Peer Revenue Now accepting positions

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Friday 9 January

Materials Science

Crystalline-dependent magnon torques in all-sputtered Hf/Cr2O3/ferromagnet heterostructures

Yuchen Pu, Guoyi Shi, Chenhui Zhang et al. (+3 more)

Electron motion in spin-orbit torque devices inevitably leads to the Joule heating issue. Magnon torques can potentially circumvent this issue, as it enables the transport of spin angular momentum in insulating magnetic materials. In this work, we fabricate a sandwich structure composed of Hf/antiferromagnetic Cr2O3/ferromagnet and demonstrate that the magnon torque is strongly dependent on the crystalline structure of Cr2O3. Magnon torques are stronger when the Neel vector of Cr2O3 aligns parallel to the spin polarization generated in Hf, while they are suppressed when the Neel vector is perpendicular to the spin polarization. The magnon torque efficiency is estimated to be -0.134 using in-plane second harmonic Hall measurements. Using magnon torques, we achieve perpendicular magnetization switching of CoFeB, with a critical switching current density of 4.09 x 10^7 A/cm^2. Furthermore, the spin angular momentum loss due to the insertion of Cr2O3 is found to be lower than that of polycrystalline NiO. Our work highlights the role of antiferromagnet crystalline structures in controlling magnon torques, broadening the potential applications of magnon torques.
Read the full abstract

All authors Yuchen Pu, Guoyi Shi, Chenhui Zhang, Xinhou Chen, Hanbum Park, Hyunsoo Yang

Materials Science

Structural and magnetic properties of co-sputtered epitaxial Fe-Sn kagome thin films

Callum Brennan-Rich, Sean M. Collins, Stuart Micklethwaite et al. (+5 more)

In recent years the intermetallic alloys of Fe and Sn have gained significant interest due to a rich variety of magnetic properties present in these materials. The crystal Fe3Sn2 is a frustrated ferromagnet, while the crystallographically similar FeSn, which differs only by the stacking sequence of its Fe-containining kagome and stanene layers, is an antiferromagnet. Thin-film growth techniques such as magnetron sputtering allow for these different stoichiometric compositions to be grown through adjustments of the rate of deposition of the individual Fe and Sn sources, while all other conditions remain constant. Here, we report the production of high quality epitaxial thin films of Fe$_3$Sn$_2$ and FeSn on sapphire with a Pt seed layer, as well as a mixed phase containing intergrowths of both crystals, all of which we have characterized using both X-ray and four-dimensional scanning transmission electron microscopy (4D-STEM) methods. The resulting crystallographic phase content is compared to the results of magnetization measurements, with correspondence between the predicted ferromagnetic phase content and the resulting magnetization. Further magnetic properties of these films can then also be compared, leading to the discovery of a unique behavior in the temperature dependent coercivity within highly mixed phase alloys, a feature that is absent in either pure Fe3Sn2 and FeSn.
Read the full abstract

All authors Callum Brennan-Rich, Sean M. Collins, Stuart Micklethwaite, Zabeada Aslam, Trevor Almeida, Stephen McVitie, Rik M. Drummond-Brydson, Christopher H. Marrows

Materials Science

Bio-resorbable magnetic tunnel junctions

Dong-Jun Kim, Beom Jin Kim, Hee-Chang Shin et al. (+7 more)

Magnetic tunnel junctions (MTJs) play a crucial role in spintronic applications, particularly data storage and sensors. Especially as a non-volatile memory, MTJs have received substantial attention due to its CMOS compatibility, low power consumption, fast switching speed, and high endurance. In parallel, bio-resorbable electronics have emerged as a promising solution for systems requiring temporary operation and secure data disposal, especially in military, intelligence, and biomedical systems where devices must safely disintegrate under physiological conditions. In this study, we investigate the bio-resorbability of MTJ by analyzing the dissolution behavior of its nanometer-thick constituent layers in phosphate-buffered saline (PBS) solution at pH 7.4, simulating physiological environments. The MTJ structures, composed of bio-resorbable materials, exhibit well-controlled degradation behaviors. Critically, as one of the ferromagnetic layers dissolves, binary information is irreversibly lost, within 10 hours of immersion. These findings highlight the potential of MTJs not only as high-performance memory elements but also as secure, transient data storage platforms. The ability to modify the dissolution lifetime by materials and thickness selection offers unique advantages for short-lived implantable devices, paving the way for integrating spintronic functionality into next-generation bioresorbable electronics.
Read the full abstract

All authors Dong-Jun Kim, Beom Jin Kim, Hee-Chang Shin, Jeongkeun Kim, Yuchen Pu, Shuhan Yang, Xinhou Chen, Byong-Guk Park, Jong-Hyun Ahn, Hyunsoo Yang

Materials Science

Spin dynamics of excitons and carriers in mixed-cation MA$_{x}$FA$_{1-x}$PbI$_{3}$ perovskite crystals: alloy fluctuations probed by optical orientation

B. F. Gribakin, N. E. Kopteva, D. R. Yakovlev et al. (+5 more)

Optical spin orientation measured by time-resolved photoluminescence provides a powerful tool to probe the spin dynamics of excitons and charge carriers in perovskite semiconductors. The impact of alloy fluctuations on the spin dynamics of mixed-cation \MAFAPI{} perovskite single crystals is studied here experimentally. The optical orientation is measured under nonresonant excitation for crystals with $x = 0.1$, $0.4$, and $0.8$ at cryogenic temperatures and compared with data on \MAPI{} crystals. The high degree of exciton optical orientation of $75-80$% for $x = 0.1$ and $0.8$ reduces to about 60% for $x = 0.4$. A similar trend is observed for the carrier spin optical orientation. This behavior is attributed to enhanced scattering of free excitons and carriers in the alloys with increased compositional and structural disorder. From the Larmor spin precession measured from spin dynamics in an external magnetic field applied in the Voigt geometry, the electron and hole $g$-factors are evaluated. Their dependence on the band gap energy in \MAFAPI{} crystals follows the universal trend previously established for lead halide perovskites.
Read the full abstract

All authors B. F. Gribakin, N. E. Kopteva, D. R. Yakovlev, I. A. Akimov, I. V. Kalitukha, B. Turedi, M. V. Kovalenko, M. Bayer

Materials Science

Observation of magnon torques mediated by orbital hybridization at the light metal/antiferromagnetic insulator interface

Yuchen Pu, Guoyi Shi, Hua Bai et al. (+5 more)

Magnon torques, which can operate without involving moving electrons, could circumvent the Joule heating issue. In conventional magnon torque systems, the spin source layer with strong spin-orbit coupling is utilized to inject magnons, and the efficiency is limited by the inherent spin Hall conductivity of the spin source layer. In this work, we observe magnon torques in the Cr/NiO/ferromagnet heterostructure with the effective spin Hall conductivity of 2.45x10^5 hbar/(2e{\Omega}m), twice that of the best conventional magnon torque system. We demonstrate the magnon-torque-driven switching of a perpendicularly magnetized CoFeB layer at room temperature, with a switching power consumption density of 0.136 mW/{\mu}m^2. We find that the magnon torque originates from the orbital hybridization and interfacial inversion symmetry breaking at the Cr/NiO interface. Our findings not only significantly enhance the efficiency of magnon torques, but also provide key insights into the fundamental mechanisms of magnon injections.
Read the full abstract

All authors Yuchen Pu, Guoyi Shi, Hua Bai, Xinhou Chen, Chenhui Zhang, Zhaohui Li, Mehrdad Elyasi, Hyunsoo Yang

Materials Science

Unraveling the effects of anionic vacancies and temperature on mechanical properties of NbC and NbN: Insights from Quantum Mechanical Study

P.W. Muchiri, K. K. Korir, N. W. Makau et al. (+2 more)

Transition metal carbides and nitrides (TMCNs), such as niobium carbide (NbC) and niobium nitride (NbN), are of great technological interest due to their exceptional hardness, high melting points, and thermal stability. While previous studies have focused on their groundstate properties (at 0 K), limited information exists on their mechanical behavior under realistic operational conditions involving elevated temperatures and the presence of defects. In this study, we employ ab initio molecular dynamics (AIMD) simulations to investigate the effects of temperature (300 to 1500 K) and anionic vacancies on the mechanical properties of NbC and NbN in rocksalt (RS), zincblende (ZB), and wurtzite (WZ) structures. The results reveal a nonlinear decrease in elastic constants, bulk, shear, and Youngs moduli with both increasing temperature and defect concentration. Hardness and toughness analyses, based on Pughs ratio and Poisson ratio, show ductility and brittleness transitions that are sensitive to structure, defect level, and thermal effects. Furthermore, vacancy migration energies computed using the nudged elastic band (NEB) method demonstrate strong structural dependence, with RS exhibiting the highest barriers and WZ the lowest. These findings provide new insights into the defect and temperature interplay in NbC and NbN, offering guidelines for their optimization in high-temperature and wear-resistant applications.
Read the full abstract

All authors P.W. Muchiri, K. K. Korir, N. W. Makau, M. O. Atambo, G. O. Amolo

Materials Science

Mechanical control of magnetic exchange and response in GdRu$_2$Si$_2$: A computational study

Sagar Sarkar, Rohit Pathak, Arnob Mukherjee et al. (+3 more)

We present a systematic computational study of the effect of uniaxial strain on the magnetic properties of GdRu$_2$Si$_2$, a centrosymmetric material known to host a field-induced skyrmion lattice (SkL). Using first-principles density functional theory, we first demonstrate the pronounced sensitivity of the exchange and anisotropy to specific structural distortions. These DFT-derived interactions are then integrated into a classical spin model to construct comprehensive magnetic phase diagrams under both compressive and tensile strain. Our key finding is that compressive strain ($\sim 2\%$) acts as an effective tuning parameter, substantially expanding the stability region of the $\vec Q_{100}$-driven topologically nontrivial phases. This results from the shifts in the critical magnetic fields and enhancement of the energy scale of the favored magnetic wave vector. In contrast, tensile strain induces a different magnetic ground-state by promoting a different magnetic ordering vector, $\vec Q_{110}$, leading to entirely distinct phase behavior. This work not only provides a quantitative understanding of the structural-magnetic coupling in GdRu$_2$Si$_2$ but also establishes strain engineering as a powerful approach to control and optimize topologically non-trivial magnetic phases in centrosymmetric magnets.
Read the full abstract

All authors Sagar Sarkar, Rohit Pathak, Arnob Mukherjee, Anna Delin, Olle Eriksson, Vladislav Borisov

Materials Science · Cross-listed from cond-mat.mes-hall

Quantized heat flow in the Hofstadter butterfly

Aifei Zhang, Gibril Aissani, Quan Dong et al. (+11 more)

When subjected to a strong magnetic field, electrons on a two-dimensional lattice acquire a fractal energy spectrum called Hofstadter's butterfly. In addition to its unique recursive structure, the Hofstadter butterfly is intimately linked to non-trivial topological orders, hosting a cascade of ground states characterized by non-zero topological invariants. These states, called Chern insulators, are usually understood as replicas of the ground states of the quantum Hall effect, with electrical and thermal conductances that should be quantized, reflecting their topological order. The Hofstadter butterfly is now commonly observed in van-der-Waals heterostructures-based moiré superlattices. However, its thermal properties, particularly the quantized heat flow expected in the Chern insulators, have not been investigated, potentially questioning their similarity with standard quantum Hall states. Here we probe the heat transport properties of the Hofstadter butterfly, obtained in a graphene~/~hexagonal boron nitride moiré superlattice. We observe a quantized heat flow, uniquely set by the topological invariant, for all investigated states of the Hofstadter butterfly: quantum Hall states, Chern insulators, and even symmetry-broken Chern insulators emerging from strong electronic interactions. Our work firmly establishes the universality of the quantization of heat transport and its intimate link with topology.
Read the full abstract

All authors Aifei Zhang, Gibril Aissani, Quan Dong, Yong Jin, Kenji Watanabe, Takashi Taniguchi, Carles Altimiras, Patrice Roche, Jean-Marc Berroir, Emmanuel Baudin, Gwendal Fève, Gerbold Ménard, Olivier Maillet, François D. Parmentier

Materials Science

First-principles analysis of in-plane anomalous Hall effect using symmetry-adapted Wannier Hamiltonians and multipole decomposition

Hiroto Saito and Takashi Koretsune

The in-plane anomalous Hall effect occurs when magnetization lies within the same plane as the electric field and Hall current, and requires magnetic point groups lacking rotational or mirror symmetries. While it is observed in both Weyl semimetals and elemental ferromagnets, the microscopic role of higher-order multipoles remains unclear. Here, we develop a microscopic framework that combines time-reversal-symmetric Wannier functions with a symmetry-adapted multipole basis to decompose the first-principles Wannier Hamiltonian into electric, magnetic, magnetic toroidal, and electric toroidal multipoles. This approach allows us to rotate the magnetization rank by rank and quantify how each multipole affects the conductivity. Applying this framework to body-centered cubic iron, we find that high-rank magnetic and magnetic toroidal multipoles contribute with magnitudes comparable to magnetic dipoles, while magnetic toroidal 16-poles act with the opposite sign. Furthermore, based on this multipole analysis, we apply uniaxial strain along the [103] direction to control the dominant multipoles contributing to the conductivity. The strain substantially modifies its angular dependence, demonstrating that multipole-resolved Hamiltonian engineering and magnetoelastic control serve as practical routes to predict and tune the in-plane anomalous Hall conductivity in simple ferromagnets.
Read the full abstract

Materials Science

Exact Electrostatic Theory of Fermi-Energy Response at Metallic Interfaces

Théophane Bernhard and Andrea Grisafi

The response of the Fermi energy to external perturbations governs key physical observables at metallic interfaces. Although this response admits a local formulation in terms of the Fukui function, its evaluation has traditionally been limited by inherent approximations, fundamentally rooted in the difficulty of adding a finite charge in a periodic system. We present an exact resolution to this problem that, within an electronic-structure framework capturing metallic behavior, exploits the screening properties of electronic conductors to compute Fukui functions via a finite electric field. The resulting linear-response theory yields strictly quadratic error scaling of Fermi-level shifts across representative platinum surfaces, achieving sub-meV accuracy up to fields of 0.1 V/Å. The approach is further validated by reproducing work-function changes under molecular perturbations, and by providing mean-field estimates of electrode potentials that yield capacitance–voltage curves consistent with experiment. Our findings establish a rigorous foundation for a local theory relating electrostatic screening and Fermi-energy variations at metallic interfaces.
Read the full abstract

Materials Science

NiTi Single Crystal Growth by Micro-Pulling-Down Method: Experimental Setup and Material Characterization

Timon Sieweke, Chris Luther, Martin Wortmann et al. (+14 more)

Nickel-titanium that has an austenite to martensite phase transition has been studied extensively in the past as a shape memory alloy, but a lot remains to be learned from such phase transitions. However, single crystals are needed for a detailed characterization of the emerging phase transition. In order to produce NiTi single crystals for research purposes, we have set up a micro-pulling-down ($\mu$PD) apparatus. The $\mu$PD process is a fast and flexible method for the fabrication of small single crystals. The apparatus is operated in vacuum. By pulling the crystal down through a hole in the crucible bottom, it is possible to reduce oxygen contamination, since oxides float on top of the melt due to their low density. Here we present a detailed characterization of as-grown NiTi crystals by electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), hot gas extraction method and differential scanning calorimetry (DSC). The characteristics of the phase transition in NiTi are very sensitive to dopants and alloying. The $\mu$PD method facilitates the introduction of different doping elements into the crystal.
Read the full abstract

All authors Timon Sieweke, Chris Luther, Martin Wortmann, Lauritz Schnatmann, Felicitas Werner, Olga Kuschel, Laila Bondzio, Inga Ennen, Judith Bünte, Karsten Rott, Oluwaseyi Oluwabi, Moritz Loewenich, Joachim Wollschläger, Andreas Hütten, Jan Frenzel, Gabi Schierning, Alexander Kunzmann

Materials Science · Cross-listed from cond-mat.mes-hall

Observation of Unconventional Ferroelectricity in Non-Moir'\e Graphene on Hexagonal Boron Nitride Boundaries and Interfaces

Tianyu Zhang, Yueyang Wang, Hongxia Xue et al. (+3 more)

Interfacial interactions in two parallel-stacked hexagonal boron-nitride (hBN) layers facilitate sliding ferroelectricity, enabling novel device functionalities. Additionally, when Bernal or twisted bilayer graphene is aligned with an hBN layer, unconventional ferroelectric behavior was observed, though its precise origin remains unclear. Here, we propose an alternative approach to engineering such an unconventional ferroelectricity in graphene-hBN van der Waals (vdW) heterostructures by creating specific types of hBN boundaries and interfaces. We found that the unconventional ferroelectricity can occur–without the alignments at graphene-hBN or hBN-hBN interfaces–when there are hBN edges or interfaces with line defects. By systematically analyzing the gate dependence of mobile and localized charges, we identified key characteristics of localized states that underlie the observed unconventional ferroelectricity, informing future studies. These findings highlight the complexity of the interfacial interactions in graphene/hBN systems, and demonstrate the potential for defect engineering in vdW heterostructures.
Read the full abstract

All authors Tianyu Zhang, Yueyang Wang, Hongxia Xue, Kenji Watanabe, Takashi Taniguchi, Dong-Keun Ki

Materials Science

Precipitate size evolution in an ultrafine-grained magnesium-manganese alloy

Julian M. Rosalie, Brian R. Pauw and Anton Hohenwarter

Precipitate size evolution during room temperature high-pressure torsion (HPT) of a Mg-1.35wt.%Mn alloy was studied using scanning transmission electron microscopy (STEM) and Small-/Wide-angle X-ray scattering (SAXS/WAXS). The volume fraction of the nm-scale $\alpha$-Mn particles increased with applied strain, however small angle X-ray scattering (SAXS) indicated that the majority of manganese remained in solution even after 10 HPT rotations, indicating that the reaction progress is still limited by the diffusivity of Mn. Analysis of the precipitate size distribution determined that the mean particle size did not increase over the course of HPT. This, in combination with the precipitate size distribution suggested that precipitate growth was subject to interfacial rather than diffusional control.
Read the full abstract

Materials Science

Symmetry-Driven Unconventional Magnetoelectric Coupling in Perovskite Altermagnets: From Bulk to the Two-Dimensional Limit

Zhou Cui, Ziye Zhu, Xunkai Duan et al. (+4 more)

The emergence of altermagnets establishes a new paradigm for multiferroics. Unlike conventional multiferroics relying on direct magnetoelectric coupling, multiferroic altermagnets host a crystal-symmetry-mediated magnetoelectric interaction that is intrinsically more efficient and robust. Among candidate material platforms, layered perovskites are particularly appealing owing to their structural diversity and synthetic versatility. However, magnetoelectric properties at the two-dimensional scale remain largely unexplored, hindering their applicability in miniaturized, highly integrated devices. Here, we systematically investigate the dimensional evolution of ferroelectric polarization and magnetism in perovskite systems through symmetry analysis. We demonstrate that altermagnetism can persist in the two-dimensional limit, yet is strongly constrained by the magnetic configuration-with only C-type antiferromagnetic order supporting it. Based on mode-decomposition calculations, we further reveal that symmetry-restricted multimode couplings simultaneously govern ferroelectric polarization and altermagnetic spin splitting. Finally, combined with first-principles calculations, we propose several strategies to lift the magnetic-configuration constraint, extending the range of viable altermagnetic systems. These results underscore the critical role of dimensionality in symmetry-driven magnetoelectric coupling in perovskite altermagnets and pave the way toward next-generation electrically controlled spintronic and multiferroic devices.
Read the full abstract

All authors Zhou Cui, Ziye Zhu, Xunkai Duan, Bowen Hao, Xianzhang Chen, Jiayong Zhang, Tong Zhou

Materials Science

Cross-hatch strain effects on SiGe quantum dots for qubit variability estimation

Luis Fabián Peña, Mitchell I. Brickson, Fabrizio Rovaris et al. (+11 more)

SiGe heterostructures integrated with Si via virtual substrate (VS) growth are promising hosts for spin qubits. While VS growth targets plastic relaxation, residual cross-hatch strain inhomogeneity propagates into heterostructure overgrowth. To quantify strain inhomogeneity's influence on interface structure and qubit properties, we measure strained-silicon (s-Si)/Si$_{0.7}$Ge$_{0.3}$ heterostructures on 25 wafers processed via standard commercial chemical vapor deposition. Spatially-aligned images of strain (Raman microscopy) and interface structure (atomic force microscopy and cross-sectional scanning transmission electron microscopy) reveal strain-roughness interplay. A strain-driven surface diffusion model predicts the roughness and its temperature dependence. Measured strains suggest spurious double-dot qubit detunings of 0.1 meV over 100 nm distances may result. Modeling shows that interface roughness (atomic steps), when convolved with alloy disorder, only modestly reduces valley splitting (70$\pm$13 vs. 77$\pm$14 $\mu$eV on average). Our findings point to thicker VS buffer layers beneath heterostructures and lower-temperature growth (T $\le$ 700 $^{\circ}$C) to limit roughening.
Read the full abstract

All authors Luis Fabián Peña, Mitchell I. Brickson, Fabrizio Rovaris, J. Houston Dycus, Anthony McDonald, Zachary T. Piontkowski, Joel Benjamin Ruzindana, Adelaide M. Bradicich, Don Bethke, Robin Scott, Thomas E. Beechem, Francesco Montalenti, N. Tobias Jacobson, Ezra Bussmann

Materials Science

Autonomous Probe Microscopy with Robust Bag-of-Features Multi-Objective Bayesian Optimization: Pareto-Front Mapping of Nanoscale Structure-Property Trade-Offs

Kamyar Barakati, Haochen Zhu, C Charlotte Buchanan et al. (+3 more)

Combinatorial materials libraries are an efficient route to generate large families of candidate compositions, but their impact is often limited by the speed and depth of characterization and by the difficulty of extracting actionable structure-property relations from complex characterization data. Here we develop an autonomous scanning probe microscopy (SPM) framework that integrates automated atomic force and magnetic force microscopy (AFM/MFM) to rapidly explore magnetic and structural properties across combinatorial spread libraries. To enable automated exploration of systems without a clear optimization target, we introduce a combination of a static physics-informed bag-of-features (BoF) representation of measured surface morphology and magnetic structure with multi-objective Bayesian optimization (MOBO) to discover the relative significance and robustness of features. The resulting closed-loop workflow selectively samples the compositional gradient and reconstructs feature landscapes consistent with dense grid "ground truth" measurements. The resulting Pareto structure reveals where multiple nanoscale objectives are simultaneously optimized, where trade-offs between roughness, coherence, and magnetic contrast are unavoidable, and how families of compositions cluster into distinct functional regimes, thereby turning multi-feature imaging data into interpretable maps of competing structure-property trends. While demonstrated for Au-Co-Ni and AFM/MFM, the approach is general and can be extended to other combinatorial systems, imaging modalities, and feature sets, illustrating how feature-based MOBO and autonomous SPM can transform microscopy images from static data products into active feedback for real-time, multi-objective materials discovery.
Read the full abstract

All authors Kamyar Barakati, Haochen Zhu, C Charlotte Buchanan, Dustin A Gilbert, Philip Rack, Sergei V. Kalinin

Materials Science

Unusually high phonon thermal conductivity in the Weyl semimetal TaP: A comparative study with TaAs

Xianyong Ding, Xin Jin, Dengfeng Li et al. (+5 more)

In many metals, thermal transport is often dominated by electrons, although the lattice contribution can remain appreciable depending on the material. Here, through rigorous first-principles calculations, we uncover a phonon-dominated thermal transport regime in the Weyl semimetals TaAs and TaP. Remarkably, despite its metallic character, TaP exhibits an exceptionally high phonon thermal conductivity ($\kappa_{\rm ph}$) of 162 Wm$^{-1}$K$^{-1}$ at room temperature, surpassing its electronic counterpart by nearly an order of magnitude. This anomalously high $\kappa_{\rm ph}$ arises from the combined effects of Weyl electronic structure, acoustic phonon bunching, and a large low-high frequency phonon gap, which together suppress phonon-electron and three-phonon scattering. The linearly dispersing bands near the Fermi level yield a low electronic density of states, limiting both electrical conductivity and electronic thermal transport in these compounds. By further surveying a broad range of topological semimetals, we show that the prominence of phonon thermal transport is a universal characteristic of this material class. Our work provides deeper insight into thermal transport mechanisms in topological semimetals and broadens the scope for discovering metals with high thermal conductivity.
Read the full abstract

All authors Xianyong Ding, Xin Jin, Dengfeng Li, Jing Fan, Peng Yu, Xiaoyuan Zhou, Xiaolong Yang, Rui Wang

Materials Science

Intertwined atomic-nanoscale-microscale structures via intralayer anisotropic Fe-chains in the layered ferromagnet FePd2Te2

Manyu Wang, Chang Li, Bingxian Shi et al. (+12 more)

Controlling mesoscale and nanoscale material structures and properties through self-organized atomic behavior is essential for atomic-scale manufacturing. However, direct and visual studies on the cross-scale effects of such atomic self-organization on mesoscopic structures remain scarce. Here, we report the intertwined atomic-nanoscale-mesoscale structures via the intralayer Fe-chains in the sandwich-like layered FePd2Te2 crystal by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The hierarchical orthogonal corrugated morphologies are directly revealed and attributed to its chain-orientation-determined twinning-domain effect. Both Fe-chains of middle-sublayer and two kinds of Te atoms of top-sublayer are further atomically resolved at the sub-Å level, indicating the critical effects of Pd-atoms/voids on the intra-layer anisotropic Fe-chains and the interlayer structural alignment. The thermal-induced and strain-related structural transitions of surface layer are further investigated and discussed based on the proposed filling model of Pd-voids by the intralayer Pd-atoms. Our work not only provides deep understanding of this exotic layered magnetic material, and will inspire more perspectives for tailoring its anisotropic atomic-to-mesoscale structures and properties.
Read the full abstract

All authors Manyu Wang, Chang Li, Bingxian Shi, Shuo Mi, Xiaoxiao Pei, Shuming Meng, Yanyan Geng, Fei Pang, Rui Xu, Li Huang, Wei Ji, Hong-Jun Gao, Peng Cheng, Le Lei, Zhihai Cheng

Materials Science · Cross-listed from cond-mat.str-el

Symmetry-engineered and electrically tunable in-plane anomalous Hall effect in oxide heterostructures

Kunjie Dai, Zhen Wang, Wenfeng Wu et al. (+19 more)

The family of Hall effects has long served as a premier probe of how symmetry, magnetic order, and topology intertwine in solids. Recently, the in-plane anomalous Hall effect (IP-AHE), a transverse Hall response driven by in-plane magnetization, has emerged as a distinct member of this family, offering innovative spintronic functionalities and illuminating intricate interplay between mirror-symmetry breaking and in-plane magnetic order. However, practical routes to deterministically and reversibly control IP-AHE remain limited. Here, we establish a symmetry-engineered IP-AHE platform, CaRuO3/La2/3Ca1/3MnO3/CaRuO3 heterostructure on NdGaO3(110), that turns strict mirror-symmetry breaking constraints into effective tuning knobs. IP-AHE in these epitaxial trilayers unambiguously couples to the CaRuO3-buffer-induced mirror-symmetry breaking and faithfully reproduces the ferromagnetic hysteresis. Ionic liquid gating further enables reversible reconfigurations of the symmetry breaking, thereby achieving electrical modulation and ON/OFF switching of IP-AHE. This highly tunable IP-AHE platform opens pathways for exploring nontrivial magnetic order and developing programmable Hall functionalities in planar geometries.
Read the full abstract

All authors Kunjie Dai, Zhen Wang, Wenfeng Wu, Feng Jin, Enda Hua, Nan Liu, Jingdi Lu, Jinfeng Zhang, Yuyue Zhao, Linda Yang, Kai Liu, Huan Ye, Qiming Lv, Zhengguo Liang, Ao Wang, Dazhi Hou, Yang Gao, Shengchun Shen, Jing Tao, Liang Si, Wenbin Wu, Lingfei Wang

Materials Science

Coupled Spin-lattice Dynamics across a Magnetostructural Phase Transition

Lokanath Patra, Zeyu Xiang, Yubi Chen et al. (+1 more)

First-order magnetostructural phase transitions underpin giant magnetocaloric effects, yet the microscopic role of lattice dynamics in these transitions remains controversial. Here we use first-principles spin-lattice dynamics simulations to investigate the coupled evolution of magnetization and phonon dispersions across the magnetostructural transition in MnAs. Our simulations quantitatively reproduce the experimentally observed Curie temperature, lattice contraction, and free-energy crossing between hexagonal and orthorhombic phases. We show that below the Curie temperature, magnetic-field-induced hardening of soft phonon modes gives rise to a sizable lattice entropy contribution that enhances the total isothermal entropy change by approximately 23% under a 5 T field. In contrast, the lattice entropy change associated with the structural phase transition itself has an opposite sign and partially compensates the lattice contribution due to field-induced phonon hardening. This competition reconciles long-standing discrepancies in the interpretation of magnetocaloric entropy measurements across first-order transitions. In addition, we demonstrate that the strong magnetic-field dependence of the phonon spectrum near the transition enables large tunability of lattice thermal conductivity, highlighting MnAs as a promising platform for magnetic-field-controlled thermal switching. Our results establish a unified microscopic picture of spin-lattice coupling in first-order magnetocaloric materials and provide design principles for engineering enhanced caloric and thermal transport functionalities.
Read the full abstract

All authors Lokanath Patra, Zeyu Xiang, Yubi Chen, Bolin Liao

Materials Science

The effect of normal stress on stacking fault energy in face-centered cubic metals

Yang Li and Yuri Mishin

Plastic deformation and fracture of FCC metals involve the formation of stable or unstable stacking faults (SFs) on (111) plane. Examples include dislocation cross-slip and dislocation nucleation at interfaces and near crack tips. The stress component normal to (111) plane can strongly affect the SF energy when the stress magnitude reaches several to tens of GPa. We conduct a series of DFT calculations of SF energies in six FCC metals: Al, Ni, Cu, Ag, Au, and Pt. The results show that normal compression significantly increases the stable and unstable SF energies in all six metals, while normal tension decreases them. The SF formation is accompanied by inelastic expansion in the normal direction. The DFT calculations are compared with predictions of several representative classical and machine-learning interatomic potentials. Many potentials fail to capture the correct stress effect on the SF energy, often predicting trends opposite to the DFT calculations. Possible ways to improve the ability of potentials to represent the stress effect on SF energy are discussed.
Read the full abstract

Thursday 8 January

Materials Science · Cross-listed from eess.SP

Differentiating through binarized topology changes: Second-order subpixel-smoothed projection

Giuseppe Romano, Rodrigo Arrieta and Steven G. Johnson

A key challenge in topology optimization (TopOpt) is that manufacturable structures, being inherently binary, are non-differentiable, creating a fundamental tension with gradient-based optimization. The subpixel-smoothed projection (SSP) method addresses this issue by smoothing sharp interfaces at the subpixel level through a first-order expansion of the filtered field. However, SSP does not guarantee differentiability under topology changes, such as the merging of two interfaces, and therefore violates the convergence guarantees of many popular gradient-based optimization algorithms. We overcome this limitation by regularizing SSP with the Hessian of the filtered field, resulting in a twice-differentiable projected density during such transitions, while still guaranteeing an almost-everywhere binary structure. We demonstrate the effectiveness of our second-order SSP (SSP2) methodology on both thermal and photonic problems, showing that SSP2 has faster convergence than SSP for connectivity-dominant cases – where frequent topology changes occur – while exhibiting comparable performance otherwise. Beyond improving convergence guarantees for CCSA optimizers, SSP2 enables the use of a broader class of optimization algorithms with stronger theoretical guarantees, such as interior-point methods. Since SSP2 adds minimal complexity relative to SSP or traditional projection schemes, it can be used as a drop-in replacement in existing TopOpt codes.
Read the full abstract

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

Theoretical investigation of non-Förster exciton transfer mechanisms in perylene diimide donor, phenylene bridge, and terrylene diimide acceptor systems

Lei Yang and Seogjoo J. Jang

The rates of exciton transfer within dyads of perylene diimide and terrylene diimide connected by oligophenylene bridge units have been shown to deviate significantly from those of Förster's resonance energy transfer theory, according to single molecule spectroscopy experiments. The present work provides a detailed computational and theoretical study investigating the source of such discrepancy. Electronic spectroscopy data are calculated by time-dependent density function theory and then compared with experimental results. Electronic couplings between exciton donor and acceptor are estimated based on both transition density cube method and transition dipole approximation. These results confirm that the delocalization of exciton to the bridge parts contribute to significant enhancement of donor-acceptor electronic coupling. Mechanistic details of exciton transfer are examined by estimating the contributions of the bridge electronic states, vibrational modes of the dyads commonly coupled to both donor and acceptor, inelastic resonance energy transfer mechanism, and dark exciton states. These analyses suggest that the contribution of common vibrational modes serves as the main source of deviation from Förster's spectral overlap expression.
Read the full abstract

Materials Science · Cross-listed from cond-mat.soft

A finite viscoelastic constitutive model for low to high strain rate response of elastomers with application of strain rate-induced glass transition

Bibekananda Datta, Sushan Nakarmi and Nitin P. Daphalapurkar

Amorphous elastomers exhibit significant rate-stiffening and unique viscous flow characteristics across a wide range of strain rates, often undergoing glass transition above a strain rate threshold. We have developed a thermodynamically-consistent and micromechanically-inspired constitutive model for soft elastomers to capture the rate-dependent stress-strain behavior and hysteresis when subjected to low to high strain rates. Our proposed constitutive model encapsulates the viscous flow of materials through molecular motion at low strain rates and intermolecular rearrangement and alignment of the molecules at high strain rates, essentially covering the glass transition. We applied our constitutive model to uniaxial compression experiments performed at low and high strain rates for polyborosiloxane (PBS) to identify the material parameters, and subsequently, performed numerical simulations of single and multi-cycle compression, stress relaxation, and small amplitude oscillatory tension-compression. Our analyses indicate that the model predicts higher total energy dissipation with increasing strain rate; however, dissipation associated with molecular relaxation decreases because, beyond a crossover strain rate, intermolecular rearrangement and alignment become dominant, which is consistent with the onset of the glass transition. For cyclic loading-unloading, we observed that dissipation over a cycle remains constant at low strain rates but decreases non-monotonically at high strain rates before becoming constant, with the peak stress over the cycle becoming higher, which can be interpreted as more loading being carried elastically by the polymer network as the intermolecular rearrangement process occurs. Additionally, our model was able to qualitatively predict the storage modulus and loss modulus in the limit of small strain over a wide range of frequency sweeps.
Read the full abstract

Materials Science · Cross-listed from math-ph

Modeling phononic band gap in microstructured solids using the Riemann-Cartan geometric framework

Ilya Peshkov and Loïc Le Marrec

This paper discusses the modeling of acoustic wave fields in microstructured elastic solids within the framework of Riemann-Cartan geometry. We consider a scenario in which microstructural deformations occur significantly faster than those of the bulk material. This time-scale separation creates apparent geometric incompatibilities at the macroscopic level, even in the absence of permanent inelastic deformation or damage. We formalize this phenomenon by using a non-holonomic frame field to represent macroscopic elastic deformations and an associated torsion field to characterize the resulting geometric incompatibilities. The spatial components of the torsion tensor quantify the instantaneous geometric incompatibility of the macroscopic deformations, while its temporal components capture the inertial effects arising from the reversible energy exchange between the micro- and macro-scales. A key finding is that the model's dispersion relation predicts a complete frequency band gap. Furthermore, the governing equations exhibit a mathematical analogy to Maxwell's equations, potentially bridging the modeling of phononic and photonic metamaterials.
Read the full abstract

Materials Science

Layered CrGe1-xSe3+y with Cr Kagome Lattice and Antiferromagnetic Ordering

Jeremy G. Philbrick, Chaoguo Wang, Xin Gui et al. (+1 more)

We report the synthesis and properties of a new layered material, CrGe1-xSe3+y. The crystal structure was determined by using single crystal x-ray diffraction and transmission electron microscopy. CrGe1-xSe3+y crystallizes with a space group R-3m, featuring a double Kagome layer of chromium atoms, sandwiched between disordered Ge-Se layers. This compound displays antiferromagnetic order below 50 K, unlike the ferromagnetic behavior in CrGeTe3. Chromium displays an effective moment of ~3.9 {\mu}B/Cr, consistent with Cr3+ oxidation. The presence of this phase limits the possibility of a ferromagnetic CrGeSe3 analogous to CrGeTe3.
Read the full abstract

All authors Jeremy G. Philbrick, Chaoguo Wang, Xin Gui, Tai Kong

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

Oxygen distribution and segregation at grain boundaries in Nb and Ta-encapsulated Nb thin films for superconducting qubits

Jaeyel Lee, Dieter Isheim, Zuhawn Sung et al. (+14 more)

We report on atomic-scale analyses of oxygen distribution and segregation at grain boundaries (GBs) of Nb and Ta-encapsulated Nb (Ta/Nb) thin films for superconducting qubits using atom-probe tomography (APT) and transmission electron microscopy (TEM). We observe oxygen segregation at grain boundaries (GBs) relative to the oxygen concentration within the grains for both Nb and Ta-capped Nb thin films for superconducting qubits and find that higher oxygen concentration in the interior of Nb grains lead to greater oxygen segregation levels at GBs. This finding emphasizes that controlling oxygen impurities in Nb during film deposition and fabrication processing is important to reduce the level of oxygen segregation at GBs in Nb. The enrichment factor (Cgb/Cgrain) for oxygen segregation at GBs in Nb is 2.7 (error bar: 0.3) for Nb films, and Ta-capped Nb thin films exhibit slightly reduced Nb GB enrichment factors of 2.3 (error bar: 0.3) while GBs in the Ta capping layer itself possess higher enrichment factors of 3.0 (error bar: 0.3). We hypothesize that the Ta capping layer can trap oxygen and thereby affect oxygen in-diffusion and segregation at GBs in the underlying Nb thin films. Finally, we find that increases in the oxygen concentration in both Nb grains and GBs correlate with a suppression in the critical temperature for superconductivity (Tc). Together, our comparative chemical and charge transport property analyses provide atomic-scale insights into a potential mechanism contributing to decoherence in superconducting qubits.
Read the full abstract

All authors Jaeyel Lee, Dieter Isheim, Zuhawn Sung, Francesco Crisa, Sabrina Garattoni, Mustafa Bal, Cameron J. Kopas, Josh Y. Mutus, Hilal Cansizoglu, Jayss Marshall, Kameshwar Yadavalli, Dominic P. Goronzy, Mark C. Hersam, David N. Seidman, Alex Romanenko, Anna Grassellino, Akshay A. Murthy

Materials Science

Control of the MoTe$_2$ Fermi Surface by Nb Doping

Andrew P. Weber, Iñigo Robredo, Philipp Rüssmann et al. (+8 more)

Ab initio calculations and angle-resolved photoemission experiments show that the bulk and surface electronic structure of Weyl semimetal candidate MoTe$_2$ changes significantly by tuning the chemical potential by less than 0.4 eV. Calculations show that several Lifshitz transitions can occur among multiple electron and hole Fermi pockets of differing orbital character. Experiments show that 18% Nb-Mo substitution reduces the occupation of bulk and (001) surface bands, effectively producing a chemical potential shift of $\approx 0.3$ eV. Orbital character and dimensionality of the bulk bands is examined by soft X-ray angle resolved photoemission with control of the excitation light polarization. The band filling at the surface is shown to increase upon deposition of alkali atoms. The results indicate that multiple regimes of electronic properties can be easily accessed in this versatile, layered material.
Read the full abstract

All authors Andrew P. Weber, Iñigo Robredo, Philipp Rüssmann, Maxim Ilyn, Arnaud Magrez, Philippe Bugnon, Nan Xu, Vladimir Strocov, J. Hugo Dil, J. Enrique Ortega, Julen Ibañez-Azpiroz

Materials Science · Cross-listed from cond-mat.str-el

Surface chiral Abelian topological order on multilayer cluster Mott insulators

Xu-Ping Yao, Chao-Kai Li and Gang v. Chen

The surface states of a symmetry protected topological state can have many possibilities. Here we propose a chiral Abelian topological order on a distinct surface of a multilayer-stacked cluster Mott insulating system. The first-principle calculation and the slave-rotor mean-field theory are applied to study the surface states of the relevant material system. The angle-resolved photoemission spectroscopic measurement is further suggested to detect the anomalous surface fractionalization of the chiral Abelian topological order on the surface. The connection with real materials is further discussed. We expect our results to inspire the interest in the emergent exotic and correlation physics among the cluster Mott insulating systems and in the interplay between the two different branches of topological phases.
Read the full abstract

Materials Science

Local Multimodal Dynamics in Mixed Ionic-Electronic Conductors and Their Fingerprints in Organic Electrochemical Transistor Operation

Shubham Tanwar, Han-Yan Wu, Chi-Yuan Yang et al. (+4 more)

Mixed ionic-electronic conductors host tightly coupled interactions among mobile ions, electronic charges, and the polymer matrix, giving rise to complex multimodal responses spanning electrical, mechanical, and morphological transformations. These materials underpin organic electrochemical transistors (OECTs), which translate such interactions into low-voltage signal amplification and sensing for applications in bioelectronics, neuromorphic computing, and memory. Despite their central role, OECT current-voltage transfer characteristics are often treated phenomenologically, as both the local multimodal dynamics and their connection to global device response remain unresolved. Here, we reveal that the transfer curve encodes a cascade of spatially localized electrochemical transitions, each associated with distinct changes in conductivity, stiffness, and morphology, fundamentally redefining it as a spatially resolved fingerprint of device's internal state. Using automated operando multimodal in-liquid scanning dielectric microscopy, we directly map these dynamics and identify region-specific electrochemical thresholds governing the interplay between source, channel, and drain. We found that the local tip-sample electrostatic force serves as a remarkable mechanistic observable of coupled multimodal dynamics in mixed conductors. A physically grounded model links it to general material, interfacial, and geometric parameters, enabling mechanistic interpretation and predictive insights. Our work provides a new framework for probing and understanding mixed conduction in ion-electron coupled systems.
Read the full abstract

All authors Shubham Tanwar, Han-Yan Wu, Chi-Yuan Yang, Ruben Millan-Solsona, Simone Fabiano, Adrica Kyndiah, Gabriel Gomila