Materials Science
Understanding Graphene-Perovskite Interactions: From Flake Chemistry to Crystallisation and Solar Cell Performance
Oussama Er-Riyahi, Dorota Biernacka, Yating Guo et al. (+7 more)
Graphene-derivatives are widely employed materials to improve bulk and interface properties of metal-halide perovskite devices. Yet the implications of their flake chemistry and interactions with the perovskite precursors remain unclear. Here, we show that pristine
graphene flakes (GF) and more conventional
graphene oxide flakes (GOF) are not interchangeable. Density functional theory calculations reveal that GOF interacts more strongly with the perovskite
lattice but induces larger structural distortions, stronger interfacial polarisation, and localised gap states. In contrast, GF forms comparatively non-disruptive contacts, a response retained across a wide compositional range. Machine-learning atomistic simulations further show that GF contacts both Pb- and I-containing regions of solvated perovskite nanocrystals, with a strong solvent dependency. Solution spectroscopic characterization indicates that GF additives serve as scaffold for preorganised Pb/I-containing precursors, favouring film crystallisation. In this sense, GF enhances solar
cell performance across perovskite compositions, but particularly those facing a more challenging crystallisation. In mixed Sn-Pb perovskite solar
cells, GF raises the champion power-conversion efficiency from 21.5% to 23.7% with improved storage stability. These results establish pristine GF as a chemically defined additive and connect its atomic-scale interactions with precursor organisation, crystallisation, device performance, and stability.
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All authors Oussama Er-Riyahi, Dorota Biernacka, Yating Guo, Mikel Ballarena Tellechea, Silver-Hamill Turren-Cruz, Dario Bercioux, Meng Li, Agnieszka Lekawa-Raus, Jorge Pascual, Karolina Z. Milowska
Materials Science
From Goldene to Noblene: exhaustive enumeration of the ordered Au-Ag-Cu monolayer alloys
Marcelo Lopes Pereira Junior
Two-dimensional metals became a laboratory reality with the isolation of Goldene, a gold sheet one atom thick released by chemical exfoliation, which raises the question of what alloying can achieve on the same close-packed
lattice. Here we combine an exhaustive enumeration of derivative superstructures with density functional theory to map the ordered Au-Ag-Cu monolayer
alloys, relaxing every
symmetry-inequivalent arrangement up to four atoms per
cell and extending the set with larger
cells selected by a fitted model. We find that the arrangement of the atoms, and not their proportion, controls the mixing energy, since the spread among the orderings of a single composition is several times the step between neighboring compositions, one composition spans more than 50~meV/atom between two arrangements of the same three atoms, and at two compositions the arrangement decides the sign. The energetics is carried by a competition between Au-Cu contacts, which bind, and Ag-Cu contacts, which do not, and bulk enthalpies computed under the same protocol show that this chemistry is not uniformly rescaled in two dimensions, since Au-Cu orders more strongly in the monolayer than in the
crystal while the other two weaken. A pair model completed by an elastic size-mismatch term reproduces the computed energies to a few meV/atom and returns a composition landscape whose convex hull no balanced ternary composition reaches. One equimolar ordering, which we name Noblene, is the only structure in which every atom is surrounded exclusively by unlike species, and it is dynamically stable and metallic, and carries a Poisson's ratio above one half, higher than that of any of the three pure monolayers. Since Noblene sits on the
lattice that Goldene already realizes, the route that produced Goldene is a plausible starting point for its synthesis.
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Materials Science · Cross-listed from cond-mat.supr-con
Electronic Structure and Superconductivity in La$_{1.55}$Sr$_{0.45}$CuO$_4$/La$_2$CuO$_4$ Artificial High-$T_c$ Superlattices Probed by Hard and Soft X-ray Spectroscopy
U. M. Jayathilake, S. Sheikh, T.-L. Lee et al. (+5 more)
In La$_{1.55}$Sr$_{0.45}$CuO$_4$/La$_2$CuO$_4$ (LSCO/LCO) artificial high-$T_c$ superlattices (AHTS), grown by
quantum material design, the superconducting dome can be tuned by varying the
geometric ratio $L/d$, where $L$ is the LCO layer thickness and $d$ is the superlattice nanoscale period. Here, we combine hard X-ray photoelectron spectroscopy (HAXPES) and polarization-dependent soft X-ray absorption spectroscopy (XAS) to probe how the electronic structure evolves across the $L/d$-tuned superconducting dome. We observe systematic chemical-potential
evolution across the series, together with enhanced spectral weight near the Fermi level, enhanced local and non-local screening signatures, and increased in-plane orbital polarization near the top of the dome. Together, these spectroscopic signatures provide insight into the emergence of Fano-Feshbach resonant superconductivity in the LSCO/LCO AHTS series.
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All authors U. M. Jayathilake, S. Sheikh, T.-L. Lee, C. Klewe, G. Logvenov, G. Campi, A. Bianconi, A. X. Gray
Materials Science
Spin Hall Magnetoresistance in Antiferromagnetic Insulators
Stephan Geprägs, Matthias Opel, Johanna Fischer et al. (+4 more)
Antiferromagnetic materials promise improved performance for spintronic applications, as they are robust against external
magnetic field perturbations and allow for faster magnetization dynamics compared to ferromagnets. The direct observation of the antiferromagnetic state, however, is challenging due to the absence of a macroscopic magnetization. We show that the
spin Hall magnetoresistance (SMR) is a versatile tool to probe the antiferromagnetic
spin structure via simple electrical transport experiments by investigating the easy-plane antiferromagnetic
insulators alpha-Fe2O3 (hematite) and NiO in bilayer
heterostructures with a Pt heavy-metal top electrode. While rotating an external
magnetic field in three orthogonal planes, we record the longitudinal and the transverse resistivities of Pt and observe characteristic resistivity modulations consistent with the SMR effect. We analyze both their amplitude and phase and compare the data to the results from a prototypical collinear ferrimagnetic Y3Fe5O12/Pt bilayer. The observed
magnetic field dependence is explained in a comprehensive model, based on two
magnetic sublattices and taking into account
magnetic field-induced modifications of the domain structure. Our results show that the SMR effect allows to readout the
spin configuration and to investigate magnetoelastic effects in antiferromagnetic multi-domain materials. We demonstrate that the SMR amplitude scales with the sum of the absolute sublattice magnetizations in ferrimagnetic and antiferromagnetic materials. In alpha-Fe2O3/Pt bilayers, we find an unexpectedly large SMR amplitude of 2.5E-3, twice as high as for prototype Y3Fe5O12/Pt bilayers, making the system particularly interesting for room-temperature antiferromagnetic spintronic applications.
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All authors Stephan Geprägs, Matthias Opel, Johanna Fischer, Philipp Schwenke, Matthias Althammer, Hans Huebl, Rudolf Gross
Materials Science · Cross-listed from cond-mat.mes-hall
Nonreciprocal Magnon Hanle Effect in Antiferromagnetic $\alpha$-Fe$_2$O$_3$
Janine Gückelhorn, Sebastián de-la-Peña, Monika Scheufele et al. (+8 more)
The precession of the
magnon pseudospin about the
equilibrium pseudofield, the latter capturing the nature of magnonic eigenexcitations in an antiferromagnet, gives rise to the
magnon Hanle effect. Its realization via electrically injected and detected
spin transport in an antiferromagnetic
insulator demonstrates its high potential for devices and as a convenient probe for
magnon eigenmodes and the underlying
spin interactions in the antiferromagnet. Here, we observe a non-reciprocity in the Hanle signal measured in alpha-Fe2O3 using two spatially separated Pt electrodes as
spin injector and detector. Interchanging their roles alters the detected
magnon spin signal. The recorded difference depends on the applied
magnetic field and reverses sign when the signal passes its nominal maximum at the so-called compensation field. Our findings unlock the high potential of antiferromagnetic magnonics towards the realization of electronics-inspired phenomena.
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All authors Janine Gückelhorn, Sebastián de-la-Peña, Monika Scheufele, Matthias Grammer, Matthias Opel, Stephan Geprägs, Juan Carlos Cuevas, Rudolf Gross, Hans Huebl, Akashdeep Kamra, Matthias Althammer
Materials Science
Colossal reversible conductivity switching by room-temperature oxygen-vacancy ordering in Aurivillius oxide films
Song Zhou, Songge Zhang, Lanting Shi et al. (+11 more)
Oxygen vacancies are central to the functionality of oxides, yet they typically exist as randomly distributed point defects, limiting the ability to precisely manipulate their collective behavior. Here, we report the room-temperature formation of a long-range-ordered oxygen-vacancy superstructure in single-crystalline Aurivillius-phase Bi2WO6 thin films via a mild nitrogen-
plasma treatment. This structural transformation unlocks a colossal, reversible modulation of electrical conductivity by more than nine orders of magnitude, accompanied by a striking optical transition from transparent to black. Atomic-resolution imaging and spectroscopy reveal that the vacancies selectively order within the perovskite-like tungsten oxide layers, forming a coherent defect
lattice that is absent in the pristine film. Oxygen-
plasma treatment removes the vacancy superstructure and restores the initial state, whereas subsequent nitrogen-
plasma treatment reconstructs it, enabling repeatable room-temperature switching between distinct structural, electronic and optical states. The phenomenon is also observed in another Aurivillius member, Bi2MoO6, suggesting its generality across the Aurivillius family. These findings establish a new paradigm for atomic-scale defect engineering - using gentle
plasma chemistry to construct ordered defect
lattices, opening avenues for reversible property modulation in complex oxides.
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All authors Song Zhou, Songge Zhang, Lanting Shi, Ping Zhang, Na Li, Jiawei Huang, Bolin Meng, Chuangye Song, Shaoxiang Sheng, Yang Chai, Lede Xian, Jinxing Zheng, Guangyu Zhang, Kehui Wu
Materials Science · Cross-listed from cond-mat.mes-hall
Direct Observation of the Zigzag Edge States of a Supramolecular Diatomic Kagome Lattice
Ryohei Nemoto, Xiangzhi Meng, Behzad Mortezapour et al. (+11 more)
Lattice geometry plays a fundamental role in the behavior of Bloch electrons in a
crystal. The diatomic Kagome
lattice, an extension of the honeycomb and Kagome
lattices, is predicted to give rise to emergent and topological phenomena, but its experimental investigation has been limited thus far. Here, we fabricate a diatomic Kagome
lattice through self-assembly of a triptycene derivative with phenazine moieties (Trip-Phz)—a $\mathrm{C_3}$-symmetric, non-planar $\pi$-conjugated molecule. Our scanning tunneling microscopy (STM) observations show that Trip-Phz forms a highly ordered diatomic Kagome
lattice terminated by zigzag-type edges on the Pb(111) surface. Combined STM measurements and tight-binding calculations provide direct evidence for the existence of the edge states that correspond to those of
graphene. These states are topological edge states dictated by the quantization of the Zak phase and the bulk-edge correspondence.This work reveals an ideal platform for exploring
quantum materials with unique
lattice geometries using supramolecular technology.
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All authors Ryohei Nemoto, Xiangzhi Meng, Behzad Mortezapour, Alexander Weismann, Saya Nakano, Masahisa Tsuchiizu, Ryuichi Arafune, Noriaki Takagi, Sho Nakamura, Katsunori Wakabayashi, Rie Suizu, Richard Berndt, Takashi Uchihashi, Kunio Awaga
Materials Science
All-dry processing of 3C-SiC nanomechanical string resonators for extreme aspect ratios and high intrinsic quality factor
Felix David, Philipp Bredol, Yannick S. Klaß et al. (+1 more)
Conventional fabrication of suspended nanomechanical resonators typically relies on wet-chemical process steps and critical point drying, which can compromise sample yield and cleanliness. Here, we present an all-dry fabrication process for strongly stressed 3C-SiC nanomechanical string resonators that entirely avoids wet-chemical etching and cleaning. Using a negative-tone electron-beam resist as an etch mask and a three-step reactive-ion etching process for both structuring and release, we achieve high fabrication yield, clean suspended structures, and extreme aspect ratios of 8.500. We perform full mechanical characterization of the resulting doubly-clamped nanostring resonators, and establish a
benchmark intrinsic quality factor for dissipation-diluted 3C-SiC of Qintr = 4.200.
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All authors Felix David, Philipp Bredol, Yannick S. Klaß, Eva M. Weig
Materials Science
A Wannier-first approach for extended chiral systems
Yashpal Singh, Juan E. Peralta, Koblar A. Jackson et al. (+1 more)
We present a real-space formulation of DFT for extended systems in which localized Wannier-like functions are constructed directly from localized Gaussian basis functions without explicitly computing canonical Bloch-like states during the self-consistent cycle. Building on the formalism of Pederson and Lin [Phys. Rev. B 35, 2273 (1987)], a variational set of Wannier-like functions is generated self-consistently within a finite Wannier domain and used to construct the charge density, electrostatic potential, and per
cell total energy of the extended system. The occupied space can be determined entirely from the Wannier-like functions. Electronic band structures can be recovered in a post-processing step by solving the full
Hamiltonian in a Bloch-like basis constructed from Gaussian orbitals. A key feature of the method is that it can incorporate combined translation–rotation, or screw,
symmetries, enabling efficient simulations of chiral and helical systems with finite twist angles at essentially the same computational cost as systems described by pure translational
symmetry. The approach is validated through calculations on linear and twisted $\mathrm{{-}C{\equiv}C{-}}$ and $\mathrm{{-}Li{-}F{-}}$ chains, as well as
graphene, where total energies and band structures show excellent agreement with reference periodic calculations. To illustrate the ability of the method to treat three-dimensional systems, it is further applied to AA graphite, in which carbon atoms in adjacent
graphene layers are aligned directly above one another, as well as helically stacked AA graphite structures. The Wannier-first framework provides a practical route for treating extended systems with nontrivial translational, rotational, and screw
symmetries, and provides a natural foundation for the implementation of orbital-dependent functionals such as the Perdew–Zunger self-interaction correction.
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All authors Yashpal Singh, Juan E. Peralta, Koblar A. Jackson, Mark R. Pederson
Materials Science
'pySNOW': a Python Suite for the NanO-World
Sofia Zinzani, Gilberto Nardi, Giacomo Becatti et al. (+4 more)
In computational materials science, numerical simulations are indispensable tools for revealing atomic-scale processes. For building blocks of the nanoworld, such as nanoparticles and nanoalloys, atomistic simulations provide detailed insight into their behaviour under diverse conditions. These simulations enable the study of formation and growth mechanisms, transport phenomena, chemophysical stability, and chemical reactions, including catalytic processes. To unravel the complex structure–property relationships that characterise nanoobjects, it is crucial to develop robust and insightful representations of their atomistic structure at global and local scales. Such descriptions enhance our understanding of nanoparticle behaviour and play a key role in guiding their rational design in silico for targeted applications.
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All authors Sofia Zinzani, Gilberto Nardi, Giacomo Becatti, Davide Alimonti, Letícia F. Basso, Kevin Rossi, Francesca Baletto
Materials Science
Spin wave freezing in Re/Co/Pt multilayers
Jan Kisielewski, Kilian Lenz, Pawel Gruszecki et al. (+7 more)
The phenomenon of
spin wave (SW) freezing occurs in the Damon-Eshbach mode in thin film
magnetic systems, when SW phase and group velocities both go to zero, and the wave ceases to oscillate and move, preserving its shape as a domain structure pattern. This effect is related to the
spin reorientation transition, where the magnetization configuration changes between the homogeneous in-plane state and domain structure with the out-of-plane magnetization component state. Here, we study the SW freezing effect in [Re/Co/Pt]$_{20}$
magnetic multilayers, induced by varying the in-plane external
magnetic field. The studies were performed on nanostructures with the quality factor $Q$ (ratio of uniaxial anisotropy to demagnetization energies) greater and smaller than one. Domain structures with an out-of-plane magnetization component were observed in these multilayers. The critical field, visible as the saturation field $H_s^{||}$ in the parallel static magnetization curve measured by superconducting
quantum interference device (SQUID), is also manifested in the field-dependent vector-network-analyzer ferromagnetic resonance (VNA-FMR) experiment, which measures the homogeneous magnetization oscillations. Brillouin Light Scattering (BLS) spectra, recorded for several values of wave vectors and several field values, probed the field-
evolution of the dispersion relation. Micromagnetic simulations allow one to obtain a full dispersion, in good agreement with VNA-FMR and BLS results. Around $H_s^{||}$ the simulated dispersion relations approach the conditions for SW freezing. Below $H_s^{||}$ low and high frequency VNA-FMR modes are related to magnetization oscillations inside domain walls and within domains, respectively. The experimental results of static and dynamic behavior, together with micromagnetic simulations, create an overall consistent picture of the investigated multilayers.
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All authors Jan Kisielewski, Kilian Lenz, Pawel Gruszecki, Ryszard Gieniusz, Urszula Guzowska, Marek Kisielewski, Artem Lynnyk, Aleksiej Pietruczik, Andrzej Wawro, Andrzej Maziewski
Materials Science
Chemical pressure and vacancies in crystals under nonhydrostatic stress
Michiel Sprik
Inhomogeneous stress is a driving force for
diffusion of vacancies in
crystals. The other way around a non-uniform distribution of vacancies induces stress. The accepted theory of composition-stress coupling in
crystals is Larché-Cahn (LC) theory. Composition is defined in terms of the population of
lattice sites with a limit of one-particle per site. Coupling is modelled by adding a compositional strain term to the elastic strain in the constitutive relation for stress. An alternative mechanism, proposed here, is letting the site binding energy vary with spatial (deformed) density. This generates a chemical pressure adding to the elastic stress. The governing equations for this model are derived using non-
equilibrium continuum thermodynamic methods. The gradient of the chemical pressure has a dual function acting both as the drift force for migration and as an effective internal one body force in the Cauchy equation for the elastic stress. The practical evaluation presented in the paper is restricted to
equilibrium properties. We examine the effect of externally applied non-hydrostatic stress, either in the form of surface tractions or a one-body force density (gravitation). The model system is a one component
crystal with a fixed number of
lattice sites. The number of particles can be variable but is always smaller than the number of
lattice sites. The linear elastic response is modelled by the standard Lamé stress tensor. The results for systems deformed by surface tractions are in qualitative agreement with LC theory allowing for differences in the expression for the elastic moduli. Deviations are more serious for the
crystal deformed by gravitation.
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Materials Science · Cross-listed from cond-mat.mes-hall
Rank-Selective Optical Tomography of Higher-Wave Altermagnetism
Meysam Bagheri Tagani, Carmine Autieri and Sahar Izadi Vishkayi
Identifying the spatial rank of higher-wave altermagnetic order optically is challenging because local electric-dipole response does not uniquely resolve distinct continuum harmonics. We show that finite
photon momentum turns one-
photon spin-resolved absorption into a rank-selective
tomography. For the planar $|m|=\ell$ sector of an even-parity $\ell$-wave component, a joint
Fourier projection in polarization and momentum angle isolates $\mathcal T_\ell\propto\eta_\ell q^{\ell-2}$, yielding the hierarchy $d:q^0$, $g:q^2$, and $i:q^4$; phase changes track rotations of the selected
magnetic harmonic. A Ward-consistent finite-$q$ microscopic calculation reproduces these powers without imposing them. Although discrete
crystal symmetry can generate lower-order local aliases, they are orthogonal to the selected momentum harmonic and cannot contaminate it below $q^{\ell-2}$. In MnTe, whose nonrelativistic parent order is three-dimensional $g$ wave while
spin–orbit coupling lowers the exact relativistic
spin-momentum-locking
symmetry, first-principles calculations show that more than $99.9\%$ of the
Fourier power of the Néel-projected $A$-region
spin-energy contrast remains in the parent $g$-wave-derived $m=3$ harmonic. Structured near fields place the required momentum window within experimental reach.
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Materials Science
Symmetry-based modal analysis of heat transport in molecular dynamics of quasi-1D systems
Yu-Jie Cen, Sandro Wieser, Georg K. H. Madsen et al. (+1 more)
Detailed analysis of thermal conductivity results obtained from molecular dynamics (MD) trajectories conventionally relies on knowledge of the harmonic vibrational modes of the system. This is the case in methods like Green-Kubo modal analysis (GKMA) and homogeneous nonequilibrium modal analysis (HNEMA). However, arbitrary mixing within degenerate
phonon subspaces makes individual modal contributions basis dependent and can obscure their
symmetry character. We propose an alternative for quasi-one-dimensional (quasi-1D) systems: we construct the modal basis for the decomposition of the thermal conductivity from line-group projection operators, so that every projected component carries well-defined
symmetry labels (including rotational information and parities) and the decomposition is unique at the level of irreducible representations (irreps). Applying the idea to a (10, 0)-(20, 0) WS2-MoS2 double-walled nanotube (DWNT) described by a neuroevolution potential (NEP), we find that at 300 K both HNEMA and GKMA yield statistically consistent total conductivities and allow the identification of several prominent
symmetry-adapted conduction channels. The GKMA pair
matrix shows that within-block and same-channel cross-k terms account for 75.6% of the total conductivity, while cross-channel correlations contribute 24.4%.
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All authors Yu-Jie Cen, Sandro Wieser, Georg K. H. Madsen, Jesús Carrete
Materials Science
Magneto-Structural Coupling Enables Cryogenic Cation Redistribution in a Spinel Oxide
Yifeng Han, Yixing Zhao, Yunbo Ou et al. (+11 more)
Ionic transport in oxides is generally frozen at cryogenic temperatures, where thermal energy lies far below typical cation-migration barriers.
Neutron powder diffraction reveals progressive Fe/Mg redistribution between tetrahedral (A) and octahedral (B) sites in the spinel Mg0.5Fe0.5TiFeO4 upon cooling from 200 K to 5 K. A-site Fe occupancy increases toward near completion at 5 K within Rietveld resolution, while Ti remains on the B site. This exchange coincides with complex
magnetic correlations rather than a classical thermally activated window. Low-temperature magnetostrictive volume changes indicate strong
spin-
lattice coupling, but do not identify magnetostriction as the sole thermodynamic driver. Room-temperature high-pressure X-ray diffraction produces the opposite occupancy trend, showing that volume contraction alone cannot explain the cryogenic site exchange. These results point to magneto-structural free-energy minimization as a plausible mechanism for unlocking cryogenic cation mobility in a correlated spinel oxide.
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All authors Yifeng Han, Yixing Zhao, Yunbo Ou, Feiran Shen, Lunhua He, Ligang Xu, Mingxue Tang, Jared Matteucci, Zexiao Zhang, Xiaoli Ma, Xiaohui Yu, Zheng Deng, Man-Rong Li, Alexandra Navrotsky
Materials Science
Ferroelastic domain switching by ultrafast photoinduced strain
Daniel G. Lourens, Maarten Kwaaitaal, Carl S. Davies et al. (+1 more)
The
crystal lattice underpins the fundamental properties of condensed matter, with ferroic order emerging sensitively from atomic coordination. Manipulating the lattic therefore promises a direct way to switch ferroics between their states. Infrared excitation provides an efficient pathway to drive
lattice motion and generate transient
crystal deformations and strains. Ferroelastics constitute a uniquely direct platform for such control, their order parameter being strain itself. However, whether ultrafast
laser-induced
lattice distortions can switch ferroelastic order remains unknown. Here we use ultrafast pump-probe microscopy to demonstrate that a single high-amplitude infrared pulse induces strain within the first nanosecond, followed by ferroelastic domain switching several nanoseconds later. The spatial distribution follows that expected from the photoinduced strain field, while their temporal
evolution is closely coupled to the strain dynamics. Our observations identify transient strain as the driving field for ferroelastic switching and suggest a general
lattice-mediated pathway for controlling ferroic order using infrared light.
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All authors Daniel G. Lourens, Maarten Kwaaitaal, Carl S. Davies, Andrei Kirilyuk
Materials Science
Vitrification-Devitrification Enables Tunable Photonic and Gas Sorption Properties of Zeolitic Imidazolate Frameworks
Zhencai Li, Zihao Wang, Minhyuk Kim et al. (+14 more)
Zeolitic imidazolate framework (ZIF) glasses represent an emerging family of melt-quenched glasses, which exhibit immense potential for applications in gas separation, energy storage, and optics. However, their intrinsic porosity remains elusive due to the inherent challenges in resolving their disordered atomistic structures. Here, we systematically investigate the porosity of ZIF-4 and ZIF-62
crystals and their corresponding glasses. CO2 sorption at 195 K enables quantitative assessment of microporosity in both crystalline and glassy states, allowing the accessible micropore volume of the ZIF glasses to be determined. Moreover, establishing a direct relationship between photonic properties and structural porosity in Zn-based ZIF glasses remains challenging. Here we demonstrate striking broadband blue-light emission from ZIF-4 glass annealed under optimized conditions. A pronounced red shift is observed when increasing the annealing temperature above the glass transition temperature. By correlating the
evolution of photoluminescence with structural porosity, we reveal the interplay between the photonic and gas sorption properties of ZIF glasses. These findings provide new insights into the structure-property relationships of ZIF glasses and offer a pathway toward the rational design of multifunctional MOF glasses.
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All authors Zhencai Li, Zihao Wang, Minhyuk Kim, Huotian Zhang, Bozhao Yin, Yong Li, Qi Zhang, Fengming Cao, Xuan Ge, Laurent Calvez, Daniel Irving, Guoping Dong, Feng Gao, Haomiao Zhu, Morten M. Smedskjaer, Hoi R. Moon, Yuanzheng Yue
Materials Science
Linker Functionalization and pH Tuning Enhance Solar-Driven Catalytic CO$_2$ Reduction in MOF-5
Julia Santana-Andreo, Joshua Edzards, Surender Kumar et al. (+1 more)
The wide band gap of metal-organic framework (MOF) 5 constrains its use in photocatalytic carbon dioxide (CO$_2$) reduction despite its high porosity and favorable mass-transport properties. Adopting a state-of-the-art first-principles approach, we systematically investigate the effects of volumetric strain, metal-node substitution, linker functionalization, and pH control as knobs to improve the CO$_2$ photocatalytic ability of MOF-5. Strain and metal-node substitution negligibly affect the gap, whereas linker functionalization narrows it into the visible range via in-gap states while preserving reduction-side
alignment at pH = 0. The resulting reduction energetics are strongly sensitive to both linker functionalization and pH. Halogenated and hydroxylated frameworks provide access primarily to HCOOH, CO, and HCHO under alkaline conditions, principally with the Mg and Zn nodes, whereas COOH functionalization offers the broadest thermodynamic accessibility across the full CO$_2$ reduction sequence. NH$_2$ retains thermodynamic feasibility for all target reduction pathways but with larger overpotentials, while NO$_2$ generally yields unfavorable reduction energetics. Crucially, within the COOH series, the choice of the metal node tunes the fundamental gap by over 1 eV with only minor changes in the reduction overpotentials, placing Sr- and Ba-based architectures as the most favorable ones for broad product selectivity with visible-light excitation. Linker functionalization substantially reduces the spatial overlap of the frontier states, promoting photoinduced charge separation. Taken together, these results establish linker functionalization and solution pH as complementary design levers for independently tuning light absorption and CO$_2$-reduction energetics in MOF-5, establishing a rational and viable route for designing efficient MOF-based photocatalysts.
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All authors Julia Santana-Andreo, Joshua Edzards, Surender Kumar, Caterina Cocchi
Materials Science
Decoding Oxygen K-edge Fingerprints of NCM-811 Degradation via Ab Initio Many-Body Theory and High-Throughput Screening of Crystal Proxies
Daniel Duarte-Ruiz, Timo Reents, Elmar Kataev et al. (+4 more)
The degradation of LiNi$_{0.8}$Co$_{0.1}$Mn$_{0.1}$O$_2$ (NCM-811) in Li-ion batteries produces complex transition-metal oxides and binary phases that fundamentally limit cathode performance. While identifying these degradation products via X-ray absorption spectroscopy (XAS) is essential for mitigating electrochemical performance loss, interpretation remains challenging due to the structural complexity of real-world samples. In this work, we present an integrated theoretical-experimental framework combining high-resolution oxygen K-edge XAS with ab initio simulations based on many-body perturbation theory and high-throughput screening from density functional theory. We first evaluate the spectroscopic fingerprints of eight layered, spinel, and nominal rock-salt reference oxides, identifying discrepancies between the idealized single-
crystal bulk phase and experimental spectra. Using high-throughput screening to analyze the oxygen $p$-projected density of states of 38 distinct polymorphs of NiO, CoO, and MnO, we propose that the spectral differences can emerge, among other factors, from a structural ensemble of local variations represented here by simplified structural proxies. Our work establishes a viable and rigorous computational pathway to interpret the complex landscape of degraded battery materials.
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All authors Daniel Duarte-Ruiz, Timo Reents, Elmar Kataev, Raul Garcia-Diez, Regan G. Wilks, Marcus Baer, Caterina Cocchi
Materials Science
The Locality Cost of Fully Flat Hopf Insulators
Feng Liu, Qifeng Liang and Wenlong Gao
Hopf
topology permits a strictly finite-range
Hamiltonian with one exactly flat topological band. We prove, however, that extending flatness to the complete two-band spectrum necessarily sacrifices strict locality or the gap: any gapped, Hermitian, translationally invariant two-band
Hamiltonian with strictly finite-range hopping and two exactly flat bands has vanishing Hopf invariant. Equivalently, within this two-band setting, a Hopf band admits no compactly supported, translation-covariant, orthonormal Wannier generator. For factorized one-flat-band Hopf parents, the unavoidable partner dispersion equals the Gram symbol of translated compact localized states and encodes their nonorthogonality. Full flattening converts this dispersion into exponentially decaying but infinitely supported hopping. Model-independent bounds provide a sufficient criterion for finite-range approximants to retain the Hopf phase. An explicit model yields the axial decay length $\xi_z/a=1/\ln 2$, parameter-free hopping tails, and residual bandwidths testable in
circuit and photonic
lattices. Hopf
topology therefore does not prohibit a flat band but forces the locality–flatness cost to appear as either partner-band dispersion or nonlocal hopping.
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Materials Science · Cross-listed from physics.optics
Multidimensional Light Detection with Symmetry-engineered Heterojunctions
Yucai Lin, Yaoqiang Zhou, Ruijuan Tian et al. (+11 more)
Miniaturised multidimensional light detection, encompassing full-Stokes polarimetry and spectroscopy in ultracompact footprints, is attracting growing interest for its potential to capture a comprehensive set of light properties in portable platforms. Although significant progress has been made in miniaturised schemes for independent polarisation and spectral detection, achieving simultaneous high-dimensional light detection remains an outstanding challenge that limits their development toward full integration. We overcome this limitation by breaking the rotational and inversion
symmetries in a
symmetry-engineered van der Waals heterojunction to realise an ultracompact multidimensional photodetector. The dual
symmetry breaking gives rise to non-trivial
quantum geometric and topological features, enabling simultaneous broadband polarisation- and spectrum-resolved light detection, in contrast to previous van der Waals material-based devices, which could detect only one of these modalities. Our device, with an effective area of only 10 micron x 10 micron, reconstructs full-Stokes polarisation with overall root-mean-square errors below 0.05 and resolves spectral peaks separated by 0.4 nm, capabilities not previously achieved in single-pixel detectors. By unifying high-fidelity polarimetry and sub-nanometre spectroscopy in a single electrically tunable junction, our work eliminates the need for cascaded detection architectures and establishes a foundation for multidimensional detector arrays for integrated photonics,
quantum information processing, and precision imaging.
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All authors Yucai Lin, Yaoqiang Zhou, Ruijuan Tian, Faisal Ahmed, Andreas C. Liapis, Youqiang Huang, Yawei Dai, Yuwei Chen, Weiwei Cai, Zongyin Yang, Weida Hu, Tawfique Hasan, Luojun Du, Zhipei Sun
Materials Science
Charge-Transfer Electronic Structure of NiX$_2$ (X = S, Se)
Atsushi Hariki, Takaki Okauchi, Daisuke Takegami et al. (+8 more)
We investigate the electronic structures of NiS$_2$ and NiSe$_2$ using density functional theory combined with dynamical mean-field theory (DFT+DMFT). A realistic electronic structure within DFT+DMFT was determined by optimizing the double-counting correction to reproduce experimental valence-band photoemission spectra. The validity of the present model is further confirmed by its successful description of the Ni 2$p$ core-level photoemission and Ni $L$-edge x-ray absorption spectra of NiS$_2$. Our results reveal a smaller charge-transfer energy than previously assumed, resulting in substantial ligand-to-Ni charge transfer and a reduced Ni local moment. We clarify how the relative position and interaction between the Ni upper Hubbard band and the antibonding chalcogen-dimer states shape the
evolution of the low-energy electronic structure across the NiS$_{2-x}$Se$_x$ series.
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All authors Atsushi Hariki, Takaki Okauchi, Daisuke Takegami, Naoki Ito, Mizuki Furo, Ayako Yamamoto, Tomoya Higo, Satoru Nakatsuji, Masato Yoshimura, Takashi Mizokawa, Jan Kunes
Materials Science · Cross-listed from cs.LG
Scalable Bayesian Optimization of Composite Functions for Image-Based Inverse Problems in Materials Characterization
Dasol Yoon, Poompol Buathong, Chia-Hao Lee et al. (+3 more)
Estimating physical parameters from scientific images is a common inverse problem in materials characterization that often relies on expensive physics-based simulations. In electron microscopy, specimen thickness and
crystal mistilt are critical parameters that govern how electrons scatter through the sample, and therefore the accuracy of any atomic-scale structure recovered from it. They are commonly inferred by matching experimental position-averaged convergent-beam electron diffraction (PACBED) patterns to simulated ones, but grid searches scale poorly and neural-network methods require extensive pretraining that may not transfer to new conditions. Here, we propose scalable
Bayesian optimization of composite functions (SBOCF), a simulation-efficient method that exploits the known composite structure of the image-matching objective and the intermediate information contained in simulated images. By representing PACBED images with patch-level summaries and two correction terms, SBOCF preserves the original pixel-wise objective while reducing the number of modeled outputs from 24,649 to 11. Under a budget of 50 simulator evaluations, SBOCF outperformed standard
Bayesian optimization with expected improvement on synthetic SrTiO3
benchmarks with thick and thin specimens, reducing the median final SSE by up to 290x in the thick-sample case. On experimental data, SBOCF produced parameter estimates consistent with previously reported values without task-specific pretraining. For a simulated mistilted specimen, using the SBOCF estimates in a downstream ptychographic reconstruction recovered sharp atoms that were otherwise blurred. These results establish SBOCF as a promising approach for inverse problems involving expensive simulators and high-dimensional structured outputs.
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All authors Dasol Yoon, Poompol Buathong, Chia-Hao Lee, Yujia Zhang, David A. Muller, Peter I. Frazier
Materials Science
EuIn2Sb2: epitaxially stabilized axion insulator candidate with strong spin-orbit coupling
Hsiang Lee, Shinichi Nishihaya, Markus Kriener et al. (+5 more)
Eu triangular
lattice layer compounds described by the general formula EuA2X2 have attracted growing
attention due to a wide range of layered
crystal structures and corresponding
magnetic topological phases, arising from the coexistence of large Eu
magnetic moments and energetically inverted A and X bands. Among the EuA2X2 family, EuIn2Sb2 has been predicted to host robust
axion insulator and higher-order topological
insulator states by stronger
spin-orbit coupling but has not been experimentally realized, including the structural identification. Here we report the epitaxial stabilization of EuIn2Sb2 by adopting the molecular beam epitaxy technique. Structural characterization reveals that EuIn2Sb2 films are based on a unique In-on-In stacking, forming a new trilayer structure distinct from previously predicted structures in the EuA2X2 family. In addition to the in-plane antiferromagnetic ordering at TN=10.5K, the stronger
spin-orbit coupling and enhanced In-In hybridization in EuIn2Sb2 make it an ideal candidate of
axion insulator and higher-order topological
insulator phases. These results establish EuIn2Sb2 as a new member of the EuA2X2 family and offer an advanced platform for exploring these
magnetic topological phases.
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All authors Hsiang Lee, Shinichi Nishihaya, Markus Kriener, Ayano Nakamura, Tadashi Yoneda, Yuki Deguchi, Makuro Goto, Masaki Uchida
Materials Science
Symmetry-enforced third-order nonlinear thermal Hall effects in altermagnets
Yun-Mei Li, Jiacheng Yao, Hua Wang et al. (+1 more)
Thermal Hall effect (THE) is a powerful probe of material properties, even in
insulators. Here we investigate the thermal response of altermagnets by developing a theory on Berry
curvature driven nonlinear THE from both electrons and
magnons. We identify
symmetry conditions under which the third-order THE dominates while linear and second-order contributions vanish. Notably, d-wave and i-wave altermagnets with out-of-plane Neel order satisfy these conditions, whereas in-plane order yields a dominant linear THE. Using KV2Se2O (a d-wave altermagnetic metal) and MnF2 (an altermagnetic
insulator) as concrete examples, we show nonzero third-order nonlinear THE from electrons and
magnons, respectively, both exhibiting a pi-periodic dependence on the direction of temperature gradient. These
symmetry-guaranteed Berry
curvature phenomena provide a diagnostic for altermagnetism in candidate materials and enable determination of the Neel vector orientation.
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All authors Yun-Mei Li, Jiacheng Yao, Hua Wang, Kai Chang
Materials Science
Machine-learning screening and first-principles lattice dynamics resolve the most stable structure of NaCa(BH$_4$)$_3$ from a data-driven candidate search
Sanaa Ismail, Ricardo Amaral, Attia A. Gadallah et al. (+2 more)
Equimolar NaCa(BH$_4$)$_3$ offers a theoretical hydrogen capacity of 11.24 wt.% and a decomposition enthalpy expected to fall between those of NaBH$_4$ and Ca(BH$_4$)$_2$, but it has never been prepared and no
crystal structure has been reported. Predictions for it have so far been built within the perovskite family that its heavier homologues adopt. Here that assumption is removed. Six candidate frameworks were assembled from three independent sources — experimentally determined ABX$_3$ borohydrides, a distorted perovskite from data-driven structure prediction, and an unbiased search over a structural database in which all 2238 generated candidates were relaxed with none excluded — and at fixed charge-neutral composition the cation arrangement of every framework was enumerated exhaustively, 420 decorations reducing to 118
symmetry-inequivalent configurations, screened with a machine-learning potential and settled from first principles. The most stable structure is not a perovskite. It is a monoclinic framework of space group Cm, reached only by the unrestricted search, at $-$4.185640 eV/atom, 7.67 meV/atom below the best framework available beforehand; two chemically unrelated donor prototypes converge on it to 0.076 meV/atom, and its ordered cation arrangement is the ground state of its own series. Its
phonon spectrum carries no imaginary mode at any wavevector the supercell resolves exactly and its relaxed-ion elastic tensor is positive definite, whereas the orthorhombic perovskite candidate is unstable to $-$2.401 THz. That contrast supplies a physical reason for the reported failure to obtain this composition in perovskite form, and the simulated diffraction pattern reported here identifies the predicted framework by seven reflections that neither parent phase nor the competing framework produces.
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All authors Sanaa Ismail, Ricardo Amaral, Attia A. Gadallah, Hassan Mohamed El-Said Azzazy, Zi-Kui Liu