Materials Science
Self-assembly and Electronic Properties of Graphyne and Graphdiyne Molecular Wires on Metallic Surfaces
Victor M. S. da Conceição, Dominike Pacine, Juliana M. Morbec et al. (+1 more)
Molecular self-assembly on solid surfaces has been the subject of extensive research, motivated by both fundamental and technological interests. On the fundamental side, these studies seek to elucidate the mechanisms governing molecular self-assembly and the resulting surface structures. From an applied perspective, they provide a route toward controlling surface reactions and engineering molecular electronic devices. Here, based on first-principles density functional theory calculations, we present a comprehensive study of self-assembled molecular wires (MWs), composed of graphyne (GY(1D)) and graphdiyne (GYD(1D))-like structures, adsorbed on Au(111), Ag(111), and Al(111) surfaces. Our total-energy calculations reveal that non-aligned MW arrays are energetically preferred on all three metal substrates. The GY(1D) and GYD(1D) molecular wires interact with the metal surfaces through van der Waals (vdW) forces, while their molecular orbitals do not contribute to the formation of metallic interface states. Simulated X-ray photoelectron spectroscopy (XPS) spectra reveal that the C 1s spectral features of the molecular wires are largely preserved upon adsorption, while the absolute binding energies undergo a substantial downshift that is nearly independent of the metal substrate, indicating that metallic screening effects dominate the adsorption-induced core-level shifts. Electronic band-structure calculations further show that the semiconducting character of the molecular wires is retained, resulting in vdW metal-
semiconductor heterostructures in which the semiconducting component consists of one-dimensional semiconducting channels. These findings demonstrate that self-assembled graphyne- and graphdiyne-based molecular wires on metal surfaces provide a promising platform for the realization of low-dimensional molecular electronic devices.
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All authors Victor M. S. da Conceição, Dominike Pacine, Juliana M. Morbec, Roberto H. Miwa
Materials Science · Cross-listed from physics.chem-ph
Polyaniline as a conductive polymer and its role in improving the efficiency and conductivity of perovskite solar cells
Mehran Hosseinzadeh Dizaj
This article investigates the role of polyaniline as a conductive
polymer in the active layer of perovskite solar
cells. Samples were created by incorporating polyaniline into the transport layers to assess its impact on enhancing efficiency and conductivity. The application of this
polymer across various layers of the
cell structure led to improved stability and performance. Given its high doping capability, polyaniline was examined in detail, particularly focusing on two types of oxidation doping and its integration into the hole transport layer.
Graphene oxide and reduced
graphene oxide were chosen as comparative models, and their performance was evaluated against the standard polyaniline configuration. Laboratory results revealed that power conversion efficiency increased by 17.5% with
graphene oxide and by 36.8% with reduced
graphene oxide. Furthermore, short-
circuit current density improved by 9.8% and 23.1%, respectively. These findings are consistent with existing studies in the field and support the validity of the approach.
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Materials Science · Cross-listed from physics.chem-ph
Multi-Species Multi-Reaction Model Parametrization of a Commercial NCA Positive Electrode from Half-Cell Open-Circuit Potential Data
Michele Galasso, Petr Čech, Ivo Horstkötter et al. (+3 more)
Physics-based models of lithium-ion batteries require the open-
circuit potential (OCP) of each electrode as a function of its lithiation. The multi-species multi-reaction (MSMR) model provides a compact, thermodynamically grounded description of this relationship, representing each insertion reaction by a standard potential, a site fraction and a disorder parameter. Here, we parametrize the MSMR model for nickel-cobalt-aluminum oxide (NCA), a cathode chemistry widespread in automotive
cells, using the positive electrode of a commercial silicon-graphite/NCA
cell. Cathode material was harvested from a pristine
cell and from
cells cycle-aged to the end of life under two state-of-charge windows, and its half-
cell OCP was measured by slow galvanostatic cycling. Smooth differential-capacity curves were obtained by histogram counting, and the charge and discharge branches were fitted with a constrained, scale-invariant optimization that keeps every reaction anchored to a visible peak. We report the first MSMR parameter set for an NCA cathode and show, through a differential-capacity peak analysis across aging states, that its thermodynamic signature is essentially unchanged by aging. This finding supports the common modeling practice of holding the electrode's intrinsic parameters fixed and ascribing aging to electrode-level capacity and
alignment changes.
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All authors Michele Galasso, Petr Čech, Ivo Horstkötter, Simon Schwunk, Zuzana Vlčková Živcová, Václav Knap
Materials Science
Localized Excitons and Exciton-Phonon Coupling in Antiferromagnetic AgCrP2S6
Jessica McDivitt, Dimitar Pashov, Mark van Schilfgaarde et al. (+4 more)
AgCrP2S6 combines a low-
symmetry thiophosphate framework with an antiferromagnetic Cr sublattice and nonmagnetic Ag sites, providing a setting in which covalency and
magnetic localization compete in the low-energy optical response. We combine single-
crystal x-ray diffraction, Raman spectroscopy,
lattice-dynamical calculations, and self-consistent vertex corrected Feynman diagrammatic many-body approaches to determine the structural, electronic, and excitonic properties of bulk AgCrP2S6. The material remains monoclinic between 100 and 300 K, with additional Ag-site disorder resolved at low temperature, and the optimized structure is dynamically stable. The many-body calculations yield a reduced quasiparticle gap relative to Cr trihalides, but the lowest
excitons remain predominantly local: the calculated low-energy (~1.4 eV) excitation cluster is best described as a weakly bright, strongly anisotropic Frenkel
exciton with dominant onsite d-d character and substantial ligand-assisted d-p admixture.
Symmetry analysis in the C2h setting identifies this state as predominantly Bu and constrains its leading
exciton-
phonon coupling channels to Ag diagonal renormalization and Bg-mediated bright-dark mixing. These results place AgCrP2S6 in a localized excitonic regime in which the stronger p-d hybridization, relative to the more ionic Cr trihalides, narrows the quasiparticle gap, while the antiferromagnetic exchange and Ag-site dilution disfavor the intersite coherence associated with strongly delocalized low-energy
excitons.
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All authors Jessica McDivitt, Dimitar Pashov, Mark van Schilfgaarde, Justin C. Johnson, Jeffrey L. Blackburn, Anna A. Berseneva, Swagata Acharya
Materials Science · Cross-listed from cond-mat.mes-hall
Isolating the natural edges of bilayer graphene in gate-defined mesoscopic devices
Francesco Blanda, Grazia Raciti, Thilo Glatzel et al. (+8 more)
We introduce a graphite-gated architecture for bilayer
graphene devices in which the active device is completely isolated from the natural
graphene edges. Using a single patterned graphite-gate layer, we realize a fully electrostatically defined Hall-bar. Longitudinal and Hall measurements reveal mesoscopic transport features, including Hall-effect quenching and magnetoresistance peaks associated with boundary scattering. The dependence of the mesoscopic features on the carrierdensity shows that the effective channel width increases with the Fermi level and the electrostatic confinement at the gate-defined boundaries, and indicates that the carriers scatter at the electrostatic boundary. Raman spectroscopy and Kelvin probe force microscopy suggest that this boundary is disordered due to the used fabrication methods. Comparably, the
quantum mobility in a fieldeffect transistor fabricated with the same architecture is not limited by boundary scattering and the visibility of
quantum oscillations down to 4 mT suggests a record value of 2.5 x 10^6 cm2/Vs.
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All authors Francesco Blanda, Grazia Raciti, Thilo Glatzel, Aurin Strathmann, Fabrizio Volante, Kenji Watanabe, Takashi Taniguchi, Ilaria Zardo, Thomas Ihn, Klaus Ensslin, Andrea Hofmann
Materials Science
Magnetic interactions and origin of high Curie temperatures in high Mn content (MnSb2Te4)x(Sb2Te3)1-x quantum materials
Candice R. Forrester, Christophe Testelin, Kaushini Wickramasinghe et al. (+3 more)
Understanding the
magnetic interactions that promote high TC in topological
quantum materials is essential to effectively design materials whose
magnetic configuration persists at high temperatures and are thus practical to integrate into commercial spintronic devices. Here we provide evidence of the origin of the high TC observed in mixed Mn1+ySb2-yTe4 septuple layers and Sb2-yMnyTe3 quintuple layer structures. Analysis of the quintuple layer/septuple layer structures explored their
magnetic behavior through different models of Mn-incorporation in the
crystal, evidenced as Mn
spin S = 5/2, and provided an explanation for the low magnetization per Mn atom observed, signature of competing ferromagnetic and antiferromagnetic interactions between Mn2+ ions. Our studies provide insight to better understand and control the Mn incorporation in our samples to optimize their properties.
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All authors Candice R. Forrester, Christophe Testelin, Kaushini Wickramasinghe, David Hrabovsky, Lia Krusin-Elbaum, Maria C. Tamargo
Materials Science
Interface-Controlled Spin-Orbit Torques in Rare-Earth Synthetic Ferrimagnets Probed by Sagnac Magneto-Optics and Harmonic Hall Measurements
Akilan K, Koral Aykin, Jose-Luis Ampuero et al. (+6 more)
Spin-orbit torque (SOT) provides an efficient route for manipulating magnetization in spintronic devices, and its accurate quantification is essential. Here, we investigate Co/Gd-based synthetic ferrimagnets using complementary magnetotransport and magneto-optical techniques. We use a Sagnac magneto-optical interferometry method to directly quantify current-induced magnetization tilting and extract the damping-like SOT effective field. The Sagnac measurements show good agreement with harmonic Hall analysis across different Co/Gd and Gd/Pt/Co
heterostructures, providing a quantitative determination of the damping-like SOT effective field that does not rely on electrical transport signatures. By varying the Gd thickness and multilayer stacking order, we demonstrate that the damping-like torque is strongly influenced by
spin transport and angular momentum conversion at rare-earth and heavy-metal interfaces. The observation of a finite torque in Gd/Pt/Co/Pt structures, where conventional Pt
spin Hall contributions are expected to compensate, highlights the active role of the Gd layer in SOT generation. Furthermore, interface engineering enables perpendicular
magnetic anisotropy in Gd/Pt/Co/Al
heterostructures with a 2-nm-thick Co layer, allowing current-induced SOT switching at current densities of 8-10 MA/cm$^2$. These results establish rare-earth-based synthetic ferrimagnets as a versatile platform for engineering
spin-orbit phenomena and optimizing low-power spintronic devices.
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All authors Akilan K, Koral Aykin, Jose-Luis Ampuero, Laurent Badie, Stephane Mangin, Sébastien Petit-Watelot, Michel Hehn, Andrew D. Kent, J.-Carlos Rojas-Sánchez
Materials Science · Cross-listed from physics.chem-ph
Coupled-cluster molecular properties across the main group that extrapolate beyond training size
Wenhao He, Xu Chen, Noah Song et al. (+10 more)
Coupled-cluster theory defines the accuracy standard for molecular electronic-structure properties but scales too steeply for routine application, whereas density-functional theory is affordable yet systematically biased. We resolve this trade-off with a single equivariant network, HARP (
Hamiltonian Read-out for Properties), that predicts an effective one-electron
Hamiltonian from one inexpensive B3LYP/def2-SVP calculation and derives a broad suite of properties from it (energy, optical gap, dipole, quadrupole, polarizability, Mulliken atomic charges, and Mayer bond orders) at coupled-cluster accuracy across nine main-group elements, including the under-served phosphorus, sulfur, and chlorine chemistries. The model is trained on a new in-house
dataset of multi-property labels computed at the CCSD(T) level for all nine elements. On a held-out test set, it reduces the error of every property by a factor of 3.8 to 270 relative to semi-local, hybrid, and double-hybrid DFT (referenced to composite CCSD(T)/cc-pVTZ), while adding only ~0.1 s wall time per molecule, delivering coupled-cluster-quality predictions at the cost of a single DFT calculation. Critically, deriving every property from a predicted
Hamiltonian rather than pooling per-atom features builds the correct size-scaling into the model architecture: on pi-conjugated oligothiophenes it matches finite-field CCSD polarizability to ~1% and the EOM-CCSD optical gap to ~3% at the largest sizes where those references remain affordable (44 and 37 atoms, where a single CCSD field point already costs ~500x the model's entire inference) and extrapolates the corrected trends to 58-atom chains, a regime where pooling-based architectures fail by construction. Accurate extrapolation is therefore set by the model's inductive bias rather than by the training data.
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All authors Wenhao He, Xu Chen, Noah Song, Haowei Xu, Tim S. Hindges, Bohan Li, Zihan Lin, Yu Yao, Avetik R. Harutyunyan, Fang Liu, Yao Wang, Hao Tang, Ju Li
Materials Science · Cross-listed from physics.optics
Bayesian Optimization for Practical H2 Sensors: Inverse Design of Pd-based Plasmonic Metasurfaces
Pernilla Ekborg-Tanner, Athanasios Theodoridis, Joachim Fritzsche et al. (+3 more)
Hydrogen detection is becoming increasingly important as its use grows across energy and industrial systems. Optical sensing platforms based on palladium (Pd) nanoparticles are attractive for this task because hydrogen uptake directly alters their plasmonic response. Organizing such nanoparticles into periodic two-dimensional arrays, known as metasurfaces, further enhances their optical response through collective resonances. However, the large design space presented by chemical composition, nanoparticle geometry, and array structure calls for systematic approaches for optimizing complex nanoalloy metasurface geometries. Here, we develop an inverse-design framework based on
Bayesian optimization that couples first-principles dielectric functions with electromagnetic simulations to identify high-performance PdAu nanodisk arrays for hydrogen sensing in the 1 to 100 mbar range where the flammability of H2 becomes a concern. We use our approach to search a five-dimensional design space, comprising nanodisk height and radius, array pitch,
polymer coating thickness, and Au fraction in order to maximize the H-induced change in extinction at a single wavelength of choice. The results show that integrating first-principles optical models with data-efficient optimization yields experimentally feasible nanoparticle metasurfaces tailored for targeted hydrogen pressures, while providing a pathway to future multiobjective sensor design. They also reveal remaining gaps in the modeling methodologies that still limit the quantitative reliability of the approach.
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All authors Pernilla Ekborg-Tanner, Athanasios Theodoridis, Joachim Fritzsche, Christoph Langhammer, Andrea Baldi, Paul Erhart
Materials Science
Writing and erasing skyrmions by single ultrafast laser pulses in monolayer Janus 2D magnets
Guangyao Miao, Yonglong Ga, Chang Liu et al. (+21 more)
Skyrmions in 2D magnets are promising candidates for nonvolatile, low-power, and high-density spintronic
memories. However, their experimental realization at the 2D limit remains challenging, owing to the difficulty in engineering the required chiral
magnetic interactions. Here, we report the creation and direct imaging of Néel-type skyrmions in Janus 2D chromium chalcogenides using synchrotron X-ray photoemission electron microscopy, and scanning nitrogen-vacancy magnetometry, which exhibit field-free stability, nonvolatility, and size tunability. First-principles calculations and micromagnetic simulations reveal that Janus-surface-induced inversion-
symmetry breaking enhances the Dzyaloshinskii-Moriya interaction, providing the microscopic mechanism for skyrmion stabilization and tunability. We further achieve reversible skyrmion writing and erasing using a single ultrafast
laser pulse in a
magnetic field as low as 300 Oe, demonstrating the excellent manipulability of this 2D
magnetic system. These results establish Janus engineering as a route to creating and manipulating nonvolatile skyrmions in atomically thin magnets, with implications for skyrmion-based low-power spintronic devices.
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All authors Guangyao Miao, Yonglong Ga, Chang Liu, Pan Chen, Yichen Jin, Florian Kronast, Wenxin Cheng, Zhaoqing Ding, Kai Hu, Zongnan Zhang, Nikolai Severin, Chenxi Meng, Patil Shubhada, Sergio Valencia, Meng Meng, Qinlin Guo, Xiaoran Liu, Jiandi Zhang, Yangmu Li, Carlos-Andres Palma, Jürgen P. Rabe, Hongxin Yang, Weihua Wang, Jiandong Guo
Materials Science · Cross-listed from cond-mat.str-el
Finite-temperature Green's function cluster expansion from thermofield doubles: Breakdown of the polaron picture
M. R. Carbone, S. Fomichev, B. Kloss et al. (+4 more)
We introduce a method, numerically exact in principle, for computing the momentum- and frequency-resolved single-particle Green's function of a polaron at finite temperature. The method, which we refer to as the finite-temperature Green's function cluster expansion, combines two ingredients: the generalized Green's function cluster expansion, a numerically exact extension of the momentum average family of methods that solves the polaron problem at zero temperature through a hierarchy of equations of motion for restricted
phonon cloud configurations; and the thermofield double formalism, which maps the thermal trace onto a pure-state expectation value over a doubled
Hilbert space. The resulting equations of motion have the same algebraic structure as those of the multi-
boson zero-temperature theory, with the temperature entering through a Bogoliubov-type mixing angle that controls the coupling to a set of fictitious bath
bosons. We implement the method in our open-source software package and
benchmark it on the one-dimensional Holstein polaron, computing spectral functions, dispersions, lifetimes, and effective masses across coupling regimes and temperatures up to $T/\Omega \sim 1$. Where finite-temperature density
matrix renormalization group results are available, we find quantitative agreement at affordable computational cost. The method recovers momentum-resolved spectra directly in frequency space, with no time
evolution or analytic continuation. We also discuss the practical costs of the approach. In particular, since the doubled
phonon Hilbert space has a non-trivial configuration structure in which real and fictitious clouds compete, convergence in the corresponding cloud parameters requires care.
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All authors M. R. Carbone, S. Fomichev, B. Kloss, A. J. Millis, M. Berciu, D. R. Reichman, J. Sous
Materials Science
Breaking the mutual exclusivity between metallicity and ferroelectricity in a non-polar covalent semiconductor via orbital selective doping
Hui Li, Yunfan Yang, Junquan Huang et al. (+18 more)
The mutual exclusion of ferroelectricity and metallic conductivity is a long-standing tenet because itinerant electrons screen long-range Coulomb forces that stabilize the bulk polar order. Here, we break this paradigm by heavily doping a non-polar covalent
semiconductor of cubic silicon carbide (3C-SiC) with nitrogen. This introduces heavy electron doping, inducing
metallicity and driving a structural transition from the non-polar F-43m to the polar R3m
symmetry via the pseudo-Jahn-Teller effect. Remarkably, we provide direct, atomic-scale visualization of about 180{\deg} polarization reversal under an external voltage bias in a ferroelectric metal. The strongly directional character of antibonding orbitals occupied by conduction electrons prevents them from screening the local Si-C polarization, resulting in the coexistence of
metallicity and ferroelectricity. Ferroelectric tunnel junctions demonstrate nonvolatile
memory properties with a well-defined high-resistance state (HRS) and low-resistance state (LRS), an ultrahigh response speed (~50 ns), an ultralow operating voltage (1 V), an endurance exceeding 85927 cycles, and a projected retention time of 100 years. Our results provide a novel strategy for pioneering ferroelectricity in a metal, a new ferroelectric metal platform for exploring exotic properties, and a ferroelectric device with high performance that meets the requirements for low consumption and high-speed non-volatile devices.
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All authors Hui Li, Yunfan Yang, Junquan Huang, Yukun Feng, Guobin Wang, Qinci Wu, Jun Deng, Zhaolong Liu, Subi Du, Dongliang Gong, Zaihui Shen, Anmin Nie, Yang Xu, Junwei Yang, Zesheng Zhang, Huaping Song, Jiangang Guo, Wenjun Wang, Hailin Peng, Yongjun Tian, Xiaolong Chen
Materials Science · Cross-listed from physics.app-ph
Achieving Long Retention in Area-Dependent Resistive Memory with Phase-Separated Amorphous Tantalum Oxide
Sangyong Lee, Anton V. Ievlev, Dongjae Shin et al. (+2 more)
Resistive random-access
memory (ReRAM) is a promising future nonvolatile
memory technology. Most ReRAM exhibit a fundamental tradeoff: filament-type ReRAM provides long data retention but suffers from poor uniformity and high switching current, whereas nonfilamentary ReRAM shows lower-current, area-dependent switching but generally poor retention. No two-terminal device has been able to overcome this tradeoff. In this work, we present a two-terminal Ta2O5/ TaOX resistive
memory cell that achieves both nonfilamentary switching and long retention. Electrical measurements and composition depth profile show that the switching is not confined to a single filament but is instead uniform across the entire switching region. Despite the nonfilamentary switching, this device can retain information for over 22 hours at 190 {\deg}C, which is comparable to the best filamentary devices. We propose that this long retention arises from composition phase separation in amorphous tantalum oxide. Our work shows that the fundamental tradeoff between information retention and switching uniformity can be overcome, and thereby provides a pathway toward more uniform and reliable oxide
memory devices.
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All authors Sangyong Lee, Anton V. Ievlev, Dongjae Shin, Jingxian Li, Yiyang Li
Materials Science · Cross-listed from cond-mat.mes-hall
Electronic Reconstruction at the Quasicrystal-Moiré Crossover in Twisted Bilayer Graphene
Kuo-En Chang, Aitor Garcia-Ruiz, Ta-Lei Chou et al. (+11 more)
Large twist angles in twisted bilayer
graphene are widely expected to be electronically trivial, with negligible interlayer coupling and no electronic reconstruction, in contrast to the rich moiré-driven band reconstruction and correlated physics that emerge at small twist angles. Here, we show that this paradigm breaks down near a twist angle of 29{\deg}, where the system crosses over between quasicrystalline and commensurate order. Atomic-resolution transmission electron microscopy directly reveals the coexistence of near-dodecagonal quasicrystalline
symmetry and emerging moiré periodicity, indicating an intermediate, nonperiodic structural regime. Magnetotransport measurements uncover strong interlayer hybridization mediated by Umklapp scattering, manifested by magneto-intersubband oscillations and a highly unconventional Landau-level spectrum. Remarkably, the Landau-level degeneracy evolves from 4- to 12-fold with increasing temperature, a behavior incompatible with two decoupled
graphene monolayers. These findings establish large-angle twisted bilayer
graphene as a platform where quasiperiodic
symmetry fundamentally reshapes low-energy electronic states beyond the conventional moiré framework.
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All authors Kuo-En Chang, Aitor Garcia-Ruiz, Ta-Lei Chou, Yen-Ting Liu, Sheng-Chin Ho, Yu-Chiang Hsieh, Ching-Hua Kao, Chiu-Hua Huang, Ying-Mei Yang, Kenji Watanabe, Takashi Taniguchi, Ming-Wen Chu, Ming-Hao Liu, Tse-Ming Chen
Materials Science
Energy-efficient, Reconfigurable Optoelectronic Artificial Synapses Based on MoWS$_2$ Alloy for Pattern Recognition and Color Image Filtering Applications
Deepak Kumar Sahu, Santu Kumar Ghosh, Sagarneel Ghoshal et al. (+2 more)
Two-dimensional transition-metal dichalcogenide
alloys are potential candidates for advanced optoelectronic and neuromorphic applications due to their strong light-matter interactions and controllable defect properties. However, large-area growth of such
alloys remains challenging, while the correlation between their physical and neuromorphic properties remains largely unclear. In this work, we present an innovative microcavity chemical vapor deposition (CVD) reactor pathway to grow uniform, and large-area MoWS$_2$ mono- and few-layer
alloy films for demonstrating optoelectronic synaptic functionalities. Driven by growth-induced intrinsic sulfur vacancies, as confirmed by XPS, KPFM, and STEM measurements, our optoelectronic synaptic device (OSD) successfully emulates essential biological synaptic features, such as excitatory postsynaptic currents (EPSC), paired-pulse facilitation (PPF~170%), and stimulus-dependent short- and long-term plasticities (STP & LTP). With picojoule-order energy consumption per synaptic event and nanoampere-order dark current, the device enables low-power neuromorphic learning, including emulation of Pavlovian associative learning. Furthermore, the experimentally measured conductance weight-update characteristics enabled an artificial neural network (ANN) simulation to achieve 92.43% recognition accuracy on the MNIST handwritten digit
dataset. Finally, we demonstrate advanced neuromorphic visual processing by executing color image filtering based on the device's wavelength-selective photoresponse characteristics. This simple, yet multifunctional device architecture provides a promising path toward energy-efficient, spectral-selective neuromorphic
vision applications.
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All authors Deepak Kumar Sahu, Santu Kumar Ghosh, Sagarneel Ghoshal, Saranya Das, Samit K. Ray
Materials Science
Optical decoherence in Er$^{3+}$-doped CeO$_2$ spin qubit platforms
Vrindaa Somjit, Ignas Masiulionis, Gregory D. Grant et al. (+7 more)
Erbium ions (Er$^{3+}$) in cerium dioxide (CeO$_2$) represent a promising
spin-
photon interface for
quantum communication, but the mechanisms limiting their optical coherence remain poorly understood. Using periodic hybrid density functional theory calculations with finite-size corrections, we identify Ce$^{3+}$ polarons and their complexes with oxygen vacancies and Er$^{3+}$ dopants as likely sources of optical decoherence. These defects exhibit finite photoionization cross-sections at 0.8 eV, coinciding with both the
laser excitation energy used experimentally and the emission energy of Er$^{3+}$. This resonance enables photoionization of the polarons and photoluminescence quenching of Er$^{3+}$, leading to the broadening of optical linewidths, shortening of excited-state lifetimes, and introduction of charge noise. Our concentration-dependent photocurrent measurements in Er$^{3+}$-doped CeO$_2$ films under 0.8 eV illumination validate the predicted decoherence pathway. Our combined computational and experimental results identify a concrete defect-engineering target for improving the Er$^{3+}$-doped CeO$_2$ platform, and point to a decoherence mechanism likely relevant to other Er$^{3+}$-doped multivalent-oxide
quantum platforms.
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All authors Vrindaa Somjit, Ignas Masiulionis, Gregory D. Grant, Weiguo Jing, Matteo Giantomassi, Supratik Guha, Gian-Marco Rignanese, F. Joseph Heremans, Jiefei Zhang, Giulia Galli
Materials Science
Electron transport in amorphous materials: from localization to predictive transport modeling
Yeonghun Lee
Amorphous materials are disordered solids without long-range structural order, making them useful systems for studying electron transport beyond the crystalline picture. This review discusses how structural disorder changes the spatial character of electron wavefunctions and how these changes govern carrier transport in amorphous materials, especially amorphous
semiconductors. Basic concepts of Anderson localization, mobility edges, diffusive transport, and hopping transport are first reviewed, followed by representative amorphous
semiconductors, including amorphous silicon and amorphous oxide
semiconductors. Computational approaches are then discussed, from conventional Boltzmann and Green's-function-based transport theories to real-space Kubo-Greenwood simulations combined with molecular dynamics. The discussion focuses on localization, spectral broadening, finite-temperature
lattice fluctuations, and electron-
phonon interactions. Recent progress and remaining issues in predictive transport modeling of amorphous materials are then outlined.
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Materials Science
Defect Geometry Selects Polar and Anomalous Hall Phases in Two-Dimensional Altermagnets
Xujia Gong, Amar Fakhredine, Hosein Alavi-Rad et al. (+6 more)
Point defects in altermagnets can create phases absent in the pristine host by selectively breaking
crystal symmetries. Combining
symmetry analysis, first-principles calculations, and
Hamiltonian modeling, we identify how point impurities modify the altermagnetic phase. Using the pristine d- wave altermagnetic monolayer V2Se2O as a testbed, we identify three distinct classes of impurities: those that preserve
spin-momentum locking, those that induce a hybrid-parity state associated with Edelstein
spin conversion, and those that produce a metallic ferrimagnetic state with an anomalous Hall effect. We further discuss the robustness of two-dimensional altermagnets against point impurities. Results for other two-dimensional systems, such as Mn4N2 and 2H-FeBr3, reveal the same
symmetry-based control across distinct
lattices and parent
spin harmonics, establishing defect geometry as a general route for engineering
spin textures and transport properties.
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All authors Xujia Gong, Amar Fakhredine, Hosein Alavi-Rad, Mahyar Hassani-Vasmejani, Xing Ming, Xiangang Wan, Carmine Autieri, Meysam Bagheri Tagani, Sahar Izadi Vishkayi
Materials Science
Polarization-Dependent Raman Selection Rules in Sb$_2$S$_3$ from First Principles and Experiment
Tobias Dierke, Michael Hüttenkofer, Stefan Wolff et al. (+4 more)
Antimony sulfide (Sb$_2$S$_3$) is a
semiconductor composed of quasi-one-dimensional ribbon-like structural units, which give rise to pronounced structural anisotropy in the bulk
crystal. Despite growing interest in Sb$_2$S$_3$, in particular Sb$_2$S$_3$ thin films, a detailed understanding of its
symmetry-based
lattice dynamics remains incomplete. Here, we present a combined experimental and theoretical study of polarization-dependent Raman scattering in Sb$_2$S$_3$ thin films. We derive the Raman selection rules from the
crystal symmetry and calculate the zone-center
phonon modes and corresponding Raman tensors using density functional theory. The calculated polarization dependencies are systematically compared with polarization-dependent Raman measurements performed on oriented crystalline domains of Sb$_2$S$_3$ thin films. This combined analysis enables reliable mode assignments, elucidates the anisotropic Raman response associated with the ribbon-like
crystal structure, and demonstrates the sensitivity of polarized Raman spectroscopy to
crystal orientation and structural order in antimony chalcogenide (Sb$_2$S$_3$, Sb$_2$Se$_3$) as well as isostructural Bi$_2$S$_3$ thin films.
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All authors Tobias Dierke, Michael Hüttenkofer, Stefan Wolff, Mingjian Wu, Julien Bachmann, Erdmann Spiecker, Janina Maultzsch
Materials Science · Cross-listed from cond-mat.supr-con
Bridging ambient- and high-pressure superconductivity in La$_2$LnNi$_2$O$_7$ films
Motoki Osada, Chieko Terakura, Shusaku Imajo et al. (+9 more)
The discovery of high critical-temperature $T_{\mathrm{c}}$ superconductivity near 80 K in bilayer nickelates under high pressure has sparked extensive studies. While superconductivity exceeding 40 K was subsequently discovered at ambient pressure in compressively strained films, the relationship between ambient- and high-pressure regimes remains an open question. Here we present a systematic investigation of superconductivity in compressively strained La$_2$LnNi$_2$O$_7$ films (Ln = lanthanides) at ambient and high pressures. The normal-state resistivity at ambient pressure, revealed by suppressing superconductivity with
magnetic fields of 59 T, tends toward $T^2$ behaviour. Under high pressure in a cubic-anvil
cell, $T_{\mathrm{c}}$ was enhanced from 41-42 K at ambient pressure to 67-73 K at 16 GPa. On the other hand,
lattice compression induced by Ln substitution, which may mimic effects of pressure, lowers $T_{\mathrm{c}}$. In both cases, $T_{\mathrm{c}}$ correlates with the
evolution of normal-state transport between $T^2$ and $T$-linear behaviour, offering insight into the interplay between
lattice structure and superconductivity in bilayer nickelates.
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All authors Motoki Osada, Chieko Terakura, Shusaku Imajo, Jean-Baptiste Morée, Akiko Kikkawa, Masamichi Nakajima, Hsiao-Yi Chen, Yusuke Nomura, Koichi Kindo, Ryotaro Arita, Yoshinori Tokura, Atsushi Tsukazaki
Materials Science
Active learning molecular beam epitaxy of complex quantum materials
Raghutheja Bollampally, Soumya Sankar, Yuqi Qin et al. (+1 more)
The integration of machine learning (ML) into materials science offers a transformative pathway toward fully autonomous synthesis workflows. For precise thin-film deposition techniques like molecular beam epitaxy (MBE), this automation is critical to overcome the time-consuming, manual navigation of high-dimensional thermodynamic phase spaces. Existing approaches for ML-assisted thin film growth predominantly rely on continuous
Bayesian optimization (BO) models that assume smooth parameter landscapes. Consequently, they struggle to capture the abrupt crystallographic phase boundaries and narrow growth windows inherent to binary
quantum materials. Here, we demonstrate an active learning protocol based on Sequential Model-Based Optimization (SMBO) designed specifically for the closed-loop MBE of such compounds. To overcome the limitations of continuous models while retaining the efficient exploration-exploitation logic of traditional BO, we combine a random forest surrogate model capable of capturing highly non-linear phase transitions and thermodynamics constraints of the growth process with an expected improvement function to predict optimum growth parameters. We apply this combined SMBO framework to the MBE of the topological Weyl ferromagnet Fe$_3$Sn, which exists as a metastable line compound. Using a small initial training set of fewer than twenty growth iterations, our active learning loop rapidly navigates a complex optimization landscape to identify an optimum growth window bounded by sharp transitions. Within only four active learning iterations, the absolute predictive error is halved to $\approx10\%$. This data-efficient framework paves the way for the autonomous discovery and thin-film synthesis of functional
quantum materials.
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All authors Raghutheja Bollampally, Soumya Sankar, Yuqi Qin, Berthold Jäck
Materials Science
Vacancy-Driven Electronic Reconstruction in Monolayer PtSe$_2$: Formation Thermodynamics and Charge States
Xiwen Gai, Jingang Wang and Tianxing Ma
Layered transition metal dichalcogenides are an important platform for two-dimensional materials, where the inevitable intrinsic defects provide new degrees of freedom for tuning their physical properties. Based on first-principles calculations, this work systematically investigates the formation energies, charge states, and electronic structural characteristics of V$_{\mathrm{Pt}}$, V$_{\mathrm{Se}}$, and composite vacancies in monolayer PtSe$_2$. The results indicate that while vacancy formation energies are highly sensitive to chemical potentials, the V$_{\mathrm{Se}}$ structure consistently exhibits the lowest formation energy. The charge defect calculation reveals the stable charge state intervals of V$_{\mathrm{Se}}$ and V$_{\mathrm{Pt}}$ as a function of the Fermi level, thus describing the
evolution of the charge states of intrinsic vacancies at different electronic chemical potentials. Climbing Image Nudged Elastic Band calculations reveal high migration barriers for V$_{\mathrm{Se}}$ and V$_{\mathrm{Pt}}$, indicating strongly hindered vacancy
diffusion at room temperature, while short Ab Initio Molecular Dynamics simulations confirm the absence of immediate structural collapse within the simulated time window. Optical property calculations indicate that point defects significantly alter the dielectric response of monolayer PtSe$_2$ and generate new low-energy absorption channels associated with in-gap defect states. These findings provide new insights into defect-mediated electronic and optical property modulation in monolayer PtSe$_2$, offering guidance for its potential device design.
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Materials Science
Atomistic Structure Generation and Neural-Network Screening of Hard Carbons to Identify High-Capacity Sodium Storage
Harry Mclean, Aiden Daniel Emery, Theodore Thomas Walton et al. (+2 more)
Hard carbons are established anodes for lithium-ion batteries and leading candidates for sodium-ion batteries, yet their electrochemical performance is governed by a heterogeneous network of graphitic domains, defects, and nanopores that conventional atomistic methods cannot model at the required length scales. We combine universal machine-learned interatomic potentials with the RAFFLE structure-generation framework to construct 13,096 realistic hard carbon models containing up to 4,378 atoms, matching experimentally measured densities, porosities, and sp$^2$/sp$^3$ bonding fractions. Explicit sodium intercalation of representative structures reproduces the characteristic sloping-to-plateau voltage profiles, revealing that capacity increases with decreasing carbon density and increasing porosity. To screen the full library, we train a lightweight neural-network surrogate that predicts capacity directly from the host using frozen universal-potential descriptors augmented by
geometric void features. The surrogate identifies high-capacity candidates exceeding 800 mAh g$^{-1}$, which are validated by full intercalation calculations. This scalable framework links hard carbon microstructure to sodium-storage performance and provides atomistic design principles for high-capacity anodes. More broadly, the workflow enables systematic exploration of synthesis-dependent amorphous microstructures, including precursor chemistry, pyrolysis, heteroatom doping, and pore engineering, providing a route toward atomistically informed hard carbon design.
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All authors Harry Mclean, Aiden Daniel Emery, Theodore Thomas Walton, Ned Thaddeus Taylor, Steven Paul Hepplestone
Materials Science
Quantized Spin Hall Effect in Three-Dimensional Nodal-Ring Semimetal: Geometric Scaling and Symmetry-Engineered Spin Response
Jiali Chen, Chaoxi Cui, Zhi-Ming Yu et al. (+2 more)
The anomalous Hall conductivity in
magnetic Weyl semimetals scales linearly with the momentum separation between Weyl nodes, establishing a
geometric paradigm for three-dimensional Hall responses. Here we discover an analogous phenomenon in the
spin Hall effect: a quantized
spin Hall conductivity (SHC) in nodal-ring semimetals that scales linearly with the nodal-ring radius $R$. From an ideal model with a single nodal ring, we derive analytically that the SHC inside the
spin-orbit-coupled gap obeys $\sigma_{\alpha \beta}^{S, 3D}=\sigma_0^{S,2D} \cdot (\pi R/2 \pi)$, where $\sigma_0^{S,2D}=(e^2/h) \cdot (\hbar/2 e)$ is the two-dimensional
quantum spin Hall conductance. Crucially, the
symmetry of the
spin-orbit coupling acts as an independent switch: Rashba coupling generates purely conventional SHC components, while Weyl coupling additionally activates unconventional ones, providing separate control over response magnitude and tensor
symmetry. We validate this principle in yttrium nitride, where strain tunes $R$ and
symmetry breaking toggles between response types. Our work establishes a new paradigm for engineering quantized
geometric responses in three dimensions, opening pathways to tailored
spin-orbit functionalities.
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All authors Jiali Chen, Chaoxi Cui, Zhi-Ming Yu, Wei Jiang, Yugui Yao
Materials Science
Chiral Spinterfaces as an Overlooked Component of the Chiral-Induced Spin Selectivity Effect
Franziska Schölzel, Aybüke Gülkaya, Rico Ehrler et al. (+11 more)
The chiral-induced
spin selectivity (CISS) effect is generally attributed to
spin-selective transport through chiral molecules, while the role of the molecule-electrode interface remains largely unexplored. Here, we show that adsorption of chiral amino acid derived molecules on ferromagnetic Ni thin films generates a remanent chirality-dependent magneto-optical response that is localized to the molecule-Ni/NiO interface and can be reversibly switched by an external
magnetic field, demonstrating its genuine
magnetic character. A comprehensive series of control experiments establishes that the response originates from the interfacial region rather than from the molecular layer or the bulk ferromagnet. First-principles calculations reveal that Boc-methionine adsorption proceeds through energetically accessible sulfur- and carboxyl-bound configurations that produce distinct molecular orientations and ligand-p/Ni-d hybridization, thereby defining structurally and electronically distinct interfaces. Together, the experimental and theoretical results support the formation of chiral spinterfaces, identifying the molecule-ferromagnet interface as an active and previously overlooked component of CISS systems. These findings broaden the microscopic picture of CISS beyond the chiral molecule itself and reveals interface electronic structure as a key design parameter for
spin-selective molecular devices.
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All authors Franziska Schölzel, Aybüke Gülkaya, Rico Ehrler, Dominik Hornig, Lokesh Rasabathina, Aleksandra Lindner, Jürgen Lindner, Aleksandr Kazimir, Christina Lamers, Dietrich R.T. Zahn, Michael Mehring, Olav Hellwig, Shuxia Tao, Georgeta Salvan
Materials Science
Multiple topological electronic and phononic quasiparticle excitations in hexagonal TTe (T=Hf, Zr & Ti) crystals
Prakash Pandey and Sudhir K. Pandey
The exploration of topological
fermions and
bosons marks a new chapter in condensed matter physics, unveiling rich and unconventional phenomena. Particularly in
quantum field theory, exotic quasiparticle excitations such as Dirac and Weyl
fermions can serve as direct analogs, and their recent experimental realizations have sparked significant interest in these topological quasiparticles. Although there are various reports on the coexistence of unconventional fermionic quasiparticles such as
spin-1/2 (type-I, type-II, & type-III),
spin-1 (threefold degeneracy), nodal line (type-I, type-II, & type-III) and others, reports on the simultaneous presence of such quasiparticles in both electronic and phononic spectra within a single material remain extremely limited. Herein, using state-of-theart ab initio calculations, we propose the HfTe class of materials, which hosts coexisting type-I, type-II, and type-III Weyl and nodal line phases, along with pseudospin-1/
spin-1 quasiparticles in both electronic and phononic states. We have found that these excitations are robust against variations in exchange-correlation functionals,
spin-orbit coupling, and
lattice parameters, confirming that multiple topological phases in this class of materials are likely to be observed experimentally.
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Materials Science
Growth of Altermagnetic {\alpha}-MnTe Films: Substrate Variation and Surface Modification
M. Dittmar, L. Hirnet, H. Haberkamm et al. (+10 more)
Manganese telluride (MnTe) in its hexagonal {\alpha}-MnTe
crystal structure has evolved as one of the altermagnet workhorse materials. The synthesis of MnTe thin films is highly relevant for both fundamental science and device applications. Here, we report on the epitaxial growth of MnTe thin films and
heterostructures. The films are studied by X-ray and electron diffraction as well as soft X-ray angle-resolved photoemission spectroscopy. We demonstrate the ability to grow high-quality {\alpha}-MnTe on various substrates, ranging from transparent band
insulators, over topological
insulators, metallic transition metal chalcogenides, to the van der Waals ferromagnet Fe$_3$GeTe$_2$. While insulating substrates are useful for transport experiments or optical spectroscopy, metallic topological surface states may trigger spintronic interface effects, such as
spin-orbit torques. Metallic substrates, in general, are highly relevant to avoid charging at the insulating MnTe films in electron spectroscopy or microscopy methods. Lastly, ferromagnetic substrates will be of interest to control magnetization across the interface. In addition, we discuss the formation of superstructures on the MnTe(0001) surfaces, that emerge directly after growth, upon subsequent tellurium evaporation and after thermal treatment. This will be relevant in further studying the surface
magnetic and electronic structure in {\alpha}-MnTe.
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All authors M. Dittmar, L. Hirnet, H. Haberkamm, F. Beisler, C.-W. Chuang, R. Ganser, P. Kagerer, M.-J. Huang, J. Buck, M. Hoesch, K. Rossnagel, M. Ünzelmann, F. Reinert