Materials Science
Relativistic Spin-momentum locking in altermagnets
Carmine Autieri and Amar Fakhredine
Spin-momentum locking in altermagnets has been deeply explored in the non-relativistic limit. Including
spin-orbit coupling, altermagnets exhibit antisymmetric exchange interactions, leading to
spin cantings. Therefore, the
spin-momentum locking differs among the three
spin components Sx, Sy, and Sz, forming the relativistic
spin-momentum locking. We consider orthorhombic YVO3 and hexagonal MnTe. For YVO3, the relativistic locking comprises s-, dxy -, and dxz-wave. In MnTe, the dominant component Sy of MnTe inherits the polarized charge distribution and the non-relativistic
spin-momentum locking bulk g-wave, but the breaking of the C6z rotational
symmetry by the Neel vector lowers the
symmetry from g-wave to d-wave. The relativistic
spin-momentum locking for MnTe is composed of dxz-, dyz- and s-wave. Despite small magnitudes in real space, the canted
spin components contribute significant spectral weight in k-space, impacting k-space properties such as the
spin-
Hall conductivity.
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Materials Science
Thickness dependent rare earth segregation in magnetron deposited NdCo$_{4.6}$ thin films studied by Xray reflectivity and Hard Xray photoemission
J. Díaz, J. Rodríguez-Fernández and J. Rubio-Zuazo
Magnetic anisotropy in disordered rare-earth-transition metals (RE-TM) compounds arises from RE atoms occupying asymmetric environments within the TM
lattice. However, the underlying mechanism that promotes such environments remains not fully understood. In this study, we investigate amorphous NdCo$_{4.6}$ thin films deposited by magnetron sputtering, where the
magnetic anisotropy evolves with thickness from in-plane to out-of-plane orientation above 40 nm. X-ray reflectivity measurements revealed the progressive formation of an additional layer between the 3 nm Si capping layer and the NdCo film with increasing film thickness. To probe the composition and distribution of Co and Nd near the surface, Hard X-ray Photoemission Spectroscopy (HAXPES) was performed on films ranging from 5 nm to 65 nm in thickness using incident
photon energies of 7, 10, and 13 keV. These correspond to inelastic electron mean free paths of 7.2-12.3 nm in cobalt. The cobalt atomic concentration, deduced from HAXPES at the Nd 3d and Co 2p excitations, was consistently below the nominal value and varied with both thickness and
photon energy. This indicates segregation of RE atoms at the film surface, which becomes more pronounced with increasing thickness. Background analysis of the Co 2p and Nd 3d peaks supports this conclusion. The thickness of the Nd segregated layer is estimated in 2-3 nm. These findings demonstrate that incorporating neodymium into the cobalt
lattice incurs an energy cost which is associated with strain due to the volume mismatch between the two elements. Reducing this strain energy promotes anisotropic atomic environments for Nd, thereby explaining the emergence of perpendicular anisotropy and its dependence on film thickness in these RE-TM compounds.
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Materials Science
Stress in chromium thin films deposited by DC magnetron sputtering on grounded cupper and stainless-steel substrate holders
M.D. Medina, H.I. Giron, K. Paucar et al. (+2 more)
Chromium thin films deposited on silicon substrates by DC magnetron sputtering were systematically investigated as a function of film thickness, using a DC power of 50 W and a post-deposition annealing temperature of 200 C. Two types of grounded substrate holders, copper and stainless steel, were employed to assess substrate-dependent effects. The intrinsic stress, determined by the wafer
curvature method, decreases with increasing film thickness but increases with the annealing temperature. It is observed that for thinner as-deposited chromium films, the stress showed a pronounced irreversible increase when measured immediately after deposition and after several days of aging. Films deposited on copper holders consistently exhibited higher stress values than those grown on stainless steel holders. These observations suggest that the intrinsic stress in as-deposited films is linked to the growth mechanism, while the stress increase after annealing may be related to thermally active
diffusion and structural relaxation. The higher stress in films grown on copper substrate holder can likely be associated with enhanced ion bombardment due to the higher electrical conductivity of copper.
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All authors M.D. Medina, H.I. Giron, K. Paucar, A. Talledo, B.R. Pujada
Materials Science · Cross-listed from cond-mat.mes-hall
Metallic Electro-Optic Effect in Twisted Double-Bilayer Graphene
D. J. P. de Sousa, N. Roldan-Levchenko, C. O. Ascencio et al. (+3 more)
Recent theoretical advances have highlighted the role of Bloch state intrinsic properties in enabling unconventional electro-optic (EO) phenomena in bulk metals, offering novel strategies for dynamic optical control in
quantum materials. Here, we identify an alternative EO mechanism in bulk metallic systems that arises from the interplay between Berry
curvature and the orbital
magnetic moment of Bloch electrons. Focusing on twisted double-
bilayer graphene (TDBG), we show that the enhanced intrinsic properties of moiré Bloch bands give rise to a sizable linear magnetoelectric EO response, a first-order, electric-field-induced non-Hermitian correction to the gyrotropic
magnetic susceptibility. This mechanism dominates in $C_{3z}$-symmetric TDBG, where EO contributions originating from the Berry
curvature dipole (BCD) are
symmetry-forbidden. Our calculations reveal
giant, gate-tunable linear and circular dichroism in the terahertz regime, establishing a robust and tunable platform for ultrafast EO modulation in two-dimensional materials beyond the BCD paradigm.
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All authors D. J. P. de Sousa, N. Roldan-Levchenko, C. O. Ascencio, J. D. S. Forte, Paul M. Haney, Tony Low
Materials Science
Surface Binding Energies for Amorphous Plagioclase Feldspar Calculated using Molecular Dynamics
Amanda Ricketts, Benjamin A. Clouter-Gergen, Anastasis Georgiou et al. (+2 more)
Despite the well-established presence of amorphous compounds on planetary bodies such as the Moon and Mercury due to space weathering, the direct effect of atomic arrangement on the surface binding energies (SBEs) of elements on these bodies remains largely unexplored. Accurate SBE values are essential for reliably predicting sputtering yields and the energy distribution of ejecta. Here, we use molecular dynamics simulations to quantify SBEs for the different elements sputtered from amorphous atomic arrangements of the plagioclase feldspar end members, albite and anorthite, and compare to their crystalline counterparts. Results show that while the mean elemental SBEs from amorphous surfaces are not significantly different from their crystalline counterparts, the random orientation in amorphous structures gives rise to a spectrum of bonding configurations, resulting in a distribution of SBEs with a wider range. This contrasts with the clearly discretized set of SBE values associated with the ordered atomic structure of crystalline surfaces. We then consider sputtering by H, He, and a
solar wind combination of 96% H and 4% He. For each of these cases, we demonstrate that there is minimal difference (<10% for albite and <20% for anorthite) between the sputtering yields of amorphous and crystalline surfaces. We attribute these results to the presence of the same elemental bonds across different atomic arrangements, which leads to similar mean SBEs and, consequently, comparable sputtering yields.
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All authors Amanda Ricketts, Benjamin A. Clouter-Gergen, Anastasis Georgiou, Deborah Berhanu, Liam S. Morrissey
Materials Science · Cross-listed from cond-mat.mes-hall
Two topological phases in exchange alternating spin-1 nanographene chains
João C. G. Henriques, Yelko del Castillo, Ricardo Segundo et al. (+2 more)
Magnetic nanographenes are emerging as versatile building blocks for artificial
spin lattices, enabling the exploration of flagship one-dimensional
quantum-magnetism models with unprecedented control. The
spin-1 Heisenberg model, including bilinear and biquadratic exchange, was first realized using [3]-triangulenes, revealing the Haldane phase. More recently, Clar's goblets enabled the
spin-1/2 Heisenberg model with exchange alternation, uncovering additional topological phases. Here we show that
spin-1 nanographenes can be used to explore bond-alternating chains both in the Haldane phase and beyond it, in a dimerized phase with emergent edge
spin-1. We use density
matrix renormalization group (DMRG) to analyze how biquadratic exchange, which is known to be large in
spin-1 nanographenes, determines the phase transition boundary. Combining multiconfigurational and first-principles calculations, we identify two realistic candidates to realize these two different phases: the recently synthesized extended Clar's goblet and a passivated [4]-triangulene. We demonstrate how to distinguish these phases experimentally using inelastic electron tunneling spectroscopy, paving the way for their observation.
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All authors João C. G. Henriques, Yelko del Castillo, Ricardo Segundo, Jan Phillips, Joaquín Fernández-Rossier
Materials Science · Cross-listed from physics.flu-dyn
High-Speed Imagery Analysis of Droplet Impact on Van der Waals and Non-Van der Waals Soft-Textured Oil-Infused Surfaces
Shubham S. Ganar, Deepak J. and Arindam Das
This study investigates the impact of surface functionalization, oil coating, and oil absorption on droplet impact behavior on textured polydimethylsiloxane(PDMS) substrates. The textured surfaces were fabricated with square micro-posts having spacings of 5 and 20 microns. The PDMS samples were functionalized with octadecyltrichlorosilane (OTS) to improve water repellency. Following, the surfaces were either coated with or allowed to absorb two different lubricants, silicone oil (SO-5cSt) and hexadecane. We performed detailed wetting measurements on both untreated and OTS-functionalized substrates. These measurements provided useful insights into how water and lubricants were retained and distributed under static conditions. High-speed imaging was used to capture droplet impact across a range of Weber numbers. On SO-5cSt-absorbed substrates, droplets consistently showed complete rebound at all Weber numbers, regardless of post spacing. This robust rebound was attributed to the oil's ability to fill the gaps between the posts through capillary action, while also forming a stable lubricating layer above the texture. This thin oil film reduced friction between the droplet and the surface, enabling the droplet to retain sufficient energy for complete rebound. In contrast, hexadecane-absorbed substrates displayed different dynamics. At low Weber numbers, only partial rebound was observed, while at intermediate values, droplets rebounded completely. However, droplets no longer rebounded at higher Weber numbers and remained deposited. Repeated droplet impacts further demonstrated that hexadecane-infused surfaces gradually lost oil from the textured gaps, resulting in a decline in rebound performance over time. This effect was not observed with SO-5cSt, underscoring the importance of lubricant affinity and stability.
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Materials Science
DeFecT-FF: a machine learning force field framework for high throughput defect modeling in CdTe-based solar cells
Md Habibur Rahman, Maitreyo Biswas and Arun Mannodi-Kanakkithodi
We developed a framework for predicting the energies and ground state configurations of native point defects, extrinsic dopants and
impurities, and defect complexes across zinc blende-phase Cd/Zn-Te/Se/S compounds, important for CdTe-based
solar cells. This framework, named DeFecT-FF, is powered by high-throughput density functional theory (DFT) computations and
crystal graph-based machine learning force field (MLFF) models trained on the DFT data. The Cd/Zn-Te/Se/S chemical space is chosen because alloying at Cd or Te sites is a promising avenue to tailor the electronic and defect properties of the CdTe absorber layer to potentially improve
solar cell performance. The sheer number of defect configurations achievable when considering all possible singular defects and their combinations,
symmetry-breaking operations, and defect charge states, as well as the expense of running large supercell calculations, makes this an ideal problem for developing accurate and widely-applicable force field models. Here, we introduce our
dataset of structures and energies from HSE06 geometry optimization, including bulk and alloyed supercells with and without defects. Data were gradually expanded using active learning and accurate MLFF models were trained to predict energies and atomic forces across different charge states. Via accelerated prediction and screening, we identified many new low energy defect configurations and obtained high-fidelity defect formation energy diagrams using HSE06 calculations with
spin-orbit coupling. The DeFecT-FF framework has been released publicly as an online tool on the nanoHUB platform, allowing users to upload any crystallographic information file, generate defects of interest, and compute defect formation energies as a function of
Fermi level and chemical potential conditions, thus bypassing expensive DFT calculations.
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Materials Science
dynsight: an Open Python Platform for Simulation and Experimental Trajectory Data Analysis
Simone Martino, Matteo Becchi, Andrew Tarzia et al. (+2 more)
The study of complex many-body systems via analysis of the trajectories of the units that dynamically move and interact within them is a non-trivial task. The workflow for extracting meaningful information from the raw trajectory data is often composed of a series of interconnected steps, such as, (i) identifying and tracking the constitutive objects/particles, resolving their trajectories (e.g., in experimental cases, where these are not automatically available as in typical molecular simulations), (ii) translating the trajectories into data that are easier to handle/analyze by using well suited descriptors, and (iii) extracting meaningful information from such data. Each of these different tasks often requires non-negligible programming skills, the use of various types of representations or methods, and the availability/development of an interface between them. Despite the considerable potential that new tools contributed to each of these individual steps, their integration under a common framework would decrease the barrier to usage (especially by diverse communities of users), avoid fragmentation, and ultimately facilitate the development of new approaches in data analysis. To this end, here we introduce dynsight, an open Python platform that streamlines the extraction and analysis of time-series data from simulation- or experimentally-resolved trajectories. dynsight simplifies workflows, enhances accessibility, and facilitates time-series and trajectories data analysis offering a useful tool to unraveling the dynamic complexity of a variety of systems (or signals) across different scales. dynsight is open source (https://github.com/GMPavanLab/dynsight) and can be easily installed using pip.
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All authors Simone Martino, Matteo Becchi, Andrew Tarzia, Daniele Rapetti, Giovanni M. Pavan
Materials Science
Thermoelectric transport and the role of different scattering processes in the half-Heusler NbFeSb
Bhawna Sahni, Yao Zhao, Zhen Li et al. (+3 more)
We perform an ab initio computational investigation of the electronic and thermoelectric transport properties of one of the best performance half-Heusler (HH)
alloys, NbFeSb. We use Boltzmann Transport equation while taking into account the full energy/momentum/band dependence of all relevant electronic scattering rates, i.e. with acoustic
phonons, non-polar optical
phonons (intra- and inter-valley), polar optical
phonons (POP), and ionized
impurity scattering (IIS). We use a highly efficient and accurate computational approach, where the scattering rates are derived using only a few ab initio extracted
matrix elements, while we account fully for intra-/inter valley/band transitions, screening from both electrons and holes, and bipolar transport effects. Our computed thermoelectric power-factor (PF) values show good agreement with experiments across densities and temperatures, while they indicate the upper limit of PF performance for this material. We show that the polar optical
phonon and ionized
impurity scattering (importantly including screening), influence significantly the transport properties, whereas the computationally expensive non-polar
phonon scattering part (acoustic and non-polar optical) is somewhat weaker, especially for electrons, and at lower to intermediate temperatures. This insight is relevant in the study of half-Heusler and other polar thermoelectric materials in general. Although we use NbFeSb as an example, the method we employ is material agnostic and can be broadly applied efficiently for electronic and thermoelectric materials in general, with more than 10x reduction in computational cost compared to fully ab initio methods, while retaining ab-initio accuracy.
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All authors Bhawna Sahni, Yao Zhao, Zhen Li, Rajeev Dutt, Patrizio Graziosi, Neophytos Neophytou
Materials Science · Cross-listed from physics.ins-det
Filling the Gap: Atom Probe Tomography of Porous Structures Enabled by Site Specific SEMGlu Curing
Lukas Worch, James O. Douglas, Kavin Arunasalam et al. (+3 more)
Porous microstructures, while central to many functional materials, remain difficult to characterize quantitatively by atom probe
tomography (APT). Although several strategies have been proposed over the past decade, most remain constrained by significant practical or technical limitations. Here, we introduce an in situ pore filling approach that integrates seamlessly into conventional specimen preparation workflows. The method employs a
vacuum compatible resin that is rapidly cured by the electron beam during standard ion beam based preparation, eliminating the need for additional instrumentation or extensive sample handling. We demonstrate the effectiveness of this approach using a porous SnSe + MXene electrode, a material system otherwise difficult to analyze via APT characterisation. This method offers a robust, accessible solution for extending APT analysis to porous materials
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All authors Lukas Worch, James O. Douglas, Kavin Arunasalam, Baptiste Gault, Valeria Nicolosi, Michele Shelly Conroy
Materials Science · Cross-listed from cond-mat.str-el
Quantum fluctuations determine the spin-flop transition in hematite
Tobias Dannegger, Imre Hagymási, Levente Rózsa et al. (+1 more)
Magnetic phase transitions between ordered phases are often understood on the basis of semi-classical
spin models. Deviations from the classical description due to the
quantum nature of the atomic
spins as well as
quantum fluctuations are usually treated as negligible if long-range order is preserved, and are rarely quantified for actual materials. Here, we demonstrate that a fully
quantum-mechanical framework is required for a quantitatively correct description of the
spin-flop transition in the insulating altermagnet hematite between the collinear
antiferromagnetic and the weakly
ferromagnetic spin-flop phase at low temperature. By applying both exact diagonalization and density-
matrix renormalization group theory to the
quantum Heisenberg
Hamiltonian, we show how a
quantum-mechanical treatment of an ab initio parametrized
spin model can significantly improve the predicted low-temperature
spin-flop field over a classical description when compared to measurements. Our results imply that
quantum fluctuations have a measurable influence on selecting the ground state of a system out of competing ordered
magnetic phases at low temperature.
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All authors Tobias Dannegger, Imre Hagymási, Levente Rózsa, Ulrich Nowak
Materials Science
fair_data.py: implementing FAIR data compliance in Tribchem
Lucrezia Berghenti, Elisa Damiani, Margherita Marsili et al. (+1 more)
The increasing complexity and volume of data generated by high-throughput computational materials science require robust tools to ensure their accessibility, reproducibility, and reuse. In particular, integrating the FAIR Guiding Principles (Findable, Accessible, Interoperable, and Reusable) into computational workflows is essential to enable open science practices. TribChem is an open source Python software developed for the automated simulation of solid-solid interfaces using density functional theory (DFT). While TribChem already incorporates several FAIR-aligned features, we present here a dedicated FAIR utility designed to transform TribChem results into FAIR-compliant
datasets. This utility comprises two tools: fair_data.py, which automatically generates standardized machine- and human-readable outputs from the TribChem database, and retrieve_data.py, which facilitates efficient data extraction through a keyword-based interface. In this paper we show the capabilities of the fair utility with examples for bulk, surface, and interface systems. The implementation allows seamless integration with public repositories such as Zenodo, paving the way for reproducible research and fostering data-driven materials discovery.
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All authors Lucrezia Berghenti, Elisa Damiani, Margherita Marsili, Maria Clelia Righi
Materials Science
Elastic modeling and total energy calculations of the structural characteristics of "free-standing",periodic, pseudomorphic GaN/AlN superlattices
Th. Karakostas, Ph. Komninou and V. Pontikis
The strain states of the components of pseudomorphic superlattices can be accurately modeled analytically through the application of linear elasticity. In this particular case of GaN/AlN 'free-standing' superlattices, the predictions derived from elastic modeling have been compared with total energy calculations of several systems made of components with varying thicknesses. We demonstrate that the elastic predictions for the
lattice constants of the components align with the values obtained from their total energy counterparts, within the limits of computational errors and uncertainties. Furthermore, a phenomenological analysis of the elastic energy stored in the superlattices facilitates the evaluation of the excess energies associated with the interfaces present in these systems. The results mentioned above are briefly contrasted with findings reported in previous literature.
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Materials Science
User-defined Electrostatic Potentials in DFT Supercell Calculations: Implementation and Application to Electrified Interfaces
Samuel Mattoso, Jing Yang, Florian Deißenbeck et al. (+5 more)
Introducing electric fields into density functional theory (DFT) calculations is essential for understanding electrochemical processes, interfacial phenomena, and the behavior of materials under applied bias. However, applying user-defined electrostatic potentials in DFT is nontrivial and often requires direct modification to the specific DFT code. In this work, we present an implementation for supercell DFT calculations under arbitrary electric fields and discuss the required corrections to the energies and forces. The implementation is realized through the recently released VASP-Python interface, enabling the application of user-defined fields directly within the standard VASP software and providing great flexibility and control. We demonstrate the application of this approach with diverse case studies, including molecular adsorption on electrified surfaces, field ion microscopy, electrochemical solid-water interfaces, and implicit solvent models.
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All authors Samuel Mattoso, Jing Yang, Florian Deißenbeck, Ahmed Abdelkawy, Christoph Freysoldt, Stefan Wipperman, Mira Todorova, Jörg Neugebauer
Materials Science
General Strategy for Large Nernst Coefficient
Junya Endo, Hiroyasu Matsuura, Manfred Sigrist et al. (+1 more)
We propose a general strategy for enhancing the anomalous Nernst coefficient based on the Sommerfeld-Bethe relation. This approach provides a systematic framework for understanding the small anomalous Nernst coefficients typically observed in ferromagnets and identifies conditions under which substantial enhancements can be realized. We further introduce simplified models that exhibit large Nernst coefficients as offering illustrative examples.
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All authors Junya Endo, Hiroyasu Matsuura, Manfred Sigrist, Masao Ogata
Materials Science · Cross-listed from physics.chem-ph
Analytic $G_0W_0$ gradients based on a double-similarity transformation equation-of-motion coupled-cluster treatment
Marios-Petros Kitsaras, Johannes Tölle and Pierre-François Loos
The accurate prediction of ionization potentials (IPs) is central to understanding molecular reactivity, redox behavior, and spectroscopic properties. While vertical IPs can be accessed directly from electronic excitations at fixed
nuclear geometries, the computation of adiabatic IPs requires
nuclear gradients of the ionized states, posing a major theoretical and computational challenge, especially within correlated frameworks. Among the most promising approaches for IP calculations is the many-body Green's function $GW$ method, which provides a balanced compromise between accuracy and computational efficiency. Furthermore, it is applicable to both finite and extended systems. Recent work has established formal connections between $GW$ and coupled-cluster doubles (CCD) theory, leading to the first derivation of analytic $GW$
nuclear gradients via a
unitary CCD framework. In this work, we present an alternative, fully analytic formulation of $GW$
nuclear gradients based on a modified version of the traditional equation-of-motion CCD formalism, enabling the inclusion of missing correlation effects in the traditional CCD methods.
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Materials Science
All-Altermagnetic Tunnel Junction of RuO2/NiF2/RuO2
Long Zhang, Guangxin Ni, Xuehao Wu et al. (+1 more)
Emerging altermagnets with zero net
magnetic moment and moment-dependent
spin splitting offer a promising avenue for
antiferromagnetic spintronic devices, yet their integration into
magnetic tunnel junctions has been hindered by reliance on
ferromagnetic electrodes (introducing stray fields) or by limited functionality (non-tunable magnetoresistance without
spin filtering). Here, we propose an all-altermagnetic tunnel junction (AAMTJ) paradigm composed exclusively of altermagnets, exemplified by experimentally feasible RuO2/NiF2/RuO2. By introducing an altermagnetic NiF2 barrier, the achieved tunneling magnetoresistances of 11,704%, 2,496% and 1,892% for RuO2/NiF2/RuO2 are much higher than that of 221% for RuO2/TiO2/RuO2 with a nonmagnetic TiO2 barrier. High
spin filtering efficiencies of ~90% are also obtained. This architecture unlocks multistate high magnetoresistance and
spin filtering via magnetization control of the electrodes and barrier, stemming from their synergistic and antagonistic
alignments of momentum-dependent altermagnetic
spin-splitting. Importantly, high tunneling magnetoresistances are still achieved in the AAMTJ with TiO2 spacer of RuO2/TiO2/NiF2/TiO2/RuO2. Our AAMTJ inherently exhibits low consumption and zero stray field, with nonrelativistic
spin splitting and vanishing
magnetic moment, combining the advantages of both
ferromagnetic and
antiferromagnetic tunnel junctions. This AAMTJ paradigm opens an interesting avenue within the area of high-performance altermagnet-based tunnel junctions.
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All authors Long Zhang, Guangxin Ni, Xuehao Wu, Guoying Gao
Materials Science
Design principles for amorphous solid-state electrolytes
Qifan Yang, Xiao Fu, Xuhe Gong et al. (+5 more)
Amorphous solid-state electrolytes (SSEs) offer unique advantages for next-generation batteries, but their rational design is hindered by an unclear structure-property relationship. This study establishes universal design principles through atomistic simulations of 32 amorphous Li-M-X systems (M = B, Al, Si, P; X = F, Cl, Br, I, O, S, Se, N). We identify four structure types governed by a rule that saturated M-X groups with more negative charges preferentially form M-X-M chains, identify paddle-wheel and cooperative migration as two favorable transport mechanisms that are significantly enhanced in amorphous structures. We also pinpoint
Oxides and fluorides as optimal for electrochemical and hydrolytic stability, and reveal bulk modulus as a simple predictor for $Li^+$ mobility. These insights are integrated into a practical design diagram, providing a novel and valuable framework for advancing high-performance amorphous SSEs.
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All authors Qifan Yang, Xiao Fu, Xuhe Gong, Jingchen Lian, Liqi Wang, Ruijuan Xiao, Yong-Sheng Hu, Hong Li
Materials Science
Platform for zero-field isolated skyrmions: 4$d$/Co atomic bilayers on Re(0001)
Moinak Ghosh, Stefan Heinze and Souvik Paul
Using first-principles density functional theory (DFT) combined with atomistic
spin simulations, we explore the possibility of realizing zero-field isolated skyrmions in three 4$d$/Co atomic
bilayers – Rh/Co, Pd/Co, and Ru/Co – grown on the Re(0001) surface. Our investigation employs an extended atomistic
spin model, which goes beyond the standard model by including the multi-
spin higher-order exchange interactions (HOI) in addition to the Heisenberg pairwise exchange interaction, Dzyaloshinskii-Moriya interaction (DMI), and magnetocrystalline anisotropy energy (MAE). All
magnetic interactions of the extended
spin model are calculated using DFT. The phase diagram obtained from atomistic
spin simulations based on this
spin model for Rh/Co and Pd/Co on Re(0001) reveals that isolated skyrmions emerge spontaneously on the
ferromagnetic background even in the absence of an external
magnetic field. The radius of zero-field isolated skyrmions in Rh/Co/Re(0001) is around 6 nm, whereas the radius of those skyrmions in Pd/Co/Re(0001) is about 12 nm. Transition-state theory calculations show that the skyrmions are protected by substantial energy barriers, approximately 150 meV, which predominantly arise from DMI, with a small contribution from the HOI interactions. The height of the barriers suggests that skyrmions could be observed in low-temperature experiments. Based on this work, we propose 4$d$/Co
bilayers on Re(0001) as a new platform to realize nanoscale zero-field isolated skyrmions.
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Materials Science
Introducing physics-informed generative models for targeting structural novelty in the exploration of chemical space
Andrij Vasylenko, Federico Ottomano, Christopher M. Collins et al. (+3 more)
Discovering materials with new structural chemistry is key to achieving transformative functionality. Generative artificial intelligence offers a scalable route to propose candidate
crystal structures. We introduce a reliable low-cost proxy for structural novelty as a conditioning property to steer generation towards novel yet physically plausible structures. We then develop a physics-informed
diffusion model that embeds this descriptor of local environment diversity together with compactness as a stability metric to balance physical plausibility with structural novelty. Conditioning on these metrics improves generative performance across
diffusion models, shifting generation away from structural motifs that dominate the training data. A chemically grounded validation protocol isolates those candidates that combine plausibility with structural novelty for physics-based calculation of energetic stability. Both the stability and the novelty of candidates emerging from this workflow can however change when the full potential energy surface at a candidate composition is evaluated with
crystal structure prediction (CSP). This suggests a practical generative-CSP synergy for discovery-oriented exploration, where AI targets physically viable yet structurally distinct regions of chemical space for detailed physics-based assessment of novelty and stability.
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All authors Andrij Vasylenko, Federico Ottomano, Christopher M. Collins, Rahul Savani, Matthew S. Dyer, Matthew J. Rosseinsky
Materials Science · Cross-listed from cond-mat.soft
Tuneable ion selectivity in vermiculite membranes intercalated with unexchangeable ions
Zhuang Liu, Yumei Tan, Jianhao Qian et al. (+8 more)
Membranes selective to ions of the same charge are increasingly sought for wastewater processing and valuable element recovery. However, while narrow channels are known to be essential, other membrane parameters remain difficult to identify and control. Here we show that Zr$^{4+}$, Sn$^{4+}$, Ir$^{4+}$, and La$^{3+}$ ions intercalated into vermiculite laminate membranes become effectively unexchangeable, creating stable channels, one to two water layers wide, that exhibit robust and tuneable ion selectivity. Ion permeability in these membranes spans five orders of magnitude, following a trend dictated by the ions' Gibbs free energy of hydration. Unexpectedly, different intercalated ions lead to two distinct monovalent ion selectivity sequences, despite producing channels of identical width. The selectivity instead correlates with the membranes' stiffness and the
entropy of hydration of the intercalated ions. These results introduce a new ion selectivity mechanism driven by entropic and mechanical effects, beyond classical size and charge exclusion.
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All authors Zhuang Liu, Yumei Tan, Jianhao Qian, Min Cao, Eli Hoenig, Guowei Yang, Fengchao Wang, Francois M. Peeters, Yi-Chao Zou, Liang-Yin Chu, Marcelo Lozada-Hidalgo
Materials Science
Unveiling the delicate "hidden" interface conditions in WS2 flakes by advanced atomic force microscopy
Yanyan Geng, Chang Li, Shuo Mi et al. (+15 more)
The delicate interfacial conditions and behaviors play critical roles in determining the valuable physical properties of two-dimensional materials and their
heterostructures on substrates. However, directly probing these complex interface conditions remains challenging. Here, we reveal the coupled in-plane strain and out-of-plane bonding conditions in strain-engineered WS2 flakes by combining dual-harmonic electrostatic force microscopy (DH-EFM) and scanning microwave impedance microscopy (sMIM). A striking contradiction is observed between the compressive-strain-induced larger bandgap (lower electrical conductivity) detected by DH-EFM, and the enhanced conductivity probed by sMIM. Comparative measurements under different sMIM modes demonstrate that this contradiction originates from a tip-loading-force-induced dynamic puckering effect, which is governed by the interfacial bonding strength. Furthermore, the progressive accumulation and subsequent release of conductivity during forward/backward sMIM-contact scans further confirms this dynamic puckering behavior, revealing pronounced differences in interface conditions between the open- and closed-ring regions of WS2. This work resolves the correlation between electrical properties and interface conditions, and provides fundamental insights for interface-engineered devices.
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All authors Yanyan Geng, Chang Li, Shuo Mi, Manyu Wang, Xinen Han, Huiji Hu, Yunzhen Wang, Haojie You, Shumin Meng, Hanxiang Wu, Jianfeng Guo, Shiyu Zhu, Yanjun Li, Yasuhiro Sugawara, Sabir Hussain, Fei Pang, Rui Xu, Zhihai Cheng
Materials Science
Thermal Transport in Ag8TS6 (T= Si, Ge, Sn) Argyrodites: An Integrated Experimental, Quantum-Chemical, and Computational Modelling Study
Joana Bustamante, Anupama Ghata, Aakash A. Naik et al. (+4 more)
Argyrodite-type Ag-based sulfides combine exceptionally low
lattice thermal and high ionic conductivity, making them promising candidates for thermoelectric and solid-state energy applications. In this work, we studied Ag8TS6 (T= Si, Ge, Sn) argyrodite family by combining chemical-bonding analysis,
lattice vibrational properties simulation, and experimental measurements to investigate their structural and thermal transport properties. Furthermore, we propose a two-channel
lattice-dynamics model based on Grüneisen-derived
phonon lifetimes and compare it to an approach using machine-learned interatomic potentials. Both approaches are able to predict thermal conductivity in agreement with experimental
lattice thermal conductivities along the whole temperature range, highlighting their potential suitability for future high-throughput predictions. Our findings also reveal a relationship between bond heterogeneity arising from weakly bonded Ag+ ions and occupied antibonding states in Ag-S and Ag-Ag interactions and strong anharmonicity, including large Grüneisen parameters, and low sound velocities, which are responsible for the low
lattice thermal conductivity of Ag8SnS6, Ag8GeS6, and Ag8SiS6. We furthermore show that thermal and ionic conductivities in all three compounds are independent of each other and can likely be tuned individually.
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All authors Joana Bustamante, Anupama Ghata, Aakash A. Naik, Christina Ertural, Katharina Ueltzen, Wolfgang G. Zeier, Janine George