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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Monday 6 April

Materials Science

Nonlocal Linear Instability Drives the Initiation of Motion of Rational and Irrational Twin Interfaces

Chang-Tsan Lu, Anthony Rollett and Kaushik Dayal

Twin boundaries play a central role in the functional behavior of martensitic materials, yet the mechanisms governing the initiation of their motion remain poorly understood for twins lying along irrational crystallographic directions. Here we present an atomistic investigation of the onset of motion of both rational and irrational twin interfaces in a two-dimensional model lattice with rectangular unit cells. Using quasistatic shear loading and full linear stability analysis, we show that the initiation of twin boundary motion is signaled by a nonlocal linear instability, marked by the vanishing of the lowest eigenvalue of the Hessian; the corresponding eigenmode predicts the atomic displacements that initiate motion. We find that irrational twin boundaries have significantly lower critical shear stress to initiate motion compared to rational twin boundaries. Further, we find that they display unusual mechanisms to initiate motion such as the formation of microtwins in directions orthogonal to the overall twin boundary. Finally, we compare various local measures against the nonlocal stability analysis, and find that the former do not capture that irrational twin boundaries initiate their motion at lower stresses compared to rational boundaries.
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Materials Science · Cross-listed from cond-mat.dis-nn

Interpretation of Crystal Energy Landscapes with Kolmogorov-Arnold Networks

Gen Zu, Ning Mao, Claudia Felser et al. (+1 more)

Characterizing crystalline energy landscapes is essential to predicting thermodynamic stability, electronic structure, and functional behavior. While machine learning (ML) enables rapid property predictions, the "black-box" nature of most models limits their utility for generating new scientific insights. Here, we introduce Kolmogorov-Arnold Networks (KANs) as an interpretable framework to bridge this gap. Unlike conventional neural networks with fixed activation functions, KANs employ learnable functions that reveal underlying physical relationships. We developed the Element-Weighted KAN, a composition-only model that achieves state-of-the-art accuracy in predicting formation energy, band gap, and work function across large-scale datasets. Crucially, without any explicit physical constraints, KANs uncover interpretable chemical trends aligned with the periodic table and quantum mechanical principles through embedding analysis, correlation studies, and principal component analysis. These results demonstrate that KANs provide a powerful framework with high predictive performance and scientific interpretability, establishing a new paradigm for transparent, chemistry-based materials informatics.
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All authors Gen Zu, Ning Mao, Claudia Felser, Yang Zhang

Materials Science

Broken Symmetry-driven Weyl Semimetal Phase in Zn-Substituted EuMn$_2$Sb$_2$

Deep Sagar and Arti Kashyap

The interplay between magnetism and electronic topology offers a powerful route to realizing emergent quantum phases. Here, we show that Zn substitution in the layered compound EuMn$_2$Sb$_2$ drives a transition from a C-type antiferromagnetic semiconductor to an intrinsic magnetic Weyl semimetal. Using first-principles calculations, we demonstrate that the parent compound hosts a gapped antiferromagnetic ground state, while Zn substitution alters the magnetic exchange interactions and stabilizes ferromagnetism. In the spin-orbit-coupled regime, the coexistence of broken time-reversal ($\mathcal{T}$) and inversion ($\mathcal{P}$) symmetries leads to the formation of Weyl nodes near the Fermi level. These nodes act as monopoles of Berry curvature and give rise to topologically protected Fermi-arc surface states. Our results identify EuMnZnSb$_2$ as a tunable platform where magnetism and topology are intrinsically coupled and establish chemical substitution as a viable strategy to engineer magnetic Weyl semimetals in correlated electron systems, with potential implications for spintronic and topological transport phenomena.
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Materials Science

Phonon-driven tuning of exchange interactions in Y3Fe5O12

Kunihiko Yamauchi and Tamio Oguchi

Yttrium iron garnet (Y3Fe5O12) is a prototypical ferrimagnetic insulator widely used in spin-wave and magnonic devices owing to its extremely low magnetic damping and long magnon propagation length, and recent experiments suggest that lattice vibrations can influence magnetic properties, motivating a microscopic understanding of how phonons modify exchange interactions. In this work, phonon-driven tuning of exchange interactions in Y3Fe5O12 is investigated from a mode-resolved perspective based on first-principles calculations. We focus on how optical phonons modify the dominant superexchange pathways and how lattice distortions affect the Fe-O-Fe bond geometry that governs the exchange interaction. To this end, phonon modes are computed from density functional theory, and the exchange interactions are evaluated from a Wannier-based tight-binding model and mapped onto a spin Hamiltonian, while displaced structures along individual infrared-active modes are used to quantify their impact on the magnetic interactions.
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Materials Science

Light-modulated exchange bias in multiferroic heterostructures

Huan Tan, Zheng Ma, Cynthia Bou Karroum et al. (+7 more)

Magnetic straintronics, the strain-mediated control of magnetic anisotropy, has emerged as a key direction for next-generation energy-efficient technologies. In multiferroic heterostructures, magnetoelectric coupling is typically achieved by applying an electric field on a ferroelectric phase, inducing strain through the converse piezoelectric effect, which is then transferred to the adjacent ferromagnetic phase. As an alternative, strain can be remotely modulated through the photostrictive effect induced by light. While light-driven control of magnetic anisotropy has been explored, optical modulation of more complex phenomena such as exchange bias remains largely unaddressed. Here, we demonstrate significant light-induced modulation of exchange bias and magnetization switching at room temperature in a Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMN-PZT)/Fe80Ga20(FeGa)/Ir20Mn80(IrMn) multiferroic heterostructure, driven by visible-light-photostriction. The magnetization state correlates with the light intensity, enabling multi-level states with light power densities as low as 0.1 W cm-2. These findings suggest a promising route toward low-power, multistate, and wireless opto-magnetic memory applications.
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All authors Huan Tan, Zheng Ma, Cynthia Bou Karroum, Matthieu Liparo, Jean-Philippe Jay, David Spenato, David T. Dekadjevi, Luis Martinez Armesto, Alberto Quintana, Jordi Sort

Materials Science

Epitaxial MgSnN2 on 4H-SiC (0001): An Earth-Abundant Nitride for Green Optoelectronics and Photovoltaics

D. Gogova, D. Tran, V. Stanishev et al. (+11 more)

Group II-IV nitrides have recently emerged as a novel class of semiconductors composed of earth-abundant elements. Owing to their tunable bandgaps, comparable to those of III-nitrides, these materials are attractive candidates for replacing expensive Ga-based alloys in photovoltaics and green-gap optoelectronics. In this work, epitaxial growth of MgSnN2 layers on 4H-SiC(0001) substrates by direct current magnetron sputtering is demonstrated. Mg and Sn metal targets have been co-sputtered in nitrogen-containing atmosphere at growth temperatures up to 500 {\deg}C. X-ray diffraction and cross-sectional transmission electron microscopy confirm the MgSnN2 layers grow epitaxially in a wurtzite crystal structure, exhibiting the epitaxial relationships with the substrate: MgSnN2 [0001]//4H-SiC [0001] and MgSnN2 [10-10]//4H-SiC[10-10]. Improved crystalline quality is observed for higher deposition temperatures and near-stoichiometric composition, as evidenced by the narrowing of rocking curve linewidths. Optical characterization reveals high absorption coefficients (1e5 cm-1) in the visible spectrum, comparable to that of GaAs, highlighting the suitability of MgSnN2 for photovoltaic applications. A photoluminescence emission band at ~2.4 eV is detected, highly desirable for optoelectronic devices operating in the challenging green spectral region. These results establish MgSnN2 as an earth-abundant, environmentally friendly material, structurally compatible with III-nitrides, with potential for cost-efficient components in sustainable optoelectronics and photovoltaics.
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All authors D. Gogova, D. Tran, V. Stanishev, D. Shafizadeh, C.-L. Hsiao, M. Kim, B. Pécz, A. Kovács, K. Frey, A. Sulyok, N. K. Singh, A. Le Febvrier, P. Eklund, V. Darakchieva

Materials Science

Atomic Structure of Grain Boundaries, Dislocations and Associated Strain in Templated Co-evaporated Photoactive Halide Perovskites

Huyen T Pham, Siyu Yan, Zhou Xu et al. (+4 more)

Structural defects, particularly grain boundaries, play a crucial role in governing charge transport and the optoelectronic properties of metal halide perovskites, thereby limiting the performance of devices. Solar cells incorporating templated FA0.9Cs0.1PbI3-xClx show significant improvements in grain orientation and steady-state power conversion efficiency; however, the underlying mechanisms remain unclear. In this study, we address this gap by employing a suite of tailored low-dose electron microscopy techniques to investigate the templated FA0.9Cs0.1PbI3-xClx film, revealing that it exhibits a preferred crystallographic orientation along the <001> zone axis, with arbitrary grain rotations about that axis, indicative of a Volmer-Weber growth mechanism. We determine the atomic structure of the resulting high-angle and low-angle grain boundaries. We also reveal the presence of edge dislocations and their associated strain fields, demonstrating the compressive strain on one side of the dislocation core and tensile strain on the opposite side. Furthermore, we find dislocations associated with stacking faults. These atomic-level insights uncover which grain boundaries and intra-grain defects are likely to act as recombination centres or modify band gaps, crucial for understanding which defects influence the performance of perovskite solar cell devices.
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All authors Huyen T Pham, Siyu Yan, Zhou Xu, Weilun Li, Sergey Gorelick, Michael B Johnston, Joanne Etheridge

Materials Science

Collective Electrostatics and Band Alignment in Janus MoSTe nanotubes

Adithya Sadanandan, Tyson Karl, Rahil Shaik et al. (+1 more)

In this work, we investigate the collective electrostatic effects of one-dimensional (1D) Janus MoSTe nanotubes and their impacts on the band alignment of nanotube heterostructures. Using first-principles calculations based on Density Functional Theory, we find that the Janus nanotube generates a large and uniform electrostatic potential of over 1.3 V within the nanotube pores, which is accumulative for double wall nanotubes. We develop an analytical model to provide a quantitative understanding of the electrostatic potential and its dependence on the quadrupole moment and nanotube radius. For double wall MoSTe nanotube, we find a substantial band edge shift of about 1.0 eV for the inner tube originated from the electrostatic effects, leading to a type-II band alignment. These results demonstrate that the electrostatic effects of 1D nanotubes can be used to tune the electronic properties and band alignment of 1D nanotube heterostructures for optoelectronic and catalytic applications.
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All authors Adithya Sadanandan, Tyson Karl, Rahil Shaik, Qunfei Zhou

Materials Science

Comprehensive determination of Burgers vectors of threading dislocations in GaN substrates by combining reflection and transmission synchrotron-radiation x-ray topography

Kazuki Ohnishi, Kenji Iso, Hirotaka Ikeda et al. (+2 more)

Burgers vectors (b) of threading dislocations (TDs) in an acidic ammonothermal-grown GaN substrate were investigated using synchrotron radiation x-ray topography (SR-XRT) by combining both reflection and transmission modes. Reflection XRT images recorded with six equivalent g vectors of 11-24 revealed spot-like contrasts corresponding to TDs. Based on the contrast conditions, the possible Burgers vectors were constrained, and the c-axis component of b for mixed-type TDs was estimated from the contrast size. Using transmission XRT images recorded under several two-beam diffraction conditions, the (0001) in-plane direction of b was evaluated based on the gb invisibility criterion. Furthermore, by analyzing the linewidths of dislocation images observed under kinematical diffraction contrast, the magnitude of the a-axis component of b was determined. By combining these analyses, the Burgers vectors of individual TDs, including edge- and mixed-type dislocations, were determined. In addition, a pair of screw-type TDs with opposite Burgers vectors, +1c, -1c, was observed in the transmission SR-XRT. These results demonstrate that the combined use of reflection and transmission SR-XRT provides a practical approach for complete determination of Burgers vectors in GaN substrates.
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All authors Kazuki Ohnishi, Kenji Iso, Hirotaka Ikeda, Yoshiyuki Tsusaka, Yongzhao Yao

Materials Science

Ultrafast Non-Volatile Weyl LuminoMem for Mid-Infrared In-Memory Computing

Delang Liang, Shiyu Wang, Yan Wang et al. (+11 more)

Integrated optoelectronic systems strive to combine the logic/memory density of electronics with the bandwidth of photonics, but monolithic realization is impeded by the inefficient electronic-to-photonic interface. Current architectures rely on separate readout circuitry and modulators, creating bottlenecks in energy and latency, while existing direct transduction methods often compromise on switching speed or non-volatility. Here, we report an ultrafast, non-volatile optoelectronic memory, named LuminoMem, that integrates electrical storage and mid-infrared light emission in a single device. The device utilizes a floating-gate architecture, in which the Weyl semiconductor tellurium serves simultaneously as a charge-trapping storage layer and an emissive medium. This design enables nanosecond-scale electrical programming of non-volatile photoluminescence at 3.4 um, allowing direct optical access to stored states without external modulation. We demonstrate 4-bit (16-level) optical storage capacity and validate the device's performance through neural network simulations that achieve high accuracy on the Fashion-MNIST dataset. By effectively bridging the gap between electronic storage and mid-infrared photonics, the demonstrated mid-infrared LuminoMem provides a hardware foundation for promoting current computation efficiency and potential intelligent platforms that co-integrate computing, memory, and sensing capabilities.
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All authors Delang Liang, Shiyu Wang, Yan Wang, Dong Li, Yuchun Chen, Bin Cheng, Mingyang Qin, Dehong Yang, Jie Sheng, Lin Li, Changgan Zeng, Dong Sun, Anlian Pan, Jing Liu

Sunday 5 April

Materials Science

Kinetics studies on $\kappa$ to $\beta$-Ga$_2$O$_3$ phase transformations via in-situ high temperature X-ray diffraction

Jingyu Tang, Po-Sen Tseng, Kunyao Jiang et al. (+3 more)

The kinetics of the $\kappa$ to $\beta$-Ga$_2$O$_3$ phase transformation were investigated in five batches of nominally phase-pure $\kappa$-Ga2O3 thin films heteroepitaxially grown on c-plane sapphire, with film thickness ranging from 700 to 1100 nm, using in-situ high-temperature X-ray diffraction. Phase fractions were quantitatively extracted through modified Rietveld refinement that accounts for preferred orientation, and the transformation kinetics were analyzed using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. The applicability of the JMAK model to thin-film materials was evaluated and its lower and upper bounds for thin films and bulk materials were established. Based on this analysis, a method specifically suited for thin-film kinetic studies was developed and yielded reproducible and robust results across all five sample batches. The results indicate that the $\kappa$ to $\beta$ phase transformation in ~700-1100 nm films is best described as an interface-controlled, site-saturated nucleation with thickness-limited or effectively two-dimensional growth.
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All authors Jingyu Tang, Po-Sen Tseng, Kunyao Jiang, Rachel C. Kurchin, Robert F. Davis, Lisa M. Porter

Materials Science · Cross-listed from physics.comp-ph

High-fidelity simulations of shock initiation of an energetic crystal-binder system due to flyer impact

Shobhan Roy, Pradeep K. Seshadri, Chukwudubem Okafor et al. (+2 more)

Meso-scale simulations of energy localization at hotspots provide closure models for multiscale frameworks of shock-to-detonation transition (SDT). Validation of such meso-scale calculations is challenging as direct comparison with experiments is constrained both by limitations of data acquisition in the experiments (e.g., of temperature fields) and modeling over-simplifications in the simulations. To address the latter problem and bring modeling closer to experiments, we advance a high-fidelity meso-scale computational framework for interface-resolved reactive calculations of shock initiation in plastic-bonded explosives (PBXs). Accurate resolution of shock and interfacial dynamics is achieved through higher-order (5th-order WENO) schemes, and sharp interface treatments are implemented for physically accurate material-material interactions. Recently obtained atomistics-consistent material models are used for HMX, with the grid resolution taken down to atomistic scale (O(nm)). The crystal geometries are obtained directly from experiments via nano-CT imaging. The impacting flyer plate, energetic crystal and binder are tracked as distinct phases, and flyer-binder impact and separation are simulated, capturing the flyer deformation and the effects of relief waves from the flyer surface. By combining these high-fidelity modeling components, we evaluate how closely simulations can approach experimental data. Overall, this work provides as assessment of which aspects of numerical treatment and material modeling have the greatest impact on meso-scale simulations of flyer-induced initiation of PBXs, and points to where further improvements are necessary.
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All authors Shobhan Roy, Pradeep K. Seshadri, Chukwudubem Okafor, Belinda P. Johnson, H. S. Udaykumar

Materials Science

Ultrafast Néel vector switching

Eddie Ivor Harris-Lee, John Kay Dewhurst, Wenhan Chen et al. (+3 more)

We predict ultrafast switching in a chiral anti-ferromagnet that occurs at femtosecond times, nearly 5 orders of magnitude faster than the torque induced nanosecond switching previously observed. The physical mechanism, quite different from that which drives slow switching, involves the creation of massive effective magnetic fields by ultrafast spin current injection. Identifying these fields as key to femtosecond rotation, we establish simple practical rules for their maximisation with wide applicability to all magnetised materials. Employing state-of-the-art time-dependent density-functional theory and using the example of chiral magnet, Mn$_3$Sn, we induce ultrafast rotation enough to drive the switching of magnetic order between the six possible non-collinear ground states. We further demonstrate the possibility of undoing this switching by subsequent injection of oppositely polarized spin current. Our findings place chiral anti-ferromagnets as a materials platform for femtosecond Néel-vector switching, opening a route towards the manipulation of magnetic matter at ultrafast times.
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All authors Eddie Ivor Harris-Lee, John Kay Dewhurst, Wenhan Chen, Shiqi Hu, Samuel Shallcross, Sangeeta Sharma

Materials Science

PATHFINDER: Multi-objective discovery in structural and spectral spaces

Kamyar Barakati, Boris N. Slautin, Utkarsh Pratiush et al. (+2 more)

Automated decision-making is becoming key for automated characterization including electron and scanning probe microscopies and nano indentation. Most machine learning driven workflows optimize a single predefined objective and tend to converge prematurely on familiar responses, overlooking rare but scientifically important states. More broadly, the challenge is not only where to measure next, but how to coordinate exploration across structural, spectral, and measurement spaces under finite experimental budgets while balancing target-driven optimization with novelty discovery. Here we introduce PATHFINDER, a framework for autonomous microscopy that combines novelty driven exploration with optimization, helping the system discover more diverse and useful representations across structural, spectral, and measurement spaces. By combining latent space representations of local structure, surrogate modeling of functional response, and Pareto-based acquisition, the framework selects measurements that balance novelty discovery in feature and object space and are informative and experimentally actionable. Benchmarked on pre acquired STEM EELS data and realized experimentally in scanning probe microscopy of ferroelectric materials, this approach expands the accessible structure property landscape and avoids collapse onto a single apparent optimum. These results point to a new mode of autonomous microscopy that is not only optimization-driven, but also discovery-oriented, broad in its search, and responsive to human guidance.
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All authors Kamyar Barakati, Boris N. Slautin, Utkarsh Pratiush, Hiroshi Funakubo, Sergei V. Kalinin

Materials Science

Temperature Dependent Magnetic and Structural Properties of Al Substituted Nanostructured Ferrites with Large Coercive Fields

P. Maltoni, R. K. Dokala, P. Pramanik et al. (+12 more)

We report a comprehensive study of the temperature-dependent structural, magnetic, vibrational, and dielectric properties of Al-substituted M-type hexaferrites SrFe$_{12-x}$Al$_x$O$_{19}$. Neutron powder diffraction and Mössbauer spectrometry show that Al$^{3+}$ preferentially replaces Fe$^{3+}$ at spin-up octahedral sites (2a, 12k), disrupting the exchange coupling with the spin-down 4f tetrahedral sites and leading to a progressive reduction of site-specific magnetic moments and a systematic decrease in the Curie temperature, supported by temperature dependent susceptibility measurements. Raman spectroscopy reveals pronounced phonon anomalies near $T_C$, particularly in modes associated with bipyramidal Fe-O vibrations, reflecting the weakening of both 4e-12k and 4e-4f exchange pathways. However, the coercive field exhibits a dramatic increase, reaching $\mu_0H_C$ $\sim$ 1.2 T for SrFe$_{9.6}$Al$_{2.4}$O$_{19}$, among the largest values reported for this class. Susceptibility measurements suggest that Al substitution, while weakening the superexchange network, contributes to the stabilization of single-domain behavior.
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All authors P. Maltoni, R. K. Dokala, P. Pramanik, R. Araujo, T. Edvinsson, S. A. Ivanov, B. Almqvist, G. Varvaro, A. Capobianchi, N. Yaacoub, C. Hervoches, A. Martinelli, R. C. Pullar, D. Peddis, R. Mathieu

Materials Science · Cross-listed from cond-mat.supr-con

Disentangling electronic and phononic contributions to high-temperature superconductivity in X2MH6 hydrides

Feng Zheng, Shiya Chen, Zhen Zhang et al. (+7 more)

Understanding the factors that control superconductivity is essential for discovering new superconducting materials using high-throughput elemental substitution. Focusing on the recently predicted ambient-pressure superconducting X2MH6 family, we disentangle the phononic and electronic contributions to Tc to determine how isoelectronic substitution alters superconductivity. While substitution affects both phononic and electronic properties, the electronic contribution plays the dominant role in determining Tc in the X2MH6 family. We show that the electronic contribution is affected by three key factors: the X-H bond distance, the electron localization function networking value of hydrogen, and the hydrogen-projected density of states at the Fermi level. A combined figure of merit derived from these parameters exhibits a robust correlation with Tc across the family. We further show that pressure produces competing effects on superconductivity: it enhances the electronic contribution by shortening X-H bonds, but simultaneously weaken the phononic contribution by increasing phonon frequencies. The net pressure dependence of Tc therefore results from the balance between these opposing tendencies. By disentangling and analyzing the electronic and phononic mechanisms, this work provides comprehensive insight into superconductivity in X2MH6 hydrides and offers practical guidance for designing new high-Tc hydride superconductors.
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All authors Feng Zheng, Shiya Chen, Zhen Zhang, Renhai Wang, Feng Zhang, Zi-zhong Zhu, Cai-Zhuang Wang, Vladimir Antropov, Yang Sun, Kai-Ming Ho

Materials Science

Production of Upgraded Metallurgical Grade (UMG) silicon for a low-cost high-efficiency and reliable PV technology

José Manuel Míguez Novoa, Volker Hoffmann, Eduardo Fornies et al. (+12 more)

UMG-Si has the potential to reduce the cost of PV technology and to improve its environmental profile. In this contribution, we summarize the extensive work made in the research and development of UMG technology for PV, which has led to the demonstration of UMG-Si as a competitive alternative to polysilicon for the production of high-efficiency multicrystalline solar cells and modules. The tailoring of the processing steps along the complete Ferrosolar's UMG-Si manufacturing value chain has been addressed, commencing with the purification stage that results in a moderately compensated material due to the presence of phosphorous and boron. Gallium is added as a dopant at the crystallization stage to obtain a uniform resistivity profile 1 Ohm*cm along the ingot height. Defect engineering techniques based on phosphorus diffusion gettering have been optimized to improve the bulk electronic quality of UMG-Si wafers. Black silicon texturing, compatible with subsequent gettering and surface passivation, has been successfully implemented. Industrial-type BSF and PERC solar cells have been fabricated, achieving cell efficiencies in the range of those obtained with conventional polysilicon substrates. TOPCon solar cell processing key steps have also been tested to further evaluate the potential of the material in advanced device architectures beyond PERC. Degradation mechanisms related to light exposure and operation temperature have been shown not to be significant in UMG PERC solar cells when a regeneration step is implemented, and PV modules with several years of outdoor operation have demonstrated similar performance to reference ones based on poly-Si. LCA has been carried out to evaluate the environmental impact of UMG-based PV technology when compared to the poly-Si-based one, considering different scenarios both for the manufacturing sites and the PV installations.
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All authors José Manuel Míguez Novoa, Volker Hoffmann, Eduardo Fornies, Laura Mendez, Marta Tojeiro, Fernando Ruiz, Manuel Funes, Carlos del Cañizo, David Fuertes Marrón, Nerea Dasilva Villanueva, Luis Jaime Caballero, Bülent Ar{\i}kan, Raşit Turan, Hasan Hüseyin Canar, Guillermo Sánchez Plaza

Materials Science

Emergent $d$-wave altermagnetism in orthogonally twisted bilayer CrPS$_4$

Alberto M. Ruiz, Diego López-Alcalá, Rafael González-Hernández et al. (+1 more)

Twistronics is a powerful strategy to engineer novel quantum states by controlling the relative orientation between layered materials. Here, we demonstrate that an orthogonally twisted bilayer CrPS$_4$ shows $d$-wave altermagnetism driven purely by structural rotation. Symmetry analysis reveals that the twisted stacking breaks partial translational combined with time-reversal symmetry, leading to a fourfold rotation relation between opposite spin sublattices, enabling altermagnetism. First-principles calculations demonstrate a sizable non-relativistic spin splitting of up to 68 meV around the Fermi level. We further show that the altermagnetic state can be further stabilized through interlayer compression and modulation of the on-site Coulomb interaction. The resulting band structure exhibits pronounced spin-dependent anisotropy, enabling efficient spin to charge conversion reaching $\sim$50% near the Fermi level and sizable giant magnetoresistance. These results establish twisted CrPS$_4$ as a realistic platform for altermagnetism and highlights twistronics as a versatile route for advanced spintronics applications.
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All authors Alberto M. Ruiz, Diego López-Alcalá, Rafael González-Hernández, José J. Baldoví

Materials Science

Weyl points enabling significant enhancement of thermoelectric performance in an antiferromagnetic van der Waals metal GdTe3

Zhigang Gui, Panshuo Wang, Wenxiang Wang et al. (+8 more)

Magneto-thermoelectric (MTE) effect has demonstrated significant ad-vantages in achieving optimal thermoelectric (TE) properties compared to conventional methods. Topological materials pro-vide a unique platform for investigating the MTE effect, leveraging their exotic electronic structure topology. In this study, we report that the topological material GdTe3 exhibits an unsaturated power factor of up to 18846 {\mu}W m-1 K-1 under a magnetic field of 13.5 T at 20 K, which represents the highest value observed in metallic systems and surpasses most state-of-the-art TE materials. The relative enhancement under magnetic field in thermopower and power factor reaches 873% and 1075%, respectively, attributed to the Weyl points contribution resulting from the field-induced topological transition, as confirmed by our theoretical calculations. Our findings demonstrate a promising candidate for solid-state cooling and reveal the substantial contribution of Weyl points to TE enhancement, thereby offering a novel approach to optimizing TE properties in topological materials.
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All authors Zhigang Gui, Panshuo Wang, Wenxiang Wang, Yuqing Zhang, Yanjun Li, Yikang Li, Qingyuan Liu, Xikai Wen, Qihang Liu, Jianjun Ying, Xianhui Chen

Materials Science · Cross-listed from physics.med-ph

Dose Validation of GRID Block Treatment Applicator within the RayStation Treatment Planning System

Blessing Akah, Edwin Quashie and Gene Cardarelli

Spatially Fractionated Radiation Therapy (SFRT) or GRID therapy has been in existence for more than a century. GRID therapy was invented as an approach to address the challenges posed by bulky tumors. To treat patients with GRID therapy, the protocol needs to be implemented within the Treatment Planning System (TPS) software. Also, the dose needed for treatment must be validated. A few TPS software vendors such as Elekta and Varian have protocols for treating patients with GRID therapy. However, we are the first to implement the protocols within RayStation TPS. To achieve these, we used the .decimal GRID block applicator to create conformal treatment plans. For the beam modeling, several dosimetry data, and measurements such as percentage depth dose (PDD), beam profile, output, and GRID factors, were obtained for different field sizes and energies. The dose distribution from the GRID openings covered the Planning Target Volume (PTV), with the QA plan having a 98% agreement with the planned dose. Also, we used the Mapcheck2 results to verify the adjustments made to the script variables such as aperture size (hole and spacing). We developed a robust way to validate the dose needed for patient treatment using the GRID block applicator. Also, we have proposed a novel approach to standardize the clinical implementation of the GRID block in RayStation TPS.
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Materials Science · Cross-listed from quant-ph

Microstructural Topology as a Prescriptor for Quantum Coherence: Towards A Unified Framework for Decoherence in Superconducting Qubits

Vinayak P. Dravid, Akshay A. Murthy, Peter Lim et al. (+5 more)

In superconducting quantum circuits, decoherence improvements are frequently obtained through process interventions that simultaneously modify surface chemistry, microstructural topology, and device geometry, leaving mechanistic attribution structurally underdetermined. Predictive materials engineering requires measurable structural statistics to be separated from geometry-dependent coupling coefficients into independently testable factors. We introduce the concept of classical and quantum microstructure. In that context, we formulate a channel-wise separable framework for decoherence in superconducting transmon qubits in which each loss channel is described by a reduced prescriptor. Here, a channel-specific microstructural state variable is determined independently of device geometry, and a geometry-dependent coupling functional is computable from field solutions without reference to surface chemistry. We derive this product form from a spatially resolved kernel representation and establish a perturbative separability criterion that defines the regime where independent variation of the variables is valid. The framework specifies five prescriptor classes for dominant loss pathways in transmon-class devices. Falsifiability is operationalized through a pre-committed 2x2 experimental protocol in which the variables must satisfy independent ratio checks within propagated uncertainty. A Minimum-Dataset Specification standardizes reporting for cross-laboratory inference. Part I establishes the conceptual and mathematical architecture; coordinated experimental validation is reserved for Part II.
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All authors Vinayak P. Dravid, Akshay A. Murthy, Peter Lim, Gabriel T. dos Santos, Ramandeep Mandia, James M. Rondinelli, Mark C. Hersam, Roberto dos Reis

Materials Science

Direct Photocurrent Detection of Optical Vortex Based on the Orbital Photo Galvanic Effect: Progress, Challenge and Perspective

Jinluo Cheng, Dehong Yang, Weiming Wang et al. (+3 more)

A photodetector that can directly distinguish the orbital angular momentum (OAM) of light is highly desirable for integrated on-chip OAM detection and focal plane array devices. The recent development of OAM detectors based on the intrinsic orbital photo galvanic effects (OPGE) of materials provide a new route for direct OAM detection that is on-chip scalable with high resolution and speed. In this paper, we summarize the current progress in direct photodetection of OAM via OPGE. We begin with a short review of the basic operation scheme of the OAM detector and provide a comprehensive symmetry analysis to sort out the favorable characteristics of the materials, incorporating considerations from device schemes based on various device performance characteristics and specific application circumstances. From that, we review the current experimental progress and technical challenges, then oversee the possible solutions to these challenges and provide a perspective on the future opportunities of this OAM detection route.
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All authors Jinluo Cheng, Dehong Yang, Weiming Wang, Chang Xu, Zipu Fan, Dong Sun

Materials Science · Cross-listed from cond-mat.stat-mech

A molecular dynamics simulation of thermalization of crystalline lattice with harmonic interaction

Zhenwei Yao

Understanding the realization of thermal equilibrium through the thermalization process in a many-body system is a fundamental and complex scientific question, bridging thermodynamics and classical dynamics and connecting to a host of physical phenomena, such as mechanical instabilities in a thermal environment. In this work, based on the harmonic lattice model, we investigate the thermalization process in both velocity and coordinate spaces, by examining microscopic dynamics on the atomic level. We show the distinct relaxation rates of the transverse and longitudinal components of the velocity, reveal the power law governing the nonlinear proliferation of dominant frequencies, and observe the concurrent rapid proliferations of frequencies and topological defects. We also show that the lattice system's persistent out-of-plane deformations exhibit two-stage fluctuation behaviors, characterized by distinct power laws of fractional exponents and associated with the broken up-down symmetry. This work demonstrates the rich dynamics underlying the thermalization process, and advances our understanding on the dynamical adaptations of many-body systems to external disturbances.
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Materials Science

Elasticity reshapes heat flow in graphene

Navaneetha K. Ravichandran

Classical thermal transport theories that preserve rotational symmetry, predict strong anharmonic scattering of out-of-plane lattice vibrational modes called flexural phonons in flat suspended graphene sheets. Such strong scattering processes cause a breakdown of the phonon quasiparticle picture, which remains valid only when several cycles of lattice vibrations occur before the mode decays. Here we show that the renormalization of elastic bending rigidity ($D$), caused by the coupling between the in-plane and the out-of-plane thermal lattice fluctuations, restores phonon quasiparticles in suspended graphene. Importantly, this $D$-renormalization weakens the momentum-dissipating Umklapp phonon scattering processes, resulting in improved thermal conductivity and amplified phonon hydrodynamics in suspended graphene. Our results unveil a previously-unrecognized connection between the macroscopic elasticity and the microscopic flexural phonon scattering in two-dimensional (2D) materials that does not occur in three-dimensional bulk crystals, thereby motivating a re-examination of the classical theories and opening up new avenues to engineer the thermal as well as the phonon-limited electronic transport and relaxation in two- and lower-dimensional materials.
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Saturday 4 April

Materials Science · Cross-listed from physics.ins-det

High-Temperature and High-Speed Atomic Force Microscopy Using a qPlus Sensor in Liquid via Quadpod Scanner and Hybrid-Loop Frequency Demodulation

Yuto Nishiwaki, Toru Utsunomiya and Takashi Ichii

Atomic-resolution imaging on molten metal/solid interfaces at temperatures above 200 {\deg}C was achieved using a high-temperature, high-speed atomic force microscope (AFM) equipped with a qPlus sensor. A tip-scanning high-speed Quadpod scanner for a large mass load of qPlus sensor (2.3 g) was developed to enhance thermal drift tolerance by high-speed scanning and thermal insulation from the heated specimen. This scanner has dominant resonant frequencies of 7.05 kHz (lateral) / 29.7 kHz (vertical) without a load. In addition, the Hybrid-loop frequency demodulation technique for low-resonant-frequency ($f_0$) sensors with a wider bandwidth than conventional phase-locked loop was also established, providing a demodulation bandwidth of $B_{\Delta f_\mathrm{inst}}\sim 0.26 f_0$ without exceeding the theoretical noise of the input deflection signal. Combining these techniques enabled atomic-resolution imaging on the molten $\mathrm{Ga/PtGa_x}$ interface at $\sim$210 {\deg}C. The topographic images obtained at $\sim$210 {\deg}C showed a relatively low-symmetry surface with an oblique lattice with a superstructure, which differed from the primitive rectangular lattice observed in the non-heated sample left at room temperature for 96 h. This demonstrates that the developed high-temperature, high-speed AFM techniques for qPlus sensors enable visualization of non-aqueous liquid/solid interfaces above 200 {\deg}C at atomic resolution, which has various potential applications, such as injection modeling, soldering, and the fabrication of liquid-metal-based catalysts.
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Materials Science

Optimizing Flux Method Growth of Rutile GeO2 Crystals

Avery-Ryan Ansbro and John T. Heron

Rutile germanium oxide (r-GeO2) has shown potential for ultrawide bandgap semiconductor applications such as power conversion and UV optoelectronics. Homoepitaxial substrates will be key for achieving phase pure and doped r-GeO2 thin films as synthesis is inhibited by strain associated with substrate lattice mismatch. Initial reports of single crystal r-GeO2 synthesis from a MoO3-Li2CO3 flux have shown mm scale crystals with dominantly (110) faceting. However, fundamental understanding of the synthesis parameters and the ability to tune size and facet are needed. Here, we report on both seeded and unseeded growth of single crystal r-GeO2 across a range of MoO3-Li2CO3 flux compositions. Small variations in Mo concentration can be used to control crystal habit, faceting, and growth rate through variation in precursor complexion, solution viscosity, and GeO2 solubility. While seed size and seeded growth rates are optimized in 40% Mo solutions, aspect ratios and seeded growth volumes are maximized in 41.5% Mo solutions without sacrificing faceting. Increased Mo concentration leads to polycrystallinity and isotropic growth. These results enable faster and tailored growth of r-GeO2 crystals using the flux growth method.
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Materials Science

Unconventional excitations and orbital-driven low-energy dispersions in chiral topological semimetals PdAsS, PdSbSe, and PdBiTe: a first-principles study

Roopam Pandey and Sudhir K Pandey

The theoretical dispersion of higher fold excitations are typically governed by space group symmetry. However, physical factors affecting local structural and electronic environment such as atomic arrangement, orbital overlaps, etc., largely alter the behavior of quasiparticle around higher fold nodes. In this work, we consider three chiral material candidates (space group P$2_13$) which exhibit systematic variations in physical parameters by virtue of their constituent elements. We perform a detailed and systematic study of these materials using DFT in absence and presence of spin-orbit coupling (SOC). Four different kinds of unconventional excitations were observed in all three materials at $\Gamma$- and R-point in the full BZ. In absence of SOC, we find spin-1 ($\Gamma$) and double Weyl (R) excitations, where a Rarita-Schwinger-Weyl fermion ($\Gamma$) and double spin-1 excitation (R) are found in presence of SOC. All of these higher fold nodes lie in energy range of $\left(-0.5,-0.85\right)$eV. Remarkably, we also find total of eight new type-II Weyl points even in absence SOC on $\Gamma$-R line in these materials. In presence of SOC, 12 new Weyl nodes of type-II nature at general momenta ($k_x,k_y,k_z$)$\frac{2\pi}{a}$ are also observed. The presence of these Weyl nodes have not been reported in any of the earlier works. Further, analyzing the low-energy dispersion of spin-1 excitations in these materials we find that otherwise flat middle band in PdBiTe is almost parabolic due strong hybridization. On the other hand, relatively flat middle bands can be observed in PdAsS and PdSbSe in low-energy scale. In case of double spin-1 excitations, surprisingly, we see linearly dispersing middle bands in PdSbSe whereas middle bands in PdAsS and PdSbSe are parabolic even in low-energy scale. Lastly, we present non-trivial surface states and Fermi arcs associated with higher fold excitations.
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Materials Science · Cross-listed from cond-mat.soft

Emergent dynamic stress regulators via coordinated thermal fluctuations and stress in harmonic crystalline lattices

Zhenwei Yao

Understanding thermal fluctuations yields insights into a wide range of behaviors in many-body systems. In this work, we analyze the dynamical adaptation of two-dimensional crystalline lattice system under harmonic interaction in response to the intricate interplay of thermal agitation and mechanical stress by developing the characteristic stress-absorbing quadrupole structures and stress-releasing fold structures. These thermally driven stress regulator structures serve as a tangible embodiment of thermal fluctuations, offering a unique perspective on the characterization and manipulation of the elusive fluctuations. Specifically, we reveal the stretch-driven alignment and linear accumulation of quadrupoles, characterize the formation and proliferation of folds, and present the phase diagram of the dynamical states defined by these characteristic structures. This work demonstrates the promising avenue of re-examining classical mechanical systems subject to thermal agitation, which is of fundamental physical interest and has potential practical significance in the design of mechanical devices in thermal environments.
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Materials Science · Cross-listed from cond-mat.mes-hall

An argument why the Spinterface model cannot explain the chirality induced spin selectivity effect

J. Fransson

In the context of chirality induced spin selectivity effect, it has been argued that a chiral molecule when adsorbed on a metal facilitates the formation of a local spin moment at the interface between the metal and molecule, given a strong spin-orbit coupling in the metal. The possibility for such spin moment formation is analyzed in terms of general arguments and effective modeling of a pertinent set-up. The conclusion from this analysis is that a strong spin-orbit coupling in the metal does not provide a sufficient mechanism to sustain a stabilized spin moment at the interface. It is, moreover, shown that an electron flux in to or out from the molecule does not provide conditions for a spin moment formation, regardless of whether the flux is spin-polarized or not.
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Materials Science

Shape of temperature dependence of spontaneous magnetization of various ferromagnets

A. Perevertov

The shape of the temperature dependence of spontaneous magnetization was analyzed for about forty ferromagnetic materials. The squareness of the shape was determined by fitting the magnetization curves with the superellipse equation (Lame curve). The agreement between the Lame curve fits and the experimental data was good for most materials. The squareness parameter (the power coefficient in the superellipse equation was found to range from 1.4 to 3.0. The largest squareness was observed for iron, whereas the smallest was found for antiferromagnetic materials and the Ni55Cu45 alloy. The squareness parameter was studied as a function of the Curie temperature, TC. For metallic alloys, a general tendency was observed: the squareness increased with increasing Curie temperature. The only exception was cobalt, which exhibited the same magnetization curve in reduced coordinates as nickel despite having a Curie temperature twice as high. The addition of either ferromagnetic or nonferromagnetic metals to iron or nickel led to a decrease in squareness. No influence of the thermal expansion coefficient on the magnetization curve was observed: zero-expansion Invar exhibited a standard shape following the Lame curve.
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