Materials Science
Finite-width adiabatic shear banding and dislocation patterning in mesoscale polycrystalline aggregates
Siddharth Singh, Rajat Arora, Janith Wanni et al. (+6 more)
Dynamic shear banding under adiabatic conditions in a mesoscale polycrystalline aggregate is studied using a model of mesoscale dislocation mechanics and experiments. The model involves a length scale related to hardening induced by excess/polar/geometrically necessary dislocation (GND) density, and utilizes a simple classical
crystal plasticity model with isotropic Voce law hardening. Simulations of statistically representative volume elements of a polycrystal determined from experimental samples are conducted. Studies in 2-d (section) and 3-d capture the experimentally observed finite-width shear bands and the formation of low-angle subgrain boundaries even in the absence of heat conduction in the model, as well as size-dependent strengthening for grain sizes from 1 to 20 $\mu$m. The 2-d and large-scale 3-d simulations, the latter involving 1 million finite elements, provide access to the progressive
evolution of material strength, stress state, and temperature in the course of large deformations. GND distributions accumulate at grain boundaries and form patterned structures within grain interiors, offering insight into the microstructural changes that precede failure in adiabatic shear bands. Mesh-converged, delocalized and localized plastic flow to very large deformations without softening is observed for a significant range of parameters, reflecting a competition between GND hardening and thermal softening in setting the non-softening steady state in the absence of other ductile damage mechanisms in the model.
Read the full abstract ▾
All authors Siddharth Singh, Rajat Arora, Janith Wanni, Charles Adkins, Raymond Rasmussen, Noah J. Schmelzer, Dan J. Thoma, Curt A. Bronkhorst, Amit Acharya
Materials Science
A comparative first-principles investigation of bilayer NbOX2 (X=Cl, Br, I) for Photocatalytic water splitting applications
Laku Dorjee Tamang, Shivraj Gurung, Bhanu Chettri et al. (+6 more)
Motivated by our previous work on bulk NbOX2 , where we have reported its high 1dielectric polarisation and finite piezoelectric response, this work extends to its 2D homo
bilayer system to explore its potential for photocatalytic water splitting. Herein, density functional theory (DFT) were employed in probing the structural, electronic, optical, and photocatalytic properties of 2D homo
bilayer NbOX2 (X = Cl, Br, and I). Our results show that structurally, NbOCl2 and NbOBr2 prefer AC
bilayer stacking,while AB stacking was preferred by NbOI2 . All the considered
bilayers are dynamically, thermally, and mechanically stable. From the analysis of electronic structure we have found a decreasing trend in the energy band gap as X goes down the group from Cl to I, with the position of the valence band maximum shifting upward along the high
symmetry points. In terms of carrier mobility, all 2D
bilayer systems possess high carrier mobility comparable to known 2D materials. It also exhibits an anisotropic carrier transfer property by which charge carriers are separated efficiently. These materials show similar trends to BiOI and PtSe2 , in which photocatalytic efficiency was increased by forming the multiple layers. The materials under investigation are suitable for photocatalytic water splitting under visible and ultraviolet regions with absorption coefficients of 105 cm-1.
Read the full abstract ▾
All authors Laku Dorjee Tamang, Shivraj Gurung, Bhanu Chettri, Nguyen Thanh Tien, Le Huu Nghia, Darwin Barayang Putungan, Ranjit Thapa, Kailash Chandra Bhamu, Dibya Prakash Rai
Materials Science · Cross-listed from cond-mat.mes-hall
Negative Differential Resistance and Ultra-High TMR in Altermagnetic Tunnel Junctions
Sajjan Sheoran, Luke Keenan, Declan Nell et al. (+1 more)
Altermagnets can replace ferromagnets in tunnel junctions, yielding large tunneling magnetoresistance, ultrafast switching, and low-power functionality. While most studies explore the linear-response regime, interesting features emerge at finite bias, where the peculiar electronic structure of altermagnets gives rise to complex non-linear behaviour. Using non-
equilibrium Green's functions implemented with density functional theory, we predict that a large low-bias negative differential resistance can be observed in an altermagnetic tunnel junction. Our proposed junction incorporates the orbital-ordered altermagnet KV2Se2O, whose quasi-2D
Fermi surface plays a crucial role in realizing the negative differential resistance. Upon the application of a finite bias voltage, the current in the parallel configuration first increases sharply and then decreases, to be almost completely suppressed at around 0.14 V. At the same time, the antiparallel configuration displays a monotonic current-voltage curve. This behaviour, in addition to the negative differential resistance, supports a large tunneling magnetoresistance with sign inversion at 0.13 V. Our results suggest that altermagnetic tunnel junctions can be used as components in applications requiring strong non-linear response at low bias.
Read the full abstract ▾
All authors Sajjan Sheoran, Luke Keenan, Declan Nell, Stefano Sanvito
Materials Science
On-demand steering of hyperbolic chiral polaritons
Andrea S. Dai, Fuyang Tay, Ding Xu et al. (+11 more)
Control of light polarization and propagation in sub-wavelength architectures is foundational to nanophotonic technologies. A frontier direction is to leverage strong optical
spin-orbit interactions to realize polarization-selective light steering, known as the photonic
spin Hall effect. In this context,
hyperbolic plasmon polaritons (HPPs) are of particular interest as they offer large optical
spin-orbit coupling from strong confinement and dielectric anisotropy, as well as ray-like propagation. Despite theoretical predictions, however, the
hyperbolic spin Hall effect in natural materials has remained elusive. Here, we demonstrate the
hyperbolic spin Hall effect in the visible and near-infrared range in the natural
hyperbolic van der Waals metal MoOCl2. Enabling this discovery is a novel far-field pump-probe microscope that facilitates the launching and imaging of HPPs with exceptional sensitivity through interference with a high-momentum reference field. This approach preserves excellent control over light polarization, overcoming a key barrier to polarization-selective interrogation of
hyperbolic materials. We show that both
hyperbolic and surface plasmons in MoOCl2 display
chiral fields, and that their propagation direction can be completely switched upon light helicity reversal. Our results demonstrate on-demand steering of
chiral plasmons, firmly establishing natural
hyperbolic materials as ideal components for reconfigurable nanophotonics and
chiral light-matter coupling.
Read the full abstract ▾
All authors Andrea S. Dai, Fuyang Tay, Ding Xu, Inki Lee, Noah Bussell, Daria Balatsky, Francesco L. Ruta, Emma Lian, Colin Nuckolls, Xavier Roy, James G. Analytis, Andrew J. Millis, D. N. Basov, Milan Delor
Materials Science · Cross-listed from cond-mat.mes-hall
Direct-write electrochemical nanofabrication of ultrasmall graphene devices
Xiao Liu and Colm Durkan
Graphene nano-ribbons, GNRs, are promising channel materials for next-generation ultra-miniaturised devices due to their exceptional electrical and thermal properties which arise from their atomic thickness, as well as their ability to have a size-dependent band-gap [1-9]. However, despite extensive efforts to reliably fabricate narrow GNR-based field-effect transistors [10-12], their integration into conventional transistor technologies remains hindered by challenges such as high fabrication costs and complex processing requirements [13, 14]. In this study, we present a direct-write, relatively low-cost and robust approach for fabricating sub-10 nm GNR-based FETs using electrochemical atomic force microscopy lithography with an alternating current (AC) bias, obviating the need for electrodes. We also explain the underlying electrochemical process and provide a model which can be used to describe it. Leveraging the high-precision positioning capability of AFM, this method enables precise nanoscale
graphene patterning with feature sizes below 10nm. Compared with conventional lithographic techniques, photo- and electron-beam lithography i.e., PL & EBL, respectively [2, 15-20], it offers higher resolution, lower defect density, contamination-free processing, and the capability for in situ nanoscale device modification and characterisation. This work provides an efficient strategy for advancing GNR-based nanoelectronics.
Read the full abstract ▾
Materials Science
Bridging perturbation and variational approaches in brittle fracture
Serafim Egorov, Antoine Sanner, Jean Sulem et al. (+2 more)
We present a variational reduced-order model for three-dimensional coplanar propagation of sharp cracks in heterogeneous perfectly brittle solids under mixed-mode I+II+III loading. The approach connects the variational fracture formulation of Francfort and Marigo (1998) and the perturbation theory of Rice (1985) by computing
equilibrium crack-front configurations through minimization of the total energy defined as the sum of (i) the elastic potential energy, evaluated asymptotically from front deformations, and (ii) the dissipated energy, set by the fracture energy field. The potential energy and its derivatives are evaluated efficiently using the Fast
Fourier Transform. The resulting nonconvex box-constrained minimization problem is solved with a
matrix-free Newton conjugate gradient
algorithm with a trust region and physics-based preconditioning, enforcing irreversibility while resolving energy barriers and long-range elastic interactions. We validate our implementation against newly derived analytical solutions. We then perform 116,000 large-scale simulations of tensile and shear crack propagation in disordered media to quantify the impact of finite-size effects, disorder intensity, and mode mixity. The simulations reproduce the transition from smooth to intermittent crack growth, and show that mode mixity has limited influence on the onset of intermittency but induces quasi-
elliptic fronts in mixed II+III loading. They reveal a size-dependent crossover from disorder-induced weakening to toughening controlled by the emergence of depinning instabilities.
Read the full abstract ▾
All authors Serafim Egorov, Antoine Sanner, Jean Sulem, Lars Pastewka, Mathias Lebihain
Materials Science · Cross-listed from physics.optics
Visible-NIR-Frequency Hyperbolic Response in Nodal-Line Semimetal PbTaSe$_2$
Vivian J. Santamaria-Garcia, Morgan G. Blevins, Simo Pajovic et al. (+2 more)
Natural
hyperbolic materials offer a powerful platform for light-matter interactions by supporting highly anisotropic electromagnetic modes without the need for artificial patterning. In this work, we experimentally demonstrate that the nodal-line semimetal PbTaSe$_2$ exhibits robust
hyperbolic optical behavior in the visible to near-infrared spectral range, which arises intrinsically from its anisotropic electronic structure and layered
crystal symmetry. By combining first-principles calculations, ellipsometry, Drude-Lorentz modeling, and reflectance measurements, we establish a consistent experimental and theoretical picture of bulk hyperbolicity in this material. This hyperbolicity is of plasmonic origin and is characterized by a competitive quality factor ($Q_\mathrm{max} \approx 2.8$) and a very large anisotropy parameter ($|R| \approx 231$) at 0.78 eV.
Read the full abstract ▾
All authors Vivian J. Santamaria-Garcia, Morgan G. Blevins, Simo Pajovic, Carolina Orona-Navar, Svetlana V. Boriskina
Materials Science
Automated multiphase identification and refinement in powder diffraction using mismatch-tolerant machine learning
Lalit Yadav, Yongqiang Cheng and Mathieu Doucet
Powder diffraction is a primary structural characterization tool in materials science, yet automated phase identification remains a major bottleneck for autonomous discovery. Existing workflows rely heavily on search–match heuristics and manual Rietveld refinement, and broadly usable end-to-end automation is especially limited for
neutron powder diffraction, where comparable tools are largely absent. Here we introduce RADAR-PD, a modality-aware machine learning framework for phase identification and quantification across both X-ray and
neutron powder diffraction. RADAR-PD couples a mismatch-tolerant neural network operating on coarse momentum-transfer fingerprints with automated
lattice nudging and physics-constrained Rietveld verification, enabling dominant-phase hypotheses to be generated from elemental constraints and secondary phases to be isolated recursively. On an experimental RRUFF PXRD
benchmark, RADAR-PD outperforms DARA in recovering the reference phase. RADAR-PD further provides robust multiphase analysis on complex time-of-flight and constant-wavelength
neutron datasets, addressing an important unmet need in automated
neutron diffraction analysis. These results establish RADAR-PD as an auditable, instrument-agnostic framework for autonomous structural discovery.
Read the full abstract ▾
Materials Science
Equivariant Space Group and Hamiltonian for Collinear Magnetic Systems
Chaoxi Cui, Zhi-Ming Yu, Yilin Han et al. (+3 more)
Condensed matter physics increasingly focuses on exploiting the
magnetic order parameter orientation n as a tuning knob for properties of collinear
magnetic materials, but a general method for constructing effective
Hamiltonians with explicit n-dependence has been lacking. Here, we develop a
symmetry-based framework, built on the equivariant space group, for constructing such
Hamiltonians, termed equivariant
magnetic Hamiltonians (EMHs). The resulting EMH lives in a higher-dimensional k-n space and exhibits unconventional
symmetry actions and topological features. Using a 1D
ferromagnetic chain and a 3D antiferromagnet as examples, we demonstrate that explicit n-dependence in EMHs enables the study of
magnetic-dynamics-driven topological pumping, including even-integer charge pumping and a second-Chern-number-induced quantized pumping of surface anomalous
Hall conductivity. Beyond model systems, we incorporate the framework into first-principles calculations to construct ab-initio EMHs that accurately capture the n-dependent band structures of real materials. The approach can also be generalized to non-collinear
magnetic systems. Our work establishes a general framework for constructing EMHs and for exploring the rich physics arising from
magnetic anisotropy and
magnetic dynamics.
Read the full abstract ▾
All authors Chaoxi Cui, Zhi-Ming Yu, Yilin Han, Run-Wu Zhang, Shengyuan A. Yang, Yugui Yao
Materials Science
Graphene lattice recoil in hard X-ray photoemission: Experiment and Theory
Simone Ritarossi, Alice Apponi, Orlando Castellano et al. (+6 more)
Hard-x-ray C 1s photoemission from monolayer
graphene probes a regime in which
nuclear recoil and intrinsic electronic asymmetry contribute on comparable energy scales to the observed spectral line shape. Here we combine experiment and modeling over the
photon-energy range 0.8 keV–8 keV to resolve this interplay quantitatively. A
graphene-specific implementation of the Fujikawa–Takata cumulant formalism, based on an anisotropic vibrational density of states constrained by first-principles
phonon calculations, captures the expected
recoil scaling with
photon energy and emission geometry but fails to reproduce the pronounced asymmetric tails of the measured spectra. To overcome this limitation, we introduce an explicit electronic convolution model in which an intrinsic,
photon-energy-independent electronic line shape extracted from near-recoilless 0.8 keV data is convolved with a
phonon recoil kernel carrying the full dependence on
photon energy and emission angle. This approach reproduces both the measured line-shape
evolution and the observed centroid shifts across the explored energy range without refitting the spectra at higher
photon energies. The results show that
recoil in
graphene cannot be described by a baseline treatment in which the
phonon recoil kernel is combined only with symmetric lifetime broadening, but must be treated together with the intrinsic many-body electronic response of the C 1s line.
Read the full abstract ▾
All authors Simone Ritarossi, Alice Apponi, Orlando Castellano, José Lorenzana, Domenica Convertino, Camilla Coletti, Tien-Lin Lee, Francesco Offi, Alessandro Ruocco
Materials Science
Decoupling size from magnetism: A length-scale boundary for curvature control in micrometer FePt Janus particles
Natalia Gonzalez-Vazquez, Eylül Suadiye, Eberhard Goering et al. (+6 more)
Curvature reshapes magnetization when a structure's dimensions approach intrinsic
magnetic length scales, but functional
magnetic colloids and microrobots are often micrometers in size, where the radius of
curvature exceeds these scales by several orders of magnitude. Whether particle diameter remains an effective parameter for tuning
magnetic response in this regime is therefore unclear. We synthesized partially ordered FePt Janus caps on spherical SiO$_2$ particles with diameters of 3–10~$\mu$m, characterized their structure and
magnetic response, and extended the investigated range to 1–20~$\mu$m using micromagnetic simulations. Across this range, coercivity, remanence, and hysteresis-loop shape showed no systematic dependence on particle diameter in either experiment or simulation. The ratio between exchange length and radius of
curvature ($\ell_{\mathrm{ex}}/R \sim 10^{-3}$–$10^{-4}$) places these particles in a locally planar regime where diameter-dependent
curvature effects are weak. Size and
magnetic response are therefore effectively decoupled within the investigated regime: particle diameter can be selected according to transport, payload, and biocompatibility requirements without introducing a measurable
magnetic penalty, but it does not provide an effective route for tuning magnetization reversal. Instead, the
magnetic response is governed primarily by material state, including the balance between magnetically hard L1$_0$ and soft A1 FePt, with additional modulation by processing-induced morphology. The resulting length-scale map identifies the regime in which this decoupling is expected to hold and where diameter-dependent
curvature effects may become significant.
Read the full abstract ▾
All authors Natalia Gonzalez-Vazquez, Eylül Suadiye, Eberhard Goering, Ruben O. Miranda-Rosales, Hilda David, Frank Thiele, Julia Unangst, Andrew K. Schulz, Gunther Richter
Materials Science
Engineering the band structure of few-layer graphene by S-doping: from linear dispersion to impurity flat bands
Armin Sahinovic and Rossitza Pentcheva
Motivated by the technological relevance of S-doped few-layer
graphene (FLG) in battery applications and in the oxygen reduction reaction, we systematically explore the effect of basal plane S-doping on the electronic properties of mono-, bi-, and four-layer
graphene, using first-principles calculations with van der Waals corrections. In the monolayer we find a variety of effects ranging from a sustained Dirac cone with localized
impurity bands away from the
Fermi level for thiophenic doping (2V1S) to a band gap opening of 0.4 eV and
impurity flat bands close to the
Fermi-level for graphitic doping (1V1S) and an additional $n$-type doping together with
spin-polarization for thiopyranic doping (4V3S). Incorporation in FLG leads to modification of the Dirac cone into a set of
hyperbolic touching bands in 2V1S; reduction (
bilayer) and closing of the band gap with additional
hyperbolic touching bands in conjunction with an
impurity flat band at the
Fermi level in 1V1S and 4V3S and a reduction of
spin polarization in the latter. Overall, S-doping enables design of the band structure and tuning the electronic behavior of FLG from metallic to insulating and from linear dispersion to
impurity flat bands that makes S-doped FLG a promising material for versatile technological applications.
Read the full abstract ▾
Materials Science
Probing Non-Equilibrium Grain Boundary Dynamics with XPCS and Domain-Adaptive Machine Learning
Mouyang Cheng, Bowen Yu, Chu-Liang Fu et al. (+14 more)
Grain-boundary (GB) dynamics control the stability, mechanical, and functional response of nanocrystalline materials, but direct experimental access to their slow non-
equilibrium motion has been limited. Here we establish X-ray
photon correlation spectroscopy (XPCS), combined with domain-adaptive machine learning, as a quantitative probe of GB dynamics. Temperature- and grain-size-dependent two-time XPCS measurements in nanocrystalline silicon reveal pronounced departures from time-translation invariance, showing that GB relaxation can remain far from
equilibrium over experimental timescales. However, direct extraction of quantitative physical information from these high-dimensional, noisy fluctuation maps faces a significant challenge. To overcome this barrier, we develop a semi-supervised learning framework that transfers physical parameter labels from continuum simulations to unlabeled experimental XPCS maps through domain-adaptive representation
alignment. This AI-augmented approach enables the extraction of key kinetic parameters, including bulk diffusivity, GB stiffness, and effective GB concentration, directly from experimental XPCS measurements. Our results show how machine learning can transform indirect fluctuation signals into quantitative materials dynamics, providing a general route to study non-
equilibrium defect motion in solids.
Read the full abstract ▾
All authors Mouyang Cheng, Bowen Yu, Chu-Liang Fu, Nina Andrejevic, Matthias T. Agne, Riley Hanus, Qiwei Wan, Nathan C. Drucker, Thanh Nguyen, Andrei Fluerasu, Lutz Wiegart, Xiaoqian M Chen, Daniel Pajerowski, Yongqiang Cheng, Joshua J Turner, G. Jeffrey Snyder, Mingda Li
Materials Science · Cross-listed from quant-ph
Understanding oxide-thickness-dependent variability in dense Si-MOS quantum dot arrays
Arne Loenders, Jacques Van Damme, Clement Godfrin et al. (+19 more)
Achieving uniform and scalable control of
semiconductor spin qubits remains a key challenge for large scale
quantum computing. In this work, we investigate how gate
oxide thickness influences uniformity in dense two dimensional silicon
quantum dot arrays. Using a 7 x 7 array fabricated in a 300 mm CMOS-process patterned by EUV lithography, we statistically characterize 392
quantum dots across four different
oxide thicknesses. The threshold voltages, capacitances, lever arms, and charging energies are extracted using parallel row based measurements and we identify an optimal SiO2 thickness of 17 nm that minimizes threshold voltage variability below 63 mV standard deviation. Our observations illustrate how multiple sources of disorder can introduce competing
oxide-thickness dependencies, resulting in non-monotonic trends. These results provide key design guidelines for dense, scalable silicon
spin qubit architectures.
Read the full abstract ▾
All authors Arne Loenders, Jacques Van Damme, Clement Godfrin, Paola Favia, Jacopo Franco, Thomas Van Caekenberghe, Bart Raes, Gulzat Jaliel, Sylvain Baudot, Luis Francisco Pinotti, Alexander Grill, George Simion, Kristof Moors, Vukan Levajac, Sofie Beyne, Sugandha Sharma, Stefan Kubicek, Yosuke Shimura, Roger Loo, Massimo Mongillo, Danny Wan, Kristiaan De Greve
Materials Science
Competing crystallization pathways and cold crystallization kinetics in 10OS5 liquid crystal
Aleksandra Deptuch, Mirosława D. Ossowska-Chruściel, Janusz Chruściel et al. (+1 more)
The
liquid crystalline 4-pentylphenyl-4'-decyloxythiobenzoate is investigated in various temperature programs for determination of crystallization kinetics and glassforming properties. The Avrami model, Augis-Bennett method and isoconversional method are used. Cooling at the 25-30 K/min rate results in formation of the glass of the tilted smectic Y phase with the herring-bone order within layers. Slower cooling leads to the partial or total (2 K/min) crystallization of the metastable Cr2 phase, which during subsequent heating or annealing in a proper temperature transforms to another Cr1 phase. Heating from the vitrified smectic Y leads to cold crystallization of the pure Cr1 phase or the Cr1/Cr2 mix. Both Cr1 and Cr2 are conformationally disordered
crystal phases, which is indicated both by the melting
entropy values and the dielectric spectra. The results demonstrate that the energy released during cold crystallization can be tuned by thermal history, highlighting 10OS5 as a candidate for thermal energy storage applications.
Read the full abstract ▾
All authors Aleksandra Deptuch, Mirosława D. Ossowska-Chruściel, Janusz Chruściel, Ewa Juszyńska-Gałązka
Materials Science
Mechanical detection of sub-band mobilities of two-dimensional electron gas on reduced SrTiO$_3$(001) surface
Akash Gupta, Marcin Kisiel, Remy Pawlak et al. (+1 more)
The two-dimensional electron gas (2DEG) in reduced strontium titanate offers a versatile platform for
oxide electronics, yet its dissipation mechanisms under field driven charge fluctuations remain poorly understood. Here, we combine low-temperature atomic force microscopy with scanning tunnelling spectroscopy to probe the force and dissipation responses of a mechanical oscillator interacting with the STO 2DEG. The observation of Rydberg like image potential states by tunnelling experiments confirm the 2DEG formation, while dissipation spectroscopy reveals bias-dependent peaks linked to local electrostatic gating and charge redistribution within the 2DEG energy sub-bands. These features are quantitatively explained by variations in
quantum capacitance as carrier density is tuned by electric fields. Under
magnetic fields, dissipation peaks obey the Kohler's rule, allowing extraction of carrier mobilities in each sub-band. Our results establish a non-invasive AFM - based methodology for quantifying energy losses in
quantum oxides, providing new insights into charge dynamics relevant for spintronic applications.
Read the full abstract ▾
All authors Akash Gupta, Marcin Kisiel, Remy Pawlak, Ernst Meyer
Materials Science
Enhanced Impact Mitigation via 3D-Multilayered Material Architectures
Thomas Butruille, Joshua C. Crone and Carlos M. Portela
Materials designed by nature commonly exhibit functional grading and laminated structures, particularly when intended for enhanced impact protection. Synthetic materials have also found success in exploiting this concept with fully dense but spatially varying architectures, as is the case with advanced fiber-based composites. In the lightweight materials space, porous architected materials have shown benefits for extreme impact mitigation, proving to be advantageous in dissipating large amounts of energy per unit mass, but rarely harness the benefits of layering or functional grading in designs. Here, a design paradigm for lightweight multilayered materials towards high impact-mitigation efficacy is demonstrated, showing that the use of alternating monolithic and beam-based architectures leads to enhanced and predictable responses under extreme conditions. These layered, mass-equivalent `
heterostructures' with different ordering and proportions of octet and monolithic layers outperform single-architecture
lattices on a mass-normalized energy dissipation basis by >50% when subjected to supersonic microparticle impact. Through analysis that combines wave-propagation analysis, nonlinear finite element simulations, and post-impact crater reconstruction, layer-by-layer mechanical properties are mapped to crater formation and energy dissipation behaviors. This
heterostructure design framework offers a simple approach towards tuning failure and impact resistance of materials for protective applications from Whipple shields to sports equipment.
Read the full abstract ▾
Materials Science
Discovery of High-Voltage Magnesium-Ion Cathodes using Machine Learning and First-Principles Calculations
Jhon Rogelnor A. Florida and Edward Aris D. Fajardo
Developing high-performance cathode materials for magnesium-ion batteries (MIBs) remains challenging because Mg$^{2+}$ ions move slowly, and conventional materials exhibit low voltage outputs. In this study, machine learning and first-principles calculations were combined to investigate topological
quantum materials (TQMs) as a new class of cathode candidates. A modified
crystal graph convolutional neural network (mCGCNN) was used to screen 917 Mg-containing TQMs, identifying a small subset of materials with predicted voltages above 3 V and high volumetric capacities. Among these, Mg$_2$VO$_4$ and Mg$_6$MnO$_8$ were selected for detailed density functional theory (DFT) analysis. Formation energy and convex-hull calculations indicate that Mg$_x$VO$_4$ exhibits a fully stable magnesiation pathway, whereas Mg$_x$MnO$_8$ demonstrates minor metastability at intermediate compositions. The calculated voltage profiles yield average voltages of 3.66 V for Mg$_2$VO$_4$ and 4.06 V for Mg$_6$MnO$_8$, in good agreement with machine learning predictions. Electronic structure analysis, supported by Wannier interpolation, confirms that both materials are semiconducting, with valence bands dominated by O $2p$ states and conduction bands by transition-metal $d$ states, indicating a charge-transfer redox mechanism. Compared to conventional Mg cathodes, these TQMs exhibit higher voltages and competitive capacities, underscoring their potential for next-generation multivalent batteries. This study demonstrates that integrating machine learning with first-principles calculations offers an efficient approach for discovering and understanding novel cathode materials.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.str-el
Magnetism and spin dynamics of Na$_5$Yb(MoO$_4$)$_4$: A weakly interacting rare-earth stretched diamond lattice
N. Rajeesh Kumar, J. Khatua, Changhyun Koo et al. (+8 more)
We report a comprehensive investigation of the structural and
magnetic properties of Na$_5$Yb(MoO$_4$)$_4$, a member of the stretched diamond
magnetic lattice family.
Neutron powder diffraction at 3.3~K confirms that the compound crystallizes in the tetragonal \textit{I4$_1$/a} space group, with a large interatomic separation of 6.33~Å between
magnetic Yb ions forming a three-dimensional stretched diamond framework.
Magnetic susceptibility and specific heat measurements reveal no evidence of long-range
magnetic order down to 60~mK. The low-temperature
magnetic behavior is governed by an effective $J_{\mathrm{eff}} = 1/2$ Kramers doublet ground state, well separated from excited
crystal-field levels, arising from the distorted dodecahedral oxygen coordination of Yb$^{3+}$. Density functional theory calculations within the DFT+$U$ framework indicate that exchange interactions between Yb ions are negligibly small, consistent with the long O–Mo–O super-superexchange pathways. The temperature dependence of the specific heat exhibits signatures of gapped
spin excitations, most likely originating from long-range dipolar correlations and further shaped by weak exchange interactions together with the strong single-ion anisotropy of the Yb moments.
Muon spin relaxation measurements reveal persistent low-energy
spin dynamics, indicating that dipolar correlations remain dynamic and are insufficient to stabilize static
magnetic order down to 50~mK. These results identify Na$_5$Yb(MoO$_4$)$_4$ as a rare example of a dipolar
quantum paramagnet in which single-ion physics and long-range dipolar interactions dominate, while exchange interactions are suppressed to the millikelvin energy scale.
Read the full abstract ▾
All authors N. Rajeesh Kumar, J. Khatua, Changhyun Koo, Izumi Umegaki, C. -E. Yin, C. -W. Wang, A. M. Strydom, H. -T. Jeng, Kwang-Yong Choi, R. Sankar, W. -T. Chen
Materials Science · Cross-listed from cond-mat.str-el
Emergent Vortex Ordering in a Multiflavor Pyrochlore-Lattice Compound GeCo$_2$O$_4$
Jiajun Mo, Otkur Omar, Shuangkui Guang et al. (+12 more)
Entangled
spin and orbital degrees of freedom provide a multiflavor route to novel
magnetic states inaccessible in conventional
spin systems. Here, we report the experimental identification of an emergent
vortex lattice in the multiflavor pyrochlore-
lattice compound GeCo$_2$O$_4$. By combining comprehensive
neutron scattering experiments with a regularized regression framework, we identify substantial Kitaev interactions among the nearest-neighboring Co$^{2+}$ pseudospins, which cooperate with
geometric frustration to stabilize the
vortex order. These results reveal an unexpected route to
vortex-
lattice order in a three-dimensional Kitaev-frustrated magnet and demonstrate a regularized protocol for
Hamiltonian determination in frustrated
quantum materials.
Read the full abstract ▾
All authors Jiajun Mo, Otkur Omar, Shuangkui Guang, Kazuki Iida, Kazuya Kamazawa, Fabio Orlandi, Wenyun Yang, Xiaobai Ma, Xiquan Zheng, Yingying Peng, Yuan Xiao, Shunhong Zhang, Oksana Zaharko, Xuefeng Sun, Shang Gao
Materials Science
Vacancy-Enhanced $N-N$ Bonding and Deep Level Complex Defect Formation in $\beta-Ga_2O_3$
Asiyeh Shokri, Yevgen Melikhov, Yevgen Syryanyy et al. (+2 more)
Nitrogen implantation can make $\beta-Ga_2O_3$ semi-insulating, but the atomic origin responsible for carrier trapping remains unresolved. Here, hybrid density functional theory is used to examine complexes derived from an interstitial-substitutional N pair, $N_{i9}-N_{OI}$, and effects of nearby O and Ga vacancies on $N-N$ bonding, stability, and electronic states. Within the configurations examined, N atoms favor co-localization. In selected Ga-vacancy-assisted complexes, the $N-N$ distance shortens to 1.09-1.19 $\mathring{\mathrm{A}}$ and exhibits electron localization consistent with substantial $N-N$ covalent character. Positive binding energies indicate favorable association relative to separated defects, although many of these complexes have high formation energies and are therefore more likely to be metastable products of implantation than abundant
equilibrium defects. Calculated N $K$-edge XANES spectra for two selected Ga-defect-assisted $N-N$ complexes reveal a pronounced sensitivity of the near-edge $\pi^*$ resonance to the local defect environment, providing an atomistic perspective on the experimentally observed
evolution toward molecular $N_{2}$ during annealing. Projected densities of states and
spin-density distributions show localized N-$2p$- and O-$2p$-derived states well inside the band gap. These vacancy-assisted N complexes therefore provide an atomistic mechanism for deep carrier trapping and current blocking rather than shallow acceptor doping in $\beta-Ga_2O_3$.
Read the full abstract ▾
All authors Asiyeh Shokri, Yevgen Melikhov, Yevgen Syryanyy, Maryna Chernyshova, Iraida N. Demchenko
Materials Science
Tailoring the material properties, nanostructure and grain alignment of Alnico magnets through micromagnetic simulations
Anda Elena Stanciu, Johann Fischbacher, Markus Gusenbauer et al. (+9 more)
Alnico magnets have gained renewed interest in the search for rare-earth free permanent magnets due to their high thermal stability and magnetisation. However, the limited coercivity of these shape-anisotropy-based
alloys constrains their performance. Starting from a reference Alnico sample, we realised a finite elements micromagnetic study of exchange-decoupled rods by varying their dimensions and interrod spacing across those observed experimentally. We computed the hysteresis properties by progressing from micromagnetic simulations of a small number of rods within the magnetostatic field of their neighbours to large systems treated statistically based on the distribution of orientations of the grains. We compared the coercivity of an isolated rod with that of the exchange-decoupled system to highlight the effect of magnetostatic interactions. We computed analytically the stray field acting on a single rod as a consequence of its surrounding rods in order to confirm the scaling of the coercivity with the packing fraction p. We explored how intrinsic material properties influence
magnetic behaviour by examining materials with different magnetocrystalline anisotropy constants and saturation polarisation values. Results from several hundred simulations were used to train a multi-layer perceptron regressor and predict the
magnetic properties as function of the dimensions of the rods, interrod spacing and orientation of the grains. With this approach, we highlight the underlying trends by which nanoscale structuring, intrinsic material properties and grain
alignment can be tailored to improve the
magnetic properties of Alnico
alloys.
Read the full abstract ▾
All authors Anda Elena Stanciu, Johann Fischbacher, Markus Gusenbauer, Alexander Kovacs, Harald Oezelt, Joachim Seland Graff, Patricia Carvalho, Anette Eleonora Gunnæs, Matej Zaplotnik, Espen Sagvolden, Spyros Diplas, Thomas Schrefl
Materials Science
Universality of magnetic susceptibility in the conical state of kagome ferromagnet Fe$_3$Sn$_2$
Lilian Prodan, Donald M. Evans, Lukas Puntigam et al. (+2 more)
We report universal behavior of the differential
magnetic susceptibility (DMS) in the conical phase that mediates the
spin-reorientation (SR) transition of the kagome ferromagnet Fe$_3$Sn$_2$. Within the SR temperature range, the DMS isotherms exhibit extremely narrow crossing regions, forming isosbestic points. Using an isosbestic-invariance analysis, we show that the isotherms collapse onto a single temperature-independent curve, revealing quadratic-in-temperature corrections to the susceptibility. Complementary field-dependent
magnetic-force-microscopy measurements uncover
evolution of
spin textures from stripe-like domains at low fields to isolated bubble-like domains near the isosbestic field ($\sim 0.6$~T), a behavior not previously reported in bulk Fe$_3$Sn$_2$ within the conical state. These findings point to a universal mechanism for the emergence of complex
magnetic textures near isosbestic points, driven by the competition between magnetocrystalline anisotropy, dipolar interactions, and external
magnetic field.
Read the full abstract ▾
All authors Lilian Prodan, Donald M. Evans, Lukas Puntigam, 1 István Kézsmárki, Vladimir Tsurkan
Materials Science · Cross-listed from physics.optics
Theory of Supercritical Coupling And Generalized Bound States in the Continuum
Sergio Balestrieri, Bruno Miranda, Silvia Romano et al. (+1 more)
Bound states in the continuum (BICs) arise from destructive interference suppressing radiation despite spectral overlap with the continuum. Here we show that Friedrich–Wintgen interference naturally emerges from a bright–dark supermode decomposition of resonances coupled through a shared radiation channel. In this basis, any finite leakage of a quasi-BIC induces a causality-driven reactive coupling enabling non-Hermitian pumping of the dark sector. We derive the optimal condition for this process and show that it corresponds to the supercritical coupling regime previously identified in [Nature 626, 765 (2024)], while naturally recovering universal quasi-BIC asymmetry scaling. Extending the theory to Dirac-like dispersions in photonic
crystal slabs, we identify an open-Dirac singularity where the Dirac gap matches the supercritical regime. A four-wave
Hamiltonian quantitatively reproduces rigorous coupled-wave analysis, revealing the breakdown of conventional critical coupling. Near this regime, absorptive cross-coupling induces coherent absorption interference and enables suppression of effective dissipative losses beyond conventional material limits. These results motivate the concept of a generalized bound state in the continuum (gBIC) as a limiting non-Hermitian state where radiative and effective gain compensate, producing a true divergence of the total quality factor. Overall, this work establishes a unified framework connecting BIC interference, Dirac
topology, and non-Hermitian physics for ultra-high-Q enhancement and loss engineering in open photonic systems.
Read the full abstract ▾
All authors Sergio Balestrieri, Bruno Miranda, Silvia Romano, Gianluigi Zito
Materials Science
Synergistic improvement of specific strength and plasticity achieved in Ti-based metallic glass designed based on quasicrystal structure
Zhengqing Cai, Zijing Li, Shidong Feng et al. (+2 more)
Achieving a balance between low density, high strength, and good ductility remains a major challenge in the development of structural materials. Ti-based bulk metallic glasses (BMGs) have attracted considerable
attention due to their exceptionally high specific strength. However, the intrinsic strength-plasticity trade-off has hindered their practical applications. Based on a quasicrystal-derived structural heredity and minor-element microalloying, this work realizes a synergistic enhancement of specific strength and plasticity in Ti-based BMGs. The resulting ((Ti_{40}Zr_{40}Ni_{20})_{72}Be_{28})_{97}Al_{3} BMGs demonstrate an ultrahigh specific strength of 5.34 \times 10^5 \text{ N}\cdot\text{m}\cdot\text{kg}^{-1}, establishing a new record for Ti-based BMGs, along with a plastic strain of 13%, breaking through the traditional strength-plasticity limitation of BMGs. Structural analyses show that Al microalloying effectively inherits and modulates the short-range order derived from quasicrystalline structures, thereby achieving an observed synergistic enhancement in both strength and plasticity. This work provides new insights into composition design and lightweight structural applications of Ti-based BMGs.
Read the full abstract ▾
All authors Zhengqing Cai, Zijing Li, Shidong Feng, Limin Wang, Riping Liu
Materials Science
Theory and Discovery of Electrides
Chengcheng Xiao, Nicholas Bristowe and Arash A. Mostofi
Electrides are materials with electrons localized at interstitial regions of the
crystal lattice and have been identified as promising candidates for a variety of applications, including catalysis, electron emission, and superconductivity. We present a theoretical framework for the origin of interstitial electrons in electrides. We demonstrate that this theory can explain electride-like behavior in prototypical electrides, and we use it to develop descriptors for the high-throughput discovery of new inorganic electride candidates from first principles. We also show that the same concepts can explain electride-like behavior in other classes of material, including high-pressure electrides and organic electrides and, more broadly, provide an alternative understanding of F-center defects and solvated electrons.
Read the full abstract ▾
Materials Science
Fast and Accurate Prediction of Lattice Thermal Conductivity via Machine Learning Surrogates
Zeyu Wang, Shuya Yamazaki, Martin Hoffmann Petersen et al. (+11 more)
The appearance of generative models has opened vast chemical spaces in the design of functional materials. Although machine learning interatomic potentials (MLIPs) have substantially accelerated
phonon calculations, high-fidelity prediction of
lattice thermal conductivity ąppa}lat still requires accurate treatment of anharmonic interactions, which remains a key challenge for existing potentials across novel chemical spaces. To address this challenge, we present a comprehensive
benchmark of 15 surrogate models for predicting ąppa}lat using the Phonix database, which contains 6,966 entries with anharmonic
phonon properties derived from first-principles calculations. Firstly, We categorize these surrogate models into three distinct groups: Physical-informed feature descriptors combined with ML models, end-to-end deep neural networks, and pre-trained MLIP-
embeddings combined with ML models. By evaluating model performance across random, space-group disjoint (testing generalization to unseen
crystal symmetries), and Out-Of-Distribution splits (OOD
dataset that testing extrapolation to property regimes beyond the training range) based on ąppa}lat, we probe both interpolation and exploration capabilities. Our results reveal that MLIP-embedded models excel in interpolation within well-sampled regions, deep neural network models especially ALiEGNN demonstrate superior robustness in OOD regimes critical for discovering novel low-ąppa}lat. Additionally, we find a systematic degradation in performance when the structural representation is reduced. Although surrogate models exhibit lower accuracy than direct simulations using first-principles calculation, they reduce computational costs by orders of magnitude, enabling efficient high-throughput screening of thermoelectric materials with minimal loss in generative design workflows.
Read the full abstract ▾
All authors Zeyu Wang, Shuya Yamazaki, Martin Hoffmann Petersen, Masato Ohnishi, Tomiya Yamamoto, Wei Nong, Jianghai Wang, Ruiming Zhu, Masatoshi Hanai, Michimasa Morita, Toyotaro Suzumura, Zekun Ren, Junichiro Shiomi, Kedar Hippalgaonkar
Materials Science · Cross-listed from physics.chem-ph
Gel-Chemistry-Controlled Heavy-Metal Transport and Retention in Cementitious Gel Nanopores: A Molecular Dynamics Study
Weiqiang Chen, Qiyao He and Kai Gong
Cementitious materials are widely used for hazardous-waste encapsulation, yet molecular mechanisms governing heavy-metal ion retention across gel chemistries remain insufficiently resolved. Previous MD studies have focused on individual gel systems and pore-averaged metrics, limiting direct comparison across gel chemistries. Here, classical molecular dynamics simulations were used to investigate adsorption-controlled mobility of Pb2+, Ba2+, and Cs+ in nanopores of C-S-H, C-(N)-A-S-H, and N-A-S-H gels. Combining pore-averaged and spatially resolved diffusivity, residence-time analysis, ion-density profiles, 2D adsorption maps, radial distribution functions, coordination analysis, and interfacial binding-strength descriptors establishes a framework linking gel surface chemistry to mobility suppression while distinguishing local mobility from spatial ion partitioning effects on pore-averaged transport. Ion mobility is reduced in all gel nanopores relative to bulk, but the extent and mechanism vary strongly with gel chemistry. C-(N)-A-S-H with higher interfacial Al/Si substitution exhibits the strongest retention, driven by ion accumulation around Al-linked oxygen species via an ion-exchange-like mechanism with charge-balancing Na+. C-S-H immobilizes ions primarily through surface hydroxyl oxygens and Ca-mediated linkages, whereas N-A-S-H exhibits more distributed binding environments. Pb2+ and Ba2+ show broadly similar immobilization mechanisms, whereas Cs+ exhibits more gel-dependent interactions with silicate and aluminosilicate oxygen sites. A relative total binding strength (rTBS) descriptor shows a strong positive correlation with ion immobilization across gel types, ion species, and pore sizes. These results clarify gel- and ion-specific retention mechanisms and link interfacial binding strength to pore-averaged mobility suppression in idealized cementitious nanopores.
Read the full abstract ▾
Materials Science
$G^0W^0$ implementation based on the pseudopotential and numerical-atomic-orbital basis-set framework: Algorithms and benchmarks
Huanjing Gong, Min-Ye Zhang, Peize Lin et al. (+4 more)
The $GW$ method delivers substantially improved accuracy in electronic band structure calculations over conventional Kohn-Sham density functional theory (KS-DFT) by explicitly incorporating the electron self-energy effect beyond mean-field approximations. Despite many existing implementations, a periodic $GW$ implementation within the framework of numerical atomic orbitals (NAO) combined with the pseudopotential (PP) scheme has not been reported. This is urgently needed given the increasing popularity of the NAO-PP framework in KS-DFT calculations and its importance for the development of machine-learning electronic-structure approaches. In this work, we present an efficient NAO-PP-based $G^0W^0$ computational framework by interfacing the first-principles software package ABACUS with LibRPA – a library for performing low-scaling random-phase approximation and $GW$ calculations based on NAOs. Our approach employs the localized resolution of identity (LRI) technique with a novel compression scheme, significantly improving both computational efficiency and numerical stability. In addition, an analytic treatment of the small-q limit of the microscopic dielectric function reduces the need for dense q-point sampling. Furthermore, we propose a practical strategy to select a suitable KS-DFT pseudopotential prior to $G^0W^0$ calculations by examining the frequency-dependent macroscopic dielectric function. Systematic
benchmarks validate the effectiveness of our compression scheme and real-space tensor filtering strategies, demonstrating both high accuracy and significant computational efficiency gains. Comparisons with established $G^0W^0$ implementations show excellent agreement in band structures and band gaps, confirming ABACUS+LibRPA as a reliable and efficient platform for large-scale $G^0W^0$ simulations.
Read the full abstract ▾
All authors Huanjing Gong, Min-Ye Zhang, Peize Lin, Bohan Jia, Ziqing Guan, Lixin He, Xinguo Ren
Materials Science · Cross-listed from physics.ins-det
Bridging the Gap between Extreme Environments and Precision Measurements: Recent Progress in Megagauss Physics
Shojiro Takeyama
Ultrastrong
magnetic fields, ranging from 100~T to 1,000~T, are generated exclusively by destructive pulsed magnets. While various generation methods exist, this review focuses on the Single-Turn Coil (STC) and Electromagnetic Flux Compression (EMFC) techniques, which provide optimal environments for high-precision measurements in materials science. First, we present recent technological breakthroughs in the EMFC method that have successfully achieved fields exceeding 1,000~T. We then describe specialized measurement infrastructures for magneto-optics, magnetization, and magneto-transport, highlighting the development of miniaturized all-plastic cryostats and custom sample holders designed for the dual extremes of cryogenic temperatures and megagauss fields. Representative physical phenomena revealed through these techniques are discussed, including
quantum phase transitions in frustrated magnets, Aharonov–Bohm effects in carbon nanotubes, and
semiconductor-to-metal transitions in strongly correlated systems. Furthermore, we address emerging measurement platforms such as magnetostriction, specific heat, and ultrasound velocity. Throughout this review, we emphasize the instrumentation and experimental refinements that ensure reliable data acquisition in the ultrastrong pulsed field regime.
Read the full abstract ▾