Materials Science
Heterointerface-Engineered Electrochemically Exfoliated MoS2/WS2 2D-Layered Nanocomposite for Efficient Visible-Light Photocatalytic Degradation of Sorafenib
I. Agnes Felicia Roy, Kuo Yuan Hwa, Aravindan Santhan et al. (+1 more)
The increasing prevalence of pharmaceutical contaminants within the aquatic environment has generated considerable environmental concerns, especially regarding persistent anticancer medications like the kinase inhibitor sorafenib (SRF), which are inadequately eliminated by standard degradation methods. A heterointerface-engineered MoS2/WS2, 2D/2D layered nanocomposite was fabricated using an electrochemical exfoliation method to facilitate effective visible-light-driven photocatalytic degradation of SRF. The electrochemical exfoliation method yielded ultrathin 9.62-layer thickness MoS2/WS2 nanosheets with numerous exposed edge sites and an increased specific surface area, facilitating the development of well-interconnected van der Waals heterointerfaces. Comprehensive structural and morphological examinations utilizing field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Raman spectroscopy, and UV-visible spectroscopy validated the effective synthesis of few-layer nanosheets and their
heterostructure interfaces. In contrast to the pure MoS2 and WS2 nanosheets, the MoS2/WS2
heterostructure composite demonstrated significantly enhanced photocatalytic efficacy, attaining roughly 92 % degradation of SRF within 2h under visible-light exposure. The enhanced catalytic efficiency is mainly due to the establishment of a Type-II band
alignment at the MoS2/WS2 interface, facilitating effective charge separation and directional charge transfer while inhibiting electron-hole recombination. The robust interfacial interaction among the transition metal dichalcogenide layers accelerates visible-light absorption and the production of reactive oxygen species. This study illustrates that electrochemically exfoliated MoS2/WS2
heterostructure composites serve as a viable catalytic platform for the successful removal of persistent pharmaceutical pollutants.
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All authors I. Agnes Felicia Roy, Kuo Yuan Hwa, Aravindan Santhan, Slava V Rotkin
Materials Science
Electrostatic Effects of Self Trapped Holes in Gallium Oxide Devices
Nathan Wriedt, Joe McGlone, Davide Orlandini et al. (+1 more)
Gallium
oxide is an ultra-wide bandgap
semiconductor with exceptional properties for power electronics and UV-C optoelectronics, but its behavior under illumination remains poorly understood. In this work, we investigate how optically generated self-trapped holes influence electrostatics and current conduction in gallium
oxide devices. Using a vertical Schottky photodiode with a semi-transparent Ni anode, we performed capacitance-voltage, current-voltage, and temperature-dependent I-V measurements under dark and above-bandgap illumination. Analysis of photocurrent gain reveals that conventional image-force barrier-lowering models require unrealistically high interfacial electric fields, suggesting the presence of an alternative mechanism. By applying Fowler-Nordheim tunneling theory, we reconcile measured photocurrents and photo-capacitance results with physically plausible fields and quantify the two-dimensional concentration of self-trapped holes. Our findings demonstrate that illumination-induced charge significantly alters device electrostatics. Understanding this tunneling-based photocurrent gain mechanism is critical for designing gallium
oxide devices for UV-C detectors and power electronics.
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All authors Nathan Wriedt, Joe McGlone, Davide Orlandini, Siddharth Rajan
Materials Science · Cross-listed from cond-mat.mes-hall
Frustrated out-of-plane Dzyaloshinskii-Moriya interaction and the onset of atomic-scale 3$q$ magnetic textures in 2D Fe$_{3}$GeXTe (X = Te, Se, S) monolayers
Rabia Caglayan, Louise Desplat, Sergey Nikolaev et al. (+5 more)
We theoretically study the effect of in- and out-of-plane Dzyaloshinskii-Moriya interaction (DMI) on the
magnetic ground states of two-dimensional (2D) Fe$_3$GeXTe (X=Te, Se, S) monolayers, where X=Se, S correspond to antisymmetric Janus structures with nonvanishing in-plane DMI. We perform atomistic
spin simulations with the extended Heisenberg
Hamiltonian parametrized by first principles calculations. While we find that the base DMI in all systems is too weak to stabilize noncollinear states, we show how the frustrated out-of-plane DMI tends to favor atomic-scale $3q$
magnetic textures at the edge of the Brillouin zone. Owing to the ability to tune the DMI in 2D magnets via applied strain or electric field, we study the
evolution of the systems' ground state with increasing DMI amplitude. We find that nonplanar $3q$ states are favored under scaling factors as low as 3, while larger DMI tends to stabilize states reminiscent of nanoskyrmion
lattices at the atomic-scale.
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All authors Rabia Caglayan, Louise Desplat, Sergey Nikolaev, Fatima Ibrahim, Jing Li, Yesim Mogulkoc, Aybey Mogulkoc, Mairbek Chshiev
Materials Science · Cross-listed from cond-mat.other
Chemical tuning of electronic and transport properties of the Bi-Se-Te family of topological insulators
Maxwell Doyle, Benjamin Schrunk, D. L. Schlagel et al. (+2 more)
We use
laser-based Angle-Resolved Photoemission Spectroscopy (ARPES) to study how chemical substitution modifies the electronic properties of the Bi2(Se{1-x}Tex)3 (BiSeTe) family of topological
insulators. We find that increasing the Te content lowers the chemical potential, leading to a decrease in the binding energy of the Dirac point and a reduction in the density of states originating from the bulk band. This reduction leads to a transition from metallic to semiconducting temperature dependence of the resistivity. For the highest Te concentration, the resistivity nearly saturates at the lowest temperatures. The presence of this plateau indicates that metallic topological surface states dominate the conductance, opening the possibility of studying their transport properties.
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All authors Maxwell Doyle, Benjamin Schrunk, D. L. Schlagel, Thomas A. Lograsso, Adam Kaminski
Materials Science · Cross-listed from cs.LG
Property-Guided Molecular Generation and Optimization via Latent Flows
Alexander Arjun Lobo, Urvi Awasthi and Leonid Zhukov
Molecular discovery is increasingly framed as an inverse design problem: identifying molecular structures that satisfy desired property profiles under feasibility constraints. While recent generative models provide continuous latent representations of chemical space, targeted optimization within these representations often leads to degraded validity, loss of structural fidelity, or unstable behavior. We introduce MoltenFlow, a modular framework that combines property-organized latent representations with flow-matching generative priors and gradient-based guidance. This formulation supports both conditioned generation and local optimization within a single latent-space framework. We show that guided latent flows enable efficient multi-objective molecular optimization under fixed oracle budgets with controllable trade-offs, while a learned flow prior improves unconditional generation quality.
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Materials Science
Giant Magnetostriction by Design: A First-Principles Screening of Co-based Heusler Alloys
Pengju Wu, Jie Du, Liang Yao et al. (+4 more)
The pursuit of high-performance, rare-earth-free magnetostrictive materials is crucial for advancing technologies in sensing, actuation, and microelectromechanical systems. Heusler
alloys represent a promising, yet underexplored, class of materials for this purpose. In this work, we perform a systematic first-principles investigation of the magnetostrictive properties of 25 Co-based full Heusler
alloys, Co$_2$YZ (Y = V, Cr, Mn, Fe, Co; Z = Al, Ga, Si, Ge, Sn). Our screening identifies 10 compounds with large predicted magnetostriction ($|\lambda_{001}| > 100$~ppm), highlighted by Co$_3$Si with a
giant value of -966~ppm. Furthermore, we demonstrate two effective strategies for engineering magnetostriction: (i) tuning the
Fermi level, which enhances the magnetostriction of Co$_3$Sn to -905~ppm via Sb doping, and (ii) amplifying the
spin-orbit coupling, which boosts the magnetostriction of Co$_2$CrGa to a colossal -1008~ppm through Re substitution. Our analysis reveals a general predictive rule, uncovering a linear relationship between the magnetostriction and the choice of the Y-site transition metal. This work not only identifies novel candidates for magnetostrictive applications but also establishes clear, physically-grounded design principles to accelerate the discovery of new functional
magnetic materials.
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All authors Pengju Wu, Jie Du, Liang Yao, Hang Li, Xiaodong Zhou, Tao Zhu, Wenhong Wang
Materials Science · Cross-listed from cond-mat.soft
Jamming and Flow in Granular Matter: A Physics Lab Course Experiment
Thomas Blochowicz, Emina Ismajli and Jan Philipp Gabriel
We describe a dynamic light scattering setup that uses diffusing wave spectroscopy (DWS) to investigate the dynamics in sand grains subjected to periodic vertical shaking by a loudspeaker. Along with the setup that is used in the undergraduate physics lab course at TU Darmstadt, the necessary DWS theory is introduced, including the proper treatment of the oscillatory excitation. Some exemplary results are presented that demonstrate the similarity of jamming in an athermal granular medium with the glass transition in thermally driven molecular systems, a relation that has frequently been pointed out but still is poorly understood. Similar, albeit more sophisticated experiments are currently conducted in microgravity environments such as the international space station ISS and the experiment may serve as an introduction to an exciting field of current research.
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Materials Science
Bubble-induced versus thermodynamic voltage losses during pressurized alkaline water electrolysis
Hannes Rox, Feng Liang, Robert Baumann et al. (+6 more)
Understanding how bubbles influence the efficiency of water electrolysis is crucial to achieve economically competitive hydrogen, generated by renewable energy sources, such as wind and
solar power. Water electrolysis is typically performed at high pressures to reduce the cost of energy-intensive mechanical compression of the produced H2. Thus, a better understanding of how the absolute pressure affects electrochemical performance and bubble size is necessary. In general, bubble sizes decrease as the pressure increases. Using different-sized pillar-patterned Ni electrodes generated by Direct
Laser Writing, the detached bubble sizes can be modified even at elevated pressures. As the pillar size increases, the bubbles become larger at all pressures investigated from 1 to 6 bar. At a current density of -25 mA/cm2, the cathodic potential increases with pressure according to the thermodynamic voltage losses given by the Nernst equation (~ 23 mV at p = 6 bar). Surprisingly, increasing the current density to 100 mA/cm2 leads to a reduction of the overpotential by up to ~ 60 mV. Reduced bubble sizes at increased pressures minimize the losses caused by the bubbles, thereby compensating for the thermodynamic voltage penalty. Applying the Buckingham {\Pi}-
theorem enables the derivation of dimensionless numbers to characterize the ratio of bubble-induced and thermodynamic voltage losses
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All authors Hannes Rox, Feng Liang, Robert Baumann, Mateusz M. Marzec, Krystian Sokołowski, Xuegeng Yang, Andrés F. Lasagni, Roel van de Krol, Kerstin Eckert
Materials Science
Anomalous phonon dispersion near yielding in athermal crystals
Fumiaki Nakai, Michio Otsuki, Kuniyasu Saitoh et al. (+1 more)
Vibrational properties of ordered athermal solids near yielding remain poorly understood. We show that yielding in a sheared
crystal is governed not by a single localized instability but by directionally extended multimode softening that forms a cross-shaped low-frequency region in wave number space. Near yielding, the acoustic dispersion $\omega\sim k$ is replaced by $\omega\sim k^2$ along the soft direction, and the vibrational density of states crosses over from Debye to non-Debye scaling, with a diverging length scale. We analytically derive these scaling laws.
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All authors Fumiaki Nakai, Michio Otsuki, Kuniyasu Saitoh, Hiroaki Katsuragi
Materials Science
Refining hydrogen positions in {\alpha}-FeOOH through combined neutron diffraction and computational techniques
Yusuke Nambu, Akihide Kuwabara, Masahiro Kawamata et al. (+3 more)
The hydrogen positions and
magnetic structure of goethite $\alpha$-FeOOH, a key component of iron rust, were examined through
neutron diffraction. All
symmetry-allowed
magnetic structures under the space group $Pnma$ with the
magnetic wavevector $\vec{q}_{\rm m} = (0, 0, 0)$ r.l.u. were analysed using irreducible representation and
magnetic space group approaches. The
magnetic moments aligned along the $b$-axis form
antiferromagnetic spin arrangements, as reproduced by first-principles calculations. Accurately determining the hydrogen positions is crucial for understanding the mechanism of catalytic reduction of CO$_2$ in $\alpha$-FeOOH. These positions were precisely identified through diffraction and calculations, highlighting the effectiveness of using both methods for undeuterated compounds.
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All authors Yusuke Nambu, Akihide Kuwabara, Masahiro Kawamata, Seira Mori, Megumi Okazaki, Kazuhiko Maeda
Materials Science · Cross-listed from physics.optics
Role of a Quarter-Wave Plate in Confocal Microscopy: Signature of Spin-Orbit Interactions
Wenze Lan, Anton Lögl, Meryem Benelajla et al. (+3 more)
Spin-orbit interactions of light couple polarization and spatial degrees of freedom, underpinning phenomena such as the
spin Hall effect of light. Although widely explored at interfaces and in tightly focused beams, their impact in nominally paraxial confocal systems remains largely unexamined. Here we show that a single quarter-wave plate embedded in a simple confocal geometry between polarizers can strongly reshape the transverse structure of a Gaussian beam. We observe an enhancement of the polarization extinction ratio by more than two orders of magnitude, accompanied by a transformation of the Gaussian intensity profile into a first-order Hermite-Gaussian-like two-lobe mode. The orientation of this pattern is continuously tunable via rotation of the wave plate, evidencing polarization-controlled reorientation of the transverse field. To explain these observations, we introduce a minimal extension of Jones
matrix formalism incorporating complex parameters that quantitatively reproduces the measurements. Our results uncover a previously overlooked form of
spin-orbit-mediated mode control in standard confocal optics and establish a simple route to on-demand spatial mode engineering for applications in resonant spectroscopy, optical imaging and
quantum optics.
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All authors Wenze Lan, Anton Lögl, Meryem Benelajla, Clemens Schäfermeier, Khaled Karrai, Bernhard Urbaszek
Materials Science
Importance of Configurational Charge Ordering for Machine Learning Interatomic Potentials
Martin Hoffmann Petersen, Steen Lysgaard, Arghya Bhowmik et al. (+2 more)
Machine learning interatomic potentials (MLIPs) enable large-scale atomistic simulations but remain challenged in describing mixed-valence materials where charge ordering strongly influences thermodynamic stability. Here we investigate the role of configurational charge ordering in MLIP structural optimization of the battery cathode material NaFePO4. We show that conventional MLIPs fail to reproduce the correct stability of intermediate Na concentrations because structural optimization leads to incorrect Fe2+/Fe3+ charge assignments, resulting in incorrect energy ordering and convex-hull predictions. Analysis of the Fe2+/Fe3+ charge assignment during structural optimization reveals that MLIPs are unable to capture the configurational charge ordering, leading to energy errors that make it difficult to identify the experimentally observed phase as the true ground-state structure. To address this limitation, we introduce an approach that encodes charge-state information directly into the MLIP representation by distinguishing between Fe2+ and Fe3+ environments during training. Retraining CHGNet, MACE and MACELES with this representation enables accurate structural optimization, correct identification of charge ordering, and improved agreement with density functional theory convex hulls. Our results demonstrate that incorporating configurational charge ordering into the MLIP representation is essential for modeling charge-disordered materials. Beyond recovering the correct ground state, this encoding allows a specific charge ordering to be imposed and held fixed during optimization, a capability unconstrained DFT struggles to guarantee, and we show that it generalizes across four polyanion frameworks and four transition-metal ions (Fe, Mn, Co, Ni), establishing a broadly applicable strategy for modeling mixed-valence transition-metal systems.
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All authors Martin Hoffmann Petersen, Steen Lysgaard, Arghya Bhowmik, Kedar Hippalgaonkar, Juan Maria Garcia Lastra
Materials Science · Cross-listed from physics.optics
Efficient Picosecond-Laser Lift-Off of Copper Oxide from Copper: Modelling and Experiment
Andrius Žemaitis, Paulius Gečys and Mindaugas Gedvilas
Laser-induced lift-off of functional surface layers is a key process in micro- and nano-fabrication; however, optimization criteria for maximizing the lifted-off area remain insufficiently defined. In analogy to the well-established theory of efficient
laser ablation, where the maximum ablated volume per pulse is achieved at a peak fluence of F_0^{\mathrm{opt}} = e^{2} F_{\mathrm{th}}, we develop a theoretical framework for efficient
laser lift-off driven by Gaussian beams. By analytically describing the lift-off area as a function of peak fluence, beam radius, and focus position, we demonstrate that the maximum lifted-off area is achieved at a substantially lower optimal fluence, namely F_0^{\mathrm{opt}} = e^{1} F_{\mathrm{th}}. Closed-form expressions for the optimal beam radius, maximal lift-off area, and optimal focus position are derived and validated by numerical modeling. The theory is applied to picosecond
laser lift-off of copper
oxide from copper, showing excellent agreement between experimental observations and model predictions. The results reveal fundamental differences between ablation- and lift-off-dominated material removal and provide practical guidelines for maximizing process efficiency in
laser-assisted delamination, selective coating removal, and surface functionalization.
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Materials Science · Cross-listed from cond-mat.str-el
Towards a unified first-principles-based description of VO$_2$ using DFT+DMFT with bond-centered orbitals
Peter Mlkvik, Nicola A. Spaldin and Claude Ederer
We present a combined density-functional theory and dynamical mean-field theory (DFT+DMFT) study of the full structural phase space of rutile-based vanadium dioxide (VO$_2$), including also the less studied M2 and T phases, using an unconventional bond-centered orbital basis. The use of bond-centered orbitals allows us to treat all main phases of VO$_2$, and the structural transitions between them, using one consistent approach with moderate computational cost and without pre-pattering of the structure into dimerized and undimerized V–V pairs. We obtain two distinct insulating states on the two different types of vanadium chains in the M2 phase, a singlet-
insulator on the dimerized chains and a Mott-
insulator on the zigzag-distorted chains, which, however, are strongly coupled in the M2 phase and thus the metal-
insulator transition always occurs concomitantly for both types of sites. We also demonstrate that the M2 phase corresponds to a local energy minimum in the structural phase space of VO$_2$, the stability of which, apart from the internal structural distortion, depends crucially on the unit
cell strain relative to the undistorted rutile phase. Our calculations further indicate that the
symmetry-distinct triclinic T phase corresponds electronically to either an M1 or an M2-type
insulator with an abrupt transition as a function of distortion. Finally, we disentangle the effect of the dimerization and zigzag distortions by constructing hypothetical structures that contain only one site type, finding that the zigzag distortion strongly favors emergence of the Mott-insulating state, both as function of distortion and on-site interaction.
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Materials Science
Emergence of ferromagnetic state due to structural disorder in pseudo-binary Ce(Fe0.9Co0.1)2 compound
Andrzej Musiał, Maria Pugaczowa-Michalska, Natalia Lindner et al. (+1 more)
The changes in
magnetic properties of Ce(Fe0.9Co0.1)2 compound with increasing disorder are discussed in the paper. Homogeneous
alloys are known to undergo the phase transition from
ferromagnetic to
antiferromagnetic state accompanied by the structural distortion of the cubic Laves C15 phase into the rhombohedral one. Various stimuli, like the structural disorder, or applied
magnetic field, can force the emergence of ferromagnetism at low temperatures. We initially introduced the structural disorder using rapid quenching. Further changes were made by severe plastic deformation. The presence of a
ferromagnetic phase in a low-temperature region is reported here and accompanies the deterioration of a first-order phase transition. We show, based on electronic calculations, that the structural motifs arising from various distortions of the initial MgCu2-type structure, caused by the partial replacement of Fe with Co atoms, are characterized by stable
antiferromagnetic order. This neglects simple structural distortions as the source of ferromagnetism. The presence of a strongly defective structure understood as a topologically disordered volume, reduced the fraction transformed from a
ferromagnetic to an
antiferromagnetic state. Therefore, a strong reduction of isothermal
entropy changes was also observed, as it decreased from 1.94 Jkg-1K-1 and -1.43 Jkg-1K-1 ({\Delta}{\mu}0H = 4 T) to 0.30 Jkg-1K-1 and -0.96 Jkg-1K-1 for
antiferromagnetic-
ferromagnetic and
ferromagnetic-paramagnetic transition, respectively.
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All authors Andrzej Musiał, Maria Pugaczowa-Michalska, Natalia Lindner, Zbigniew Śniadecki
Materials Science
Coherent Ultrafast Excitonic Oscillations in Monolayer WS$_2$
Jorge Cervantes-Villanueva, Alberto García-Cristóbal, Davide Sangalli et al. (+1 more)
Monolayer transition metal dichalcogenides are a suitable platform for studying excitonic coherence in the light-matter coupling regime. We present an ab initio time-dependent GW-Bethe-Salpeter equation (GW-BSE) investigation of coherent excitonic dynamics in monolayer WS$_2$. By solving the coherent coupling between the A, A$^{*}$, and B
excitons under linearly polarized pump fields, we identify the microscopic origin of the resulting oscillatory dynamics and rationalize it using an effective theoretical model. Our results provide the interpretation of recently reported coherent excitonic phenomena in monolayer WS$_2$ (Nano Lett. 24, 8117 (2024)). Building on this first-principles time-resolved framework, we propose a tailored pump-probe scheme that enables the controlled generation and regeneration of coherent oscillations between excitonic states. These findings establish a predictive route for controlling excitonic coherence in two-dimensional materials, with direct relevance for ultrafast optoelectronic switches and solid-state
quantum logic devices.
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All authors Jorge Cervantes-Villanueva, Alberto García-Cristóbal, Davide Sangalli, Alejandro Molina-Sánchez
Materials Science
Strain-released epitaxy of GaN enabled by compliant single-crystalline metal foils
Yaqing Ma, Junwei Cao, Huaze Zhu et al. (+16 more)
Heteroepitaxy conventionally relies on rigid crystalline substrates, implicitly assuming that
lattice and thermal mismatch must be accommodated within the epitaxial layer, leading to residual strain and defects that worsen with increasing substrate size. Here we demonstrate a substrate-mediated strain-partitioning regime in which
lattice and thermal mismatch are preferentially partitioned into the substrate rather than stored in the epitaxial layer. We report the epitaxial growth of single-crystalline GaN on mechanically compliant yet crystallographically ordered single-crystalline copper foils. Atomic-resolution microscopy,
geometric phase analysis and density functional theory reveal that mismatch-induced stress is primarily screened by elastic deformation of the Cu
lattice, accompanied by localized interfacial slip confined to a few atomic layers, leaving the AlN and GaN epilayers nearly strain-free despite large nominal mismatch. Leveraging this strain-released epitaxial platform, we further demonstrate dense GaN micro-light-emitting diode arrays that benefit from efficient vertical electrical conduction and thermal dissipation enabled by the metallic substrate. By establishing compliant single-
crystal metal foils as a new substrate class, this work identifies mechanical contrast as an underexplored governing parameter in heteroepitaxial design, with implications extending beyond GaN.
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All authors Yaqing Ma, Junwei Cao, Huaze Zhu, Yijian Song, Huicong Chen, Menglin He, Jun Yang, Ping Jiang, Tong Jiang, Han Chen, Xiang Xu, Yuqiao Zheng, Hao Wang, Muhong Wu, Yu Zou, Xiaochuan Chen, Tongbo Wei, Kaihui Liu, Wei Kong
Materials Science · Cross-listed from physics.chem-ph
Microscopic Structure and Dynamics of Interfacial Water at Fluorinated vs Nonfluorinated Surfaces – Insights from Ab-Initio Simulations and IR Spectroscopy
Maximilian R. Becker, Ruben Cruz, Kenichi Ataka et al. (+2 more)
Per- and polyfluoroalkyl substances are a class of synthetic chemical compounds widely used as coatings to lower surface energies. Yet the microscopic mechanisms of their weak interaction with water and organic compounds remain poorly understood. Here, we perform large-scale density-functional-theory molecular dynamics simulations to investigate water at self-assembled monolayers (SAMs) of fluorinated and non-fluorinated hydrocarbons. We analyze the interfacial water structure and compare it to the prototypical hydrophobic air-water interface. The interfacial water structure at both SAMs closely resembles that at the air-water interface, featuring a distinct depletion layer and a two-dimensional hydrogen-bond network parallel to the surface. Computed anisotropic infrared spectra reproduce key experimental signatures observed in surface-enhanced infrared absorption spectroscopy (SEIRAS), including the presence of free OH vibrations directly probing the local surface-water interactions. Notably, while the free OH stretch at the hydrocarbon SAM-water interface exhibits a red shift relative to the air-water interface, indicative of weak binding, the fluorinated SAM-water interface displays a weakly blue-shifted free OH mode, in agreement with experiment. This frequency behavior defies common interpretations based on the vibrational Stark effect. Further, we show that the reorientation dynamics of water molecules are significantly slower near the fluorinated surface, which we correlate with spectral line shapes, an effect rather expected at hydrophilic surfaces. This indicates that fluorinated SAMs, despite being macroscopically more hydrophobic than their unfluorinated counterparts, exhibit spectroscopic characteristics that neither qualify it as hydrophobic nor hydrophilic.
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All authors Maximilian R. Becker, Ruben Cruz, Kenichi Ataka, Joachim Heberle, Roland R. Netz
Materials Science
Hunting Structural Demons in Digital Reticular Chemistry: Lessons from Metal-Organic Frameworks
Yongchul G. Chung and Myoung Soo Lah
Digital reticular chemistry relies on accurate
crystal structures to power computational screening, data-driven discovery, and structure-property analysis, yet recent studies reveal that more than half of the top-performing candidates in major computational screening campaigns are chemically invalid. In experimental MOF databases, structural errors arise when disordered or incomplete structural models are incorrectly converted into fully specified simulation inputs. In hypothetical MOF database, structures are complete by construction but may encode chemically implausible oxidation states, coordination environments, or charge distributions. We term these erroneous structural models "structural demons." This mini-review asks three questions: where these errors enter, how we find them, and how we prevent them. On the prevention side, the key steps are keeping diffraction data and synthesis details together from the start, using consistent curation when structures enter a database, and filtering
topology choices before structure generation. Connecting these steps can keep many bad structures out of downstream databases and reduce the need to fix them later.
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Materials Science
Ultrafast Formation and Annihilation of Strongly Bound, Anisotropic Excitons
Lawson T. Lloyd, Tommaso Pincelli, Mohamed Amine Wahada et al. (+12 more)
Van der Waals (vdW) layered materials with long-range
magnetic order have the potential to enable novel optoelectronic and spintronic applications. Among these, CrSBr is an air-stable, direct band gap
semiconductor that hosts interlayer
antiferromagnetic order, a highly anisotropic electronic structure, and strongly bound
excitons. In particular,
excitons in CrSBr have been shown to inherit the quasi-one-dimensional nature of the material and also couple to the underlying spinorder. However, mechanisms of
exciton formation, dissociation, and interaction with free carriers remain largely unexplored, despite being crucial for spintronic and optoelectronic applications. Here, we employ time- and angle-resolved photoemission spectroscopy to map the electronic structure and excited state dynamics in CrSBr. We directly resolve an exceptionally large
exciton binding energy (~800 meV) and a highly anisotropic momentum space distribution of the
exciton, revealing its quasi-1D real-space character. We observe an excitation-density-dependent interconversion between bound
excitons and quasi-free carriers on sub- to few-picosecond timescales, indicating that many-body effects govern the excited-state dynamics and optical properties during the initial stages of relaxation. Our work highlights the strongly bound, anisotropic character of
excitons in CrSBr, as well as the microscopic interactions steering relaxation pathways after photoexcitation in elevated density regimes relevant for future device applications.
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All authors Lawson T. Lloyd, Tommaso Pincelli, Mohamed Amine Wahada, Alessandro De Vita, Ferdinand Menzel, Kseniia Mosina, Túlio H. L. G. Castro, Alexander Neef, Andreas V. Stier, Nathan P. Wilson, Zdeněk Sofer, Jonathan J. Finley, Martin Wolf, Laurenz Rettig, Ralph Ernstorfer
Materials Science
Emergence of multiple quasi-ferromagnetic magnon modes induced by strong magnetoelastic coupling in $TmFeO_3$ single crystal
Sourabh Manna, Felix Fuhrmann, Sergio Rodríguez Fernández et al. (+8 more)
We investigate the magnetization dynamics of $TmFeO_3$ single
crystals across the
spin-reorientation phase transition using broadband microwave absorption spectroscopy up to 87.5 GHz. Temperature- and
magnetic-field-dependent
antiferromagnetic resonance measurements reveal the characteristic softening of the quasi-
ferromagnetic (q-FM) resonance mode at the $\Gamma_2\rightarrow\Gamma_{24}$ and $\Gamma_{24}\rightarrow\Gamma_4$ transition points. The finite
magnon gap observed at the transition points reflects the strong magnetoelastic coupling. In addition to the uniform q-FM mode, multiple
magnon modes appear in the intermediate $\Gamma_{24}$ phase, separated by approximately 0.5–2 GHz and exhibiting similar field and temperature dependence. These additional modes are attributed to nonuniform
spin-wave excitations arising from the periodic
magnetic domain structure present in the intermediate phase and their hybridization with acoustic
phonons mediated by strong magnetoelastic coupling. Our results demonstrate that the
spin-reorientation transition in $TmFeO_3$ provides a natural platform for generating multiple hybridized
magnon modes, offering new opportunities for tunable magnonic excitations in rare-earth orthoferrites.
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All authors Sourabh Manna, Felix Fuhrmann, Sergio Rodríguez Fernández, Xiaoxuan Ma, Haiyang Chen, Luca M. Carrella, Edgar Galindez-Ruales, Gerhard Jakob, Olena Gomonay, Shixun Cao, Mathias Kläui
Materials Science
Crystalline b-Ga2O3 thin films deposited via reactive magnetron sputtering of a liquid Ga target
Petr Novak, Jan Koloros, Stanislav Haviar et al. (+2 more)
Ga2O3 thin films were deposited by reactive magnetron sputtering from a
liquid gallium target. The influence of deposition temperature, substrate type, and discharge parameters on the structural and electrical properties was systematically investigated. Films deposited on silicon and quartz glass exhibit polycrystalline growth, whereas sapphire substrates enable highly oriented growth of b-Ga2O3 with a preferred (-201) orientation. The lowest electrical resistivity of 7x10_3 ohm.cm was obtained for films deposited on sapphire at a temperature of 585C. At this temperature, the films reach sufficient crystalline quality to enable efficient charge carrier transport and thus the manifestation of unintentional conductivity. At higher deposition temperatures, pronounced crystallization occurs; however, it is not homogeneous throughout the entire film thickness, which leads to a deterioration of the electrical properties. These results demonstrate that, despite intrinsic limitations, reactive magnetron sputtering can be successfully employed for the preparation of Ga2O3 thin films with optimized electrical properties when appropriate substrates and deposition temperatures are selected.
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All authors Petr Novak, Jan Koloros, Stanislav Haviar, Jiri Rezek, Pavel Baroch
Materials Science · Cross-listed from cond-mat.mes-hall
Sign control of photocurrents by spin-group-symmetry breaking in altermagnetic insulators
Gastón Blatter, Xiao Zhang, Jeroen van den Brink et al. (+2 more)
Controlling physical responses through
symmetry breaking is a central paradigm in
quantum materials, enabling novel functionalities. Here we determine the effects of
spin-group-
symmetry breaking on nonlinear optical responses of collinear altermagnetic
insulators. Using shear strain as an example, we show that the direction of
symmetry-breaking induced components of charge and
spin photocurrents are locked to the sign of the strain. In the absence of
spin-orbit coupling, this effect is intuitively captured by the
spin-gap asymmetry–an imbalance between
spin-up and
spin-down direct band gaps which couples trilinearly with the Néel order and the strain. We demonstrate this mechanism with density functional theory calculations on the recently proposed altermagnet CuWP$_2$S$_6$. Having
symmetry-guided control of both charge and
spin photocurrents allows, vice versa, to reveal and investigate altermagnetism in insulating materials by exploration of their optical responses.
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All authors Gastón Blatter, Xiao Zhang, Jeroen van den Brink, Mengli Hu, Shu Zhang
Materials Science
Probing deuterium-induced magnetic phase transitions in TbCo alloys with in-situ polarized neutron reflectometry
Robbie G. Hunt, Gunnar K. Pálsson, Matías P. Grassi et al. (+3 more)
Hydrogen-based magneto-ionics is a promising approach for rapid magnetoelectric control of spintronic devices. Most investigations so far into the magneto-ionic manipulation of rare-earth transition-metal
alloys have used electrochemical methods for evaluating the magnetoelectric properties, but this technique makes it difficult to discriminate between the effects of competing ionic species. In this work, we use atmospheric loading to evaluate the effect of an isotope of hydrogen, deuterium, on the
magnetic properties of TbCo films using in-situ polarized
neutron reflectometry. With this approach, we are able to simultaneously measure the magnetization, thickness expansion and deuterium concentration of TbCo films. We quantitatively observe the deuterium concentrations at which the paramagnetic phase transition occurs for a Tb-rich film, and the weakening of out-of-plane
magnetic anisotropy for a Co-rich film. For the Tb-rich film the expansion of the film thickness is the primary mechanism identified for the paramagnetic phase transition, while for the Co-rich film no thickness expansion is observed. We also find that an oxidized interface is insensitive to deuterium loading, but remains exchange coupled to the rest of the film and can be indirectly manipulated by loading of deuterium in the
alloy. We expect these results to be directly translatable to that of hydrogen.
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All authors Robbie G. Hunt, Gunnar K. Pálsson, Matías P. Grassi, Victoria Kabanova, Alexey Vorobiev, Gabriella Andersson
Materials Science
Photoinduced strain and polarization switching in barium titanate in the far-infrared spectral range
Maarten Kwaaitaal, Daniel Lourens, Carl S. Davies et al. (+1 more)
Short mid-infrared
laser pulses efficiently facilitate ultrafast manipulation of ferroic order parameters, including full reversal of magnetization or ferroelectric polarization, with the invoked mechanisms relating to the properties of polar
phonons in ionic
crystals. Much less is known, however, about the behaviour of such order parameters in response to an excitation in the far-infrared range, where
phonons are more collective and less polar. Here we investigate transient crystallographic strains and polarization switching in ferroelectric barium titanate (BaTiO3) driven by an excitation in the frequency range of 5-8 THz, or wavelengths of 35-60 um. We find that switching persists in a large part of this range, but is governed primarily by optical absorption rather than by the longitudinal optical
phonons or epsilon-near-zero conditions that dominate in the mid-infrared regime.
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All authors Maarten Kwaaitaal, Daniel Lourens, Carl S. Davies, Andrei Kirilyuk
Materials Science
The Unreconstructed {\alpha}-Al$_{2}$O$_{3}$(0001) Surface is Inhomogeneous and Rough
Johanna I. Hütner-Reisch, Andrea Conti, David Kugler et al. (+4 more)
Alumina (Al$_{2}$O$_{3}$) is a key material for thin-film growth and heterogeneous catalysis, where the atomic surface structure critically impacts performance. Using noncontact atomic force microscopy (nc-AFM) combined with density functional theory (DFT) calculations, we challenge the common assumption that the unreconstructed $\alpha$-Al$_{2}$O$_{3}$(0001) surface is atomically flat and uniformly Al-terminated. This widely accepted bulk termination satisfies polarity compensation requirements but results in highly undercoordinated surface Al cations at the surface. Despite substantial inward relaxation of these Al cations, we find that the (1 ${\times}$ 1) surface remains inherently metastable, relative to the thermodynamically stable $(\sqrt{31} \times \sqrt{31})R\pm9\deg$ surface reconstruction that forms at high temperatures above 1000 {\deg}C. Nc-AFM imaging of the unreconstructed surface reveals a rough and disordered morphology, with only nanometer-scale regions exhibiting the ordered Al-terminated (1 $\times$ 1) structure. Our results show that the unreconstructed Al$_{2}$O$_{3}$(0001) surface is intrinsically inhomogeneous, reconciling conflicting experimental observations and challenging the validity of commonly used atomistic models.
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All authors Johanna I. Hütner-Reisch, Andrea Conti, David Kugler, Florian Mittendorfer, Michael Schmid, Ulrike Diebold, Jan Balajka
Materials Science
A Sc2C2@C88 cluster based ultra-compact multi-level probabilistic bit for matrix multiplication
Haoran Qi, Guohao Xi, Yuan-Biao Zhou et al. (+19 more)
Information units are progressively approaching the fundamental physical limits of the integration density, including in terms of extremely small sizes, multistates and probabilistic traversal. However, simultaneously encompassing all of these characteristics in a unit remains elusive. Here, via real-time in situ electrical monitoring, we clearly observed
stochastic alterations of multiple conductance states in Sc2C2@C88. The true random bit sequence generated exhibited an autocorrelation function whose confidence interval fell within \pm 0.02, demonstrating high-quality randomness. The alterations of multiple conductance states are controllable, that is, whose probability distributions could traverse from 0 to 1, enabling us to factorize 551 into its
prime factors. Furthermore, we proposed a
matrix-chain multiplication scheme and experimentally verified the multiplication of two 4 \times 4 state-transition
matrices with a small maximum error < 0.05. Combined with theoretical calculations, the
stochastic but controllable multistates are probably attributed to the rich energy landscape, which could be stepwise changed by the electric field. Our findings reveal extremely small multi-level probabilistic bit for
matrix multiplication, which pave the way for ultracompact intelligent electronic devices.
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All authors Haoran Qi, Guohao Xi, Yuan-Biao Zhou, Xinrong Liu, Yifu Mao, Jian Yang, Jun Chen, Kuojuei Hu, Weiwei Gao, Shuai Zhang, Xiaoqin Gao, Jianguo Wan, Da-Wei Zhou, Junhong An, Xuefeng Wang, De-Chuan Zhan, Minhao Zhang, Cong Wang, Wei ji, Yuan-Zhi Tan, Su-Yuan Xie, Fengqi Song