Materials Science · Cross-listed from cond-mat.supr-con
First-principles prediction of high-temperature superconductivity in stretched carbon nanotubes
Hua-Zhen Li and Xun-Wang Yan
Superconductivity in quasi-one-dimensional systems is an significant but undervalued research field. In this work, based on the electron-
phonon coupling mechanism, we systematically investigate the superconductivity in quasi-one-dimensional carbon nanotube under uniaxial tensile strain. The calculated superconducting critical temperature attains its peak value of 162 K at a uniaxial tensile strain of 4.5%, being drastically higher than the counterpart in the unstrained carbon nanotube. An overall softening of
phonons, strong electron-
phonon coupling, and an increase of electronic density of states at the
Fermi level, play key roles in achieving high-temperature superconductivity in this system. Our research demonstrates that stretching is an effective approach to modulating the superconductivity one-dimensional materials, and more importantly, indicates that high-temperature superconductivity may occur in carbon nanotubes.
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Materials Science
A biomimetic feedback loop for sustaining self-lubrication and wear resistance
Fuyan Kang, Shilin Deng, Panpan Li et al. (+7 more)
Intelligent materials that self-sense and self-regulate are an emerging frontier in sustainable technology. Here we introduce Cu(Au)/C nanocomposite films that act as bioinspired self-adjusting lubricants. In these films, frictional heating triggers melting and migration of soft metal nanoparticles (NPs) such as Cu or Au along nano-pores to the friction interface, where the metal catalyzes the in-situ formation of ordered carbon nano-structures. Real-time monitoring of friction coefficient, electrical resistance(R), and metal release confirms an autonomous cycle: high friction coefficient generates heat, melting the metal NPs; the migrating metal then lowers friction coefficent by creating low-friction nanostructures, which reduces heat and arrests further migration until friction rises again. This self-limiting feedback enables stable ultra-low friction (~0.04) and an exceptional wear life (>40 km) even in high
vacuum. By utilizing friction-derived heat as an intrinsic activation signal, our system establishes a general paradigm for intelligent, self-regulating materials with applications extending beyond tribology.
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All authors Fuyan Kang, Shilin Deng, Panpan Li, Rui Zhao, Xiaohong Liu, Hongxuan Li, Huidi Zhou, Jianmin Chen, Wengen Ouyang, Li Ji
Materials Science
Decoding the Complexity of Ferroelectric Orthorhombic HfO2: A Unified Mode Expansion Approach
Chenxi Yu, Jiajia Zhang, Xujin Song et al. (+2 more)
The ferroelectricity in $\mathrm{HfO}_2$ thin films is widely attributed to the formation of a polar orthorhombic phase named OIII phase. However, the complexity of OIII phase originated from its low
symmetry becomes an obstacle for studying ferroelectric properties of $\mathrm{HfO}_2$. Here, we developed a unified framework based on
phonon mode expansion for studying ferroelectric $\mathrm{HfO}_2$. In this framework, phase structures, domain walls and switching paths of orthogonal
crystal system can be studied from the same basis of mode analysis. The OIII phase and other orthogonal phases can be represented by the high-
symmetry cubic phase with the excitation of cubic
phonon modes, into which the complexity of orthogonal phases is faithfully coded. To present the capability of this mode expansion approach, we clarified the origin of orthorhombic stability from the energy functional of modes; enumerated inequivalent domain walls and calculated their stable criteria; and summarized all possible switching mechanisms. This unified framework can be used to simplify the study of domain wall structures and transition paths. Furthermore, it can provide a new perspective for ferroelectricity in $\mathrm{HfO}_2$ from
phonon mode analysis.
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All authors Chenxi Yu, Jiajia Zhang, Xujin Song, Fei Liu, Jinfeng Kang
Materials Science
Monolithic integration of diverse crystalline thin films on diamond for near-junction thermal management
Tiancheng Zhao, Tianqi Bai, Yang He et al. (+20 more)
The pursuit of extreme miniaturization and high power in 6G RF front-ends has cast thermal dissipation as the central challenge. Here, we have demonstrated the monolithic integration of functionally distinct single-
crystal thin films, including e̱ta}-Ga2O3, Si, GaN, and LiTaO3, onto a single diamond substrate using a multi-step transfer printing technique. Focusing on the critical e̱ta}-Ga2O3/diamond interface, we achieve an exceptional interfacial thermal conductance (ITC) of 149 MW m-2 K-1 through ultra-high
vacuum (UHV) annealing, creating an atomically sharp interface featuring covalent bonding. Vibrational electron energy-loss spectroscopy (EELS) analysis combining with molecular dynamics (MD) simulations reveal that distinctive interfacial
phonon modes at the e̱ta}-Ga2O3/diamond heterointerface dominate ultrahigh ITC. We experimentally demonstrate that by improving the ITC, the thermal resistance (Rth) of a diamond-based e̱ta}-Ga2O3 MOSFET is driven to a record-low value of 1.58 K mm W-1, underscoring the critical role of interface engineering in near-junction thermal management for diamond-integrated devices. This work demonstrates a scalable, diamond-based monolithic integration platform designed to solve the near-junction thermal challenges in high-power RF front-ends.
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All authors Tiancheng Zhao, Tianqi Bai, Yang He, Wenhui Xu, Xinxin Yu, Ruochen Shi, Zhenyu Qu, Jiaxin Liu, Rui Shen, Haodong Jiang, Yeliang Wang, Jiaxin Ding, Dongchen Sui, Shibin Zhang, Lei Zhu, Ailun Yi, Kai Huang, Min Zhou, Huarui Sun, Zhonghui Li, Peng Gao, Tiangui You, Xin Ou
Materials Science · Cross-listed from cond-mat.mes-hall
Moiré Ferroelectricity-Driven Band Engineering in Twisted Square Bilayers
Kejie Bao, Rui Shi, Huan Wang et al. (+2 more)
We develop the moiré band theory for M-valley twisted square homobilayers with layer groups $P$-$42m$ and $P$-$4m2$, and propose candidate material realizations. We show that moiré ferroelectricity-originating from sliding ferroelectricity in the untwisted
bilayers-provides an independent control knob for miniband engineering in addition to interlayer tunneling. The competition between these two effects enables controlled switching between layer-resolved
bilayer minibands and an effective single isolated miniband. Remarkably, these systems exhibit an emergent momentum-space nonsymmorphic
symmetry in the absence of external
magnetic fields. Large-scale ab initio calculations identify Cu$_2$WS$_4$ and GeCl$_2$ as representative materials realizing the ferroelectricity- and tunneling-dominated regimes, respectively. Our results establish twisted square homobilayers as a promising platform for correlated band engineering beyond moiré hexagonal systems.
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All authors Kejie Bao, Rui Shi, Huan Wang, Linghao Huang, Jing Wang
Materials Science
Probing a two-dimensional soft ferromagnet Cr$_2$Ge$_2$Te$_6$ by a tuning fork resonator
Hengrui Gui, Zekai Shi, Jiawen Zhang et al. (+3 more)
Magnetic anisotropy encodes key information about the free-energy landscape of
magnetic materials, but its quantitative characterization often requires probes beyond conventional magnetometry. A quartz tuning-fork resonator provides direct access to the magnetotropic susceptibility. Here we use this technique to investigate the
magnetic anisotropy of the layered ferromagnet Cr$_2$Ge$_2$Te$_6$. The temperature-, field-, and angle-dependent responses are consistently described by a quasi-two-dimensional (2D) easy-axis
ferromagnetic model. In particular, the
evolution of the magnetotropic susceptibility reveals how the angular profile changes from a conventional cos(2$\theta$) form to a pronounced dip structure as the magnetization approaches directional saturation. These results establishCr$_2$Ge$_2$Te$_6$ as an ideal reference system for tuning-fork-based magnetotropic measurements. More broadly, they provide a useful framework for distinguishing
spin-origin anisotropy from orbital magnetism, as in the case of CsV3Sb5. Our work demonstrates that tuning-fork resonators offer a sensitive thermodynamic probe of the rotational stiffness of magnetization in anisotropic low-dimensional magnets.
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All authors Hengrui Gui, Zekai Shi, Jiawen Zhang, Yu Liu, Huiqiu Yuan, Lin Jiao
Materials Science · Cross-listed from cond-mat.supr-con
Probing the Meissner effect in single crystals of $\mathbf{Bi_2Sr_2Ca_2Cu_3O_{10+\delta}}$ via wide-field quantum microscopy under high pressure
Masahiro Ohkuma, Ryo Matsumoto, Shintaro Adachi et al. (+5 more)
We investigated the pressure dependence of the superconducting transition temperature ($T_{\rm c}$) in optimally doped Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$ (Bi-2223) single
crystals using different pressure-transmitting media. Previous high-pressure studies have reported conflicting behaviors, ranging from a resurgence of $T_{\rm c}$ of optimally doped Bi-2223 in fluid media to an insulating-like transition in solid media. However, a direct comparison of the effects of different pressure-transmitting media is lacking. Here, we employed wide-field
quantum microscopy based on nitrogen-vacancy centers to probe the
magnetic response under high pressure, utilizing cBN and KBr as media. We observed that a diamagnetic response near 70 K, indicative of the superconducting transition, persisted up to 23 GPa in KBr, whereas it disappeared above 11 GPa and 70 K in cBN. These results demonstrate the high sensitivity of Bi-2223 to the pressure environment and highlight the critical role of hydrostatic pressure in cuprate
superconductors.
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All authors Masahiro Ohkuma, Ryo Matsumoto, Shintaro Adachi, Shinobu Onoda, Takao Watanabe, Kenji Ohta, Yoshihiko Takano, Keigo Arai
Materials Science
Persistent incommensurate amorphous/crystalline meta-interfaces enable engineering-grade superlubricity
Wan Wang, Zijun Ding, Panpan Li et al. (+7 more)
Friction dissipates a substantial portion of global energy, motivating the pursuit of superlubricity, a state of near-zero friction, in real-world systems. Conventional approaches rely on crystalline
lattice mismatch to suppress periodic energy barriers, but real interfaces invariably contain defects, edges and grain boundaries that restore high-friction states. Here we introduce a materials-agnostic strategy based on amorphous/crystalline heterointerfaces to achieve robust superlubricity under engineering-relevant conditions. Using diamond-like carbon (DLC) and crystalline MoS2 as a model system, we show through experiments and atomistic simulations that their interface remains incommensurate at all orientations and exhibits vanishing energy barriers during friction. In contrast, twisted MoS2
bilayers readily reorient into commensurate, high-friction states. We scale this effect by fabricating
laser-patterned arrays of DLC/MoS2 meta-contacts reinforced with Ti3C2Tx MXene, forming hierarchical interfaces that sustain a friction coefficient of ~0.008 over 100000 cycles under combined extreme conditions: millimetre-scale contact size, 12.7 GPa contact pressure and RH 40% air. This unprecedented performance arises from four synergistic factors: intrinsic incommensurability at amorphous/crystalline interface, the
rigidity of DLC support, MXene-based mechanical reinforcement and normalized load distribution by
geometric patterning. These findings establish a general design paradigm that extends structural superlubricity from nanoscale model systems to practical technologies for sustainable engineering.
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All authors Wan Wang, Zijun Ding, Panpan Li, Wanying Ying, Hongxuan Li, Xiaohong Liu, Huidi Zhou, Jianmin Chen, Wengen Ouyang, Li Ji
Materials Science
Domain Walls Stabilized by Intrinsic Phonon Modes and Engineered Defects Enable Robust Ferroelectricity in HfO2
Chenxi Yu, Jiajia Zhang, Xujin Song et al. (+6 more)
Ferroelectric $\mathrm{HfO}_2$ has attracted extensive research interest for its applications in AI era. The domain walls play a crucial role in phase structure stabilization and polarization switching of ferroelectric $\mathrm{HfO}_2$, however, a thorough understanding is still lacking. Here, we developed a unified framework based on
phonon mode expansion to systematically study the effects of
phonon modes and defects on domain wall structures. Using this approach combined with first-principle calculations, we revealed that the interface
phonon modes play a key role in stability of domain walls; defects pin and stabilize ferroelectric domains, which in turn stabilizes the metastable orthorhombic phase and facilitates polarization switching. This provides an insight from the microscopic physics origin into the enhanced ferroelectricity in $\mathrm{HfO}_2$ by doping and defect engineering. Furthermore, the theoretically predicted domain structures and defect distributions were observed in La-doped $\mathrm{HfO}_2$ ferroelectric films by EELS and STEM experiments, which confirms the validity of our findings.
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All authors Chenxi Yu, Jiajia Zhang, Xujin Song, Dijiang Sun, Shangze Li, Fei Liu, Xiaoyan Liu, Wei Xi, Jinfeng Kang
Materials Science
Loss of altermagnetic order and smooth restoration of Kramers' spin degeneracy with increasing temperature in CrSb and MnTe
Christopher D. Woodgate, Nabil Menai, Arthur Ernst et al. (+1 more)
We describe how thermally induced
spin fluctuations modify the electronic structures of two prototypical altermagnets, CrSb and MnTe, via application of the disordered local moment picture. For both materials, our self-consistent, ab initio calculations demonstrate that local
magnetic moments persist on Cr and Mn atoms in their paramagnetic states, necessitating a
spin-polarised description of the electronic structure even above the Néel temperature, $T_\mathrm{N}$. Moreover, Kramers'
spin degeneracy, which is broken for both materials in their altermagnetic ground states, is shown to be smoothly restored - on the average - as the local moments thermally disorder. In metallic CrSb, this occurs at temperatures well below $T_\mathrm{N}$ and the signature effects of its altermagnetism are lost as the
magnetic disorder induces heavy smearing of strongly dispersive electronic states around the
Fermi energy. By contrast, in semiconducting MnTe, with its band gap largely unaffected by
magnetic disorder, the
spin degeneracy only returns at temperatures close to and above $T_\mathrm{N}$. We quantify the temperature dependence of the altermagnetic order parameter and the underlying electronic structures of both materials, with significant implications for their
spin transport properties.
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All authors Christopher D. Woodgate, Nabil Menai, Arthur Ernst, Julie B. Staunton
Materials Science
Electric-Field-induced Two-Dimensional Fully Compensated Ferrimagnetism and Emergent Transport Phenomena
Jin-Yang Li, Yong-Kun Wang, Ying Zhang et al. (+2 more)
The recent discovery of altermagnetism has demonstrated that
spin-split electronic band structures can emerge in
magnetic systems with zero net magnetization. In contrast, fully compensated ferrimagnetic (fFIM) systems remain far less explored, despite exhibiting similar characteristics such as vanishing magnetization and
spin-split bands. Here, based on first-principles calculations combined with theoretical analysis, we demonstrate that monolayer CoS and CoSe can be driven into fFIM states by an external electric field. These materials possess collinear
antiferromagnetic ground states with out-of-plane Néel vectors, and their electronic bands are
spin degenerate due to $\mathcal{PT}$
symmetry. When an out-of-plane electric field is applied, $\mathcal{PT}$
symmetry is broken, inducing fFIM states with pronounced
spin splitting. Moreover, we show that the resulting fFIM states host fully
spin-polarized currents, anomalous
Hall effects, and magneto-optical Kerr and Faraday effects. Our results establish monolayer CoS and CoSe as promising platforms for electric-field-controlled fFIM states and spintronic applications.
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All authors Jin-Yang Li, Yong-Kun Wang, Ying Zhang, Si Li, Wen-Li Yang
Materials Science
Bond-selective modulation of scalar spin chirality in strained Mn4N
Xin Liu, Mingyue Zhao, Shun Niu et al. (+10 more)
Scalar
spin chirality (SSC) underlies a variety of Berry-phase-driven transport phenomena in noncoplanar magnets. Mn4N is a unique ferrimagnetic system in which both collinear and noncoplanar
magnetic configurations have been reported at different
lattice parameters, featuring vanishing and finite SSC, respectively. However, the microscopic mechanism governing the competition between these
magnetic states and the associated modulation of SSC remains unclear. This issue is particularly important for Mn4N because its high
magnetic ordering temperature (TN = 740 K) provides an attractive platform for exploring
chiral magnetic states and their associated topological functionalities at elevated temperatures. Here, using first-principles calculations, we investigate the strain-driven
evolution of the
magnetic ground state and SSC in Mn4N and uncover the microscopic origin of the collinear-to-noncoplanar
magnetic transition. We demonstrate that tensile strain continuously stabilizes the noncoplanar configuration and enhances SSC, as quantified by the magnitude of the chirality-order vector. Orbital-resolved
crystal orbital Hamilton population and charge-density-difference analyses reveal that strain selectively weakens the Mn3c-N hybridization while preserving direct Mn3c-Mn3c interactions, leading simultaneously to the activation of the Mn3c in-plane
magnetic moment and the suppression of N-mediated
ferromagnetic superexchange between nearest-neighbor Mn3c atoms. This bond-selective electronic response governs the
magnetic ground state and consequently controls the emergence and enhancement of SSC in Mn4N. Our work establishes bond selectivity as an effective strategy for engineering SSC in high-temperature ferrimagnetic materials.
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All authors Xin Liu, Mingyue Zhao, Shun Niu, Yu Liu, Yang Li, Jiayao Zhu, Yiwen Zhang, Fengxian Ma, Dewei Zhao, Guoke Li, Li Ma, Congmian Zhen, Denglu Hou
Materials Science
Ductility and Brittle Fracture of Tungsten by Disconnection Pile-up on Twin Boundaries
Omar Hussein, Nicolas Bertin, Jakub Veverka et al. (+5 more)
Refractory body-centered cubic (BCC) metals and
alloys are of extraordinary importance in modern technological and structural applications. However, their wider adoption in science and technology is severely restricted by low-temperature brittleness, quantified by an unacceptably high value of the brittle-to ductile transition temperature (DBTT). The DBTT of these
alloys is known to depend strongly on the particular microstructure of the material following mechanisms that are not well understood. Here we apply cross-scale molecular dynamics (MD), a simulation approach that preserves full atomic resolution while capturing the collective
evolution of dislocations, twins, and cracks in near-micron-scale volumes, to investigate ductility and fracture in single-
crystal tungsten pillars as a function of initial defect microstructure, deformation conditions, and temperature. The simulations reveal a sequence of microscopic processes conducive to failure: dislocation starvation, nucleation and growth of twins, pinning of the twin boundaries at surface asperities, resulting in disconnection pile-ups that trigger crack nucleation and propagation at low macroscopic stresses along incoherent boundary segments. By resolving these processes within a single atomistic framework, our simulations connect defect-level dynamics to macroscopic fracture behavior and identify microstructural pathways capable of shifting the DBTT through targeted promotion or suppression of the underlying deformation mechanisms.
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All authors Omar Hussein, Nicolas Bertin, Jakub Veverka, Tomas Oppelstrup, Jaime Marian, Fadi Abdeljawad, Shen J. Dillon, Timofey Frolov
Materials Science
Hybrid Tribo/piezoelectic Electrospun Nanofibers for Energy Harvesting Enhancement in Flexible Electronics
Hao Zhang, Yurong He, Yaofeng Jin et al. (+4 more)
Triboelectric nanogenerators or TENGs and piezoelectric nanogenerators or PENGs have emerged as promising platforms for harvesting mechanical energy and converting it into electrical energy for powering flexible electronic devices. However, the material selection and structure design of such hybrid nanogenerator, and mechanisms of energy output still remain challenges. In this work, electrospinning is employed for the fabrication of nanofibers, particularly polyvinylidene fluoride or PVDF based nanofibers, due to its capability to generate high beta phase contents that effectively increase the piezoelectric performance of the PVDF friction layer, thereby enhancing the overall electrical performance for flexible electronics by merging tribo-piezoelectric power. Furthermore, various concentrations carbon nanotubes or CNT or
graphene nanosheets or GNS are individually incorporated into the PVDF solution as nanofillers or NF to enhance the piezoelectric responses of the PVDF based nanofibers. The introduction of nanofillers is found to not only alter the fiber diameter but also modify the surface roughness of the electrospun nanofibers, and thus, enhancing the triboelectric effect. In addition, the output performance of the fabricated nanogenerator is predominantly governed by the piezoelectric effect rather than triboelectric effect, as the electrical output shows a strong positive correlation with the beta phase content of PVDF based nanofibers: the highest beta phase content reached to 85.3 percent and consistently resulted in the optimal energy output of 1.133 watt per meter square. Notably, the power density achieved by the prototype device reaches to the level of watt/m2, representing a substantial improvement compared with that of the conventional TENGs or PENGs reported to date, providing expanded opportunities for flexible electronic devices
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All authors Hao Zhang, Yurong He, Yaofeng Jin, Hui Wang, Wanqi Ye, Lidong Chen, Kaiyang Zeng
Materials Science · Cross-listed from astro-ph.EP
Coupled Space Weathering: Nanophase Iron Formation by Micrometeoroid Impact and Solar Wind Sputtering
Ziyu Huang and Masatoshi Hirabayashi
Understanding the interplay between micrometeoroid impacts and
solar wind irradiation is crucial for interpreting lunar surface
evolution. Using reactive molecular dynamics simulations and surface binding energy (SBE) analyses, this study investigates the coupled effects of these two dominant space weathering processes on lunar regolith composed of Fe$_2$SiO$_4$. Our simulations reveal that micrometeoroid impacts significantly modify the lunar surface, creating structurally heterogeneous zones with varying SBEs across microcrater morphologies. Specifically, microcrater floors exhibit enhanced surface cohesion due to high-density compaction, whereas microcrater walls and ejecta show weakened structures. Applying Sigmund's sputtering theory with these SBEs indicates differential sputtering yields for Fe, Si, and O suggesting preferential retention of heavier elements like Fe. This selective sputtering mechanism supports the formation and growth of nanophase metallic iron (npFe$^0$) clusters, influencing the optical and compositional maturation of the lunar surface. These findings advance our understanding of lunar space weathering processes.
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Materials Science
Predicting electron-phonon coupling and electronic transport at the moiré scale in twisted bilayer graphene
David J. Abramovitch and Marco Bernardi
First-principles calculations can accurately describe electron-
phonon (e-ph) interactions and electronic transport in a wide range of materials, but are currently limited to unit
cells with up to $\sim$100 atoms due to computational cost. Here, we develop an atomistic electronic potential with Holstein- and Peierls-like terms for modeling e-ph interactions and
phonon-limited electronic transport that enables the study of moiré systems with thousands of atoms per unit
cell. This method can accurately reproduce first-principles e-ph coupling and resistivity in
graphene and large-angle twisted
bilayer graphene (TBG). Using this approach, we study TBG over a range of twist angles down to 1.6$^\circ$ (5044-atom unit
cell), and report the
evolution of e-ph interactions and
phonon-limited resistivity with twist angle. The predicted resistivity increases by two orders of magnitude between 13.2$^\circ$ and 1.6$^\circ$, driven by the progressive reduction of the electronic energy scale. Our calculations can predict key experimental trends in 2.0$^\circ$ and 1.6$^\circ$ TBG, including the resistivity and its dependence on temperature and band filling. Our work establishes a scalable approach for quantitative studies of e-ph interactions and transport in moiré materials and other systems with previously inaccessible length scales.
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Materials Science
Interfacial exchange and magnetostatic coupling in a CoFeB/Thulium Iron Garnet heterostructure
Walid Al Misba, Jenae E. Shoup, Miela J. Gross et al. (+5 more)
We investigate the exchange coupling between a ferrimagnetic
insulator (FI) thulium iron garnet (TmIG) deposited on a gadolinium gallium garnet (GGG) substrate, which shows perpendicular
magnetic anisotropy and a
ferromagnetic metal (FMM) stack with
oxide capping that consists of CoFeB(x)/W(0.4 nm)/CoFeB(0.8 nm)/MgO(1 nm)/W(5 nm). Vibrating sample magnetometry, magneto-optical Kerr microscopy and first-order reversal curve studies coupled with micromagnetic simulations are used to analyze the coupling between these layers. Strong interlayer exchange coupling and magnetostatic coupling are observed in the samples where the relative strength between these interactions can be controlled by varying the thickness of the CoFeB layer. Films with CoFeB thickness x <=1 nm are strongly exchange coupled, whereas the magnetostatic coupling dominates when the thickness is increased to 3 nm or above. These findings have important implications towards realizing fast and energy efficient spintronic devices using a FI, as its coupling to the FMM layer can be used for effective electrical read out of the
magnetic state of the FI.
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All authors Walid Al Misba, Jenae E. Shoup, Miela J. Gross, Dhritiman Bhattacharya, Kai Liu, Caroline A. Ross, Daniel B. Gopman, Jayasimha Atulasimha
Materials Science
Synchrotron-radiation X-ray topography and reticulography of bulk $\beta$-Ga$_2$O$_3$ crystals grown by the cold crucible method
Yongzhao Yao, Koki Mizuno, Kazuki Ohnishi et al. (+9 more)
The structural properties of a $\beta$-Ga$_2$O$_3$ single
crystal grown by the
oxide crystal growth from cold crucible (OCCC) method were investigated using synchrotron radiation X-ray topography and X-ray reticulography. The region grown beneath the seed exhibits high crystalline quality with a rocking curve full width at half maximum of about 26 arcsec. During diameter enlargement, a twist-type
lattice misorientation develops between the central and laterally expanded regions, originating near the shoulder and propagating along boundaries parallel to the $\langle010\rangle$ growth direction. Dislocation analysis reveals that $\langle010\rangle$-oriented screw dislocations dominate the defect structure with densities of ~$10^{5}$cm$^{-2}$, while higher densities (~$10^{6}$cm$^{-2}$) appear in the wing region. These results clarify defect formation in OCCC-grown $\beta$-Ga$_2$O$_3$ and provide insights for optimizing growth conditions.
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All authors Yongzhao Yao, Koki Mizuno, Kazuki Ohnishi, Yukari Ishikawa, Masanori Kitahara, Taketoshi Tomida, Rikito Murakami, Vladimir Kochurikhin, Liudmila Gushchina, Kei Kamada, Koichi Kakimoto, Akira Yoshikawa
Materials Science
Decoupling structural and bonding effects on ferroelectric switching in ScAlN via molecular dynamics under an applied electric field
Ryotaro Sahashi, Po-Yen Chen and Teruyasu Mizoguchi
ScxAl1-xN has emerged as a promising wurtzite-type ferroelectric material, where increasing the Sc composition reduces both the coercive field (Ec) and remanent polarization (Pr). This composition-dependent behavior is physically attributed to two simultaneous changes: the increase in the internal structural parameter u (structural effect) and the weakening of bond strength (bonding effect). Because these factors are strongly coupled in experiments, their individual contributions to ferroelectric switching remain unclear. In this study, we systematically decoupled these effects using machine-learning force field-based molecular dynamics (MD) simulations under an applied electric field. By artificially tuning u via in-plane strain at a fixed composition, we demonstrated that Pr is determined exclusively by the structural effect, exhibiting a universal linear dependence regardless of the composition. In contrast, Ec deviated from this structural trend, implying an additional compositional contribution. To isolate this, we evaluated configurations with identical u but varying Sc compositions; Pr remained constant, whereas Ec systematically decreased due to bond weakening. Furthermore, static nudged elastic band (NEB) calculations revealed that the static switching barrier depends solely on u, failing to explicitly capture the bonding effect on Ec. These results establish that while Pr is governed strictly by the structural effect, Ec is determined by a superposition of structural and bonding effects. Our findings highlight the necessity of dynamic MD simulations for fully understanding ferroelectric switching in compositionally tunable materials.
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Materials Science · Cross-listed from cond-mat.mes-hall
Spatiotemporal Magnonic Vortex Beams with Alternating Transverse Orbital Angular Momentum
Muyang Xie, Chenchen Liu, Jian Huang et al. (+3 more)
Recent theoretical and experimental advances have demonstrated spatiotemporal photonic and acoustic
vortex beams in free space. Such spatiotemporal
vortex beams possess orbital angular momentum oriented perpendicular to the wave propagation direction. Herein, we report the discovery of spatiotemporal magnonic
vortex beams in a confined
ferromagnetic nanostrip geometry. The spatiotemporal magnonic
vortex beam features stationary phase dislocations and exhibits wave propagation along a zigzag-like trajectory. Notably, the transverse orbital angular momentum carried by these phase dislocations displays spatial alternation. Our results differ distinctly from their photonic and acoustic counterparts, offering new insights into the fundamental research of spatiotemporal
vortex beams.
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All authors Muyang Xie, Chenchen Liu, Jian Huang, Zhenyu Wang, Xinwei Dong, Ruifang Wang
Materials Science · Cross-listed from cond-mat.str-el
Giant anomalous Hall conductivity in frustrated magnet EuCo2Al9
Sheng Xu, Jian-Feng Zhang, Shu-Xiang Li et al. (+16 more)
The interaction between conduction electrons and localized
magnetic moments profoundly influences the electrical and
magnetic properties of materials, giving rise to a variety of fascinating physical phenomena and
quantum effects. Here, we discover a
giant anomalous
Hall effect (AHE) in a frustrated Eu-based magnet, exhibiting a
giant anomalous
Hall conductivity (AHC) of 31000 {\Omega}-1cm-1 and a remarkable anomalous
Hall angle (AHA, tan{\theta}H) of 12 %–surpassing conventional mechanisms (either intrinsic or extrinsic) by two orders of magnitude. Combining magnetotransport,
quantum oscillations,
neutron diffraction and ab initio calculations, we establish that the
giant AHC originates from fluctuating
spin chirality skew scattering, generated by indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions of Eu-4f moments. Simultaneously, Hund's coupling of itinerant electrons and localized Eu-4f
spins triggers
giant exchange splitting, evidenced by temperature-dependent
Fermi surface reconstruction. This work establishes a frustrated
magnetic platform for engineering the AHE and elucidates the governing role of exchange interactions and
spin textures in
quantum transport, while also providing a framework for designing unconventional spintronic systems that harness emergent
spin-texture dynamics.
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All authors Sheng Xu, Jian-Feng Zhang, Shu-Xiang Li, Junfa Lin, Xiaobai Ma, Wenyun Yang, Jun-Jian Mi, Zheng Li, Tian-Hao Li, Yue-Yang Wu, Jiang Ma, Qian Tao, Wen-He Jiao, Xiaofeng Xu, Zengwei Zhu, Yuanfeng Xu, Hanjie Guo, Tian-Long Xia, Zhu-An Xu
Materials Science · Cross-listed from physics.chem-ph
Stochastic Collision Theory of Magnetism in Radical Fluids
Yoshiaki Uchida and Ryohei Kishi
How
stochastic, microscopic events generate deterministic, macroscopic properties is a fundamental question in physics. We address this question by developing a
quantum master equation model for concentrated radical solutions, where random molecular collisions govern the
magnetic properties of the system. Our theory reveals a simple mechanism: the first-order exchange contribution averages to zero over collisions, while the second-order term survives as an effective
ferromagnetic coupling that enhances magnetization. The model captures the experimentally observed trends in
magnetic behavior that deviate from conventional theories. Because the mechanism arises from statistical averaging, it may apply to a broader class of soft matter phenomena, including
liquid crystals.
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Materials Science
Acrylamide Conformers: A Revision of Published Density Functional Theory Studies
William Scott and Estela Blaisten-Barojas
Acrylamide, with PubChem identifier CID=6579 is broadcasted to have four stable conformers contrasting with several journal publications characterizing only two or three. In this revision summary the discrepancy is clarified. Through very high precision density functional theory (DFT) calculations, three stable conformers and the three transition state barriers existing between them are verified to exist and validated with our own DFT calculations The most stable conformer is a planar molecular structure termed "sys" or "trans" in the literature. Meanwhile, a less stable structure termed "skew" pertains to two 3-dimensional structures that are energy-degenerate, but differ in their structure for being mirrored images of each other. Vibrational spectra, partial atomic charges, Cartesian coordinates, and Intrinsic Reaction Coordinate paths are summarized and recalculated with DFT at the $\omega$B97XD/Def2TZVPP level for the three stable acrylamide isomers: the sys/trans lowest in energy structure, and the two skew mirrored structures.
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