Materials Science · Cross-listed from physics.comp-ph
Discovery of Hyperelastic Constitutive Laws from Experimental Data with EUCLID
Arefeh Abbasi, Maurizio Ricci, Pietro Carrara et al. (+4 more)
We assess the performance of EUCLID, Efficient Unsupervised Constitutive Law Identification and Discovery, a recently proposed framework for automated discovery of constitutive laws, on experimental data. Mechanical tests are performed on natural rubber specimens spanning simple to complex geometries, from which we collect both global, force elongation, and local, full-field displacement, measurements. Using these data, we obtain constitutive laws via two routes, the conventional identification of unknown parameters in a priori selected material models, and EUCLID, which automates model selection and parameter identification within a unified model-discovery pipeline. We compare the two methodologies using global versus local data, analyze predictive accuracy, and examine generalization to unseen geometries. Moreover, we quantify the experimental noise, investigate the coverage of the material state space achieved by each approach and discuss the relative performance of different
datasets and different a priori chosen models versus EUCLID.
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All authors Arefeh Abbasi, Maurizio Ricci, Pietro Carrara, Moritz Flaschel, Siddhant Kumar, Sonia Marfia, Laura De Lorenzis
Materials Science · Cross-listed from physics.app-ph
A novel approach to modelling the properties of HEMTs operating in the saturation region
Kaiyuan Zhao, Guangfen Yao, Xiaoyu Cheng et al. (+3 more)
Currently, the ASM-HEMT model, QPZD model and EPFL model are all based on the three-terminal potential as the core, and relate the electrical characteristics such as I-V and C-V to Vd, Vs and Vg, so as to accurately build the HEMT model with high accuracy and fast convergence. However, there has not yet been a model based on three-terminal potentials that can quickly model the velocity saturation effect as well as the carrier concentration distribution and the electric field distribution inside the HEMT, which makes the existing models have to rely on a number of empirical parameters in the modelling process, which lacks the actual physical significance. In previous publications, models for the electric field, carrier concentration distribution based on the effective length of the gate were presented. In this paper, the model proposed in previous publications is improved to enable: (1) the calculation of the current Ids without relying on the Newton iterative method with fast simulation convergence behavior; (2) The Vdsat when the HEMT reaches saturation at different Vgo is redefined instead of using Vdsat = Vgo; (3) The expression of the v-E relationship is redefined relying on the different transport of carriers, which solves the problem of the large model error of the electric field distribution in the region below the gate, and makes the model's accuracy of the I-V characteristic further improved. The model was validated by characterising the I-V and E-V of the HEMT through TCAD simulation with RMSE below 5%.
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All authors Kaiyuan Zhao, Guangfen Yao, Xiaoyu Cheng, Luqiao Yin, Kailin Ren, Jianhua Zhang
Materials Science · Cross-listed from physics.flu-dyn
Water wave scattering by a surface-mounted rectangular anisotropic elastic plate
Ben Wilks, Michael H. Meylan, Zachary J. Wegert et al. (+2 more)
This paper considers the problem of water wave scattering by a rectangular anisotropic elastic plate mounted on the ocean surface, with either free, clamped or simply-supported edges. The problem is obtained as an expansion over the dry modes of the elastic plate, which are computed using a Rayleigh–Ritz method. In turn, the component diffraction and radiation problems are solved by formulating a boundary integral equation and solving numerically using a constant panel method. The results are presented to highlight the resonant responses of the plate under different forcing scenarios. In particular, we illustrate how the excitation of certain modes can be forbidden due to
symmetry.
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All authors Ben Wilks, Michael H. Meylan, Zachary J. Wegert, Vivien J. Challis, Ngamta Thamwattana
Materials Science · Cross-listed from physics.optics
Visible Imaging of Incoherent 1200-nm Light via Triplet–Triplet Annihilation Upconversion
Pournima Narayanan, Rabeeya Hamid, Linda Pucurimay et al. (+13 more)
Upconversion of low-energy
photons to higher-energy
photons provides an opportunity to surpass traditional limitations in fields such as 3D printing, photovoltaics, and photocatalysis. Triplet–triplet annihilation upconversion (TTA-UC) is particularly appealing for such applications as it can efficiently upconvert low-intensity, incoherent light. However, previously demonstrated thin-film TTA systems are simultaneously constrained by modest efficiencies and limited reach into the near infrared (NIR). Here, we design a single-layer thin-film bulk heterojunction that integrates PbS
quantum dots (QDs) as tunable NIR absorbers within an organic
semiconductor matrix of TES-ADT, achieving large anti-Stokes shifts up to 500 nm and high internal
quantum efficiencies across the NIR-I and NIR-II windows (800-1200 nm). Through the incorporation of 5-tetracene carboxylic acid ligands on the PbS QD surface, the yield of sensitized triplets was boosted, as confirmed by transient absorption and time-resolved photoluminescence measurements. The resulting films demonstrated a 15-fold improvement in UC efficiency. Furthermore, we demonstrate visible imaging of incoherent 1200 nm light via thin-film TTA-UC at incident intensities at the imaging mask as low as 20 mWcm$^2$, marking a significant advance toward practical implementation of solid-state NIR-to-visible upconversion.
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All authors Pournima Narayanan, Rabeeya Hamid, Linda Pucurimay, Ona Segura Lecina, Ben P. Carwithen, Jacob Schopp, Justin S. Edwards, Oluwaseun Noah Adeyeye, Demeng Feng, Diptarka Hait, Todd J. Martinez, Timothy W. Schmidt, Michael P. Nielsen, Murad J. Y. Tayebjee, Mikhail A. Kats, Daniel N. Congreve
Materials Science
Development and Validation of Interatomic Potential for Sc and Al-Sc Alloys: Thermodynamics, Solidification, and Intermetallic Ordering
Avik Mahata
We present a second-nearest-neighbor Modified Embedded Atom Method (2NN–MEAM) potential for Scandium (Sc) and Aluminum-Scandium (Al–Sc)
alloys that unifies cohesive, thermodynamic, and solidification behavior within a single transferable framework. The Sc component accurately reproduces cohesive energy,
lattice constants, defect energetics, and the experimental melting point obtained from two-phase coexistence, demonstrating reliable description of both hcp and
liquid phases. The Al–Sc binary interaction parameters were fitted using the L1$_2$–Al$_3$Sc reference and benchmarked against first-principles and calorimetric data. The potential reproduces the strong negative formation enthalpy of Al$_3$Sc (–0.45~eV~atom$^{-1}$), correct relative stability of competing phases, and realistic elastic properties. Mixing enthalpies of the
liquid alloy agree with ideal-associated-solution and CALPHAD models, confirming that the potential captures exothermic Al–Sc association in the melt. Molecular-dynamics simulations of solidification reveal the expected temperature and composition dependence of homogeneous nucleation. Pure Al crystallizes readily, while Al–1~at.%~Sc exhibits a longer incubation and slower growth at the same absolute temperature due to reduced undercooling and solute drag. Within the
alloy, ordered Al$_3$Sc-type L1$_2$ embryos appear spontaneously, with Sc atoms occupying cube-corner (B) sites surrounded by twelve Al neighbors. Energy–volume trajectories confirm that the potential links thermodynamics to microstructural
evolution. Overall, the developed 2NN–MEAM potential provides a quantitatively grounded basis for modeling melting, solidification, and intermetallic ordering in Sc and Al–Sc systems, enabling future multicomponent
alloy design and large-scale nucleation studies.
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Materials Science
Advancing AI-Driven Analysis in X-ray Absorption Spectroscopy: Spectral Domain Mapping and Universal Models
Nina Cao, Pavan Ravindra, Shubha R. Kharel et al. (+6 more)
In recent years, rapid progress has been made in developing artificial intelligence (AI) and machine learning (ML) methods for x-ray absorption spectroscopy (XAS) analysis. Compared to traditional XAS analysis methods, AI/ML approaches offer dramatic improvements in efficiency and help eliminate human bias. To advance this field, we advocate an AI-driven XAS analysis pipeline that features several inter-connected key building blocks:
benchmarks, workflows, databases, and AI/ML models. Specifically, we present two case studies for XAS ML. In the first study, we demonstrate the importance of reconciling the discrepancies between simulation and experiment using spectral domain mapping (SDM). Our ML model, which is trained solely on simulated spectra, predicts an incorrect oxidation state trend for Ti atoms in a combinatorial zinc titanate film. After transforming the experimental spectra into a simulation-like representation using SDM, the same model successfully recovers the correct oxidation state trend. In the second study, we explore the development of universal XAS ML models that are trained on the entire periodic table, which enables them to leverage common trends across elements. Looking ahead, we envision that an AI-driven pipeline can unlock the potential of real-time XAS analysis to accelerate scientific discovery.
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All authors Nina Cao, Pavan Ravindra, Shubha R. Kharel, Chuntian Cao, Boyang Li, Xuance Jiang, Matthew R. Carbone, Xiaohui Qu, Deyu Lu
Materials Science
Morphotropic Phase Boundary (MPB) Induced Enhancement of Ferroelectric and Piezoelectric Properties in Li and Ta modified K0.5Na0.5NbO3
Satyaranjan Sahoo, Dhiren K. Pradhan, Shalini Kumari et al. (+9 more)
Lead-free (K0.48Na0.48Li0.04)(Nb1-xTax)O3 (KNLNT-x) ceramics were synthesized to study the effects of Li and Ta substitution on phase transition behavior, microstructure, and ferroelectric, dielectric, and piezoelectric properties. X-ray diffraction and Raman spectroscopy show that compositions with x < 0.10 exhibit a single orthorhombic (Amm2) phase, while 0.10 <= x <= 0.20 show coexistence of orthorhombic and tetragonal (Amm2 + P4mm) phases. For x > 0.20, a single tetragonal (P4mm) phase is obtained. Microstructural analysis shows a dense ceramic with decreasing grain size as Ta concentration increases. Temperature-dependent dielectric studies reveal two transitions: orthorhombic-tetragonal (TO-T) and tetragonal-cubic (TC). Both transition temperatures decrease systematically with increasing Ta, and TO-T shifts below room temperature for x > 0.15. The composition KNLNT-0.20 exhibits the highest dielectric constant (Er = 556) and piezoelectric coefficient (d33 = 159 pC/N). The enhanced piezoelectric response is attributed to a morphotropic phase boundary rather than a shift of the polymorphic phase boundary temperature. A composition-temperature phase diagram was constructed based on XRD, Raman, and dielectric data.
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All authors Satyaranjan Sahoo, Dhiren K. Pradhan, Shalini Kumari, Abhisikta Sahu, Koyal Suman Samantaray, Vikas N. Thakur, Anupam Mishra, M. M. Rahaman, Ashok Kumar, Reji Thomas, Philip D. Rack, Dillip K. Pradhan
Materials Science
Unusual dependence on the angle of magnetic field for the spin Hall magnetoresistance of monodomain epitaxial BiFeO3 thin films
Yongjian Tang, Pratap Pal, Matthew Roddy et al. (+7 more)
Spin Hall magnetoresistance (SMR) measurements provide a way to probe the surface
spin structure of insulating
magnetic materials. Such measurements produce resistance signals of the form {$\Delta$}R {$\propto$} cos[2($\alpha$-$\alpha$$_0$)], where $\alpha$ is the angle between the current and the external in-plane
magnetic field. Previous experiments on a wide range of materials have found $\alpha$$_0$ = 0$\deg$ for ferromagnets and $\alpha$$_0$ = 90$\deg$ for antiferromagnets. Here we investigate SMR in
bilayers of Pt with monodomain BiFeO$_3$ multiferroic epitaxial thin films. We observe signals of the form {$\Delta$}R {$\propto$} cos[2($\alpha$-$\alpha$$_0$)] but surprisingly the angle $\alpha$$_0$ can take values very different from 90$\deg$ or 0$\deg$, with large variations from sample to sample. The aim of the paper is to report this striking departure from the expected
magnetic field dependence of SMR and to encourage consideration of possible microscopic mechanisms.
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All authors Yongjian Tang, Pratap Pal, Matthew Roddy, Jon Schad, Ruofan Li, Joongwon Lee, Farhan Rana, Tianxiang Nan, Chang-Beom Eom, Daniel C. Ralph
Materials Science · Cross-listed from cond-mat.str-el
Robust Orbital-Selective Flat Bands in Transition-Metal Oxychlorides
Xiangyu Luo, Ludovica Zullo, Sahaj Patel et al. (+10 more)
Flat electronic bands, which amplify electron correlations by quenching kinetic energy, provide an ideal foundation for exotic
quantum phases. However, prevailing strategies – including geometrically frustrated
lattices, moire superlattices and heavy-
fermion physics – suffer from inherent trade-offs among robustness, tunability and orbital selectivity, limiting their broad applicability. Here, we unveil an intrinsic orbital-selective flat-band mechanism in the van der Waals materials NbOCl2 and TaOCl2, directly observed by angle-resolved photoemission spectroscopy (ARPES) and understood through density functional theory (DFT) and Wannier analysis. Crucially, we experimentally demonstrate that this momentum-independent flat band exhibits remarkable robustness, surviving from the bulk
crystal down to the few-layer limit at room temperature. Our theoretical analysis traces its origin to the hybridization between Nb-dz2 orbital chains and the Lieb-like dx2-y2 sublattice, which is further reinforced by Peierls dimerization. Our findings not only establish transition-metal oxychlorides as a robust and tunable platform for flat-band-driven correlated phases under ambient conditions, but also uncover a new orbital-selective design principle for realizing flat bands in
quantum materials.
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All authors Xiangyu Luo, Ludovica Zullo, Sahaj Patel, Dongjin Oh, Qian Song, Asish K. Kundu, Anil Rajapitamahuni, Elio Vescovo, Natalia Olszowska, Rafal Kurleto, Dawid Wutke, Giorgio Sangiovanni, Riccardo Comin
Materials Science · Cross-listed from cond-mat.str-el
Reconstructing Spin Hamiltonians of 2D Gutzwiller-Projected Wavefunctions
Lucas Z. Brito and J. B. Marston
We apply the correlation
matrix Hamiltonian reconstruction technique to the two-dimensional Gutzwiller-projected
Fermi sea and {\pi}-flux states on finite-sized square and triangular
lattices. Our results indicate no
spin Hamiltonian with simple local interaction terms stabilizes such states for finite system sizes. We develop a quantitative assessment of the importance of local interactions to the stabilization of these
liquid states. Lastly, we systematically assess arguments for the origin of local terms driving a Gutzwiller-projected ground state.
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Materials Science · Cross-listed from cond-mat.mes-hall
Néel vector controlled charge and spin transport in altermagnetic junctions
Shubham Ghadigaonkar, Sachchidanand Das and Abhiram Soori
Altermagnets (AMs) -
magnetic materials that have
spin-split bandstructure with zero net
spin polarization can be classified as weak or strong depending upon the strength of altermagnetic term in the
Hamiltonian. We theoretically investigate electron transport in junctions between the two AMs in strong and weak altermagnetic phases. The charge and
spin conductivities are analyzed as functions of angle $\theta$ between the Néel vectors of the two AMs. In the strong AM regime, the charge conductivity vanishes as $\theta \to \pi$, while in the weak AM regime it remains finite. Introducing a normal metal (NM) between two AMs leads to Fabry-Pérot-type oscillations in charge conductivity which can be controlled by an applied gate voltage. In the strong regime, transport in AM-NM-AM junctions is dominated by up-
spin electrons, whereas both
spin channels contribute in the weak regime. These results highlight the potential of AM-based
heterostructures for spintronic applications, such as
spin filters, and
quantum interference-based spintronic devices, where tunable
spin-dependent transport and interference effects can be utilized in electronic devices without a need for externally applied
magnetic field.
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Materials Science · Cross-listed from cond-mat.mes-hall
Disorder-assisted Spin-Filtering at Metal/Ferromagnet Interfaces: An Alternative Route to Anisotropic Magnetoresistance
Ivan Iorsh and Mikhail Titov
We introduce a minimal interface-scattering mechanism that produces a sizable anisotropic magnetoresistance (AMR) in metal/ferromagnet
bilayers (e.g., Pt/YIG) without invoking bulk
spin or orbital
Hall currents. In a $\delta$-layer model with interfacial exchange and Rashba
spin-orbit coupling, charge transfer at a high-quality interface creates a
spin-selective phase condition (interfacial
spin filtering) that suppresses backscattering for one
spin projection while enhancing momentum relaxation for the other. The resulting resistance anisotropy peaks at an optimal metal thickness of a few nanometers, quantitatively reproducing the thickness and angular dependences typically attributed to
spin Hall magnetoresistance (SMR), as well as its characteristic magnitude. Remarkably, the maximal AMR scales linearly with the smaller of the two coupling strengths - exchange or
spin-orbit, highlighting a mechanism fundamentally distinct from SMR. Our scattering formulation maps onto Boltzmann boundary conditions and predicts other clear discriminants from SMR, including strong sensitivity to interfacial charge transfer and disorder.
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Materials Science · Cross-listed from cond-mat.soft
Aging and configurational memories at rough frictional interfaces
Kasra Farain and Daniel Bonn
Frictional interfaces retain distinct
memories of how they were sheared and how long they have rested, yet rate-and-state descriptions typically compress these histories into a single state variable. Here we combine nanometer-per-second sliding experiments on rough multi-asperity contacts with different protocols to disentangle temporal and configurational
memories at frictional onset. We identify a broad friction force peak associated with shear-driven reorganization of the load-bearing contact network. By contrast, holding a previously sheared system at rest in an arrested configuration produces a much narrower friction force peak that grows approximately logarithmically with hold time and relaxes over nanometer-scale slip distances. Configurational disorder without waiting regenerates only the broad peak, whereas waiting without configurational disorder generates only the aging peak. These results show that aging and configurational disorder write and read experimentally separable frictional
memories, and that static friction is a protocol-dependent quantity rather than a fixed material property.
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Materials Science
Identification of formation of amorphous Si phase in SiOxNy films produced by plasma enhanced chemical vapor deposition
M. V. Voitovych, A. Sarikov, V. O. Yukhymchuk et al. (+2 more)
Peculiarities of formation of inclusions of amorphous Si (a-Si) phase in Si-rich Si oxynitride films grown by
plasma-enhanced chemical vapor deposition (PECVD) are studied by combined Raman scattering and infrared (IR) absorption spectroscopy. The Raman scattering results identify presence of a-Si phase in the studied films at the relative Si content exceeding a threshold value of about 0.4. The a-Si amount correlates with the concentration of hydrogen in the films, the presence of which is detected by characteristic IR absorption bands corresponding to Si-H bending (about 660 cm-1) and stretching (a composite band in the range of about 1900-2400 cm-1) vibrations. The method of deconvolution of IR absorbance spectra in the range of about 600 to 1300 cm-1 developed earlier is used to reliably separate the IR band at about 660 cm-1. This band is identified to origin from the amorphous Si phase within the studied Si oxynitride films. This makes it possible to propose IR spectroscopy with analysis of the low-wavenumber part of the spectra as an efficient method of identifying phase composition of Si-rich Si oxynitride films. The obtained results contribute to understanding of the regularities of formation of phase compositions of PECVD grown Si oxynitride films and are useful for controlling the films properties for practical applications.
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All authors M. V. Voitovych, A. Sarikov, V. O. Yukhymchuk, V. V. Voitovych, M. O. Semenenko
Materials Science
Unique Hierarchical Rotational Dynamics Induces Ultralow Lattice Thermal Conductivity in Cyanide-bridged Framework Materials
Zhunyun Tang, Xiaoxia Wang, Jin Li et al. (+4 more)
The pursuit of materials combining light constituent elements with ultralow
lattice thermal conductivity ($\kappa_{\mathrm{L}}$) is crucial to advancing technologies like thermoelectrics and thermal barrier coatings, yet it remains a formidable challenge to date. Herein, we achieve ultralow $\kappa_{\mathrm{L}}$ in lightweight cyanide-bridged framework materials (CFMs) through the rational integration of properties such as the hierarchical vibrations exhibited in superatomic structures and rotational dynamics exhibited in perovskites. Unique hierarchical rotation behavior leads to multiple negative peaks in Grüneisen parameters across a wide frequency range, thereby inducing pronounced negative thermal expansion and strong cubic anharmonicity in CFMs. Meanwhile, the synergistic effect between large four-
phonon scattering phase space (induced by
phonon quasi-flat bands and wide bandgaps) and strong quartic anharmonicity (associated with rotation modes) leads to
giant quartic anharmonic scattering rates in these materials. Consequently, the $\kappa_{\mathrm{L}}$ of these CFMs decreases by one to two orders of magnitude compared to the known perovskites or perovskite-like materials with equivalent average atomic masses. For instance, the Cd(CN)$_{2}$, NaB(CN)$_{4}$, LiIn(CN)$_{4}$, and AgX(CN)$_{4}$ (X = B, Al, Ga, In) exhibit ultralow room-temperature $\kappa_{\mathrm{L}}$ values ranging from 0.35 to 0.81 W/mK. This work not only establishes CFMs as a novel and rich platform for studying extreme
phonon anharmonicity, but also provides a new paradigm for achieving ultralow thermal conductivity in lightweight materials via the conscious integration of hierarchical and rotational dynamics.
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All authors Zhunyun Tang, Xiaoxia Wang, Jin Li, Chaoyu He, Mingxing Chen, Chao Tang, Tao Ouyang
Materials Science
Substitutional sulfur and its vibrational fingerprints in Sb$_2$Se$_3$
F. Herklotz, E. V. Lavrov, A. Herklotz et al. (+4 more)
The configurational behavior of sulfur in antimony triselenide (Sb$_2$Se$_3$) is investigated by combining infrared absorption spectroscopy with density functional theory. Four sulfur-related local vibrational modes are identified at 249, 273, 283, and 312~cm$^{-1}$ in melt-grown single
crystals prepared from Sb$_2$Se$_3$ granulate. Their assignment to sulfur is confirmed through controlled indiffusion experiments using Sb$_2$S$_3$ and elemental sulfur, as well as isotope-substitution studies with $^{34}$S, which produce the expected frequency shifts. Polarization-resolved measurements, together with theoretical calculations of local vibrational modes, demonstrate that the observed spectral features are fully consistent with substitutional sulfur on the three inequivalent selenium sites of Sb$_2$Se$_3$.
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All authors F. Herklotz, E. V. Lavrov, A. Herklotz, V.V. Melnikov, T. P. Shalvey, J. D. Major, and K. Durose
Materials Science
Orbital magnetization in Sierpinski fractals
L. L. Lage, Tarik. P. Cysne and A. Latgé
Orbital magnetization (OM) in Sierpinski carpet (SC) and triangle (ST) fractal is theoretically investigated by using Haldane model as a prototypical example. The OM calculation is performed following two distinct approaches; employing the definition and local markers formalism. Both methods coincides for all systems analyzed. For the SC, higher fractal generations create a dense set of edge states, resulting in a staircase profile, leading to oscillations in the magnetization as a function of the chemical potential. In contrast, the ST self-similarity produces distinct fractal-induced spectral gaps, which manifest as constant plateaus in the magnetization. The STs exhibit a pronounced sensitivity to edge terminations. Our results reveal how
quantum confinement in fractal structures affects the electronic orbital angular momentum, pointing to possible pathways for exploring novel orbitronics in systems with complex geometries.
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Materials Science
Contrasting properties of free carriers in $n$- and $p$-type Sb$_2$Se$_3$
F. Herklotz, E. V. Lavrov, T. D. C. Hobson et al. (+3 more)
We report persistent photoconductivity in $p$-type Sb$_2$Se$_3$ single
crystals doped with Cd or Zn, where enhanced conductivity remains for hours after illumination ceases at temperatures below $\sim$25~K. Comparative transport and infrared absorption measurements, including on $n$-type Cl-doped counterparts, reveal strong indications that hole transport in Sb$_2$Se$_3$ is more strongly affected by intrinsic carrier scattering than electron transport. These results point to a fundamental asymmetry in charge carrier dynamics and highlight the potential role of polaronic effects in limiting hole mobility in this quasi-one-dimensional
semiconductor.
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All authors F. Herklotz, E. V. Lavrov, T. D. C. Hobson, T. P. Shalvey, J. D. Major, K. Durose
Materials Science
Uniaxial Magnetic Anisotropy and Type-X/Y Current-Induced Magnetization Switching in Oblique-Angle-Deposited Ta/CoFeB/Pt and W/CoFeB/Pt Heterostructures
Amir Khan, Shalini Sharma, Tiago de Oliveira Schneider et al. (+1 more)
Planar current-induced magnetization switching (CIMS) driven by
spin-orbit torque (SOT) requires an in-plane uniaxial
magnetic anisotropy (UMA), which can be induced by oblique-angle sputter deposition of the heavy-metal underlayer in heavy-metal/ferromagnet
heterostructures. To enhance the SOT efficiency, we employ trilayer
heterostructures of (Ta or W)/CoFeB/Pt, where the CoFeB layer exhibits a UMA of 50 mT at 2 nm thickness of Ta or W. The magnetization reversal in
Hall-bar devices is detected through unidirectional
spin Hall magnetoresistance (USMR) for the type Y geometry (easy-axis transverse to current) and planar
Hall measurements for the type X geometry (easy-axis parallel to current). Both configurations exhibit CIMS with sub-microsecond current pulses, reaching switching current densities as low as $2 \times 10^{11}$ A/m$^2$ for a W (4 nm)/CoFeB (1.4 nm)/Pt (2 nm) stack with a UMA of 146 mT. Macrospin simulations reproduce the type Y switching as coherent magnetization rotation, whereas the type X devices switch at much lower currents than predicted, indicating that nucleation and domain-wall propagation dominate reversal in this geometry. Our results show that combining oblique-angle deposition with easy-axis engineering enables deterministic, field-free switching, paving the way for future low-power spintronic devices.
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All authors Amir Khan, Shalini Sharma, Tiago de Oliveira Schneider, Markus Meinert
Materials Science
Enhanced Secondary Electron Detection of Single Ion Implants in Silicon Through Thin SiO2 Layers
Ella B Schneider, Oscar G Lloyd-Willard, Kristian Stockbridge et al. (+7 more)
Deterministic placement of single dopants is essential for scalable
quantum devices based on group-V donors in silicon. We demonstrate a non-destructive, high-efficiency method for detecting individual ion implantation events using secondary electrons (SEs) in a focused ion beam (FIB) system. Using low-energy Sb ions implanted into undoped silicon, we achieve up to 98% single-ion detection efficiency, verified by calibrated ion-current measurements before and after implantation. The technique attains ~30 nm spatial resolution without requiring electrical contacts or device fabrication, in contrast to ion-beam-induced-current (IBIC) methods. We find that introducing a controlled SiO2 capping layer significantly enhances SE yield, consistent with an increased electron mean free path in the
oxide, while maintaining high probability of successful ion deposition in the underlying substrate. The yield appears to scale with ion velocity, so higher projectile mass (e.g. Yb, Bi etc) requires increased energy to maintain detection efficiency. Our approach provides a robust and scalable route to precise donor placement and extends deterministic implantation strategies to a broad range of material systems and
quantum device architectures.
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All authors Ella B Schneider, Oscar G Lloyd-Willard, Kristian Stockbridge, Mark Ludlow, Sam Eserin, Luke Antwis, David C Cox, Roger P Webb, Ben N Murdin, Steve K Clowes
Materials Science
Ferroelectric amplitude switching and continuous memory
Gye-Hyeon Kim, Tae Hyun Jung, Seungjoon Sun et al. (+11 more)
Although ferroelectric systems inherently exhibit binary switching behavior, recent advances in analog
memory device have spurred growing interest in achieving continuous
memory states. In this work, we demonstrate ferroelectric amplitude switching at the mesoscopic scale in compositionally graded Ba1-xSrxTiO3
heterostructures, enabling continuous modulation of polarization magnitude without altering its direction, which we defined as amplitude switching. Using switching current measurement, piezoresponse force microscopy and Landau-Ginzburg-Devonshire simulations, we reveal that compositionally graded ferroelectric
heterostructure can possess amplitude switching behavior through a double well potential with flattened minima. This behavior supports stable, continuous polarization states and establishes a new platform for analog
memory applications. These findings introduce amplitude switching as a new dynamic of the order parameter, paving the way for energy-efficient and reliable analog
memory systems.
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All authors Gye-Hyeon Kim, Tae Hyun Jung, Seungjoon Sun, Jung Kyu Lee, Jaewoo Han, P. Karuna Kumari, Jin-Hyun Choi, Hansol Lee, Tae Heon Kim, Yoon Seok Oh, Seung Chul Chae, Se Young Park, Sang Mo Yang, Changhee Sohn
Materials Science
First-Principles Approach to Spin Excitations in Noncollinear Magnetic Systems
Hsiao-Yi Chen, Ryotaro Arita and Yusuke Nomura
We present a first-principles method based on density functional theory and many-body perturbation theory for computing
spin excitations in
magnetic systems with noncollinear
spin textures. Traditionally, the study of
magnetic excitations has relied on
spin models that assume
magnetic moments to be localized. Beyond this restriction, recent $ab~initio$ methods based on Green's functions within the local
spin-density approximation have emerged as a general framework for calculating
magnetic susceptibilities. However, their application has so far been largely limited to collinear
ferromagnetic and
antiferromagnetic systems. In this work, we extend this framework and enable the treatment of large-scale noncollinear
magnetic systems by leveraging a Wannier-basis representation and implementing an ansatz potential method to reduce computational cost. We apply our method to the
spin-spiral state of LiCu$_2$O$_2$, successfully capturing its steady-state
spin-rotation pitch in agreement with the experimental measurement and resolving the characteristic
magnon dispersion. We further analyze the interplay between the spiral
spin structure and the on-site
spin-exchange splitting, and elucidate the crucial role of
magnetic dipoles on ligand ions in mediating effective
ferromagnetic interaction among the primary
spins on Cu$^{2+}$ ions. Finally, we provide a theoretical prediction of the
magnon dispersion on top of the helical
spin background in high agreement with the experimental measurement. Overall, this work establishes a general and computationally efficient framework for simulating collective
spin dynamics in noncollinear
magnetic systems from first principles, exemplified by – but not limited to –
spin-spiral states.
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Materials Science
Multiscale Models For Perovskite Optimisation
Philippe Baranek, James P. Connolly, Antoine Gissler et al. (+3 more)
This paper presents a multiscale approach to evaluate perovskite
solar cell performance which determines material properties at the atomistic scale with first-principles calculations, and applies them in macro-scale device models. This work focuses on the MAPbI3 (MA = CH3NH3) perovskite and how its phase transitions impact on its optical, electronic, and structural properties which are investigated at the first-principles level. The obtained data are coupled to a numerical drift-
diffusion device model enabling evaluation of the performance of corresponding single junction devices. The first-principles simulation applies a hybrid exchange-correlation functional adapted to the studied family of compounds. Validation by available experimental data is presented from materials properties to device performance, justifying the use of the approach for predictive evaluation of existing and novel perovskites. The coupling between atomistic and device models is described in terms of a framework for exchange of optical, vibrational, and electronic parameters between the two scales. The result of this theoretical investigation is a methodology for designing and optimising perovskite materials for both
cell performance and stability, the key obstacle in the societal implementation of these record-breaking new materials.
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All authors Philippe Baranek, James P. Connolly, Antoine Gissler, Philip Schulz, Michel Rérat, Roberto Dovesi
Materials Science
Laser-Induced Heating in Diamonds: Influence of Substrate Thermal Conductivity and Interfacial Polymer Layers
Md Shakhawath Hossain, Jiatong Xu, Thi Ngoc Anh Mai et al. (+9 more)
Diamonds hosting color centers possess intrinsically high thermal conductivity; therefore,
laser-induced heating has often received little
attention. However, when placed on substrates with low thermal conductivity, localized heating of diamonds under
laser excitation can become significant, and the presence of an interfacial
polymer layer between substrate and diamond further amplifies this effect. Yet, the relationship between substrate thermal conductivity,
polymer thickness, and
laser heating remains to be established. Here, a systematic investigation is presented on
laser-induced heating of silicon-vacancy diamond on substrates with varying thermal conductivity and interfacial
polymer thickness. Results reveal that even at a low excitation power of 737~$\mu$W/$\mu$m$^2$, thin amorphous holey carbon – the lowest-conductivity substrate ($\sim$0.2~W~m$^{-1}$~K$^{-1}$) studied – exhibits substantial heating, while glass ($\sim$1.4~W~m$^{-1}$~K$^{-1}$) and polydimethylsiloxane (PDMS, $\sim$0.35~W~m$^{-1}$~K$^{-1}$) show noticeable heating only above 2.95~mW/$\mu$m$^2$. For
polymer interlayers, a thickness of just 2.2~$\mu$m induces significant heating at 2.95~mW/$\mu$m$^2$ and above, highlighting strong influence of both substrate and
polymer thickness on local heating response. Experimental findings are further validated using COMSOL Multiphysics simulations with a steady-state 3D heat transfer model. These results provide practical guidance for substrate selection and sample preparation, enabling optimization of conditions for optical thermometry and
quantum sensing applications.
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All authors Md Shakhawath Hossain, Jiatong Xu, Thi Ngoc Anh Mai, Nhat Minh Nguyen, Trung Vuong Doan, Chaohao Chen, Qian Peter Su, Yongliang Chen, Evgeny Ekimov, Toan Dinh, Xiaoxue Xu, Toan Trong Tran
Materials Science · Cross-listed from cond-mat.supr-con
Effect of decorating NiO nanoparticles on superconducting properties of YBCO
D.M. Gokhfeld, S.V. Semenov, M.I. Petrov et al. (+4 more)
The influence of adding 23 nm NiO nanoparticles on the
magnetic hysteresis loops and critical current density of the high-temperature
superconductor YBa2Cu3O7-d has been investigated. The samples were prepared using a fast annealing method that prevents chemical interaction between the components and does not reduce the critical temperature of the
superconductor. Compared to the undoped YBCO sample, the critical current density increases in the samples doped with NiO nanoparticles in
magnetic fields greater than 6 kOe. The sample containing 0.5 weight percent of NiO nanoparticles exhibits the greatest enhancement in critical current density at 10 kOe (1.36 times greater than the undoped sample).
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All authors D.M. Gokhfeld, S.V. Semenov, M.I. Petrov, I.V. Nemtsev, M.S. Molokeev, V.L. Kirillov, O.N. Martyanov
Materials Science
Magnetization, excitations, and microwave power absorption in transition-metal/rare-earth ferrimagnets with disorder
D. A. Garanin and E. M. Chudnovsky
Efficient numerical routines are developed for numerical studies of the dependence of the
equilibrium magnetic states, excitations, and microwave power absorption on temperature and composition in transition-metal/rare-earth ferrites, including the reversal of the Néel vector occurring on both temperature and the concentration of the rare-earth atoms. It results in a drastic change in the behavior at the magnetization and angular-momentum compensation points. Dominant uniform oscillation modes are obtained by computing the magnetization correlation function. They are compared with the analytical solution, which is analyzed in detail. The fluctuation-dissipation
theorem is used to compute the frequency dependence of the absorbed microwave power. A good agreement with analytical results is demonstrated. Disorder caused by random positions of rare-earth atoms in a diluted RE system leads to multiple localized modes that converge into broad absorption maxima as the size of the system increases. The power absorption integrated over frequency exhibits a minimum at the compensation point.
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Materials Science · Cross-listed from cond-mat.str-el
Impurity-induced spin density wave in the thermoelectric layered cobaltite [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$]
Motoya Takenaka, Shogo Yoshida, Yoshiki J. Sato et al. (+1 more)
We investigate the Sn-substitution effect on the thermoelectric transport properties of the layered cobaltite [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$] single
crystals, which exhibit a non-monotonic temperature variation of the electrical resistivity and the Seebeck coefficient owing to the complex electronic and
magnetic states. We find that the onset temperature of the short-range
spin-density-wave (SDW) formation increases with the substituted Sn content, indicating the
impurity-induced stabilization of the SDW order, reminiscent of the disorder/
impurity-induced
spin order in the cuprate
superconductors. The Seebeck coefficient is well related to such
impurity effects, as it is slightly enhanced below the onset temperatures, implying a decrease in the carrier concentration due to a pseudo-gap formation associated with the SDW ordering. We discuss the site-dependent substitution effects including earlier studies, and suggest that substitution to the conducting CoO$_2$ layers is essential to increase the onset temperature, consistent with the
impurity-induced SDW picture realized in the conducting layers with the cylindrical
Fermi surface.
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All authors Motoya Takenaka, Shogo Yoshida, Yoshiki J. Sato, Ryuji Okazaki
Materials Science
Comparison of Electroluminescence and Photoluminescence Imaging of Mixed-Cation Mixed-Halide Perovskite Solar Cells at Low Temperatures
Hurriyet Yuce-Cakir, Haoran Chen, Isaac Ogunniranye et al. (+4 more)
Halide perovskites have emerged as promising candidates for high-performance
solar cells. This study investigates the temperature-dependent optoelectronic properties of mixed-cation mixed-halide perovskite
solar cells using electroluminescence (EL) and photoluminescence (PL) hyperspectral imaging, along with current-voltage analysis. Luminescence images, which were converted to EL and PL external radiative efficiency (ERE) maps, revealed significant changes in the optoelectronic behavior of these devices at low temperatures. Specifically, we found that a significant source of heterogeneity in the low-temperature EL ERE maps below 240 K is related to local charge injection and extraction bottlenecks, whereas PL ERE maps show suppressed non-radiative recombination and significant improvements in efficiency throughout the investigated temperature range. The spatial distribution of ERE and its variation with applied current were analyzed, offering insights into charge-carrier dynamics and defect behavior. Our results reveal that while the perovskite layer exhibits enhanced ERE at low temperatures, charge injection barriers at the interfaces of the perovskite
solar cells significantly suppress EL and degrade the fill factor below 240 K. These findings reveal that a deeper understanding of the performance of perovskite
solar cells under low-temperature conditions is an essential step toward their potential application in space power systems and advanced
semiconductor devices.
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All authors Hurriyet Yuce-Cakir, Haoran Chen, Isaac Ogunniranye, Susanna M. Thon, Yanfa Yan, Zhaoning Song, Behrang H. Hamadani