independent probes exceeds the number of the target bands, our framework yields an effective band projector. This enables the determination of Wilson loop spectra and the extraction of an effective
quantum geometric tensor, providing a model-independent measurement of the non-Abelian Berry
curvature and
quantum metric as resolved by the experimental probes.
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Materials Science
Ultra-Stable Weyl Topology Driven by Magnetic Textures in the Shandite Compound Co3Sn2S(2-x)Sex
Dang Khoa Le, Eklavya Thareja, Bektur Konushbaev et al. (+5 more)
We employ state-of-the-art first-principles calculations to investigate the shandite compounds Co3Sn2S2, Co3Sn2SeS, and Co3Sn2Se2, which host Weyl
fermions and complex
magnetic textures. Their
magnetic structures are governed primarily by exchange interactions and magnetocrystalline anisotropy, whereas the
symmetry-allowed alternating-layer Dzyaloshinskii-Moriya interaction (DMI) is found to be negligible. We identify a previously unrecognized
spin-
chiral interaction (SCI) arising from the kagome
lattice topology, which plays a decisive role in stabilizing the experimentally observed
magnetic textures. The extracted
magnetic parameters reproduce experimental trends, with the SCI emerging as a novel and dominant contribution. The calculated SCI strengths are 0.78 meV, 0.86 meV, and 0.87 meV for Co3Sn2S2, Co3Sn2SeS, and Co3Sn2Se2, respectively. Furthermore, we demonstrate that short-wavelength
magnetic textures drive phase transitions of the Weyl nodes, resulting in band flattening and the opening of an emergent gap. This newly identified SCI, together with the associated electronically driven phase transitions, provides a promising route for manipulating transport properties in spintronic devices.
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All authors Dang Khoa Le, Eklavya Thareja, Bektur Konushbaev, Gina Pantano, Tom Saunderson, Manh-Huong Phan, Yuriy Mokrousov, Jacob Gayles
Materials Science · Cross-listed from physics.hist-ph
Viewpoint: On the Emergence of van der Waals Magnets: A Personal Reflection
Je-Geun Park
The observation of magnetism in atomically thin van der Waals (vdW) antiferromagnets (FePS$_3$, NiPS$_3$, and MnPS$_3$) in 2016 marked an important moment in the development of two-dimensional (2D) physics. In this personal reflection, I describe how a simple question, posed in the early 2010s, motivated experimental efforts that culminated in the demonstration of
antiferromagnetic order in monolayer FePS$_3$. Alongside subsequent reports of vdW ferromagnets in 2017, these developments helped establish intrinsic magnetism as a viable degree of freedom in atomically thin materials. I close with personal lessons drawn from this period and a perspective on the opportunities that now shape the field's second decade and beyond.
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Materials Science · Cross-listed from cond-mat.str-el
Revisiting Jahn–Teller Transitions in Correlated Oxides with Monte Carlo Modeling
Liam A. V. Nagle-Cocco, Andrew L. Goodwin, Clare P. Grey et al. (+1 more)
Jahn–Teller (JT) distortions are a key driver of physical properties in many correlated
oxide materials. Cooperative JT distortions, in which long-range orbital order reduces the
symmetry of the average structure macroscopically, are common in JT-distorted materials at low temperatures. This long-range order will often melt on heating, via a transition to a high-temperature state without long-range orbital order. The nature of this transition has been observed to vary with different materials depending on
crystal structure; in LaMnO$_3$ the transition has generally been interpreted as order-disorder, whereas in layered nickelates $A$NiO$_2$ ($A$=Li,Na) there is a displacive transition. Alternatively, recent theoretical work has suggested that previous attributions of order-disorder may in fact be a consequence of
phonon anharmonicity, rather than persistence of JT distortions, which would suggest that the displacive transition may be more common than currently believed. In this work, we run Monte Carlo simulations with a simple
Hamiltonian which is modified to include terms dependent on the JT amplitude $\rho$, which is allowed to vary within the simulation via the Metropolis
algorithm. Our simulations yield distributions of JT amplitudes consistent with displacive rather than order-disorder behaviour for both perovskites and layered nickelates, suggesting that displacive-like JT transitions may be more common than previously assumed in both perovskites and layered nickelates. We also find significant differences between the transition observed for perovskites compared with layered nickelates, which we attribute to differing extensivity of configurational
entropy on the two
lattices, showing the crucial role of
lattice geometry in determining behaviour.
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All authors Liam A. V. Nagle-Cocco, Andrew L. Goodwin, Clare P. Grey, Siân E. Dutton
Materials Science
Electronic structure and elasticity of the Ta-W solid solution
Kareem Abdelmaqsoud, John R. Kitchin and Michael Widom
The brittleness or ductility of metals has long been attributed to their elastic constants, with high Poisson ratio, or equivalently high Pugh ratio, favoring greater ductility. Growing evidence links ductility with their electronic structure. Consequently, it is desirable to understand how the electronic structure affects the elastic constants. Here, we examine the Ta-W binary
alloy system, which evolves from ductile character at Ta-rich compositions to brittleness at high W. We show that a change in slope of the composition-dependent shear modulus near the equiatomic composition coincides with an abrupt change in the
Fermi level density of states. We relate the behaviors of the elastic constants to the characters of occupied electronic orbitals close to the
Fermi level. Finally, we consider additional
alloy systems from groups V and VI and show that qualitatively similar behavior occurs more broadly.
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Materials Science
Geometric dependence of exchange bias in tilted three-dimensional CoFe/IrMn microwires
Balram Singh, Aman Singh, Stefan Mikulik et al. (+3 more)
The exchange bias (EB) effect, arising from interfacial coupling between
ferromagnetic (FM) and
antiferromagnetic (AF) layers, induces a unidirectional
magnetic anisotropy and underpins a wide range of spintronic functionalities. Extending the EB effect to three-dimensional (3D) architectures enables investigation of interfacial coupling in non-planar structures, which is a key step toward realizing spintronic functionalities beyond planar systems. Achieving this requires the fabrication of FM/AF
bilayers with smooth interfaces and well-defined thicknesses on non-planar scaffolds, together with suitable characterization methods. In this work, we realize exchange-biased 3D FM/AF microwires by combining two-
photon lithography with magnetron sputtering. CoFe/IrMn
bilayers are deposited on microwire scaffolds with inclination angles of 0 deg, 30 deg, 45 deg relative to the substrate, and their magnetization reversal is probed using dark-field magneto-optical Kerr effect (DF-MOKE) magnetometry. We find that the EB and coercive fields vary in a characteristic way with the inclination angle, consistent with the systematic reduction in film thickness expected from inclined directional deposition. In addition, the EB magnitude is influenced by the combined effects of surface roughness of non-planar geometries and the directional growth of the
bilayer, highlighting the importance of 3D scaffold surface quality for integrating
magnetic multilayers. These results provide insight into the growth and
magnetic behavior of sputter-deposited
magnetic multilayers with functional interfaces on 3D geometries.
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All authors Balram Singh, Aman Singh, Stefan Mikulik, Jakub Jurczyk, Volker Neu, Amalio Fernández-Pacheco
Materials Science
Light-induced Magnetization by Quantum Geometry
Hiroki Yoshida and Takehito Yokoyama
We propose a mechanism for the inverse Faraday and the inverse Cotton–Mouton effects arising from
quantum geometry, characterized by the
quantum metric quadrupole and the weighted
quantum metric. Within a semiclassical framework based on the Boltzmann transport theory, we establish a general formalism describing light-induced magnetization in electronic systems as a second-order response to the electric field of light. Using continuum and tight-binding models, we discuss the
symmetry constraints on these effects and estimate the magnitudes of the resulting magnetizations. Our results highlight a direct manifestation of
quantum-
geometric quantities in nonlinear magneto-optical responses and suggest a viable pathway for experimental detection.
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Materials Science
Ferroelectric polarization mapping through pseudosymmetry-sensitive EBSD reindexing
Claire Griesbach, Tizian Scharsach, Morgan Trassin et al. (+1 more)
Ferroelectric materials exhibit a switchable, spontaneous polarization at the unit
cell level–an attractive property utilized in many emerging technologies including, among others, high-density
memory storage, low-power transistors, and high-speed fiber optic communication. Understanding the local polarization switching behavior, through domain nucleation and
evolution, is critical to advancing these technologies and requires characterization of the local domain microstructure. However, in application-relevant polycrystalline materials exhibiting a distribution of grain orientations, a direct mapping of the polarization direction in three dimensions has remained inaccessible using conventional experimental approaches. Here, taking barium titanate single
crystals and lead zirconium titanate polycrystals as our bulk model systems, we map the local polarization directions using a new electron backscatter diffraction indexing technique based on simulated pattern-matching. Through improved pre-processing techniques (including optimized pattern processing, a new pseudosymmetry-sensitive neighbor pattern averaging method, and DIC-based global sample-detector geometry calibration) and a new pseudosymmetry confidence index (which considers not only pattern similarity but pattern dissimilarity trends with other domain variant patterns), we successfully distinguish between the six polarization directions, despite the challengingly small unit
cell aspect ratio of the selected materials. The methods developed in this work are not only applicable to ferroelectrics but any material which exhibits close crystallographic pseudosymmetries–extending the current capabilities of EBSD.
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All authors Claire Griesbach, Tizian Scharsach, Morgan Trassin, Dennis M. Kochmann
Materials Science · Cross-listed from cond-mat.mes-hall
Dynamical Stabilization of Inverted Magnetization and Antimagnons by Spin Injection in an Extended Magnetic System
Emir Karadza, Hanchen Wang, Niklas Kercher et al. (+4 more)
Dynamical perturbations can modify the energy landscape of a physical system, such that unstable
equilibrium configurations become stable when subject to an external drive. The
magnetic analog of such dynamical stabilization corresponds to saturation of the magnetization against an external field. Here we report dynamical stabilization of the magnetization in thin film bismuth-substituted yttrium iron garnet by
spin current injection from an adjacent Pt layer. Magneto-optical Kerr effect measurements demonstrate magnetization reversal against
magnetic fields up to 3000 times larger than the film's coercivity once the
spin injection surpasses a critical threshold associated with negative damping. Micromagnetic simulations reveal that this process is mediated by the excitation of a large population of incoherent
magnons with non-zero wave vector, leading to a transient shortening and subsequent stabilization of the inverted magnetization. The elementary excitations of the high-energy inverted magnetization state are shown to be antimagnons, quasi-particles carrying opposite energy and
spin relative to
magnons. Our results further reveal how the system's size and minimization of nonlinear
magnon scattering processes play a key role in dynamical stabilization, opening new avenues for
magnetic state control beyond conventional magnetization switching. Dissipation-driven phase transitions in large-area
magnetic systems provide a solid-state platform to study magnonic analogs of relativistic phenomena, such as Klein tunneling and black holes, as well as
spin-wave amplification and lasing.
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All authors Emir Karadza, Hanchen Wang, Niklas Kercher, Paul Noel, William Legrand, Richard Schlitz, Pietro Gambardella
Materials Science
Is it possible to determine unambiguously the Berry phase solely from quantum oscillations?
Bogdan M. Fominykh, Valentin Yu. Irkhin and Vyacheslav V. Marchenkov
The Berry phase, a fundamental
geometric phase in
quantum systems, has become a crucial tool for probing the topological properties of materials.
Quantum oscillations, such as Shubnikov-de Haas (SdH) oscillations, are widely used to extract this phase, but its unambiguous determination remains challenging. This work highlights the inherent ambiguities in interpreting the oscillation phase solely from SdH data, primarily due to the influence of the
spin factor $R_S$, which depends on the Landé $g$-factor and effective mass. While the Lifshitz-Kosevich (LK) theory provides a framework for analyzing oscillations, the unknown g-factor introduces significant uncertainty. For instance, a zero oscillation phase could arise either from a nontrivial Berry phase or a negative $R_S$. We demonstrate that neglecting $R_S$ in modern studies, especially for topological materials with strong
spin-orbit coupling, can lead to doubtful conclusions. Through theoretical analysis and numerical examples, we show how the interplay between the Berry phase and Zeeman effect complicates phase determination. Additionally, we also discuss another underappreciated mechanism - the
magnetic field dependence of the
Fermi level. Our discussion underscores the need for complementary experimental techniques to resolve these ambiguities and calls for further research to refine the interpretation of
quantum oscillations in topological systems.
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Materials Science · Cross-listed from cond-mat.supr-con
Nanoscale Spatial Tuning of Superconductivity in Cuprate Thin Films via Direct Laser Writing
Irene Biancardi, Valerio Levati, Jordi Alcalà et al. (+9 more)
Cuprate high-temperature
superconductors, such as Yttrium Barium Copper
Oxide (YBCO), are extremely promising for emerging technologies such as low-power computing, data storage,
quantum sensors and superconducting electronics. However, the realization of high-performance functional nanostructures presents formidable challenges due to the difficulty of applying conventional nanofabrication methods to such sensitive materials, making the search for alternative methods a key enabling factor. Since YBCO's superconducting and normal-state properties are highly dependent on oxygen stoichiometry, precise nanoscale control of the oxygen content represents a highly appealing approach for creating advanced nanoengineered devices. In this work, we demonstrate the precise fabrication of sub-micrometer, grayscale patterns over large areas in epitaxial YBCO thin films, achieving finely tuned optical and superconducting transport properties by locally controlling the stoichiometry through maskless direct
laser writing under ambient conditions. Cryogenic magneto-optical imaging and transport measurements in irradiated devices directly demonstrate the spatial tuning of the critical temperature and carrier density with the patterning conditions. Correlated Raman microscopy and reflectometry indicate a
laser-power dependent oxygen depletion in the irradiated regions. The proposed
laser-controlled stoichiometry approach provides a direct and scalable method to navigate the phase diagram of high-TC superconducting
oxides, offering new possibilities for integrating functional nanostructures into superconducting devices.
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All authors Irene Biancardi, Valerio Levati, Jordi Alcalà, Thomas Günkel, Nicolas Lejeune, Riccardo Girelli, Alejandro V. Silhanek, Valeria Russo, Narcís Mestres, Daniela Petti, Anna Palau, Edoardo Albisetti
Materials Science
Ab initio study of carrier mobility in Bi$_2$O$_2$Se
Yubo Yuan, Ziye Zhu, Jiaming Hu et al. (+1 more)
Bi$_2$O$_2$Se is an emerging high-performance layered
semiconductor with excellent stability. While experimental studies have explored carrier transport across various doping levels for both $n$-type and $p$-type conduction, a comprehensive theoretical understanding remains incomplete. In this work, we present parameter-free first-principles calculations of the electron and hole mobilities in Bi$_2$O$_2$Se, based on iterative solution of the Boltzmann transport equation that includes electron-
phonon scattering and ionized
impurity scattering on an equal footing. Intriguingly, we find that Bi$_2$O$_2$Se exhibits high electron mobilities in both the in-plane and out-of-plane directions, whereas the hole mobilities are only significant in the in-plane direction, displaying a unique three-dimensional (3D) electron transport and two-dimensional (2D) hole transport behavior. At 300~K, the calculated intrinsic electron and hole mobilities along the in-plane direction are 447~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$ and 29~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$, respectively, which are primarily affected by Fröhlich electron-
phonon interactions. Due to its large static dielectric permittivity, Bi$_2$O$_2$Se exhibits an exceptionally high low-temperature electron mobilities above $1.0\times10^5~\mathrm{cm^2\,V^{-1}\,s^{-1}}$, and its electron mobilities above 50~K is robust against ionized
impurity scattering over a wide range of
impurity concentrations. By incorporating the
Hall effect into our analysis, we predict an in-plane electron
Hall mobility of 517~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$ at 300~K, in excellent agreement with experimental data. These results provide valuable insights into the carrier transport mechanisms in Bi$_2$O$_2$Se, and offer predictive
benchmarks for future theoretical and experimental investigations.
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All authors Yubo Yuan, Ziye Zhu, Jiaming Hu, Wenbin Li
Materials Science · Cross-listed from cond-mat.mes-hall
Interface effects and dielectric mismatch in ultrathin silicon on insulator films
Andrea Pulici, Gabriele Seguini, Fabiana Taglietti et al. (+6 more)
The role of interface states and dielectric mismatch is studied in ultrathin P-doped silicon-on-
insulator (SOI) films with thickness of the device layer ($H_{SOI}$) varying from 30 to 8 nm and dopant concentration ($n_{D}$) ranging from 10$^{18}$ to nearly 10$^{20}$ cm$^{-3}$. P concentration is determined by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Sample resistivity ($\rho$), carrier concentration ($n_e$), and mobility ($\mu_e$) are extracted by combining sheet resistance and
Hall measurements in van der Pauw configuration. When $H_{SOI}$ = 30 nm, transport properties at room temperature are fully compatible with those of a similarly doped bulk Si. Progressive 2D confinement by reduction of $H_{SOI}$ below 30 nm results in a reduction of the carrier concentration and a concomitant degradation of $\mu_e$. These effects, which are steadily enhanced decreasing $n_D$, are attributed to non-passivated interface states at the SiO$_2$/Si interface and can be significantly mitigated by high temperature rapid thermal oxidation (RTO). The effectiveness of this approach was verified by electron-paramagnetic resonance (EPR) spectra and capacitance-voltage (CV) measurements, which allowed the assessment of the quality of the RTO-SiO$_2$/Si interface and the correlation with observed electrical properties. After effective interface engineering, low temperature electrical characterization revealed a significant increase in P ionization energy in samples with $H_{SOI}$ <= 15 nm, a result directly related to the dielectric mismatch.
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All authors Andrea Pulici, Gabriele Seguini, Fabiana Taglietti, Roman Gumeniuk, Riccardo Chiarcos, Michele Laus, Johannes Heitmann, Marco Fanciulli, Michele Perego
Materials Science
Batch-Fabricated PDMS Templates for the Robotic Transfer of 2D Materials
Zhili Lin, Luosha Han, Jinkun He et al. (+5 more)
Robotic stacking of van der Waals
heterostructures has been at the verge thanks to the convergence between artificial intelligence (AI) and two-dimensional (2D) materials research. Key ingredients to fulfill this pursuit often include
algorithms to identify layer compounds on chips, hard-wares to realize sophisticated operations of motion and/or rotation in a microscale, and, as importantly, highly-standardized and uniform transfer stamps that are often used in picking up layered materials under a microscope. Here, we report a hot-casted-droplet batch fabrication method for polydimethylsiloxane (PDMS) templates tailored for dry transfer of 2D materials. Controlled precursor formulation, degassing, and motorized-syringe dispensing produce dome-shaped PDMS templates with ultra-smooth surfaces (root-mean-square roughness about 0.3 nm at relatively low curing temperatures). By tuning the curing temperature, the reproducible and controllable apex
curvature allows precisely defined contact area between the organic adhesive film and substrate, via thermal expansion. Our results further reveals thermalmechanical behaviors with different casting parameters of such PDMS domes. This scalable and parameterized fabrication protocol gives rise to uniform transfer-stamps with ultra-smooth surface, which may be beneficial for future AI-driven robotic assembly of 2D material
heterostructures.
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All authors Zhili Lin, Luosha Han, Jinkun He, Xiaoxue Fan, Tongyao Zhang, Xiaoxi Li, Baojuan Dong, Kai Zhao
Materials Science
Molecular-based coordination polymer as reversible and precise acetonitrile electro-optical readout
Esther Resines-Urien, Enrique Burzurí, Estefania Fernandez-Bartolome et al. (+5 more)
Efficient detection of harmful organic volatile compounds is a major health and environmental need in industrialized societies. Tailor-made metal-organic frameworks and other coordination
polymers are emerging as promising sensing molecular materials thanks to their responsivity to a wide variety of external stimuli, and could be used to complement conventional sensors. Here, a non-porous crystalline 1D Fe(II) coordination
polymer acting as a porous acetonitrile host is presented. The desorption of interstitial acetonitrile is accompanied by magneto-structural transitions easily detectable in the optical and electronic properties of the material. The structural switch and therefore its (opto)electronic readout are reversible under exposition of the
crystal to acetonitrile vapor. Coordination
polymers can be versatile sensors for volatile acetonitrile and potentially other organic compounds.
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All authors Esther Resines-Urien, Enrique Burzurí, Estefania Fernandez-Bartolome, Miguel Ángel García García-Tuñón, Patricia de la Presa, Roberta Poloni, Simon J. Teat, Jose Sanchez Costa
Materials Science
Field report from Collaborative Research Center 1625: Heterogeneous research data management using ontology representations
Doaa Mohamed, Samuel García Vázquez, Behnam Mardani et al. (+4 more)
The goal of the Collaborative Research Center 1625 is the establishment of a scientific basis for the atomic-scale understanding and design of multifunctional compositionally complex solid solution surfaces. Next to materials synthesis in form of thin-film materials libraries, various materials characterization and simulations techniques are used to explore the materials data space of the problem. Machine learning and artificial intelligence techniques guide its exploration and
navigation. The effective use of the combined heterogeneous data requires more than just a simple research data management plan. Consequently, our research data management system maps different data modalities in different formats and resolutions from different labs to the correct spatial locations on physical samples. Besides a graphical user interface, the system can also be accessed through an application programming interface for reproducible data-driven workflows. It is implemented by a combination of a custom research data management system designed around a relational database, an ontology which builds upon materials science-specific ontologies, and the construction of a Knowledge Graph. Along with the technical solutions of research data management system and lessons learned, first use cases are shown which were not possible (or at least much harder to achieve) without it.
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All authors Doaa Mohamed, Samuel García Vázquez, Behnam Mardani, Victor Dudarev, Alfred Ludwig, Maribel Acosta, Markus Stricker
Materials Science
The Diffusion Kinetics of Ba Cations in Perovskite BaTiO$_3$: A Combined Tracer Diffusion and Metadynamics Study
Sylvia Koerfer, Bianca Dißmann, Norman Schier et al. (+3 more)
Tracer
diffusion experiments and metadynamics (MtD) simulations were used to study the
diffusion of Ba cations in the cubic phase of the perovskite
oxide BaTiO$_3$. $^{130}$BaTiO$_3$ thin films were used as
diffusion sources to introduce barium tracer
diffusion profiles into single-
crystal samples at temperatures $1348 \leq T/\mathrm{K} \leq 1498$. The $^{130}$Ba profiles were determined by time-of-flight secondary ion mass spectrometry, and then analysed to yield Ba tracer
diffusion coefficients ($D_\mathrm{Ba}^\ast$). MtD simulations were performed in order to obtain barium-vacancy
diffusion coefficients ($D_\mathrm{v_{Ba}}$) for selected vacancy mechanisms as a function of temperature. $D_\mathrm{v_{Ba}}$ is predicted to be increased significantly by an adjacent oxygen vacancy, and even more, by an adjacent titanium vacancy. From the combined consideration of $D_\mathrm{Ba}^\ast$ and $D_\mathrm{v_{Ba}}$, we conclude that Ba
diffusion in these samples occurred most probably by the migration of defect associates, and not by the migration of isolated barium vacancies. More generally, our results draw
attention to the dangers of relying solely on activation enthalpies to interpret
diffusion data.
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All authors Sylvia Koerfer, Bianca Dißmann, Norman Schier, Han-Ill Yoo, Manfred Martin, Roger A. De Souza
Materials Science
Chemical heterogeneity at conducting ferroelectric domain walls
Kasper A. Hunnestad, Guo-Dong Zhao, Mao-Hua Zhang et al. (+7 more)
Natural interfaces in ferroic
oxides have developed into versatile playgrounds for studying electronic correlation effects in 2D systems. The microscopic origin of the emergent local electronic properties is often debated, however, as quantitative atomic-scale characterization remains challenging. A
prime example is enhanced conductivity at ferroelectric domain walls, attributed to mechanisms ranging from local band gap reduction to point defect accumulations. Here, we resolve the microscopic mechanisms for domain wall conduction in the ferroelectric model system BiFeO3, by combining transport measurements with atom probe
tomography to quantify the local chemical composition and correlate it with the electrical properties. Significant chemical variations along the walls are observed, demonstrating an outstanding chemical flexibility at domain walls, which manifest in spatially varying physical properties. The results give a unifying explanation for the diverse electronic behavior observed and establish the fundamental notion that multiple conduction mechanisms can coexist within individual domain walls.
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All authors Kasper A. Hunnestad, Guo-Dong Zhao, Mao-Hua Zhang, Tiannan Yang, Elzbieta Gradauskaite, Antonius T. J. van Helvoort, Morgan Trassin, Long-Qing Chen, Tadej Rojac, Dennis Meier
Materials Science · Cross-listed from cond-mat.mes-hall
RKKY signatures as a probe for intrinsic magnetism and AI/QAH phase discrimination in MnBi$_2$Te$_4$ films
Ya-Xi Li, Zi-Jian Chen, Rui-Qiang Wang et al. (+2 more)
We present a systematic study of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in MnBi$_2$Te$_4$ films under both dark and illuminated conditions. In the dark, the intrinsic magnetism of MnBi$_2$Te$_4$ is shown to yield a stronger anisotropic RKKY
spin model compared to nonmagnetic topological
insulators, providing a clear signature for differentiating these systems. Furthermore, key band properties – such as energy gap, band degeneracy/splitting, and topological deformations of the
Fermi surface – imprint distinct signatures on the RKKY interaction, enabling clear discrimination between
axion insulators (AI) and
quantum anomalous
Hall (QAH)
insulators in even- and odd-septuple-layer (SL) films. This discrimination manifests in multiple ways: through the
Fermi-energy dependence or spatial oscillations of the interaction for
impurities on the same surface, or via the presence versus absence of
spin-frustrated terms for those on different surfaces. Under off-resonant circularly polarized light, additional phase-transition-related fingerprints also emerge to distinguish these two phases, such as sign reversals of
spin-frustrated terms in even-SL films versus chirality-selective double-dip structures of collinear RKKY components in odd-SL films. Overall, this work establishes RKKY interactions as a sensitive
magnetic probe for distinguishing between AI phase (even-SL) and QAH phase (odd-SL), thereby complementing conventional electrical measurements while providing new insights into the influence of intrinsic magnetism on the surface-state band structure.
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All authors Ya-Xi Li, Zi-Jian Chen, Rui-Qiang Wang, Ming-Xun Deng, Hou-Jian Duan
Materials Science · Cross-listed from cs.LG
Enhancing Spatial Reasoning in Large Language Models for Metal-Organic Frameworks Structure Prediction
Mianzhi Pan, JianFei Li, Peishuo Liu et al. (+5 more)
Metal-organic frameworks (MOFs) are porous crystalline materials with broad applications such as carbon capture and drug delivery, yet accurately predicting their 3D structures remains a significant challenge. While Large
Language Models (LLMs) have shown promise in generating
crystal structures, their application to MOFs is hindered by MOFs' high structural complexity arising from the large number of atoms in unit
cell. Inspired by the success of block-wise paradigms in deep generative models for MOFs, we pioneer the application of LLMs in this domain by introducing MOF-LLM, the first LLM framework specifically adapted for block-level MOF structure prediction. To effectively harness LLMs for this 3D modular assembly task, our training paradigm integrates spatial-aware continual pre-training (CPT), structural supervised fine-tuning (SFT), and matching-driven reinforcement learning (RL). By incorporating explicit spatial priors and optimizing structural stability via Soft Adaptive Policy Optimization (SAPO), our approach substantially enhances the spatial
reasoning in a Qwen-3 8B model for MOF structure prediction. Comprehensive experiments demonstrate that MOF-LLM achieves state-of-the-art performance with a match rate of 35.78% while exhibiting superior sampling efficiency of 0.04 seconds per structure.
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All authors Mianzhi Pan, JianFei Li, Peishuo Liu, Botian Wang, Yawen Ouyang, Yiming Rong, Hao Zhou, Jianbing Zhang
Materials Science · Cross-listed from cond-mat.mes-hall
Tunnel-Barrier-Engineered Ultrafast Demagnetization and Spin Transport in Graphene-Based Heterostructures
Suchetana Mukhopadhyay, David Muradas-Belinchon, Francesco Foggetti et al. (+3 more)
Heterostructures combining
graphene with 3d transition metal ferromagnets (FMs) enable various
spin-based phenomena at ultrafast timescales. However, challenges such as the interfacial impedance mismatch, FM deposition-induced defect generation, and interface modification by interfacial coupling or hybridization can impede their functionalization for
spin-orbitronics. In this work, we utilize insulating TiOx barrier layers (BLs) to modify the interfacial
spin conductance structurally, disentangle
spin pumping and
magnetic proximity effects (MPE), and establish external control over ultrafast magnetization dynamics in single-layer
graphene/TiOx/Co systems. All-optical time-resolved magneto-optical Kerr effect measurements of femtosecond to nanosecond
spin dynamics reveal systematic tunability of ultrafast
magnetic parameters via barrier engineering. The thickness-dependent damping modulation in Co indicates strong
spin pumping, with interfacial
spin transparency close to half its physical limit in the presence of an ultrathin BL, where MPE is eliminated. Our results show that appropriately chosen ultrathin BLs can prevent interfacial alterations from
ferromagnetic metals, facilitating efficient
spin detection in
graphene and enhancing control over
spin angular momentum dissipation in
graphene/FM interfaces.
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All authors Suchetana Mukhopadhyay, David Muradas-Belinchon, Francesco Foggetti, Peter M. Oppeneer, M. Venkata Kamalakar, Anjan Barman
Materials Science · Cross-listed from cond-mat.str-el
Magneto-optical Kerr effect measurements under bipolar pulsed magnetic fields
Soichiro Yamane, Sota Nakamura, Atsutoshi Ikeda et al. (+3 more)
The magneto-optical Kerr effect (MOKE) is a powerful probe of magnetism. Its contact-free optical nature makes it potentially well suitable for measurements under pulsed
magnetic fields if various difficulties are overcome. In this paper, we report the establishment of MOKE measurements under bipolar pulsed
magnetic fields up to 13.1 T. The accuracy of the setup was demonstrated by the excellent agreement with static-field results on the (001) surface of a Fe3O4 single
crystal. Furthermore, clear hysteresis loops of various commercial permanent magnets were successfully observed. The capability for rapid characterization of hysteretic properties highlights the versatility of our pulsed-field MOKE setup for both fundamental materials science and engineering applications.
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All authors Soichiro Yamane, Sota Nakamura, Atsutoshi Ikeda, Kosuke Noda, Akihiko Ikeda, Shingo Yonezawa
Materials Science · Cross-listed from cond-mat.soft
Active alignment-driven coarsening in confined near-critical fluids
Parameshwaran A and Bhaskar Sen Gupta
We investigate vapor-
liquid phase separation of an active near critical Lennard-Jones fluid confined within a cylindrical pore using molecular dynamics simulations. Activity is introduced via Vicsek-type
alignment interactions, enabling a systematic study of how self-propulsion modifies domain morphology and coarsening kinetics under quasi-one-dimensional confinement. In the passive limit, the system undergoes early-time spinodal decomposition (diffusive growth characterized by the Lifshitz-Slyozov exponent $\alpha = 1/3$), followed by the formation of periodically modulated, plug-like
liquid domains along the pore axis. At late times, coarsening becomes kinetically arrested, and the system remains trapped in a metastable striped state. Introducing activity destabilizes this arrested morphology by enhancing collective domain transport, leading to frequent domain mergers and complete phase separation at sufficiently high activity. The late-stage coarsening then exhibits a crossover to faster, ballistic growth with an effective exponent $\alpha = 2/3$, consistent with a cluster-coalescence mechanism. Analysis of two-point correlation functions and structure factors confirms dynamic scaling across all activity regimes. Our results demonstrate that
alignment-induced activity can overcome confinement-driven kinetic arrest, providing new insight into phase separation in confined active fluids. The relevant growth laws are analyzed and interpreted using appropriate theoretical frameworks.
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Materials Science
Data-Driven Exploration and Insights into Temperature-Dependent Phonons in Inorganic Materials
Huiju Lee, Zhi Li, Jiangang he et al. (+1 more)
Phonons, quantized vibrations of the atomic
lattice, are fundamental to understanding thermal transport, structural stability, and phase behavior in crystalline solids. Despite advances in computational materials science, most predictions of vibrational properties in large materials databases rely on the harmonic approximation and overlook crucial temperature-dependent anharmonic effects. Here, we present a scalable computational framework that combines machine learning interatomic potentials, anharmonic
lattice dynamics, and high-throughput calculations to investigate temperature-dependent
phonons across thousands of materials. By fine-tuning the universal M3GNet interatomic potential using high-quality
phonon data, we improve
phonon prediction accuracy by a factor of four while preserving computational efficiency. Integrating this refined model into a high-throughput implementation of the
stochastic self-consistent harmonic approximation, we compute temperature-dependent
phonons for 4,669 inorganic compounds. Our analysis identifies systematic elemental and structural trends governing anharmonic
phonon renormalization, with particularly strong manifestations in alkali metals, perovskite-derived frameworks, and related systems. Machine learning models trained on this
dataset identify key atomic-scale features driving strong anharmonicity, including weak bonding, large atomic radii, and specific coordination motifs. First-principles validation confirms that anharmonic effects can dramatically alter
lattice thermal conductivity by factors of two to four in some materials. This work establishes a robust and efficient data-driven approach for predicting finite-temperature
phonon behavior, offering new pathways for the design and discovery of materials with tailored thermal and vibrational properties.
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All authors Huiju Lee, Zhi Li, Jiangang he, Yi Xia
Materials Science
Unexpected type-II multiferroic phase in GdMnO3 under high magnetic fields
Ming Yang, Jun Chen, Junfeng Wang et al. (+6 more)
Perovskite manganites with small A-site ions, as the first and canonical branch of type-II multiferroics, are ideal systems to exhibit magnetism-induced ferroelectricity. Despite their established magnetoelectric phase diagrams under low
magnetic fields, here an unidentified phase with a large magnetism-induced polarization (up to 1500 {\mu}C/m2) is revealed in GdMnO3 under high
magnetic fields up to 60 T. Based on multiprobe experiments, a complete phase diagram is constructed with successive polar-nonpolar-polar-nonpolar transitions. Such a nonmonotonic
evolution is well mimicked by model simulation, while the
spin-
lattice coupling is the key ingredient for the reentrant ferroelectric phase.
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All authors Ming Yang, Jun Chen, Junfeng Wang, Chao Dong, Chengliang Lu, Gang Xu, Jinguang Cheng, Jianshi Zhou, Shuai Dong
Materials Science
Electronic procrystalline state in moire structures
Hui Guo, Zihao Huang, Yixuan Gao et al. (+15 more)
Solid state materials can display varieties of atomic structural orders ranging from crystalline to amorphous, underlying their properties and diverse functionalities. Procrystal has emerged as a new category of solids, featuring a long-range ordered
lattice framework tiled with disordered atomic or molecular structures on the
lattice sites, arousing great interest due to its novel structural and physical properties. However, the electronic analogue of a procrystal, dubbed as an electronic procrystalline (EPC) state, has never been experimentally observed. Here, we report the observation of an EPC state in a moire superstructure formed between a monolayer metallic NiTe2 and a
superconductor NbSe2 with incommensurate
lattice wavevectors. The observed EPC state exhibits a long-range periodic charge modulation at the moire scale inlaid with short-range irregular orders within each moire
cell. Strikingly, the short-range charge orders inside the moire unit
cells have proximately root3*root3 quasi-period, which is absent in pristine NiTe2. Intriguingly, the EPC order is also observed in the superconducting state of the moire superstructure. Furthermore, the emergent EPC state and short-range charge order, coexisting with the proximity induced superconductivity, can be precisely modulated with the thickness of NiTe2. Our findings uncover the potential of moire platform for understanding and tuning novel correlated
quantum phases with this exotic procrystalline order.
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All authors Hui Guo, Zihao Huang, Yixuan Gao, Haowei Chen, Hao Zhang, Qian Fang, Yuhan Ye, Xianghe Han, Zhongyi Cao, Jiayi Wang, Runnong Zhou, Zhilin Li, Chengmin Shen, Haitao Yang, Hui Chen, Wang Yao, Ziqiang Wang, Hong-Jun Gao
Materials Science · Cross-listed from quant-ph
Mechanistic principles of exciton-polariton relaxation
Ian Haines, Arshath Manjalingal, Logan Blackham et al. (+2 more)
Exciton-polaritons are light-matter hybrid quasi-particles that have emerged as a flexible platform for developing
quantum technologies and engineering material properties. However, the fundamental mechanistic principles that govern their dynamics and relaxation remain elusive. In this work, we provide the microscopic mechanistic understanding of the
exciton-polariton relaxation process that follows from an excitation in the upper polariton. Using both mixed
quantum-classical simulations and analytical analysis, we reveal that
phonon-induced upper-to-lower polariton relaxation proceeds via two steps: the first step is a vertical inter-band transition from the upper to the lower polariton, which is followed by a second step that is a
phonon-induced Fröhlich scattering within the lower polariton. We find that in materials of finite thickness (which include filled cavities),
phonon-induced polaritonic intraband Fröhlich scattering is significantly suppressed. We show that the microscopic origin of this suppression is
phonon-fluctuations synchronization (or self-averaging) due to the polaritonic spatial delocalization in the quantization direction. Finally, we show that the same
phonon fluctuation-synchronization effect plays a central role across polaritonic relaxation pathways, and we derive simple analytical expressions that relate a material's finite thickness to the corresponding relaxation rate constants.
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All authors Ian Haines, Arshath Manjalingal, Logan Blackham, Saeed Rahamanian Koshkaki, Arkajit Mandal