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Ultrafast Demagnetization Governed by Spin Fluctuations in CaRuO$_{3}$/SrTiO$_{3}$ Superlattice
Authors:
Yu-Han Gao,
Wen-Xiao Shi,
Yuan-Sha Chen,
Ji-Rong Sun,
Qing-Lin Yang,
Xu Yang,
Zhuo Deng,
Peng-Tao Yang,
Zheng Chang,
Hong-Mei Feng,
Wei He,
Xiang-Qun Zhang,
Zhao-Hua Cheng
Abstract:
For ultrafast magnetization switching devices, critical slowing down in conventional ferromagnets near their Curie temperature constitutes a key challenge that must be overcome. In contrast to this typical behavior, we observe an anomalous acceleration of demagnetization in CaRuO$_{3}$/SrTiO$_{3}$ superlattices, a moderately correlated weak itinerant ferromagnet. The demagnetization rate increases…
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For ultrafast magnetization switching devices, critical slowing down in conventional ferromagnets near their Curie temperature constitutes a key challenge that must be overcome. In contrast to this typical behavior, we observe an anomalous acceleration of demagnetization in CaRuO$_{3}$/SrTiO$_{3}$ superlattices, a moderately correlated weak itinerant ferromagnet. The demagnetization rate increases with rising temperature, pump fluence, and applied magnetic field. To explain these anomalous phenomena, we develop a phenomenological model integrating the three-temperature model with self-consistent renormalization theory. Because the intrinsic gradient magnetism of the superlattice suppresses the typical divergence of specific heat, the conventional thermodynamic bottleneck is bypassed. Our model reveals that this decoupling enables the ultrafast dynamics to be predominantly governed by the spin-fluctuation-driven enhancement of the electron-spin scattering vertex. Our work demonstrates how spatial inhomogeneity can decouple macroscopic thermodynamic singularities from microscopic scattering processes, offering a new paradigm for manipulating ultrafast spin dynamics in correlated quantum materials. The pronounced sensitivity of the demagnetization rate to external parameters further suggests the potential for designing highly tunable ultrafast spintronic devices that leverage enhanced fluctuations near the magnetic instability.
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Submitted 2 July, 2026;
originally announced July 2026.
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Ultrafast Magneto-optical Fingerprints of Altermagnetism in MnTe
Authors:
Xu Yang,
Xingkai Cheng,
Zhuo Deng,
Yu-Han Gao,
Qing-Lin Yang,
Zheng Chang,
Peng-Tao Yang,
Hong-Mei Feng,
Xiang-Qun Zhang,
Wei He,
Junwei Liu,
Zhao-Hua Cheng
Abstract:
Recently identified altermagnets exhibit a distinctive dual-space nature: they possess spin-split electronic bands akin to ferromagnets in momentum space while maintaining the fully compensated magnetization of antiferromagnets in real space. This inherent duality, originating from the same crystal symmetry, gives rise to various intriguing physical phenomena unique to altermagnets. Consequently,…
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Recently identified altermagnets exhibit a distinctive dual-space nature: they possess spin-split electronic bands akin to ferromagnets in momentum space while maintaining the fully compensated magnetization of antiferromagnets in real space. This inherent duality, originating from the same crystal symmetry, gives rise to various intriguing physical phenomena unique to altermagnets. Consequently, a robust and efficient experimental signature capable of revealing this dual character is critically needed. The magneto-optical Kerr and Voigt effects, given their high sensitivity to ferromagnetism and antiferromagnetism, respectively, are ideally suited to probe this duality. Here, using time-resolved pump-probe magneto-optical measurements, we report the coexistence of pronounced Kerr and Voigt effects in the altermagnet MnTe. Combining the magnetization measurement and first-principles calculations, we demonstrate that the Kerr effect originates from the intrinsic Berry curvature of altermagnetism distribution in momentum space, while the Voigt effect arises from an anisotropic permittivity induced by the in-plane Néel order in real space, directly revealing the dual-space nature of altermagnets. Furthermore, the transient Kerr signal exhibits faster relaxation dynamics than the transient Voigt signal, underscoring their distinct origins in Berry curvature and Néel order, respectively. These findings establish transient magneto-optical responses as distinctive fingerprints of altermagnetism and position altermagnets as promising platforms for manipulating magneto-optical phenomena in ultrafast spin optoelectronics.
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Submitted 22 May, 2026;
originally announced May 2026.
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Computing ground states of Bose-Einstein condensation by normalized deep neural network
Authors:
Weizhu Bao,
Zhipeng Chang,
Xiaofei Zhao
Abstract:
We propose a normalized deep neural network (norm-DNN) for computing ground states of Bose-Einstein condensation (BEC) via the minimization of the Gross-Pitaevskii energy functional under unitary mass normalization. Compared with the traditional deep neural network for solving partial differential equations, two additional layers are added in training our norm-DNN for solving this kind of unitary…
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We propose a normalized deep neural network (norm-DNN) for computing ground states of Bose-Einstein condensation (BEC) via the minimization of the Gross-Pitaevskii energy functional under unitary mass normalization. Compared with the traditional deep neural network for solving partial differential equations, two additional layers are added in training our norm-DNN for solving this kind of unitary constraint minimization problems: (i) a normalization layer is introduced to enforce the unitary mass normalization, and (ii) a shift layer is added to guide the training to non-negative ground state. The proposed norm-DNN gives rise to an efficient unsupervised approach for learning ground states of BEC. Systematical investigations are first carried out through extensive numerical experiments for computing ground states of BEC in one dimension. Extensions to high dimensions and multi-component are then studied in details. The results demonstrate the effectiveness and efficiency of norm-DNN for learning ground states of BEC. Finally, we extend the norm-DNN for computing the first excited states of BEC and discuss parameter generalization issues as well as compare with some existing machine learning methods for computing ground states of BEC in the literature.
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Submitted 5 October, 2024;
originally announced October 2024.
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Ineffectiveness of Formamidine in Suppressing Ultralow Thermal Conductivity in Cubic Hybrid Perovskite FAPbI3
Authors:
Jiongzhi Zheng,
Zheng Chang,
Changpeng Lin,
Chongjia Lin,
Yanguang Zhou,
Baoling Huang,
Ruiqiang Guo,
Geoffroy Hautier
Abstract:
Fundamentally understanding the lattice dynamics and microscopic mechanisms of thermal transport in cubic hybrid organic-inorganic perovskites remains elusive, primarily due to their strong anharmonicity and frequent phase transitions. In this work, we comprehensively investigate the thermal transport behavior in cubic hybrid perovskite FAPbI3, integrating first principles-based anharmonic lattice…
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Fundamentally understanding the lattice dynamics and microscopic mechanisms of thermal transport in cubic hybrid organic-inorganic perovskites remains elusive, primarily due to their strong anharmonicity and frequent phase transitions. In this work, we comprehensively investigate the thermal transport behavior in cubic hybrid perovskite FAPbI3, integrating first principles-based anharmonic lattice dynamics with a linearized Wigner transport formula. The Temperature Dependent Effective Potential (TDEP) technique allows us to stabilize the negative soft modes, primarily dominated by organic cations, at finite temperatures in cubic FAPbI3. We then predict an ultra-low thermal conductivity of ~0.63 Wm^(-1) K^(-1) in cubic FAPbI3 at 300 K, with a temperature dependence of T^(-0.740), suggesting a good crystalline nature of phonon transport. Notably, the ultra-low thermal conductivity in cubic FAPbI3 is primarily attributed to the [PbI3]1- units, challenging the conventional focus on organic FA+ cations. This shift in focus is due to the presence of Pb(s)-I(p) anti-bonding sates within the [PbI3]1- units. Furthermore, thermal transport in cubic FAPbI3 is predominantly governed by the particle-like phonon propagation channel across the entire temperature range of 300-500 K, a result of diminished suppression of low-frequency phonons by FA+ cations and large inter-branch spacings. Finally, our findings underscore that the anharmonic force constants are highly temperature-sensitive, leading to underestimations of thermal conductivity when relying on 0-K anharmonic force constants. Our study not only elucidates the microscopic mechanisms of thermal transport in cubic FAPbI3 but also provides a crucial framework for the discovery, design, and understanding of hybrid organic-inorganic compounds with ultra-low thermal conductivity.
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Submitted 14 May, 2025; v1 submitted 3 June, 2024;
originally announced June 2024.
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Tunable topological phase transition in soft Rayleigh beam system with imperfect interfaces
Authors:
Tao Feng,
Letian Gan,
Shiheng Zhao,
Zheng Chang,
Siyang Li,
Yaoting Xue,
Xuxu Yang,
Tuck-Whye Wong,
Tiefeng Li,
Weiqiu Chen
Abstract:
Acoustic metamaterials, particularly the topological insulators, exhibit exceptional wave characteristics that have sparked considerable research interest. The study of imperfect interfaces affect is of significant importance for the modeling of wave propagation behavior in topological insulators. This paper models a soft Rayleigh beam system with imperfect interfaces, and investigates its topolog…
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Acoustic metamaterials, particularly the topological insulators, exhibit exceptional wave characteristics that have sparked considerable research interest. The study of imperfect interfaces affect is of significant importance for the modeling of wave propagation behavior in topological insulators. This paper models a soft Rayleigh beam system with imperfect interfaces, and investigates its topological phase transition process tuned by mechanical loadings. The model reveals that the topological phase transition process can be observed by modifying the distance between imperfect interfaces in the system. When a uniaxial stretch is applied, the topological phase transition points for longitudinal waves decrease within a limited frequency range, while they increase within a larger frequency scope for transverse waves. Enhancing the rigidity of the imperfect interfaces also enables shifting of the topological phase transition point within a broader frequency range for longitudinal waves and a confined range for transverse waves. The transition of topologically protected interface modes in the transmission performance of a twenty-cell system is verified, which include altering frequencies, switching from interface mode to edge mode. Overall, this study provides a new approach and guideline for controlling topological phase transition in composite and soft phononic crystal systems.
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Submitted 28 July, 2023;
originally announced July 2023.
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Probability distributions for kinetic roughening in the Kardar-Parisi-Zhang growth with long-range temporal and spatial correlations
Authors:
Zhichao Chang,
Hui Xia
Abstract:
We investigate numerically the effects of long-range temporal and spatial correlations based on the rescaled distributions of the squared interface width $W^2(L,t)$ and the interface height $h(x,t)$ in the (1+1)-dimensional Kardar-Parisi-Zhang (KPZ) growth system within the early growth regimes. Through extensive numerical simulations, we find that long-range temporally correlated noise could not…
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We investigate numerically the effects of long-range temporal and spatial correlations based on the rescaled distributions of the squared interface width $W^2(L,t)$ and the interface height $h(x,t)$ in the (1+1)-dimensional Kardar-Parisi-Zhang (KPZ) growth system within the early growth regimes. Through extensive numerical simulations, we find that long-range temporally correlated noise could not significantly impact the distribution form of the interface width. Generally, $W^2(L,t)$ obeys approximately lognormal distribution when the temporal correlation exponent $θ\ge 0$. On the other hand, the effects of long-range spatially correlated noise are evidently different from the temporally correlated case. Our results show that, when the spatial correlation exponent $ρ\le 0.20$, the distribution forms of $W^2(L,t)$ approach the lognormal distribution, and when $ρ> 0.20$, the distribution becomes more asymmetric, steep, and fat-tailed, and tends to an unknown distribution form. As a comparison, probability distributions of the interface height are also provided in the temporally and spatially correlated KPZ system, exhibiting quite different characteristics from each other within the whole correlated regimes. For the temporal correlation, the height distributions satisfy Tracy-Widom Gaussian orthogonal ensemble (TW-GOE) when $θ\to 0$, and with increasing $θ$, the height distributions crossover continously to an unknown distribution. However, for the spatial correlation, the height distributions gradually transition from the TW-GOE distribution to the standard Gaussian form.
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Submitted 23 February, 2025; v1 submitted 17 May, 2022;
originally announced May 2022.
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Conformal Three-Dimensional Interphase of Li Metal Anode Revealed by Low Dose Cryo-Electron Microscopy
Authors:
Bing Han,
Xiangyan Li,
Shuang Bai,
Yucheng Zou,
Bingyu Lu,
Minghao Zhang,
Xiaomin Ma,
Zhi Chang,
Ying Shirley Meng,
Meng Gu
Abstract:
Using cryogenic transmission electron microscopy, we revealed three dimensional (3D) structural details of the electrochemically plated lithium (Li) flakes and their solid electrolyte interphase (SEI), including the composite SEI skin-layer and SEI fossil pieces buried inside the Li matrix. As the SEI skin-layer is largely comprised of nanocrystalline LiF and Li2O in amorphous polymeric matrix, wh…
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Using cryogenic transmission electron microscopy, we revealed three dimensional (3D) structural details of the electrochemically plated lithium (Li) flakes and their solid electrolyte interphase (SEI), including the composite SEI skin-layer and SEI fossil pieces buried inside the Li matrix. As the SEI skin-layer is largely comprised of nanocrystalline LiF and Li2O in amorphous polymeric matrix, when complete Li stripping occurs, the compromised SEI three-dimensional framework buckles, forming nanoscale bends and wrinkles. We showed that the flexibility and resilience of the SEI skin-layer plays a vital role in preserving an intact SEI 3D framework after Li stripping. The intact SEI network enables the nucleation and growth of the newly plated Li inside the previously formed SEI network in the subsequent cycles, preventing additional large amount of SEI formation between newly plated Li metal and the electrolyte. In addition, cells cycled under the accurately controlled uniaxial pressure can further enhance the repeated utilization of the SEI framework and improve the coulombic efficiency (CE) by up to 97%, demonstrating an effective strategy of reducing the formation of additional SEI and inactive dead Li. The identification of such flexible and porous 3D SEI framework clarifies the working mechanism of SEI in lithium metal anode for batteries. The insights provided in this work will inspire researchers to design more functional artificial 3D SEI on other metal anodes to improve rechargeable metal battery with long cycle life.
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Submitted 10 June, 2021;
originally announced June 2021.
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Elastic Wave Propagation and Bandgaps in Finitely Stretched Soft Lattice Material
Authors:
Shiheng Zhao,
Tao Feng Han Zhang,
Yang Gao,
Zheng Chang
Abstract:
In this study, the in-plane Bloch wave propagation and bandgaps in a finitely stretched square lattice were investigated numerically and theoretically. To be specific, the elastic band diagram was calculated for an infinite periodic structure with a cruciform hyperelastic unit cell under uniaxial or biaxial tension. In addition, an elastodynamic "tight binding" model was proposed to investigate th…
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In this study, the in-plane Bloch wave propagation and bandgaps in a finitely stretched square lattice were investigated numerically and theoretically. To be specific, the elastic band diagram was calculated for an infinite periodic structure with a cruciform hyperelastic unit cell under uniaxial or biaxial tension. In addition, an elastodynamic "tight binding" model was proposed to investigate the formation and evolution of the band structure. The elastic waves were found to propagate largely under "easy" modes in the pre-stretched soft lattice, and finite stretch tuned the symmetry of the band structure, but also "purify" the propagation modes. Moreover, the uniaxial stretch exhibits the opposite impacts on the two "easy" modes. The effect of the biaxial stretch was equated with the superposition of the uniaxial stretches in the tessellation directions. The mentioned effects on the band structure could be attributed to the competition between the effective shear moduli and lengths for different beam components. Next, the finite stretch could tune the directional bandgap of the soft lattice, and the broadest elastic wave bandgaps could be anticipated in an equi-biaxial stretch. In this study, an avenue was opened to design and implement elastic wave control devices with weight efficiency and tunability. Furthermore, the differences between the physical system and the corresponding simplified theoretical model (e.g., the theoretically predicted flat bands) did not exist in the numerical calculations.
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Submitted 7 June, 2021;
originally announced June 2021.
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Elastic wave velocities in finitely pre-stretched soft fibers
Authors:
Shiheng Zhao,
Zheng Chang
Abstract:
Elastic wave velocity in a soft fiber that varies depending on material constitution and axial stress level is an essential measure of mechanical signals in many technical applications. In this work, based on the small-on-large theory, we establish a model of linear elastic wave propagation in a finitely pre-stretched soft fiber. The formulas of longitudinal (Primary, P-) and transverse (Secondary…
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Elastic wave velocity in a soft fiber that varies depending on material constitution and axial stress level is an essential measure of mechanical signals in many technical applications. In this work, based on the small-on-large theory, we establish a model of linear elastic wave propagation in a finitely pre-stretched soft fiber. The formulas of longitudinal (Primary, P-) and transverse (Secondary, S-) wave velocities are provided and validated by numerical simulations as well as by experimental data on spider silk. The influences of material constitution, compressibility, and pre-stress on the wave propagation are investigated. We found that with increasing pre-stress, the variation of P-wave velocity highly relies on the concavity of the stress-strain curve. In contrast, an increase of S-wave velocity exhibits regardless of any constitutive model. For both P- and S-waves, the variation of the velocities is more significant in a compressible fiber than that in a nearly-incompressible one. Moreover, for minuscule pre-stress, we propose a modified formula for S-wave velocity based on the Rayleigh beam theory, which reveals the competition mechanism between "string vibration" and "beam vibration." This may provide a reliable theoretical basis for precise mechanical characterization of soft fibers and open a route for lightweight, tunable wave manipulation devices.
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Submitted 30 January, 2021;
originally announced February 2021.
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Knot theory for two-band model of two-dimensional square lattice with high topological numbers
Authors:
Xin Liu,
Zhiwen Chang,
Weichang Hao
Abstract:
A knot theory for two-dimensional square lattice is proposed, which sheds light on design of new two-dimensional material with high topological numbers. We consider a two-band model, focusing on the Hall conductance σxy = e^2/hbar*P, where P is a topological number, the so-called Pontrjagin index. By re-interpreting the periodic momentum components kx and ky as the string parameters of two entangl…
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A knot theory for two-dimensional square lattice is proposed, which sheds light on design of new two-dimensional material with high topological numbers. We consider a two-band model, focusing on the Hall conductance σxy = e^2/hbar*P, where P is a topological number, the so-called Pontrjagin index. By re-interpreting the periodic momentum components kx and ky as the string parameters of two entangled knots, we discover that P becomes the Gauss linking number between the knots. This leads to a successful re-derivation of the typical P-evaluations in literature: P = 0;{\pm}1. Furthermore, with the aid of this explicit knot theoretical picture we modify the two-band model to achieve higher topological numbers, P = 0;{\pm}1;{\pm}2.
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Submitted 23 June, 2020;
originally announced June 2020.
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Shear-wave manipulation by embedded soft devices
Authors:
Linli Chen,
Chao Ma,
Pingping Zheng,
Qian Zhao,
Zheng Chang
Abstract:
Hyperelastic transformation theory has proven shear-wave manipulation devices with various functions can be designed by utilizing neo-Hookean material with appropriate pre-deformation. However, it is still elusive that how can such devices match with the background medium in which they embedded. In this work, we present a systematic formulation of the transmission and reflection of elastic waves a…
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Hyperelastic transformation theory has proven shear-wave manipulation devices with various functions can be designed by utilizing neo-Hookean material with appropriate pre-deformation. However, it is still elusive that how can such devices match with the background medium in which they embedded. In this work, we present a systematic formulation of the transmission and reflection of elastic waves at the interface between un-deformed and pre-deformed hyperelastic materials. With the combination of theoretical analyses and numerical simulations, we specifically investigate the shear-wave propagation from an un-deformed neo-Hookean material to the one subject to different homogeneous deformations. Among three typical deformation modes, we found "constrained" uniaxial tension and simple shear guarantee total transmission, whereas "ordinary" uniaxial tension and hydrostatic compression cause wave reflection. On this basis, three embedded shear-wave manipulation devices, including a unidirectional cloak, a splicable beam bend, and a concave lens, are proposed and verified through numerical simulations. This work may pave the way for the design and realization of soft-matter-based wave control devices. Potential applications can be anticipated in nondestructive testing, structure impact protection, biomedical imaging, and soft robotics.
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Submitted 2 September, 2019;
originally announced September 2019.
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Spin-valley locking, bulk quantum Hall effect and chiral surface state in a noncentrosymmetric Dirac semimetal BaMnSb$_2$
Authors:
J. Y. Liu,
J. Yu,
J. L. Ning,
H. M. Yi,
L. Miao,
L. J. Min,
Y. F. Zhao,
W. Ning,
K. A. Lopez,
Y. L. Zhu,
T. Pillsbury,
Y. B. Zhang,
Y. Wang,
J. Hu,
H. B. Cao,
F. Balakirev,
F. Weickert,
M. Jaime,
Y. Lai,
Kun Yang,
J. W. Sun,
N. Alem,
V. Gopalan,
C. Z. Chang,
N. Samarth
, et al. (3 additional authors not shown)
Abstract:
Spin-valley locking in the band structure of monolayers of MoS$_2$ and other group-VI dichalcogenides has attracted enormous interest, since it offers potential for valleytronic and optoelectronic applications. Such an exotic electronic state has sparsely been seen in bulk materials. Here, we report spin-valley locking in a bulk Dirac semimetal BaMnSb$_2$. We find valley and spin are inherently co…
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Spin-valley locking in the band structure of monolayers of MoS$_2$ and other group-VI dichalcogenides has attracted enormous interest, since it offers potential for valleytronic and optoelectronic applications. Such an exotic electronic state has sparsely been seen in bulk materials. Here, we report spin-valley locking in a bulk Dirac semimetal BaMnSb$_2$. We find valley and spin are inherently coupled for both valence and conduction bands in this material. This is revealed by comprehensive studies using first principle calculations, tight-binding and effective model analyses, angle-resolved photoemission spectroscopy and quantum transport measurements. Moreover, this material also exhibits a stacked quantum Hall effect. The spin-valley degeneracy extracted from the plateau height of quantized Hall resistivity is close to 2. This result, together with the observed Landau level spin splitting, further confirms the spin-valley locking picture. In the extreme quantum limit, we have also observed a two-dimensional chiral metal at the side surface, which represents a novel topological quantum liquid. These findings establish BaMnSb$_2$ as a rare platform for exploring coupled spin and valley physics in bulk single crystals and accessing 3D interacting topological states.
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Submitted 4 November, 2020; v1 submitted 14 July, 2019;
originally announced July 2019.
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A Linear Strain Energy Function for Hyperelastic Transformation Method
Authors:
Linli Chen,
Chao Ma,
Zheng Chang
Abstract:
Hyperelastic transformation method provides a promising approach to manipulate elastic waves by utilizing soft materials. However, no existing constitutive model can rigorously achieve the requirement of such method. In this Letter, a linear strain energy function (SEF) which is valid for small deformation is proposed, which can be implemented to control the longitudinal and shear elastic waves si…
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Hyperelastic transformation method provides a promising approach to manipulate elastic waves by utilizing soft materials. However, no existing constitutive model can rigorously achieve the requirement of such method. In this Letter, a linear strain energy function (SEF) which is valid for small deformation is proposed, which can be implemented to control the longitudinal and shear elastic waves simultaneously. In comparison with the neo-Hookean and the semi-linear SEFs, the wave propagation and the impedance of pre-deformed linear hyperelastic material are exploited. Numerical simulations are performed to validate the theoretical results. The investigation may pave the ways for the design and realization of soft transformation devices.
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Submitted 27 September, 2018; v1 submitted 15 July, 2018;
originally announced July 2018.
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Longitudinal elastic wave control by pre-deforming semi-linear materials
Authors:
Dengke Guo,
Yi Chen,
Zheng Chang,
Gengkai Hu
Abstract:
An incremental wave superimposed on a pre-deformed hyper-elastic material perceives an elastic media with the instantaneous modulus of the current material. This offers a new route with a broadband feature to control elastic waves by purposely creating finite deformation field. This study proves that the governing equation of a semi-linear material under a symmetric pre-deformation condition maint…
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An incremental wave superimposed on a pre-deformed hyper-elastic material perceives an elastic media with the instantaneous modulus of the current material. This offers a new route with a broadband feature to control elastic waves by purposely creating finite deformation field. This study proves that the governing equation of a semi-linear material under a symmetric pre-deformation condition maintains the form invariance for longitudinal wave, so the longitudinal wave control can be made by transformation method without the constraint condition on principle stretches, but this is not the case for shear waves. Therefore pre-deforming a semi-linear material provides a potential method for treating longitudinal and shear waves differently. Examples with elastic wave control and band structure shift through pre-deforming a semi-linear material are provided to illustrate this finding. Finally, a one-dimensional spring lattice is proposed to mimic a semi-linear material, and the dispersion relation for longitudinal waves in a sandwich structure with such spring lattice is shown to be invariant during elongation, confirming the result found based on a homogeneous semi-linear material. These results may stimulate researches on designing new hyper-elastic microstructures as well as designing new devices based on pre-deformed hyper-elastic materials.
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Submitted 9 September, 2017;
originally announced September 2017.
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Elastic wave propagation in simple-sheared hyperelastic materials with different constitutive models
Authors:
Linli Chen,
Zheng Chang,
Taiyan Qin
Abstract:
We investigate the elastic wave propagation in various hyperelastic materials which subjected to simple-shear deformation. Two compressible types of three conventional hyperelastic models are considered. We found pure elastic wave modes can be obtained in compressible neo-Hookean materials constructed by adding a bulk strain energy term to the incompressible strain energy function. Whereas for the…
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We investigate the elastic wave propagation in various hyperelastic materials which subjected to simple-shear deformation. Two compressible types of three conventional hyperelastic models are considered. We found pure elastic wave modes can be obtained in compressible neo-Hookean materials constructed by adding a bulk strain energy term to the incompressible strain energy function. Whereas for the compressible hyperelastic models which are reformulate into deviatoric and hydrostatic parts, only quasi modes can propagate, with abnormal ray directions can be observed for longitudinal waves. Moreover, the influences of material constants, material compressibility and external deformations on the propagation and refraction for elastic waves in these hyperelastic models are systematically studied. Numerical simulations are carried out to validate the theoretical results. This investigation may open a promising route for the realization of next generation metamaterials and novel wave manipulation devices.
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Submitted 10 April, 2017;
originally announced April 2017.
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Stable Band-Gaps in Phononic Crystals by Harnessing Hyperelastic Transformation Media
Authors:
Yan Liu,
Zheng Chang,
Xi-Qiao Feng
Abstract:
The band structure in phononic crystals (PCs) is usually affected by the deformations of their soft components. In this work, hyperelastic transformation media is proposed to be integrated in the PCs'design, to achieve stable elastic band-gaps which is independent with finite mechanical deformations. For a one-dimensional (1D) PC, we demonstrate the semi-linear soft component can keep all elastic…
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The band structure in phononic crystals (PCs) is usually affected by the deformations of their soft components. In this work, hyperelastic transformation media is proposed to be integrated in the PCs'design, to achieve stable elastic band-gaps which is independent with finite mechanical deformations. For a one-dimensional (1D) PC, we demonstrate the semi-linear soft component can keep all elastic wave bands unchanged with the external deformation field. While for neo-Hookean soft component, only S-wave bands can be precisely retained. The change of the P-wave bands can be predicted by using a lumped mass method. Numerical simulations are performed to validate our theory predictions and the robustness of the proposed PCs.
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Submitted 13 October, 2016; v1 submitted 9 October, 2016;
originally announced October 2016.
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Piezoelectric properties of graphene oxide from the first-principles calculations
Authors:
Zhenyue Chang,
Wenyi Yan,
Jin Shang,
Jefferson Zhe Liu
Abstract:
Some highly ordered compounds of graphene oxide (GO), e.g., the so-called clamped and unzipped GO, are shown to have piezoelectric responses via first-principles density functional calculations. By applying an electric field perpendicular to the GO basal plane, the largest value of in-plane strain and strain piezoelectric coefficient, d31 are found to be 0.12% and 0.24 pm/V, respectively, which ar…
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Some highly ordered compounds of graphene oxide (GO), e.g., the so-called clamped and unzipped GO, are shown to have piezoelectric responses via first-principles density functional calculations. By applying an electric field perpendicular to the GO basal plane, the largest value of in-plane strain and strain piezoelectric coefficient, d31 are found to be 0.12% and 0.24 pm/V, respectively, which are comparable with those of some advanced piezoelectric materials. An in-depth molecular structural analysis reveals that deformation of the oxygen doping regions in the clamped GO dominates its overall strain output, whereas deformation of the regions without oxygen dopant in the unzipped GO determines its overall piezoelectric strain. This understanding explains the observed dependence of d31 on oxygen doping rate, i.e., higher oxygen concentration giving rise to a larger d31 in the clamped GO whereas leading to a reduced d31 in the unzipped GO. As the thinnest two-dimensional piezoelectric materials, GO has a great potential for a wide range of MEMS/NEMS actuators and sensors.
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Submitted 6 April, 2014;
originally announced April 2014.
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Fabrication of CeO2 by sol-gel process based on microfluidic technology as an analog preparation of ceramic nuclear fuel microspheres
Authors:
Bin Ye,
Jilang Miao,
Jiaolong Li,
Zichen Zhao,
Zhenqi Chang,
Christophe A. Serra
Abstract:
Microfluidics integrated with sol-gel processes is introduced in preparing monodispersed MOX nuclear fuel microspheres using nonactive cerium as a surrogate for uranium or plutonium. The detailed information about microfluidic devices and sol-gel processes are provided. The effects of viscosity and flow rate of continuous and dispersed phase on size and size distribution of CeO2 microspheres have…
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Microfluidics integrated with sol-gel processes is introduced in preparing monodispersed MOX nuclear fuel microspheres using nonactive cerium as a surrogate for uranium or plutonium. The detailed information about microfluidic devices and sol-gel processes are provided. The effects of viscosity and flow rate of continuous and dispersed phase on size and size distribution of CeO2 microspheres have been investigated. A comprehensive characterization of the CeO2 microspheres has been conducted, including XRD pattern, SEM, density, size and size distribution. The size of prepared monodisperse particles can be controlled precisely in range of 10μm to 1000μm and the particle CV is below 3%.
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Submitted 15 December, 2012;
originally announced December 2012.
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Ashkin-Teller formalism for elastic response of DNA molecule to external force and torque
Authors:
Zhe Chang,
Ping Wang,
Ying-Hong Zheng
Abstract:
We propose an Ashkin-Teller like model for elastic response of DNA molecule to external force and torque. The base-stacking interaction is described in a simple and uniform way. We obtain the phase diagram of dsDNA, and in particular, the transition from B form to the S state induced by stretching and twisting. The elastic response of the ssDNA is presented also in a unified formalism. The close…
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We propose an Ashkin-Teller like model for elastic response of DNA molecule to external force and torque. The base-stacking interaction is described in a simple and uniform way. We obtain the phase diagram of dsDNA, and in particular, the transition from B form to the S state induced by stretching and twisting. The elastic response of the ssDNA is presented also in a unified formalism. The close relation of dsDNA molecule structure with elastic response is shown clearly. The calculated folding angle of the dsDNA molecule is $59.2^o$.
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Submitted 10 January, 2008;
originally announced January 2008.
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Anomalous k-dependent spin splitting in wurtzite AlxGa1-xN/GaN heterostructures
Authors:
Ikai Lo,
M. H. Gau,
J. K. Tsai,
Y. L. Chen,
Z. J. Chang,
W. T. Wang,
J. C. Chiang,
T. Aggerstam
Abstract:
We have confirmed the k-dependent spin splitting in wurtzite AlxGa1-xN/GaN heterostructures. Anomalous beating pattern in Shubnikov-de Haas measurements arises from the interference of Rashba and Dresselhaus spin-orbit interactions. The dominant mechanism for the k-dependent spin splitting at high values of k is attributed to Dresselhaus term which is enhanced by the Delta C1-Delta C3 coupling o…
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We have confirmed the k-dependent spin splitting in wurtzite AlxGa1-xN/GaN heterostructures. Anomalous beating pattern in Shubnikov-de Haas measurements arises from the interference of Rashba and Dresselhaus spin-orbit interactions. The dominant mechanism for the k-dependent spin splitting at high values of k is attributed to Dresselhaus term which is enhanced by the Delta C1-Delta C3 coupling of wurtzite band folding effect.
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Submitted 9 November, 2006; v1 submitted 15 September, 2006;
originally announced September 2006.
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Study of two-subband population in Fe-doped AlxGa1-xN/GaN heterostructures by persistent photoconductivity effect
Authors:
Ikai Lo,
J. K. Tsai,
M. H. Gau,
Y. L. Chen,
Z. J. Chang,
W. T. Wang,
J. C. Chiang,
K. R. Wang,
Chun-Nan Chen,
T. Aggerstam
Abstract:
The electronic properties of Fe-doped Al0.31Ga0.69N/GaN heterostructures have been studied by Shubnikov-de Haas measurement. Two subbands of the two-dimensional electron gas in the hetero-interface were populated. After the low temperature illumination, the electron density increases from 11.99 x 1012 cm-2 to 13.40 x 1012 cm-2 for the first subband and from 0.66 x 1012 cm-2 to 0.94 x 1012 cm-2 f…
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The electronic properties of Fe-doped Al0.31Ga0.69N/GaN heterostructures have been studied by Shubnikov-de Haas measurement. Two subbands of the two-dimensional electron gas in the hetero-interface were populated. After the low temperature illumination, the electron density increases from 11.99 x 1012 cm-2 to 13.40 x 1012 cm-2 for the first subband and from 0.66 x 1012 cm-2 to 0.94 x 1012 cm-2 for the second subband. The persistent photoconductivity effect (~13% increase) is mostly attributed to the Fe-related deep-donor level in GaN layer. The second subband starts to populate when the first subband is filled at a density n1 = 9.40 x 1012 cm-2. We calculate the energy separation between the first and second subbands to be 105 meV.
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Submitted 14 September, 2006;
originally announced September 2006.
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Supersonic strain front driven by a dense electron-hole plasma
Authors:
M. F. DeCamp,
D. A. Reis,
A. Cavalieri,
P. H. Bucksbaum,
R. Clarke,
R. Merlin,
E. M. Dufresne,
D. A. Arms,
A. M. Lindenberg,
A. G. MacPhee,
Z. Chang,
B. Lings,
J. S. Wark,
S. Fahy
Abstract:
We study coherent strain in (001) Ge generated by an ultrafast laser-initiated high density electron-hole plasma. The resultant coherent pulse is probed by time-resolved x-ray diffraction through changes in the anomalous transmission. The acoustic pulse front is driven by ambipolar diffusion of the electron-hole plasma and propagates into the crystal at supersonic speeds. Simulations of the stra…
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We study coherent strain in (001) Ge generated by an ultrafast laser-initiated high density electron-hole plasma. The resultant coherent pulse is probed by time-resolved x-ray diffraction through changes in the anomalous transmission. The acoustic pulse front is driven by ambipolar diffusion of the electron-hole plasma and propagates into the crystal at supersonic speeds. Simulations of the strain including electron-phonon coupling, modified by carrier diffusion and Auger recombination, are in good agreement with the observed dynamics.
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Submitted 31 December, 2002;
originally announced January 2003.
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Thermodynamics of a deformed Bose gas
Authors:
Zhe Chang,
Shao-Xia Chen
Abstract:
By making use of the double-time Green function technique, we study thermodynamics of a deformed Bose gas, which describes well properties of density intensive photonic gas and radiation fields of the early universe. General form of statistical distribution function is obtained. We show explicitly the expression of the distribution function in some limitation cases. The free energy, equation of…
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By making use of the double-time Green function technique, we study thermodynamics of a deformed Bose gas, which describes well properties of density intensive photonic gas and radiation fields of the early universe. General form of statistical distribution function is obtained. We show explicitly the expression of the distribution function in some limitation cases. The free energy, equation of state, specific heat and other thermodynamic properties of the deformed Bose gas are presented.
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Submitted 21 October, 2002; v1 submitted 10 May, 2002;
originally announced May 2002.