Materials Science · Cross-listed from cond-mat.mes-hall
Optical control of conductivity type and valley polarization via persistent photoconductivity in (Pb,Sn)Se quantum wells
Alexander Kazakov, Gauthier Krizman, Valentine V. Volobuev et al. (+8 more)
The ability to tune the
Fermi level of
semiconductors is at the heart of modern electronics. Here, we demonstrate that persistent photoconductivity (PPC) enables tuning of carrier density, conductivity type, and, consequently, the valley polarization in (Pb,Sn)Se/(Pb,Eu)Se
quantum wells. Illumination of these samples induces
Fermi level shifts that convert the system from a threefold-degenerate $\bar{M}$-valley two-dimensional hole gas to a single $\bar{\Gamma}$-valley-polarized electron gas with similar values of mobility. The optically induced state persists for more than $10^{3}$ minutes at cryogenic temperatures and enables stepwise optical gating without the need for device processing. These transitions are confirmed by the sign inversion of the
Hall slope and the modification of
quantum Hall plateau degeneracies measured in
magnetic fields up to 35 T. Landau level $k\cdot p$ model calculations quantitatively reproduce the experimental data. Furthermore, studies of weak-field magnetoresistance demonstrate the significance of
quantum localization phenomena at the transition between the weakly and strongly localized regimes in compensated narrow-gap
semiconductors. Spectral studies allow us to identify the critical role of the barrier material and determine the
photon energies that can reverse the PPC effect. The persistent light-induced upward shift of the
Fermi level in the $p$-type
quantum well is explained in terms of specific energy positions of donor and acceptor defect states in the studied system. Our results demonstrate that PPC is a powerful optical gating tool for the IV-VI
quantum wells, a versatile platform for reconfigurable valleytronic architectures.
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All authors Alexander Kazakov, Gauthier Krizman, Valentine V. Volobuev, Michał Szot, Wojciech Wołkanowicz, Chang-Woo Cho, Benjamin A. Piot, Tomasz Wojciechowski, Gunther Springholz, Tomasz Wojtowicz, Tomasz Dietl
Materials Science · Cross-listed from nlin.PS
Bifurcation of the quasi-stationary velocity of strongly discrete transition waves driven by gravity
Zehuan Tang, Qing Xia, Hui Chen et al. (+2 more)
Transition waves are common in multistable mechanical metamaterials, and the dynamics of weakly discrete transition waves under driving forces have been extensively discussed. However, as
lattice effects become more pronounced, strongly discrete transition waves may exhibit dynamics that cannot be predicted by the continuum limit. Here, by tilting a bistable chain, we introduce a gravitational perturbation term into the dynamical equations, under which the transition waves are continuously accelerated. In the strongly discrete regime, we find that transition waves under gravitational driving possess quasi-stationary velocity plateaus (QSVPs), and the number of these plateaus first increases and then decreases as the tilt angle increases. We theoretically elucidate that the emergence of the velocity plateaus originates from the balance between gravitational driving and
phonon radiation. In further analysis, the theoretical model reveals that the balance point undergoes a bifurcation at the radiation resonance, which leads to a change in the number of velocity plateaus. Our study extends the investigation of transition waves into the strongly discrete regime, and the emergence of multiple velocity plateaus opens up new possibilities for programmable solitary waves.
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All authors Zehuan Tang, Qing Xia, Hui Chen, Songyang Fu, Yuanwen Gao
Materials Science
Electronic mechanism of sub-100-fs demagnetization induced by a femtosecond light pulse
Konrad J. Kapcia, Victor Tkachenko, Flavio Capotondi et al. (+4 more)
A quantitative understanding of the processes that trigger light-induced demagnetization on ultrashort timescales is crucial for achieving an ultrafast, radiation-controlled
magnetic response in materials. This milestone is essential for developing next-generation
magnetic storage devices and ultrafast
magnetic switches. In this theoretical study, we investigated demagnetization triggered in a single
magnetic domain by light pulses ranging from a few to a few tens of femtoseconds in duration, with
photon energies spanning the optical and X-ray regimes, under strongly non-
equilibrium conditions. We predicted a loss of magnetization in the sub-100-fs range in all cases, primarily due to the excitation of the electronic system and the subsequent redistribution of electrons within the magneto-sensitive band. The considered timescales were too short for
phonon-mediated processes or inter-site Heisenberg exchange processes to contribute significantly. These findings pave the way for highly accurate, radiation-driven magnetization control in
magnetic materials at sub-100-femtosecond timescales with potential practical applications.
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All authors Konrad J. Kapcia, Victor Tkachenko, Flavio Capotondi, Alexander Lichtenstein, Serguei Molodtsov, Przemysław Piekarz, Beata Ziaja
Materials Science
Defect Control via Cu Enrichment Enhances Multifunctional Properties in the Polar Semiconductor Cu1+xMn1-ySiTe3
Subrata Ghosh, Yu Liu, Saugata Sarker et al. (+15 more)
Polar materials have recently attracted significant interest due to their rich multifunctional properties. The chalcogenide polar
semiconductor Cu1-xMn1+ySiTe3 (Cu-deficient) is an emerging multiferroic system in which electric polarization is coupled to magnetization. However, its macroscopic ferroelectric polarization is strongly suppressed due to the presence of a high density of stacking faults. In this work, we demonstrate that these
crystal defects, likely originating from non-stoichiometry, can be substantially reduced by increasing the Cu content. Cu-enriched samples, Cu1+xMn1-ySiTe3, crystallize in a noncentrosymmetric monoclinic structure (space group Pm) as the Cu-deficient counterpart but show a nearly stacking-fault-free phase, which is attributed to the emergence of an interstitial site. Consequently, the Cu-enriched samples show a pronounced enhancement of the second-harmonic generation (SHG) response compared to Cu-deficient compositions. Magnetically, the Cu-enriched
crystals retain long-range
antiferromagnetic order with a Neel temperature of TN ~ 33 K without a glassy state but manifest a distinct
spin-flop transition along the polar b-axis that is absent in the Cu-deficient compositions. Furthermore, the electronic ground state evolves from insulating to doped semiconducting behavior upon Cu enrichment. Together, these results establish this material system as a unique and versatile platform for elucidating the interplay among composition,
crystal defects, and multifunctional properties, offering a route to design
magnetic polar systems with tunable
quantum functionalities.
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All authors Subrata Ghosh, Yu Liu, Saugata Sarker, Boyang Zheng, Sreekant Anil, Soumi Mondal, Yuxi Zhang, Sai Venkata Gayathri Ayyagari, Mingyu Xu, Yingdong Guan, Tsung-Han Yang, Xiaoping Wang, Vincent H. Crespi, Nasim Alem, Weiwei Xie, Venkatraman Gopalan, Qiang Zhang, Zhiqiang Mao
Materials Science · Cross-listed from cond-mat.str-el
Charge order on a triangular lattice with Mott physics and arbitrary charge density
Aleksey Alekseev, Agnieszka Cichy and Konrad Jerzy Kapcia
Triangular-
lattice systems attract a lot of
attention due to various frustration-induced and strongly correlated effects. Here, we focus on the charge-ordering phenomenon by means of investigation of the extended Hubbard model with dynamical mean-field theory (DMFT). By considering the intersite nearest-neighbor interaction we have found a very rich phase diagram that contains large number of features, phases, and phase transitions. Among them are pinball-
liquid (PL) phases where we distinguish charge-transfer-driven and Mott-localization-driven PLs; phase transitions that change their order as model parameters evolve (from discontinuous to continuous); very strong particle-hole asymmetry. Various features of the phase diagram are found to be better understood by means of the simple mean-field approximation (MFA). Moreover, besides helping with interpretation of the phase diagram, the MFA results together with results for the atomic-limit model are found to be able to set rather good expectations on how the DMFT phase diagram should look like. Nevertheless, a few features were not expected and are found within the DMFT, such as a small-region intermediate metallic phase on an electron-doped side of the phase diagram.
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Materials Science · Cross-listed from cs.AI
A Practical Noise2Noise Denoising Pipeline for High-Throughput Raman Spectroscopy
David Martin-Calle, Cesar Alvarez Llamas, Vincent Motto- Ros et al. (+3 more)
A lightweight and reproducible denoising pipeline for high-throughput Raman spectroscopy is presented. The approach relies on a one-dimensional convolutional autoencoder trained using a Noise2Noise strategy, requiring neither external spectral libraries nor high signal-to-noise reference spectra for training. From a reduced training subset composed of repeated short-exposure acquisitions, the model learns to reconstruct Raman spectra while efficiently suppressing
stochastic noise. The method is evaluated on a heterogeneous mineral sample, using both quantitative spectral fidelity metrics (RMSE, SNR, SSIM) and task-oriented criteria based on unsupervised K-means classification. Results demonstrate that integration times as short as 5 ms per spectrum, which are typically insufficient for reliable interpretation, yield denoised spectra with high fidelity to the reference data while preserving chemically coherent maps. This work provides a practical trade-off between spectral quality and acquisition speed, enabling fast, adaptable Raman workflows compatible with routine laboratory use. It also offers a transferable framework for other one-dimensional spectroscopic modalities.
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All authors David Martin-Calle, Cesar Alvarez Llamas, Vincent Motto- Ros, Christophe Dujardin, Jérémie Margueritat, David Rodney
Materials Science · Cross-listed from cond-mat.mes-hall
Probing Dielectric Screening in van der Waals Heterostructures via Pressure-Tuned Exciton Rydberg Series
Shalini Badola, Adlen Smiri, Thomas Pelini et al. (+7 more)
Excitons in two-dimensional
semiconductors are directly exposed to the environment and are sensitive to the dielectric properties of their surrounding. Here, we show that the Rydberg series of excited states of
excitons in a monolayer WSe$_2$ encapsulated in hexagonal boron nitride (hBN) can be used to probe the pressure-induced modifications of the surrounding dielectric properties. We propose a model based on the pressure induced
evolution of the interlayer distances in this van der Waals
heterostructure and on the bulk dielectric properties of hBN. This approach allows a direct measurement of the dielectric constant of pressurized hBN and establishes a new methodology for dielectric sensing.
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All authors Shalini Badola, Adlen Smiri, Thomas Pelini, Aditi Moghe, Tristan Riccardi, Amit Pawbake, Kenji Watanabe, Takashi Taniguchi, Iann C. gerber, Clement Faugeras
Materials Science · Cross-listed from quant-ph
Quantum Emitters at Telecommunication Wavelengths based on Carbon Defects in Transition Metal Dichalcogenides
Chanaprom Cholsuk, Sujin Suwanna and Tobias Vogl
Low-dimensional materials have emerged as promising hosts for
quantum emitters, whose emission typically arises from either strain-induced band bending or defect-induced two-level systems. Among these materials, transition metal dichalcogenide (TMD) monolayers have attracted particular
attention; however, their performance is limited by strong photoluminescence (PL) quenching at room temperature. As TMDs transition from a direct to an indirect bandgap when moving from monolayers to multilayers, we herein propose a strategy to overcome this quenching limitation by exploiting the indirect bandgap of TMD
bilayers in combination with a point defect doping. The indirect gap suppresses excitonic PL, while specific defects enable robust defect-mediated
quantum emission. Using hybrid-functional density functional theory, we investigate substitutional carbon defects at chalcogen sites (S and Se) in WS2, WSe2, MoS2, and MoSe2
bilayers and comprehensively characterize their optical properties. Both neutral and singly negative charge states are found to be thermodynamically stable. Neutral defects exhibit singlet configurations with emission in the O- and C-band telecommunication windows, whereas negatively charged defects adopt doublet configurations featuring
spin-selective transitions and near-infrared emission. The electron-
phonon coupling strength, radiative lifetime, and dipole orientation are found to depend sensitively on both the host material and defect site, providing distinct fingerprints for experimental identification. Our findings, therefore, establish carbon-doped TMD
bilayers as promising platforms for room-temperature defect-based
quantum emitters operating at telecommunication wavelengths.
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Materials Science
Termination-Preserved Ultra-high Tunneling Magnetoresistance in Altermagnetic KV2Se2O
Junnan Guo, Himanshu Mavani, Wenhui Fang et al. (+6 more)
Altermagnets exhibit nonrelativistic
spin splitting without net magnetization, establishing a new platform for next-generation spintronic devices. Although altermagnetic tunnel junctions (AMTJs) represent the most promising realizations, their practical applications are hindered by low tunnel magnetoresistance (TMR) ratios and strong sensitivity to interfacial configurations. Here, we systematically explore the transport properties and microscopic mechanisms of AMTJs based on the recently discovered d-wave altermagnet KV2Se2O. Using first-principles calculations and orbital-resolved analysis, we demonstrate that the synergy between compressed nodal-point like
spin-degenerate channels and coplanar interfacial
magnetic order yields an ultra-high intrinsic TMR above 105% for all interfacial terminations. More importantly, K-termination effectively preserves bulk
spin polarization through its unique passivation characteristics, leading to an ultra-high TMR up to 1012%. These results identify the coupling between momentum-space
topology and interfacial passivation provides a reliable strategy for realizing
giant magnetoresistive responses in altermagnetic spintronic devices.
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All authors Junnan Guo, Himanshu Mavani, Wenhui Fang, Jifeng Tang, Wenhao Li, Weikang Wu, Hui Li, Evgeny Y. Tsymbal, Lishu Zhang
Materials Science
Spatially-Localized Second Harmonic Generation via Spin Wave Concentration in Patterned YIG Structures
Stephanie R. Lake, Marc Eger, Philipp Geyer et al. (+3 more)
The anisotropic dispersion and inherent nonlinearity of magnetostatic
spin waves in thin films and confined structures provide unique opportunities for implementation in next-generation magnonic devices for data and signal processing. A particular challenge is to establish an effective means to locally generate higher harmonics and subsequently exploit them while avoiding extraneous nonlinear losses. Here we demonstrate that deterministically and locally tuning the dispersion relation by
geometric confinement through standard patterning processes, allows the creation spatially localized, high-intensity
magnons hundreds of $\mu m$ or even further from the excitation source. The local intensity obtained in passive, lithographically patterned YIG funnel structures is sufficient to achieve second harmonic generation in localized regions via conventional
magnon scattering processes. We verify these effects are truly nonlinear processes by direct measurement and comparison of the 1-$\omega$ and 2-$\omega$
magnon signals as determined by highly sensitive frequency- and spatially-resolved SNS-MOKE technique. This lays the foundation for using similar devices in future
magnon-based infrastructures to localize and enhance sensitivity of readout, downstream
magnon-based logic operations, and for other higher harmonic generation-related phenomena and low-power magnonics applications.
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All authors Stephanie R. Lake, Marc Eger, Philipp Geyer, Rouven Dreyer, Seth W. Kurfman, Georg Schmidt
Materials Science · Cross-listed from cond-mat.str-el
Frustration from Localized Zhang-Rice States: A Unified Theory of Doping-Driven Magnetic Transitions in Cuprates
Xiaodong Wang, Ping Xu, Jiong Mei et al. (+5 more)
The microscopic mechanism by which doped holes disrupt the
antiferromagnetic (AFM) order is one of the fundamental questions in cuprates. In this work, we propose a unified microscopic theory in which doped holes form spatially localized Zhang-Rice singlets which actively mediate emergent
spin exchange. Rather than acting as simple non-
magnetic vacancies, these localized states introduce emergent next-nearest $J_2$ and third-nearest $J_3$ neighbor superexchanges. This dopant-induced exchange pathway generates significant
magnetic frustration, naturally explaining the rapid collapse of the Néel AFM order and the emergence of a
spin-glass phase on the hole-doped side. In contrast, electron doping primarily leads to
spin dilution, allowing AFM order to persist to substantially higher doping levels, consistent with the experimentally observed electron-hole asymmetry. Our findings provide a unified microscopic framework for understanding doping-driven
magnetic transitions in lightly doped cuprates.
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All authors Xiaodong Wang, Ping Xu, Jiong Mei, Shao-Hang Shi, Zi-Xiang Li, Mingpu Qin, Kun Jiang, Hui-Ke Jin
Materials Science · Cross-listed from cond-mat.supr-con
Direction-selective triplet pairing and spin-edge locking in altermagnetic metals
Lie Yuan, Junkang Huang, Yu-Xuan Li et al. (+1 more)
We investigate self-consistent unconventional superconductivity in a two-dimensional $d$-wave altermagnetic metal. We find that momentum-dependent altermagnetic
spin splitting suppresses opposite-
spin singlet pairing and stabilizes highly anisotropic equal-
spin triplet order. In the
spin-conserving limit, this directional triplet pairing gives rise to nearly dispersionless Majorana boundary states associated with effective one-dimensional topological channels. Rashba
spin-orbit coupling mixes
spin sectors, activates additional pairing components, and drives the system into a mixed-parity superconducting state with dispersive Majorana boundary states. The
spin-resolved boundary spectra further reveal a characteristic locking between boundary orientation and
spin polarization, reflecting the underlying altermagnetic
symmetry. These results identify altermagnetic
spin splitting as an intrinsic mechanism for selecting unconventional pairing and generating
spin-resolved Majorana boundary states without external
magnetic fields.
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All authors Lie Yuan, Junkang Huang, Yu-Xuan Li, Tao Zhou
Materials Science
Epitaxial growth and magnetic phase transitions in non-centrosymmetric EuPdSi$_3$ thin films
Sebastian Kölsch, Alfons G. Schuck, Olena Fedchenko et al. (+9 more)
Non-centrosymmetric
magnetic materials are a promising platform for stabilizing
chiral spin textures, such as skyrmions and cycloidal
magnetic states. This is particularly true in epitaxial thin film geometries, where strain and interface effects offer additional control. Herein, we report on the first epitaxial thin films of EuPdSi$_3$ grown by molecular beam epitaxy on MgO(001). X-ray diffraction confirms an epitaxial relationship of tetragonal EuPdSi$_3$ in the BaNiSn$_3$ structure with out-of-plane c-axis orientation and parallel in-plane a-axes. Hard x-ray photoelectron spectroscopy reveals a stable Eu valence of 2.0, yielding a large
magnetic moment of approximately 7 $\mu_B$ per Eu atom in accordance with Hund's rule. Owing to the non-centrosymmetric
crystal structure, non-collinear
magnetic states such as Néel-type skyrmions and cycloidal phases are allowed by
symmetry. Electronic transport measurements reveal two
magnetic phase transitions at 19 K and 15 K in zero applied field. Under
magnetic fields applied along the crystallographic [100] and [001] directions, distinct temperature dependent
magnetic phases emerge, demonstrating the sensitivity of the
magnetic ground state to field orientation in epitaxial EuPdSi$_3$ thin films.
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All authors Sebastian Kölsch, Alfons G. Schuck, Olena Fedchenko, Dmitry Vasilyev, Olena Tkach, Sergeij Chernov, Christoph Schlüter, Andrii Gloskowski, Hans-Joachim Elmers, Gerd Schönhense, Jens Müller, Michael Huth
Materials Science · Cross-listed from cond-mat.mes-hall
Qumus: Realization of An Embodied AI Quantum Material Experimentalist
Lihan Shi, Zhaoyi Joy Zheng, Xinzhe Juan et al. (+14 more)
While modern Large
Language Models (LLMs) and agentic artificial intelligence (AI) have demonstrated transformative capabilities in digital domains, the realization of
embodied AI capable of real-world scientific discovery remains a difficult frontier. The advancements are hindered by the inherent complexity of integrating high-level
reasoning,
multimodal information processing and real-time physical execution. Here we introduce Qumus, the first AI
quantum materials experimentalist. Physically
embodied within a robotic mini-laboratory, Qumus is an intelligent,
multimodal, and multi-
agent system designed for the creation and nano-processing of atomically thin two-dimensional (2D) materials and stacked van der Waals (vdW) structures. Qumus autonomously navigates the full scientific cycle, from hypothesis generation and protocol planning to multi-step experimental execution, result analysis and reporting, acting as an experimentalist. Markedly, the system has achieved, for the first time, the AI-creation of
graphene, as well as the first AI-fabrication of complex nanodevices including atomically thin field-effect transistors via vdW stacking. Qumus excels at these tasks by demonstrating autonomous error correction and closed-loop experimentation. Our results establish a generalizable framework for self-improving
embodied AI systems that learn directly from the
quantum world, opening a pathway toward accelerated discovery in
quantum materials, electronics and beyond.
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All authors Lihan Shi, Zhaoyi Joy Zheng, Xinzhe Juan, Yimin Wang, Ming Yin, Mayank Sengupta, Kristina Wolinski, Yanyu Jia, Jingzhi Shi, Derek Saucedo, Neill Saggi, Haosen Guan, Kenji Watanabe, Takashi Taniguchi, Ali Yazdani, Mengdi Wang, Sanfeng Wu
Materials Science
Metastable Cu$_{1-x}$CrTe$_2$ – Completing the copper chromium delafossite series through soft chemistry
Kai D. Röseler, Geo Sciarini, Felix Eder et al. (+3 more)
In the layered copper chromium dichalcogenide series CuCr$X_2$, the
oxide, the sulfide, and the selenide analogues have been reported, but the telluride CuCrTe$_2$ has remained unsynthesized so far. Here, we report the synthesis of Cu$_{1-x}$CrTe$_2$ ($x \approx 0.3$), which forms only within a narrow temperature window near 90 {\deg}C by solvothermal cation exchange of K$_{1-x}$CrTe$_2$ ($x \approx 0.3$) and CuBr. Cu$_{1-x}$CrTe$_2$ undergoes a magnetostructural transition to an
antiferromagnetic state at $T_\mathrm{N}=239$ K, a Néel temperature that is high relative to other $A$CrTe$_2$ phases and comparable to that of
ferromagnetic, fully-deintercalated CrTe$_2$. Cu$_{1-x}$CrTe$_2$ is metastable and decomposes at temperatures as low as 250 {\deg}C to form spinel CuCr$_2$Te$_4$. These results highlight the importance of low-temperature topochemical routes for accessing metastable Cu(I)-containing tellurides that are inaccessible by conventional solid-state synthesis.
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All authors Kai D. Röseler, Geo Sciarini, Felix Eder, Samuel Moody, Vladimir Pomjakushin, Fabian O. von Rohr
Materials Science · Cross-listed from physics.ins-det
A single multi-configuration Direct Electron Detector for various electron imaging and diffraction-based techniques in SEM
Nohayla El-Khairaoui, Julien Guyon, Nathalie Gey et al. (+2 more)
Addressing the need for efficient and integrated multiscale crystallographic and defect analyses of advanced materials, this paper presents the implementation of a new multi-configuration detection system, integrating a single Timepix3-based direct electron detector (DED) in a scanning electron microscope (SEM). By combining precise translation and rotation movements, this system enables, for the first time, the use of the same detector to realize all principal diffraction geometries. These include conventional Electron BackScatter Diffraction (EBSD), off-axis Reflexion Kikuchi Diffraction (RKD), and Transmission Kikuchi Diffraction (TKD) in on-, off- and near-axis configurations. Furthermore, transitions between all these geometries are accomplished without hardware modification. On the other hand, this work presents efficient reconstruction of electron images using the detector data-driven feature, extending thus its applicability to BackScattered Electron imaging (BSE), Electron Channelling Contrast Imaging (ECCI) and Scanning Transmission Electron Imaging in SEM (STEM-in-SEM) characterizations. High-quality Kikuchi patterns easily indexable were acquired across all geometries as well as micrographs of dislocations in both reflection and transmission modes. This is achieved thanks to the flexibility of the implemented detector, the optimizations made in acquisition parameters, such as energy filtering settings, and the efficiency of the developed custom approach used for electron data post-processing. Through this work, it is demonstrated that with a single DED assisted by an orientable support, it is possible to perform multiple advanced microstructural characterizations of both bulk samples and thin foils in the same SEM.
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All authors Nohayla El-Khairaoui, Julien Guyon, Nathalie Gey, Luc Morhain, Nabila Maloufi
Materials Science
Tuning the Charge Transfer of Transition Metal Dichalcogenides via Misfit Layer Compounds
Hugo Le Du, Ludovica Zullo, Justine Cordiez et al. (+16 more)
Misfit layer compounds (MLCs) are a versatile platform for exploring the electronic phase diagram of two dimensional (2D) materials beyond the limits of conventional gating techniques. This work demonstrates the precise tunability of electron doping in NbSe2 monolayers through chemical alloying within the rocksalt layer of (LaxPb1xSe)1.14(NbSe2)2
heterostructures. By combining first principles density functional theory (DFT) calculations with angle resolved photoemission spectroscopy (ARPES), we prove that the rocksalt unit acts as an universal electron donor. We show that varying the La Pb ratio results in a rigid
Fermi level shift, still preserving the NbSe2 electronic structure. Crucially,
photon energy dependent ARPES confirms that the NbSe2 layers nearly maintain their intrinsic 2D character and orbital identity within the three dimensional misfit. This study establishes MLCs as a reliable platform for engineering emergent states in 2D transition metal dichalcogenides through precise stoichiometric control.
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All authors Hugo Le Du, Ludovica Zullo, Justine Cordiez, Robin Salvatore, Giovanni Marini, Marie Hervé, Debora Pierucci, Shunsuke Sasaki, Florent Pawula, Etienne Janod, Chiara Bigi, Marta Zonno, François Bertran, Thomas Jaouen, Patrick Le Fèvre, Matteo Calandra, Laurent Cario, Tristan Cren, Marie D Angelo
Materials Science · Cross-listed from cond-mat.soft
Coalescence of Polymer Droplets Moving on a Surface with Stiffness Gradient
Divyansh Tripathi, Vimal Kishore, Panagiotis E. Theodorakis et al. (+1 more)
Here, we study the coalescence of two droplets that are moving in the same direction on a soft surface; the motion of the droplets is caused by a gradient in the surface stiffness. As reference, stationary coalescence of the same droplets is also studied on the corresponding uniform surfaces for different stiffness values. To describe the coalescence phenomenon on a surface with stiffness gradient, a relevant range of velocity ratios of the leading and the trailing droplet was considered to elucidate the effect of this parameter on coalescence. Moreover, to analyze the dynamics of the process, the temporal growth of the bridge height $(h)$ was investigated, which follows a power law $(h \sim t^{\alpha})$, before eventually attaining a constant value. The obtained values of $\alpha$ show a transition from a higher to a lower value as a function of time, pointing to the presence of two distinct power-law growth regimes, where the transition signifies the crossover from the capillarity-dominated regime to the viscoelasticty-dominated regime of coalescence. In addition, varying attractive strengths for droplet–droplet and intra-droplet interactions were considered. The results indicate that both the dynamics and the degree of the coalescence strongly depend on these interaction parameters. Thus, we anticipate that our results will shed more light on the durotaxis-driven coalescence of polymeric droplets for various relevant system parameters, which will have practical implications for applications ranging from microfluidics to ink-jet printing, where substrate properties may vary. In addition, results may add to the fundamental understanding of the interactions among multicellular aggregates moving on biological surfaces.
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All authors Divyansh Tripathi, Vimal Kishore, Panagiotis E. Theodorakis, Swarn Lata Singh
Materials Science
Why hole polaron formation on oxygen is limiting the Fermi level in Fe acceptor doped BaTiO$_{3}$ under oxidizing conditions
Mohammad Amirabbasi, Emre Erdem, Denis Sudarikov et al. (+3 more)
Oxidizing Fe-doped BaTiO$_3$ is commonly expected to convert substitutional Fe$^{3+}$ acceptors into formal Fe$^{4+}$ centers. Yet, the experimentally accessible picture based on electron-paramagnetic resonance (EPR) is dominated by Fe$^{3+}$-related signatures, while Fe$^{4+}$ is not a straightforward observable. Here we show that this apparent discrepancy reflects the preferred location of the oxidizing hole: not on Fe, but on oxygen. Using density-functional theory with with occupation-
matrix control and a piecewise-linearity-based Hubbard correction (DFT+$U$) for O-2$p$ states, we find that an oxygen-centered hole polaron is forming a Fe$^{3+}$-O$^{-}$ complex that is lower in energy than the formal Fe$^{4+}$ configuration. Our results identify ligand-hole formation as a favorable charge-compensation mechanism in oxidized Fe-doped BaTiO$_3$ and provide an explanation for the predominance of Fe$^{3+}$-based centers in spectroscopy. More broadly, they show how oxygen polarons can limit
Fermi-level shifts and control the electronic response of acceptor-doped ferroelectric perovskites.
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All authors Mohammad Amirabbasi, Emre Erdem, Denis Sudarikov, Jochen Rohrer, Andreas Klein, Karsten Albe
Materials Science
Short-range order in the CoCrFeMnNi high-entropy alloy from cluster expansion
Wei Chen, Gian-Marco Rignanese and Geoffroy Hautier
We investigate the short-range order (SRO) and phase stability of the equiatomic CoCrFeMnNi high-
entropy alloy using cluster expansion supplemented by an eigen-decomposition analysis of the SRO parameters. Our results reveal that the primary ordering behavior is determined by strong Cr-Cr repulsive interactions, complemented by attractive heteroatomic Cr-$X$ pairs in the first nearest-neighbor shell. This chemical affinity is consistent with the emergence of ordered local environments and appears to be a major contributor to the primary order-disorder transition. At lower temperatures, the spectral SRO analysis suggests two additional lower-temperature instabilities: a collective ordering instability and an Fe-rich local clustering instability.
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Materials Science
First-principles investigation of small polarons in rhombohedral NaNbO$_{3}$
Mohammad Amirabbasi, Lorenzo Villa, Elaheh Ghorbani et al. (+2 more)
Sodium niobate (NaNbO$_{3}$) is a perovskite
oxide and a key component of emerging lead-free antiferroelectric capacitors for high-energy-density applications. However, its performance can be hindered by irreversible phase transitions and leakage currents associated with low electrical resistivity. Defect and doping engineering offers a potential way to overcome these problems, but its use requires a detailed understanding of electronic, ionic, and polaron charge-compensation mechanisms, where the role of polarons remains largely unexplored. Here, we investigate the stability of small hole and electron polarons in rhombohedral NaNbO$_{3}$, which is a structurally well-defined model system that avoids
lattice-dynamical instabilities. Trapping energies are calculated using density-functional theory corrected by a Hubbard $U$, using the enforced-piecewise-linearity approach including finite-size scaling. For the small hole-polaron centered on O-2$p$ orbital, we find a trapping energy of $-$0.65 (eV) and an adiabatic migration barrier of 0.32 (eV) determined by nudged-elastic-band calculations. In contrast, we show that excess electrons do not self-trap on Nb-4$d$ orbitals, reflecting weak electron-
phonon coupling in the conduction band
manifold. These results identify oxygen as an intrinsic hole trap in NaNbO$_{3}$ and highlight the importance of including hole polarons in defect models of NaNbO$_{3}$-based electroceramics.
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All authors Mohammad Amirabbasi, Lorenzo Villa, Elaheh Ghorbani, Jochen Rohrer, Karsten Albe
Materials Science
High-Density Horizontal Arrays of Single-Chirality Carbon Nanotubes
Yanzhao Liu, Zilong Qiu, Yuguang Chen et al. (+18 more)
Highly ordered high-density arrays of single-chirality single-walled carbon nanotubes (SWCNTs) are greatly desired for exploring the intrinsic anisotropic properties and collective performance of such 1-dimensional (1D) nanomaterials. Here we present a Marangoni flow-induced self-assembly (MISA) strategy to fabricate monolayered SWCNT arrays achieving a packing density of ~200 ${\mu m}^{-1}$ and a 2-dimensional order parameter ($S_{2\mathrm{D}}$) of ~0.95. Relying on its general compatibility with both organic and aqueous dispersions, we prepare single-chirality and enantiomer-pure SWCNT arrays from organic and aqueous dispersions resulting from the sorting processes. The anisotropic optical and electrical properties of the arrays are demonstrated by the polarization-dependent Rabi splitting as well as polarized near-infrared light emission and detection. With the great tolerance to solutions, substrates, and materials, as well as the feasibility and controllability, MISA shows great potential in the assembly of 1D nanomaterials.
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All authors Yanzhao Liu, Zilong Qiu, Yuguang Chen, Nie Zhang, Bing Han, Huimin Yin, Bojun Liu, Min Lyu, Zhihong Li, Yiran Ma, Jian Sheng, Jiahui Shao, Zeyao Zhang, Li Ding, Hao Hong, Chuanhong Jin, Sheng Wang, Kaihui Liu, Xiaowei He, Lian-Mao Peng, Yan Li
Materials Science
Characterisation of fire-damaged batteries,implications for recycling
Wafaa AlShatty, Tom Dunlop, Rhys Charles et al. (+2 more)
As lithium-ion battery demand grows, so do fire safety challenges. Despite this, research on fire-damaged batteries remains limited. This study explores the distribution of valuable metals (such as Ni, Mn, Co, Cu) in two types of waste derived from lithium-ion nickel-manganese-cobalt
oxide batteries (NMC811), black mass (BM) and fire-damaged waste (FD). It emphasizes that cobalt, manganese, and nickel-rich NMC811 particles are predominantly found in smaller particle size fractions (<125 microns), where they can account for up to 85 percent of total metal content. Fire-damaged (FD) batteries show a similar, though less pronounced, trend. Evidence of structural degradation suggests that fire temperatures exceeded 500{\deg}C; however, the presence of residual organic binders indicates that heat was unevenly distributed during the fire. FD batteries become friable and easily fragment into fine particles, which can hinder the effective separation of copper and aluminium current collectors, increasing their presence in processed material. The inclusion of FD batteries in standard BM processing introduces variability in output composition, potentially lowering the concentration of high-value NMC811 materials present. To maintain product quality and recycling output values, it is recommended that FD batteries are processed separately. Alternatively, particle size separation may allow for tailored outputs aligned with specific customer requirements.
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All authors Wafaa AlShatty, Tom Dunlop, Rhys Charles, Davide Deganello, Jenny Baker
Materials Science · Cross-listed from nucl-th
Systematic study of one-point kinetic energy density functionals for atomic nuclei
Tian Shuai Shang, Jian Li, Haozhao Liang et al. (+5 more)
To explore the applicability of orbital-free density functional theory (OF-DFT) in
nuclear physics, we perform a systematic
benchmark of 36 one-point kinetic energy density functionals, which are originally developed for electron systems in condensed matter physics. It is found that the direct use of the original parameters for electron systems leads to inconsistent performance, with certain functionals exhibiting physically unacceptable asymptotic behaviors. However, through parameter re-optimization targeting
nuclear densities, different mathematical forms of generalized gradient approximation (GGA) functionals converge to a consistent root-mean-square error of approximately 13 MeV. From a physical perspective, this consistent behavior signifies that the optimized semi-local GGAs have successfully captured the macroscopic,
liquid-drop-like background of the
nucleus, while the residual deviations appear as periodic oscillations at the magic numbers that could reflect the
quantum shell effects.
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All authors Tian Shuai Shang, Jian Li, Haozhao Liang, Xinhui Wu, Cheng Ma, Wenhui Mi, Xuecheng Shao, Yanchao Wang
Materials Science
Chemo-mechanical coupling stabilizes mixed $\mathrm{Ag}_{x}\mathrm{Cu}_{1-x}\mathrm{GaSe}_{2}$ solar-cell absorbers: Insights from Monte-Carlo simulations assisted by ab initio informed machine-learning potentials
Vasilios Karanikolas, Delwin Perera, Linus Erhard et al. (+2 more)
Alloying Ag into Cu(In,Ga)Se$_2$ has enabled record
solar-
cell efficiencies ($\sim23.6\%$), yet their long-term stability remains in question because initio calculations predict a Ag-Cu miscibility gap near ambient temperature. By off-
lattice Monte-Carlo simulations using a newly developed machine learning (ML) interatomic potential we show that the presence of coherency strain is resolving the controversy between experimental observations and the predicted phase stability. Incorporating elastic energy contributions present in a coherent setup results in complete Ag-Cu miscibility, whereas the expected phase separation occurs in the absence of coherency strains with respect to the end boundary phases, which are mimicked by an incoherent interface with misfit dislocations. The developed ML-MC framework provides a novel approach for resolving discrepancies in thermodynamic stability for systems where mechanical and chemical effects compete.
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All authors Vasilios Karanikolas, Delwin Perera, Linus Erhard, Jochen Rohrer, Karsten Albe
Materials Science
Combinatorial Survey of Structural Phase Distribution and Magnetism in Fe-Ge-Te Composition-spread Thin Film Libraries
Chih-Yu Lee, Takahiro Yamazaki, Peng Yan et al. (+5 more)
Recently,
magnetic 2-dimensional (2D) van der Waals (vdW) materials have garnered tremendous
attention. The vdW ferromagnet Fe5Ge1Te2 has a Curie temperature Tc of ~ 270 K, which is tailorable by tuning the stoichiometry and the Fe deficiency to reach room temperature. To explore the expanded compositional space, we implemented combinatorial synthesis and high-throughput characterization to investigate the structural phase distribution and ferromagnetism of a Fe-Ge-Te thin film library. The library was prepared by magnetron co-sputtering followed by annealing in
vacuum or in an inert environment. Composition and structural phase distribution of the 177 pads in the library were characterized using high-throughput wavelength dispersive spectroscopy (WDS), X-ray diffraction (XRD), and two-point probe resistance measurements. We leverage unsupervised machine learning to cluster the XRD
dataset into groups of compositions with similar structural phases, and further study the
ferromagnetic properties via SQUID magnetometry and X-ray
magnetic circular dichroism (XMCD) across different clusters. The results are compared against magnetization and structural models calculated using DFT. Our results demonstrate that the hexagonal
crystal structure is a critical prerequisite for ferromagnetism in this system, and that unexplored materials adopting this structure can be efficiently identified as possible
ferromagnetic materials using our high-throughput, ML-assisted framework. This workflow based on the combinatorial strategy allows us to rapidly capture the composition-structure-
magnetic property map across a broad compositional landscape of novel
magnetic materials.
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All authors Chih-Yu Lee, Takahiro Yamazaki, Peng Yan, Ryan Kim, Masato Kotsugi, Efrain E. Rodriguez, Joseph W. Bennett, Ichiro Takeuchi
Materials Science
Real-time Multi-instrument Autonomous Discovery of Novel Phase-change Memory Materials
Chih-Yu Lee, Haotong Liang, Ryan Kim et al. (+4 more)
Autonomous labs enable the integration of automated experiment execution, data analysis and decision making. The main challenge remains the integration of diverse data streams from multiple instruments, where the data is often heterogeneous and unsynchronized. The standard learning process of undetermined synthesis-process-structure-property relationships (SPSPR) usually relies on post-experiment analysis after data is fully collected, not during live experiments, and decision making is carried out independently across characterization equipment. Here, we demonstrate the Multi-instrument Autonomous Discovery (MAD) framework – combining structural property mapping and functional property optimization simultaneously in a closed-loop manner. As an example, we applied MAD to phase change
memory (PCM) materials, and, in particular on the Mn-Sb-Te ternary, a previously unexplored materials system for PCM. A multi-output model is employed to merge data from x-ray diffraction (XRD) and electrical resistance measurements simultaneously through a co-regionalization kernel that models the relationship between them. The output probabilistic posterior and uncertainty quantification facilitate decision making with shared knowledge, while the goals are different across tasks. We aimed to maximize the knowledge of
crystal structure distribution using non-negative
matrix factorization (NMF), while in parallel, we find the composition with the maximum resistance value, an important figure of merit for PCM. Leveraging MAD, we found promising electrical PCMs and identified the SPSPR within 25 closed-loop iterations, corresponding to a seven-fold speed-up. The framework opens a new path of study in large-scale autonomous facilities, where future experiments can be run in parallel together, not independently.
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All authors Chih-Yu Lee, Haotong Liang, Ryan Kim, Austin McDannald, Carlos A Rios Ocampo, A. Gilad Kusne, Ichiro Takeuchi
Materials Science
Examining the microscopic origin of a computationally inexpensive thermal-conductivity-based indicator for phonon hydrodynamics
Nikhil Malviya and Navaneetha K. Ravichandran
Hydrodynamic heat flow, where out-of-
equilibrium phonons collectively drift in response to a temperature gradient, has attracted renewed interest following its experimental observation in graphite from cryogenic to room temperatures. To rapidly screen for other materials exhibiting this unconventional non-
Fourier regime, the computationally inexpensive thermal conductivity ratio $\kappa_{LPBE}/\kappa_{RTA}$ obtained from a complete solution of the linearized Peierls-Boltzmann equation (LPBE) for
phonon transport and the relaxation time approximation (RTA) for
phonon decay, has often been used as an indicator for
phonon hydrodynamics. Yet, a clear connection between $\kappa_{LPBE}/\kappa_{RTA}$ and the signatures of drifting hydrodynamic
phonon populations has not been established in the literature. Here we show that $\kappa_{LPBE}/\kappa_{RTA}$ directly correlates with the microscopic hydrodynamic signatures arising from the spectral properties of the
phonon collision operator, which is often computationally expensive to compute, thus establishing the former as a reliable low-cost indicator for
phonon hydrodynamics. On the other hand, other indicators in the literature that are derived only from the
phonon scattering rates do not correlate with $\kappa_{LPBE}/\kappa_{RTA}$, and so, are inadequate to predict
phonon hydrodynamics. Our study also reveals that $\kappa_{LPBE}/\kappa_{RTA}$, and therefore the strength of hydrodynamic signatures, decrease with increasing Brillouin zone (BZ) sampling density for several ultrahigh-$\kappa$ materials at low temperatures, thus underscoring the need for careful BZ sampling for robust predictions of
phonon hydrodynamics. Our work justifies the use of $\kappa_{LPBE}/\kappa_{RTA}$ as a computationally inexpensive indicator of
phonon hydrodynamics, thus enabling accelerated search for new materials that exhibit such unconventional heat flow regimes.
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Materials Science · Cross-listed from cond-mat.mes-hall
Geometric symmetry and size-dependent skyrmion phase transitions in magnetic nanostructures
J. Y. Wang, C. X. Zhao, Y. F. Duan et al. (+1 more)
We investigate the interplay of
geometric symmetry, size, and external
magnetic fields in regulating individual skyrmion states within
magnetic nanostructures. By analyzing nanodisks, nanosquares, and nanorectangles, we demonstrate that rotational
symmetry in nanodisks enables rich topological phase transitions, from
ferromagnetic states to skyrmions, skyrmioniums, and multi-states, as their diameter increases. In contrast, square and rectangular structures exhibit suppressed topological complexity due to corner-induced demagnetization effects and reduced
symmetries. Under perpendicular
magnetic fields, nanodisks show field-driven transitions between skyrmionium and skyrmion states. By leveraging asymmetry, square and rectangular nanostructures stabilize skyrmions over a broader parameter range than nanodisks. These findings highlight
geometric symmetry as a critical design parameter for tailoring skyrmion stability and functionality in spintronic applications such as multi-state
memory and reconfigurable logic devices.
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All authors J. Y. Wang, C. X. Zhao, Y. F. Duan, H. M. Dong
Materials Science
Metal-free heteroatom doping of carbon nitride for enhanced photocatalytic hydrogen peroxide production
Eneko Sebastian-Garate, Bruna F. Gonçalves, Jordi Llusar et al. (+5 more)
The photocatalytic production of hydrogen peroxide (H$_2$O$_2$) from water is a promising strategy for
solar-to-chemical energy conversion. Herein, we investigate the effect of metal-free heteroatom doping (B, O, P, and S) on the structural, electronic, and photocatalytic properties of graphitic carbon nitride (C$_3$N$_4$) for H$_2$O$_2$ production under simulated
solar irradiation. While pristine C$_3$N$_4$ exhibits stacked nanosheets, doping induces disorder, partial exfoliation, and changes in interlayer spacing, confirming successful heteroatom incorporation and modification of the electronic and optical properties. Photocatalytic experiments reveal that H$_2$O$_2$ production strongly depends on the sacrificial
agent, pH, and reactive-species scavengers. All doped catalysts show enhanced activity compared to pristine C$_3$N$_4$, with 9.6-, 14.8-, 11.0-, and 16.4-fold increases for B-, P-, O-, and S-doped C$_3$N$_4$, respectively. S-doped C$_3$N$_4$ achieved the highest H$_2$O$_2$ production rate of 3022.1 $\mu$mol h$^{-1}$ g$^{-1}$ and an apparent
quantum yield of 8.1%, attributed to improved charge separation and optimized selectivity. Mechanistic studies indicate that oxygen activation mainly follows a two-electron (2e$^{-}$) pathway driven by charge-carrier modulation and reactive oxygen species dynamics, with singlet oxygen and photogenerated holes playing a dominant role. In addition, S-doped C$_3$N$_4$ retained over 95% of its activity after five cycles. These results highlight metal-free heteroatom doping as an effective strategy for sustainable photocatalytic H$_2$O$_2$ generation.
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All authors Eneko Sebastian-Garate, Bruna F. Gonçalves, Jordi Llusar, Pawel Gluchowski, Ivan Infante, Senentxu-Lanceros Mendez, Qi Zhang, Hugo Salazar