Showing 1–34 of 34 results for author: Yuan, C

Unraveling the Defect Physics of SiC Micropipe Sidewalls by Non-Line-of-Sight Confocal Spectromicroscopy: Amphoteric Giant Traps

Authors: Irwan Saleh Kurniawan, Russel Cruz Sevilla, Ruth Jeane Soebroto, Hsiu-Ying Huang, Hsiu-Ming Hsu, Ji-Lin Shen, Sheng Hsiung Chang, Wen-Chung Li, Chi-Tsu Yuan

Abstract: Micropipes are among the most detrimental defects in SiC wafer and are closely linked to catastrophic device failure. However, the microscopic defect nature of their internal sidewalls and the mechanism of the associated leakage current remain poorly understood, because their high-aspect-ratio geometry severely restricts direct optical probing. Here, we develop a non-line-of-sight confocal multipl… ▽ More Micropipes are among the most detrimental defects in SiC wafer and are closely linked to catastrophic device failure. However, the microscopic defect nature of their internal sidewalls and the mechanism of the associated leakage current remain poorly understood, because their high-aspect-ratio geometry severely restricts direct optical probing. Here, we develop a non-line-of-sight confocal multiple-reflection spectromicroscopy technique combined with direct defect photoionization to unravel the defect physics of micropipe sidewalls. We show that these sidewalls host a high density of donor-like and acceptor-like deep-level states, giving rise to ultrabroad emission bands composed of intrinsic DAP-like recombination and detrapping-mediated free-to-bound transitions. Unlike conventional defect luminescence, the DAP-like emission remains dominant even at room temperature across all excitation powers. This behavior is attributed to rapid carrier capture by the sidewall defects, as evidenced by fast-rising and nanosecond-scale decay dynamics, along with coupled carrier kinetics. These results suggest that micropipe sidewalls can serve as extended amphoteric giant traps and carrier reservoirs, facilitating leakage current through trap-assisted transport. Our work provides a nondestructive optical approach for directly probing high-aspect-ratio extended defects and offers deep mechanistic insight into their defect physics and leakage mechanisms. △ Less

Submitted 6 May, 2026; originally announced May 2026.

Comments: Total 20 pages (main text 17 pages, supplementary information 3 pages), total 6 figures (5 main text, 1 supplementary information)

Physics Informed Generative AI Enabling Labour Free Segmentation For Microscopy Analysis

Authors: Salma Zahran, Zhou Ao, Zhengyang Zhang, Chen Chi, Chenchen Yuan, Yanming Wang

Abstract: Semantic segmentation of microscopy images is a critical task for high-throughput materials characterisation, yet its automation is severely constrained by the prohibitive cost, subjectivity, and scarcity of expert-annotated data. While physics-based simulations offer a scalable alternative to manual labelling, models trained on such data historically fail to generalise due to a significant domain… ▽ More Semantic segmentation of microscopy images is a critical task for high-throughput materials characterisation, yet its automation is severely constrained by the prohibitive cost, subjectivity, and scarcity of expert-annotated data. While physics-based simulations offer a scalable alternative to manual labelling, models trained on such data historically fail to generalise due to a significant domain gap, lacking the complex textures, noise patterns, and imaging artefacts inherent to experimental data. This paper introduces a novel framework for labour-free segmentation that successfully bridges this simulation-to-reality gap. Our pipeline leverages phase-field simulations to generate an abundant source of microstructural morphologies with perfect, intrinsically-derived ground-truth masks. We then employ a Cycle-Consistent Generative Adversarial Network (CycleGAN) for unpaired image-to-image translation, transforming the clean simulations into a large-scale dataset of high-fidelity, realistic SEM images. A U-Net model, trained exclusively on this synthetic data, demonstrated remarkable generalisation when deployed on unseen experimental images, achieving a mean Boundary F1-Score of 0.90 and an Intersection over Union (IOU) of 0.88. Comprehensive validation using t-SNE feature-space projection and Shannon entropy analysis confirms that our synthetic images are statistically and featurally indistinguishable from the real data manifold. By completely decoupling model training from manual annotation, our generative framework transforms a data-scarce problem into one of data abundance, providing a robust and fully automated solution to accelerate materials discovery and analysis. △ Less

Submitted 2 February, 2026; originally announced February 2026.

Ge hole spin control using acoustic waves

Authors: Chun-Yang Yuan, Tzu-Kan Hsiao

Abstract: Germanium hole spin qubits based on strained Ge/SiGe quantum well have attracted much research attention due to the strong spin-orbit coupling. In particular, the strain dependence of the heavy-hole--light-hole mixing and thus the $g$-tensor anisotropy offer unique opportunities for acoustic driving and spin-phonon coupling. In this work we numerically simulate the coherent control of a Ge hole sp… ▽ More Germanium hole spin qubits based on strained Ge/SiGe quantum well have attracted much research attention due to the strong spin-orbit coupling. In particular, the strain dependence of the heavy-hole--light-hole mixing and thus the $g$-tensor anisotropy offer unique opportunities for acoustic driving and spin-phonon coupling. In this work we numerically simulate the coherent control of a Ge hole spin using surface acoustic waves. The periodic strain dynamically modulates the $g$-tensor matrix and causes fast spin rotation under a small acoustic amplitude. Moreover, we show a strong anisotropy and confinement dependence of the Rabi frequency coming from the phase-shifted longitudinal and shear strain components. Our work lays the foundations for acoustic-driven spin control and spin-phonon coupling using Ge hole spin qubits. △ Less

Submitted 29 December, 2025; originally announced December 2025.

Toward fast, accurate and robust AI prediction of ground states in rotating BEC

Authors: Zhizhong Kong, Jerry Zhijian Yang, Cheng Yuan, Xiaofei Zhao

Abstract: We propose an unsupervised deep learning approach for computing the ground state (GS) of rotating Bose-Einstein condensation. To minimize the energy under a mass constraint, our approach introduces two key and novel ingredients: a normalized loss function that exactly enforces the mass constraint, and a training strategy named virtual rotation acceleration that is essential for avoiding local mini… ▽ More We propose an unsupervised deep learning approach for computing the ground state (GS) of rotating Bose-Einstein condensation. To minimize the energy under a mass constraint, our approach introduces two key and novel ingredients: a normalized loss function that exactly enforces the mass constraint, and a training strategy named virtual rotation acceleration that is essential for avoiding local minima and guiding the learning process to the correct quantized vortex phase. Extensive numerical experiments demonstrate the proposed approach as an effective and accurate method to predict GS across physical conditions--from slow to fast rotation and from isotropic to anisotropic confinement. Through further distillation, we establish a unified operator network capable of efficiently generalizing physical parameters across different phases. It enables rapid GS predictions while correctly capturing phase transitions and is applied for inverse problems. △ Less

Submitted 10 November, 2025; originally announced November 2025.

MSC Class: 35Q55; 68T07; 81-08

The physics and mathematics of living and dying matter

Authors: Tanniemola B. Liverpool, Kristian K. Müller-Nedebock, Xichen Chao, Chang Yuan

Abstract: We introduce and study a class of active matter models in which we keep track of fuel (stored energy) consumption. They are by construction, thermodynamically consistent. Using these models it is possible for us to observe and follow how active behaviour develops and also how it dissipates as the energy runs out. It is also straightforward to define, calculate and keep track of macroscopic thermod… ▽ More We introduce and study a class of active matter models in which we keep track of fuel (stored energy) consumption. They are by construction, thermodynamically consistent. Using these models it is possible for us to observe and follow how active behaviour develops and also how it dissipates as the energy runs out. It is also straightforward to define, calculate and keep track of macroscopic thermodynamic quantities. △ Less

Submitted 18 July, 2025; originally announced July 2025.

Comments: 5 pages, 4 figures

Infinite Stability in Disordered Systems

Authors: Andrew C. Yuan, Nick Crawford

Abstract: In quenched disordered systems, the existence of ordering is generally believed to be only possible in the weak disorder regime (disregarding models of spin-glass type). In particular, sufficiently large random fields is expected to prohibit any finite temperature ordering. Here, we prove that this is not necessarily true, and show rigorously that for physically relevant systems in $\mathbb{Z}^d$… ▽ More In quenched disordered systems, the existence of ordering is generally believed to be only possible in the weak disorder regime (disregarding models of spin-glass type). In particular, sufficiently large random fields is expected to prohibit any finite temperature ordering. Here, we prove that this is not necessarily true, and show rigorously that for physically relevant systems in $\mathbb{Z}^d$ with $d\ge 3$, disorder can induce ordering that is \textit{infinitely stable}, in the sense that (1) there exists ordering at arbitrarily large disorder strength and (2) the transition temperature is asymptotically nonzero in the limit of infinite disorder. Analogous results can hold in 2 dimensions provided that the underlying graph is non-planar (e.g., $\mathbb{Z}^2$ sites with nearest and next-nearest neighbor interactions). △ Less

Submitted 15 April, 2025; originally announced April 2025.

Journal ref: Commun. Math. Phys. 407, 133 (2026)

Infinitely Stable Disordered Systems on Emergent Fractal Structures

Authors: Andrew C. Yuan, Nick Crawford

Abstract: In quenched disordered systems, the existence of ordering is generally believed to be only possible in the weak disorder regime (disregarding models of spin-glass type). In particular, sufficiently large random field is expected to prohibit any finite temperature ordering. Here, we show that this is not necessarily true. We provide physically motivated examples of systems in which disorder induces… ▽ More In quenched disordered systems, the existence of ordering is generally believed to be only possible in the weak disorder regime (disregarding models of spin-glass type). In particular, sufficiently large random field is expected to prohibit any finite temperature ordering. Here, we show that this is not necessarily true. We provide physically motivated examples of systems in which disorder induces an ordering that is *infinitely stable* in the sense that: (1) there exists ordering at arbitrarily large disorder strength and (2) the transition temperature remains, asymptotically, nonzero in the limit of infinite disorder. The ordering is spatially localized on the boundary of a disorder-induced, emergent percolating fractal structure. The examples we give are most naturally described when the spatial dimension $d \ge 3$, but can also be formulated when $d=2$, provided that the underlying graph is non-planar. △ Less

Submitted 23 December, 2024; originally announced December 2024.

Comments: 5 pages, 5 figures

On the Path to High-temperature Josephson Multi-junction Devices

Authors: Xu Wang, Fucong Chen, Zefeng Lin, Changhong Yuan, Shibing Tian, Chunguang Li, Victor Kornev, Nikolay Kolotinskiy

Abstract: We report our progress in the high-temperature superconductor (HTS) Josephson junction fabrication process founded on using a focused helium ion beam damaging technique and discuss the expected device performance attainable with the HTS multi-junction device technology. Both the achievable high value of characteristic voltage $V_c=I_cR_N$ of Josephson junctions and the ability to design a large nu… ▽ More We report our progress in the high-temperature superconductor (HTS) Josephson junction fabrication process founded on using a focused helium ion beam damaging technique and discuss the expected device performance attainable with the HTS multi-junction device technology. Both the achievable high value of characteristic voltage $V_c=I_cR_N$ of Josephson junctions and the ability to design a large number of arbitrary located Josephson junctions allow narrowing the existing gap in design abilities for LTS and HTS circuits even with using a single YBCO film layer. A one-layer topology of active electrically small antenna is suggested and its voltage response characteristics are considered. △ Less

Submitted 5 September, 2024; v1 submitted 19 April, 2024; originally announced April 2024.

Comments: v2: accepted manuscript; 7 pages, 5 figures

Journal ref: EM Science, 2(3), 0070092, 2024

Phase sensitive information from a planar Josephson junction

Authors: Andrew C. Yuan, Steven A. Kivelson

Abstract: Josephson tunneling across a planar junction generally depends on the relative twist angle, $θ$, between the two layers. However, if under a discrete rotation, the order parameter in one layer is odd and the other is even (as, e.g., for a $s$-wave to $d_{x^2-y^2}$-wave junction under a $π/2$ rotation) then the bulk Josephson current vanishes for all $θ$. Even in this case, we show that for a finit… ▽ More Josephson tunneling across a planar junction generally depends on the relative twist angle, $θ$, between the two layers. However, if under a discrete rotation, the order parameter in one layer is odd and the other is even (as, e.g., for a $s$-wave to $d_{x^2-y^2}$-wave junction under a $π/2$ rotation) then the bulk Josephson current vanishes for all $θ$. Even in this case, we show that for a finite junction, the Josephson current, $J$, has a nonzero edge contribution that depends on $θ$ and the orientation of the junction edges in ways that can serve as an unambiguous probe of the order parameter symmetry of any time-reversal preserving system (including multiband systems and those in which spin-orbit coupling is significant). We also analyze the microscopic considerations that determine the magnitude of $J$. △ Less

Submitted 25 November, 2024; v1 submitted 17 April, 2024; originally announced April 2024.

Journal ref: npj Quantum Mater. 9, 93 (2024)

Topological States Decorated by Twig Boundary in Plasma Photonic Crystals

Authors: Jianfei Li, Jingfeng Yao, Ying Wang, Zhongxiang Zhou, Zhihao Lan, Chengxun Yuan

Abstract: The twig edge states in graphene-like structures are viewed as the fourth states complementary to their zigzag, bearded, and armchair counterparts. In this work, we study a rod-in-plasma system in honeycomb lattice with twig edge truncation under external magnetic fields and lattice scaling and show that twig edge states can exist in different phases of the system, such as quantum Hall phase, quan… ▽ More The twig edge states in graphene-like structures are viewed as the fourth states complementary to their zigzag, bearded, and armchair counterparts. In this work, we study a rod-in-plasma system in honeycomb lattice with twig edge truncation under external magnetic fields and lattice scaling and show that twig edge states can exist in different phases of the system, such as quantum Hall phase, quantum spin Hall phase and insulating phase. The twig edge states in the negative permittivity background exhibit robust one-way transmission property immune to backscattering and thus provide a novel avenue for solving the plasma communication blackout problem. Moreover, we demonstrate that corner and edge states can exist within the shrunken structure by modulating the on-site potential of the twig edges. Especially, helical edge states with the unique feature of pseudospin-momentum locking that could be excited by chiral sources are demonstrated at the twig edges. Our results show that the twig edges and interface engineering can bring new opportunities for more flexible manipulation of electromagnetic waves. △ Less

Submitted 21 April, 2024; v1 submitted 15 November, 2023; originally announced November 2023.

Exactly Solvable Model of Randomly Coupled Twisted Superconducting Bilayers

Authors: Andrew C. Yuan

Abstract: Motivated by recent experiments on twisted junctions of cuprate superconductors (SC), it was proposed [1] that at zero temperature, a random first order Josephson coupling $J_1(\textbf{r}) \cos φ$ generates an "effective" global second order coupling, $J_2\cos(2φ)$, with a sign that favors $φ= \pm π/2$, i.e., spontaneous breaking of time reversal symmetry (TRS). To obtain a more controlled underst… ▽ More Motivated by recent experiments on twisted junctions of cuprate superconductors (SC), it was proposed [1] that at zero temperature, a random first order Josephson coupling $J_1(\textbf{r}) \cos φ$ generates an "effective" global second order coupling, $J_2\cos(2φ)$, with a sign that favors $φ= \pm π/2$, i.e., spontaneous breaking of time reversal symmetry (TRS). To obtain a more controlled understanding of the suggested "disorder-induced-order" mechanism, we construct an exactly solvable lattice mean field model and prove that when the disorder-average $\bar{J}_1=0$, the model exhibits a TRS breaking phase for all temperatures below the SC transition, i.e., $T_c = T_{\mathrm{TRSB}}$, regardless of the specific form of disorder. In the presence of nonzero $\bar{J}_1\ne 0$, we show that the two transitions split linearly for small $\bar{J}_1 \ll κ$ (where $κ$ is the in-plane SC stiffness), and that $T_{\mathrm{TRSB}}$ vanishes for $\bar J_1> J_c$ where $ J_c= \overline{J^2_1}/κ$ in the weak disorder limit. [1] A. C. Yuan, Y. Vituri, E. Berg, B. Spivak, and S. A. Kivelson, Inhomogeneity-induced time-reversal symmetry breaking in cuprate twist-junctions, arXiv preprint arXiv:2305.15472 (2023) △ Less

Submitted 2 December, 2023; v1 submitted 29 August, 2023; originally announced August 2023.

Comments: 21 pages (5 main + 16 appendix), 2 figures

Journal ref: Phys. Rev. B 108, 184515 (2023)

Phases and magnetism at the microscale in compounds containing nominal Pb10-xCux(PO4)6O

Authors: Chang Liu, Wenxin Cheng, Xiaoxiao Zhang, Juan Xu, Jiaxin Li, Qiuyan Shi, Changhong Yuan, Li Xu, Honglin Zhou, Shilin Zhu, Jianping Sun, Wei Wu, Jianlin Luo, Kui Jin, Yangmu Li

Abstract: Achieving superconductivity at room temperature could lead to substantial advancements in industry and technology. Recently, a compound known as Cu-doped lead-apatite, Pb10-xCux(PO4)6O (0.9 < x < 1.1), referred to as "LK-99", has been reported to exhibit unusual electrical and magnetic behaviors that appear to resemble a superconducting transition above room temperature. In this work we collected… ▽ More Achieving superconductivity at room temperature could lead to substantial advancements in industry and technology. Recently, a compound known as Cu-doped lead-apatite, Pb10-xCux(PO4)6O (0.9 < x < 1.1), referred to as "LK-99", has been reported to exhibit unusual electrical and magnetic behaviors that appear to resemble a superconducting transition above room temperature. In this work we collected multiphase samples containing the nominal Pb10-xCux(PO4)6O phase (no superconductivity observed in our measured samples), synthesized by three independent groups, and studied their chemical, magnetic, and electrical properties at the microscale to overcome difficulties in bulk measurements. Through the utilization of optical, scanning electron, atomic force, and scanning diamond nitrogen-vacancy microscopy techniques, we are able to establish a link between local magnetic properties and specific microscale chemical phases. Our findings indicate that while the Pb10-xCux(PO4)6O phase seems to have a mixed magnetism contribution, a significant fraction of the diamagnetic response can be attributed to Cu-rich regions (e.g., Cu2S derived from a reagent used in the synthesis). Additionally, our electrical measurements reveal the phenomenon of current path switch and a change in resistance states of Cu2S. This provides a potential explanation for the electrical behavior observed in compounds related to Pb10-xCux(PO4)6O. △ Less

Submitted 17 August, 2023; v1 submitted 15 August, 2023; originally announced August 2023.

Comments: 14 pages, 5 figures; Physical Review Materials

Journal ref: Phys. Rev. Materials 7, 084804 (2023)

Absence of Floating Phase in Superconductors with Time-reversal Symmetry Breaking on any Lattice

Authors: Andrew C. Yuan

Abstract: Due to the interplay of multi-component order parameters (e.g., a twisted bilayer superconductor with inter-layer Josephson coupling or a frustrated ($n\ge 3$)-band superconductor), a superconductor can possess a $U(1)\times \mathbb{Z}_2$ symmetry, corresponding to the superconducting $T_c$ and time-reversal symmetry breaking transition $T_\text{TRSB}$, respectively. It was then conjectured that i… ▽ More Due to the interplay of multi-component order parameters (e.g., a twisted bilayer superconductor with inter-layer Josephson coupling or a frustrated ($n\ge 3$)-band superconductor), a superconductor can possess a $U(1)\times \mathbb{Z}_2$ symmetry, corresponding to the superconducting $T_c$ and time-reversal symmetry breaking transition $T_\text{TRSB}$, respectively. It was then conjectured that in this class of Hamiltonians, there exists a vast parameter regime $\mathcal{O}$ such that the system exhibits vestigial TRSB, i.e., $T_\text{TRSB} > T_c$, while at the boundary $\partial \mathcal{O}$, the system possesses a single phase transition $T_\text{TRSB}=T_c$. In this paper, we provide evidence towards this conjecture by mathematically eliminating the possibility of a floating phase, i.e., $T_\text{TRSB} < T_c$, for the strong coupling regime. More specifically, we prove that the correlation functions of $U(1)$ spins are bounded above by that of $\mathbb{Z}_2$ spins for all temperatures and lattice structures (e.g., $\mathbb{Z}^d$ for all $d$). In particular, this guarantees the existence of high-$T_c$ TRSB (and consequently topological) superconductivity in a large class of Hamiltonians. Note that the same property can also be proven for a certain parameter regime ($Δ\ge 4/5$) of the generalized XY model on any lattice structure, despite belonging to an entirely distinct class of $U(1)\times \mathbb{Z}_2$ Hamiltonians. △ Less

Submitted 27 February, 2024; v1 submitted 14 August, 2023; originally announced August 2023.

Inhomogeneity-Induced Time-Reversal Symmetry Breaking in Cuprate Twist-Junctions

Authors: Andrew C. Yuan, Yaar Vituri, Erez Berg, Boris Spivak, Steven A. Kivelson

Abstract: The lowest order Josephson coupling, $J_1(θ)\cos(φ)$, between two d-wave superconductors with phase-difference $φ$ across the junction vanishes when their relative orientation is rotated by $θ=π/4$. However, in the presence of inhomogeneity, $J_{1}(\mathbf{r})$ is non-zero locally, with a sign that fluctuates in space. We show that such a random $J_1$ generates a global second-harmonic Josephson c… ▽ More The lowest order Josephson coupling, $J_1(θ)\cos(φ)$, between two d-wave superconductors with phase-difference $φ$ across the junction vanishes when their relative orientation is rotated by $θ=π/4$. However, in the presence of inhomogeneity, $J_{1}(\mathbf{r})$ is non-zero locally, with a sign that fluctuates in space. We show that such a random $J_1$ generates a global second-harmonic Josephson coupling, $J_2\cos(2φ)$, with a sign that favors $φ= \pm π/2$, i.e., spontaneous breaking of time reversal symmetry. The magnitude of $J_2$ is substantially enhanced if the spatial correlations of $J_1(\mathbf{r})$ extend over large distances, such as would be expected in the presence of large amplitude twist-angle angle disorder or significant local electronic nematicity. We argue that this effect likely accounts for the recent observations in twisted Josephson junctions between high temperature superconductors. △ Less

Submitted 24 May, 2023; originally announced May 2023.

Comments: 5 (main text) +5 (appendix) pages, 1 (main text) +1 (appendix) figures

Journal ref: Phys. Rev. B 108, L100505 (2023)

Self-doping effect in confined copper selenide semiconducting quantum dots for efficient photoelectrocatalytic oxygen evolution

Authors: Jie Ren, Chenya Zhao, Lanshan He, Congcong Wu, Wenting Jia, Shengwen Xu, Daojian Ye, Weiyang Xu, Fujin Huang, Hang Zhou, Chengwu Zou, Ce Hu, Ting Yu, Xingfang Luo, Cailei Yuan

Abstract: Self-doping can not only suppress the photogenerated charge recombination of semiconducting quantum dots by self-introducing trapping states within the bandgap, but also provide high-density catalytic active sites as the consequence of abundant non-saturated bonds associated with the defects. Here, we successfully prepared semiconducting copper selenide (CuSe) confined quantum dots with abundant v… ▽ More Self-doping can not only suppress the photogenerated charge recombination of semiconducting quantum dots by self-introducing trapping states within the bandgap, but also provide high-density catalytic active sites as the consequence of abundant non-saturated bonds associated with the defects. Here, we successfully prepared semiconducting copper selenide (CuSe) confined quantum dots with abundant vacancies and systematically investigated their photoelectrochemical characteristics. Photoluminescence characterizations reveal that the presence of vacancies reduces the emission intensity dramatically, indicating a low recombination rate of photogenerated charge carriers due to the self-introduced trapping states within the bandgap. In addition, the ultra-low charge transfer resistance measured by electrochemical impedance spectroscopy implies the efficient charge transfer of CuSe semiconducting quantum dots-based photoelectrocatalysts, which is guaranteed by the high conductivity of their confined structure as revealed by room-temperature electrical transport measurements. Such high conductivity and low photogenerated charge carriers recombination rate, combined with high-density active sites and confined structure, guaranteeing the remarkable photoelectrocatalytic performance and stability as manifested by photoelectrocatalysis characterizations. This work promotes the development of semiconducting quantum dots-based photoelectrocatalysis and demonstrates CuSe semiconducting quantum confined catalysts as an advanced photoelectrocatalysts for oxygen evolution reaction. △ Less

Submitted 13 April, 2023; originally announced April 2023.

Yade Documentation

Authors: Vaclav Smilauer, Vasileios Angelidakis, Emanuele Catalano, Robert Caulk, Bruno Chareyre, William Chevremont, Sergei Dorofeenko, Jerome Duriez, Nolan Dyck, Jan Elias, Burak Er, Alexander Eulitz, Anton Gladky, Ning Guo, Christian Jakob, Francois Kneib, Janek Kozicki, Donia Marzougui, Raphael Maurin, Chiara Modenese, Gary Pekmezi, Luc Scholtes, Luc Sibille, Jan Stransky, Thomas Sweijen , et al. (2 additional authors not shown)

Abstract: Yade is an extensible open-source framework for discrete numerical models, focused on the Discrete Element Method. The computation parts are written in c++ using a flexible object model and allowing independent implementation of new algorithms and interfaces. Python is used for rapid and concise scene construction, simulation control, postprocessing and debugging. Yade is located at yade-dem.org,… ▽ More Yade is an extensible open-source framework for discrete numerical models, focused on the Discrete Element Method. The computation parts are written in c++ using a flexible object model and allowing independent implementation of new algorithms and interfaces. Python is used for rapid and concise scene construction, simulation control, postprocessing and debugging. Yade is located at yade-dem.org, which contains this documentation. Development is kindly hosted on launchpad and GitLab ; they are used for source code, bug tracking and source downloads and more. Building, regression tests and packages distribution are hosted on servers of the Grenoble Geomechanics group at Laboratoire 3SR, UMS Gricad and Gdańsk University of Technology. Yade supports high precision calculations and Python 3. The development branch is on GitLab. △ Less

Submitted 2 January, 2023; originally announced January 2023.

Multiband mean-field theory of the $d+ig$ superconductivity scenario in Sr$_2$RuO$_4$

Authors: Andrew C. Yuan, Erez Berg, Steven A. Kivelson

Abstract: Many seemingly contradictory experimental findings concerning the superconducting state in Sr$_2$RuO$_4$ can be accounted for on the basis of a conjectured accidental degeneracy between two patterns of pairing that are unrelated to each other under the $(D_{4h})$ symmetry of the crystal: a $d_{x^2-y^2}$-wave $(B_{1g})$ and a $g_{xy(x^2-y^2)}$-wave $(A_{2g})$ superconducting state. In this paper, w… ▽ More Many seemingly contradictory experimental findings concerning the superconducting state in Sr$_2$RuO$_4$ can be accounted for on the basis of a conjectured accidental degeneracy between two patterns of pairing that are unrelated to each other under the $(D_{4h})$ symmetry of the crystal: a $d_{x^2-y^2}$-wave $(B_{1g})$ and a $g_{xy(x^2-y^2)}$-wave $(A_{2g})$ superconducting state. In this paper, we propose a generic multi-band model in which the $g$-wave pairing involving the $xz$ and $yz$ orbitals arises from second-nearest-neighbor interactions. Even if time-reversal symmetry is broken in a $d+ig$ state, such a superconductor remains gapless with a Bogoliubov Fermi surface that approximates a (vertical) line node. The model gives rise to a strain-dependent splitting between the critical temperature $T_c$ and the time-reversal symmetry-breaking temperature $T_\text{trsb}$ that is qualitatively similar to some of the experimental observations in Sr$_2$RuO$_4$. △ Less

Submitted 26 July, 2023; v1 submitted 28 September, 2022; originally announced September 2022.

Comments: 21 pages (including Appendix), 4 figures

Journal ref: Phys. Rev. B 108, 014502 (2023)

Ultrafast optical observation of spin-pumping induced dynamic exchange coupling in ferromagnetic semiconductor/metal bilayer

Authors: X. Liu, P. Liu, H. C. Yuan, J. Y. Shi, H. L. Wang, S. H. Nie, F. Jin, Z. Zheng, X. Z. Yu, J. H. Zhao, H. B. Zhao, G. Lüpke

Abstract: Spin angular momentum transfer in magnetic bilayers offers the possibility of ultrafast and low-loss operation for next-generation spintronic devices. We report the field- and temperature- dependent measurements on the magnetization precessions in Co$_2$FeAl/(Ga,Mn)As by time-resolved magneto-optical Kerr effect (TRMOKE). Analysis of the effective Gilbert damping and phase shift indicates a clear… ▽ More Spin angular momentum transfer in magnetic bilayers offers the possibility of ultrafast and low-loss operation for next-generation spintronic devices. We report the field- and temperature- dependent measurements on the magnetization precessions in Co$_2$FeAl/(Ga,Mn)As by time-resolved magneto-optical Kerr effect (TRMOKE). Analysis of the effective Gilbert damping and phase shift indicates a clear signature of an enhanced dynamic exchange coupling between the two ferromagnetic (FM) layers due to the reinforced spin pumping at resonance. The temperature dependence of the dynamic exchange-coupling reveals a primary contribution from the ferromagnetism in (Ga,Mn)As. △ Less

Submitted 7 May, 2022; v1 submitted 7 March, 2022; originally announced March 2022.

Comments: arXiv admin note: text overlap with arXiv:2203.00293

Report number: Scientific Reports 12, 20093 (2022)

Journal ref: Scientific Reports 12, 20093 (2022)

Ultrafast enhancement of interfacial exchange coupling in ferromagnetic bilayer

Authors: X. Liu, H. C. Yuan, P. Liu, J. Y. Shi, H. L. Wang, S. H. Nie, F. Jin, Z. Zheng, X. Z. Yu, J. H. Zhao, H. B. Zhao, G. Lüpke

Abstract: Fast spin manipulation in magnetic heterostructures, where magnetic interactions between different materials often define the functionality of devices, is a key issue in the development of ultrafast spintronics. Although recently developed optical approaches such as ultrafast spin-transfer and spin-orbit torques open new pathways to fast spin manipulation, these processes do not fully utilize the… ▽ More Fast spin manipulation in magnetic heterostructures, where magnetic interactions between different materials often define the functionality of devices, is a key issue in the development of ultrafast spintronics. Although recently developed optical approaches such as ultrafast spin-transfer and spin-orbit torques open new pathways to fast spin manipulation, these processes do not fully utilize the unique possibilities offered by interfacial magnetic coupling effects in ferromagnetic multilayer systems. Here, we experimentally demonstrate ultrafast photo-enhanced interfacial exchange interactions in the ferromagnetic Co$_2$FeAl/(Ga,Mn)As system at low laser fluence levels. The excitation efficiency of Co$_2$FeAl with the (Ga,Mn)As layer is 30-40 times higher than the case with the GaAs layer at 5 K due to a photo-enhanced exchange coupling interaction via photoexcited charge transfer between the two ferromagnetic layers. In addition, the coherent spin precessions persist to room temperature, excluding the drive of photo-enhanced magnetization in the (Ga,Mn)As layer and indicating a proximity-effect-related optical excitation mechanism. The results highlight the importance of considering the range of interfacial exchange interactions in ferromagnetic heterostructures and how these magnetic coupling effects can be utilized for ultrafast, low-power spin manipulation. △ Less

Submitted 3 March, 2022; v1 submitted 1 March, 2022; originally announced March 2022.

Strain-induced time reversal breaking and half quantum vortices near a putative superconducting tetra-critical point in Sr$_2$RuO$_4$

Authors: Andrew C. Yuan, Erez Berg, Steven A. Kivelson

Abstract: It has been shown [1] that many seemingly contradictory experimental findings concerning the superconducting state in Sr$_2$RuO$_4$ can be accounted for as resulting from the existence of an assumed tetra-critical point at near ambient pressure at which $d_{x^2-y^2}$ and $g_{xy(x^2-y^2)}$ superconducting states are degenerate. We perform both a Landau-Ginzburg and a microscopic mean-field analysis… ▽ More It has been shown [1] that many seemingly contradictory experimental findings concerning the superconducting state in Sr$_2$RuO$_4$ can be accounted for as resulting from the existence of an assumed tetra-critical point at near ambient pressure at which $d_{x^2-y^2}$ and $g_{xy(x^2-y^2)}$ superconducting states are degenerate. We perform both a Landau-Ginzburg and a microscopic mean-field analysis of the effect of spatially varying strain on such a state. In the presence of finite $xy$ shear strain, the superconducting state consists of two possible symmetry-related time-reversal symmetry (TRS) preserving states: $d \pm g$. However, at domain walls between two such regions, TRS can be broken, resulting in a $d+ig$ state. More generally, we find that various natural patterns of spatially varying strain induce a rich variety of superconducting textures, including half-quantum fluxoids. These results may resolve some of the apparent inconsistencies between the theoretical proposal and various experimental observations, including the suggestive evidence of half-quantum vortices [2]. [1] Steven A Kivelson, Andrew C Yuan, BJ Ramshaw, and Ronny Thomale, "A proposal for reconciling diverse experiments on the superconducting state in Sr$_2$RuO$_4$," npj Quantum Mater 5 (2020). [2] J Jang, DG Ferguson, V Vakaryuk, Raffi Budakian, SB Chung, PM Goldbart, and Y Maeno, "Observation of half-height magnetization steps in Sr$_2$RuO$_4$," Science 331, 186-188 (2011). △ Less

Submitted 2 June, 2021; originally announced June 2021.

Comments: 18 pages including Appendix, 8 figures

Journal ref: Phys. Rev. B 104, 054518 (2021)

Phonon heat conduction in Al1-xScxN thin films

Authors: Chao Yuan, Mingyo Park, Yue Zheng, Jingjing Shi, Rytis Dargis, Samuel Graham, Azadeh Ansari

Abstract: Aluminum scandium nitride alloy (Al1-xScxN) is regarded as a promising material for high-performance acoustic devices used in wireless communication systems. Phonon scattering and heat conduction processes govern the energy dissipation in acoustic resonators, ultimately determining their performance quality. This work reports, for the first time, on phonon scattering processes and thermal conducti… ▽ More Aluminum scandium nitride alloy (Al1-xScxN) is regarded as a promising material for high-performance acoustic devices used in wireless communication systems. Phonon scattering and heat conduction processes govern the energy dissipation in acoustic resonators, ultimately determining their performance quality. This work reports, for the first time, on phonon scattering processes and thermal conductivity in Al1-xScxN alloys with the Sc content (x) up to 0.26. The thermal conductivity measured presents a descending trend with increasing x. Temperature-dependent measurements show an increase in thermal conductivity as the temperature increases at temperatures below 200K, followed by a plateau at higher temperatures (T> 200K). Application of a virtual crystal phonon conduction model allows us to elucidate the effects of boundary and alloy scattering on the observed thermal conductivity behaviors. We further demonstrate that the alloy scattering is caused mainly by strain-field difference, and less by the atomic mass difference between ScN and AlN, which is in contrast to the well-studied Al1-xGaxN and SixGe1-x alloy systems where atomic mass difference dominates the alloy scattering. This work studies and provides the quantitative knowledge for phonon scattering and the thermal conductivity in Al1-xScxN, paving the way for future investigation of materials and design of acoustic devices. △ Less

Submitted 24 February, 2021; originally announced February 2021.

Influence of different exchange-correlation potentials on twisted structures of bilayer XS2 (X= Mo, Cr)

Authors: Feng Sun, Ting Luo, Lin Li, Aijun Hong, Cailei Yuan, Wei Zhang

Abstract: In this work, we employ the LDA, GGA and GGA with four vdW corrections to study crystal and electronic structures of bilayer transition metal dichalcogenides (TMDs) with different twist angles. We find the GGA interlayer distance of bilayer MoS2 has good agreement with experimental value while vdW correction method still needs to be further improved. Our results indicate the GGA interlayer distanc… ▽ More In this work, we employ the LDA, GGA and GGA with four vdW corrections to study crystal and electronic structures of bilayer transition metal dichalcogenides (TMDs) with different twist angles. We find the GGA interlayer distance of bilayer MoS2 has good agreement with experimental value while vdW correction method still needs to be further improved. Our results indicate the GGA interlayer distances of bilayer XS2 (X= Mo, Cr) with twist angles are smaller than that of normal bilayer, which is the opposite in the LDA case. The GGA results show that reduced bandgap is due to the reduction of interlayer distance and, flat valley and conductivity bands appear owing to twist angle. Our study not only supports valuable information for application possibility of twisted two-dimensional (2D) materials but also stimulates more related research. △ Less

Submitted 4 December, 2020; v1 submitted 22 March, 2020; originally announced March 2020.

Journal ref: Computational Materials Science (2020)

A proposal for reconciling diverse experiments on the superconducting state in Sr2RuO4

Authors: Steven A. Kivelson, Andrew C. Yuan, B. J. Ramshaw, Ronny Thomale

Abstract: A variety of precise experiments have been carried out to establish the character of the superconducting state in Sr2RuO4. Many of these appear to imply contradictory conclusions concerning the symmetries of this state. Here, we propose that these results can be reconciled if we assume that there is a near-degeneracy between a d_{x^2-y^2} (B_{1g} in group theory nomenclature) and a g_{xy(x^2-y^2)}… ▽ More A variety of precise experiments have been carried out to establish the character of the superconducting state in Sr2RuO4. Many of these appear to imply contradictory conclusions concerning the symmetries of this state. Here, we propose that these results can be reconciled if we assume that there is a near-degeneracy between a d_{x^2-y^2} (B_{1g} in group theory nomenclature) and a g_{xy(x^2-y^2)} (A_{2g}) superconducting state. From a weak-coupling perspective, such an accidental degeneracy can occur at a point at which a balance between the on-site and nearest-neighbor repulsions triggers a d-wave to g-wave transition. △ Less

Submitted 31 January, 2020; originally announced February 2020.

Comments: 24 pages, 2 figures

Journal ref: npj Quantum Mater. 5, 43 (2020)

Prediction for structure stability and ultrahigh hydrogen evolution performance of monolayer 2H-CrS2

Authors: Feng Sun, Aijun Hong, Wenda Zhou, Cailei Yuan, Wei Zhang

Abstract: By a combination of the first-principles calculations and climbing image nudged elastic band method (ciNEB) we investigate structure stabilities and hydrogen evolution reaction (HER) performance of monolayer 2H-CrS2. The results suggest the free energy for the Volmer reaction in the monolayer 2H-CrS2 with S vacancy is 0.07 eV, comparable with Pt-based catalyst, and HER on the surface of the monola… ▽ More By a combination of the first-principles calculations and climbing image nudged elastic band method (ciNEB) we investigate structure stabilities and hydrogen evolution reaction (HER) performance of monolayer 2H-CrS2. The results suggest the free energy for the Volmer reaction in the monolayer 2H-CrS2 with S vacancy is 0.07 eV, comparable with Pt-based catalyst, and HER on the surface of the monolayer is prone to the Volmer-Heyrovsky mechanism with no energy barrier. We propose that high HER performance stems from the reduction of the energy level of d-band center. Additionally, the S vacancy leads to defect states in the middle of electronic bandgap and the reduction of potential barrier between the S atom layer and the vacuum, which is conducive to improve HER performance. △ Less

Submitted 2 October, 2020; v1 submitted 17 January, 2020; originally announced January 2020.

Effects of biaxial strain and local constant potential on electronic structure of monolayer SnSe

Authors: Feng Sun, Ting Luo, Lin Li, Aijun Hong, Cailei Yuan, Wei Zhang

Abstract: We use the modified Becke-Johnson exchange potential (mBJ) with the spin-orbit coupling effect (SOC) to study effects of biaxial strain and local constant potential on electronic structure of monolayer SnSe. Our results show the fundamental band gap size can be tuned via biaxial strain. Compressive strain (tensile strain) can narrow (enlarge) band gap, and compressive strain causes the transition… ▽ More We use the modified Becke-Johnson exchange potential (mBJ) with the spin-orbit coupling effect (SOC) to study effects of biaxial strain and local constant potential on electronic structure of monolayer SnSe. Our results show the fundamental band gap size can be tuned via biaxial strain. Compressive strain (tensile strain) can narrow (enlarge) band gap, and compressive strain causes the transition from quasi-direct to indirect band gap. Moreover, considering that any tuning of electronic structure is realized by changing the periodic potential distribution in the crystalline, we directly add constant potential (CP) to muffin-tin spheres. The results demonstrate that positive and negative CPs can narrow and enlarge band gap, respectively. At CP of 0.9 Ry, semiconductor-metal transition appears, and interestingly a new type of nearly linear dispersions occur at band edge. Our work is good for inspiring more experimental and further theoretical research works. △ Less

Submitted 19 February, 2020; v1 submitted 17 November, 2019; originally announced November 2019.

Quaternary compounds Ag2XYSe4 (X=Ba, Sr; Y=Sn, Ge) as novel potential thermoelectric materials

Authors: A. J. Hong, C. L. Yuan, J. M. Liu

Abstract: Experimental results have shown that the quaternary compound Cu2ZnSnSe4 is an excellent thermoelectric material. This inspires us to seek the other quaternary compounds with similar chemical formula to Cu2ZnSnSe4 as thermoelectric materials. In this paper, we use the first-principle method to systematically explore the electronic and phonon structures, mechanical, thermal and thermoelectric proper… ▽ More Experimental results have shown that the quaternary compound Cu2ZnSnSe4 is an excellent thermoelectric material. This inspires us to seek the other quaternary compounds with similar chemical formula to Cu2ZnSnSe4 as thermoelectric materials. In this paper, we use the first-principle method to systematically explore the electronic and phonon structures, mechanical, thermal and thermoelectric properties of p- and n-type Ag2XYSe4 (X=Ba, Sr; Y=Sn, Ge). It is found that the ZT maximum for n-type Ag2SrGeSe4 can reach up to 1.22 at 900 K, and those for p-type Ag2SrSnSe4, Ag2SrGeSe4 and Ag2BaSnSe4 can reach up to 1.20, 1.13 and 1.12, respectively. Our work not only shows that Ag2XYSe4 (X=Ba, Sr; Y=Sn, Ge) are a kind of potential thermoelectric materials, but also can inspire more theoretical and experimental researches on thermoelectric properties of quaternary compounds. △ Less

Submitted 15 February, 2021; v1 submitted 6 August, 2019; originally announced August 2019.

Thick adherent diamond films on AlN with low thermal barrier resistance

Authors: Soumen Mandal, Jerome Cuenca, Fabien Massabuau, Chao Yuan, Henry Bland, James W. Pomeroy, David Wallis, Tim Batten, David Morgan, Rachel Oliver, Martin Kuball, Oliver A. Williams

Abstract: Growth of $>$100 $μ$m thick diamond layer adherent on aluminium nitride is presented in this work. While thick films failed to adhere on untreated AlN films, hydrogen/nitrogen plasma treated AlN films retained the thick diamond layers. Clear differences in zeta potential measurement confirms the surface modification due to hydrogen/nitrogen plasma treatment. Areal Raman maps showed an increase in… ▽ More Growth of $>$100 $μ$m thick diamond layer adherent on aluminium nitride is presented in this work. While thick films failed to adhere on untreated AlN films, hydrogen/nitrogen plasma treated AlN films retained the thick diamond layers. Clear differences in zeta potential measurement confirms the surface modification due to hydrogen/nitrogen plasma treatment. Areal Raman maps showed an increase in non-diamond carbon in the initial layers of diamond grown on pre-treated AlN. The presence of non-diamond carbon has minimal effect on the interface between diamond and AlN. The surfaces studied with x-ray photoelectron spectroscopy (XPS) revealed a clear distinction between pre-treated and untreated samples. The surface aluminium goes from nitrogen rich environment to an oxygen rich environment after pre-treatment. Cross section transmission electron microscopy shows a clean interface between diamond and AlN. Thermal barrier resistance between diamond and AlN was found to be in the range of 16 m$^2$K/GW which is a large improvement on the current state-of-the-art. △ Less

Submitted 4 July, 2019; originally announced July 2019.

A Hybrid multiphase model based on lattice Boltzmann method direct simulations

Authors: Eduard Puig Montellà, Chao Yuan, Bruno Chareyre, Antonio Gens

Abstract: By means of the multicomponent Shan-Chen lattice Boltzmann method (LBM), we investigate the multiphase flow through porous media. Despite the excellent accuracy of the LBM, large domains result in unaffordable computational expenses. The Hybrid model developed in this study is based on a pore-network (PN) approach that enhances a decomposition of the granular assembly into small subsets (pore thro… ▽ More By means of the multicomponent Shan-Chen lattice Boltzmann method (LBM), we investigate the multiphase flow through porous media. Despite the excellent accuracy of the LBM, large domains result in unaffordable computational expenses. The Hybrid model developed in this study is based on a pore-network (PN) approach that enhances a decomposition of the granular assembly into small subsets (pore throats). Lattice Boltzmann simulations are performed for each pore throat to determine the hydrodynamic properties (entry capillary pressure, primary drainage curve, liquid morphology, etc) at the microscale. The local properties obtained with LBM are incorporated at the network to solve the larger-scale problem. This strategy leads to a significant decrease of the computation time at the sample-scale compared to a fully resolved method. Fluid morphology and phase distribution are evaluated during the drainage of a small granular assembly using the Hybrid model (PN-LBM). Results are contrasted with those obtained in a fully resolved simulation (LBM). The agreement between the two models illustrates the capability of the Hybrid method, which combines the efficiency of the PN approach and the accuracy of the LBM at the pore scale. △ Less

Submitted 11 June, 2019; originally announced June 2019.

Comments: Proceedings of the VIII International Conference on Computational Methods for Coupled Problems in Science and Engineering

Journal ref: CIMNE 2019

Interaction-induced metallic state in graphene on hexagonal boron nitride

Authors: Jin-Rong Xu, Ze-Yi Song, Chen-Guang Yuan, Yu-Zhong Zhang

Abstract: The Coulomb interaction is widely known to enhance the effective mass of interacting particles and therefore tends to favor a localized state at commensurate filling. Here, we will show that, in contrast to this consensus, in a van der Waals heterostructure consisting of graphene and hexagon boron nitride (h-BN), the onsite Coulomb repulsion will at first destroy the localized state. This is due t… ▽ More The Coulomb interaction is widely known to enhance the effective mass of interacting particles and therefore tends to favor a localized state at commensurate filling. Here, we will show that, in contrast to this consensus, in a van der Waals heterostructure consisting of graphene and hexagon boron nitride (h-BN), the onsite Coulomb repulsion will at first destroy the localized state. This is due to the fact that the onsite Coulomb repulsion tends to suppress the asymmetry between neighboring carbons induced by h-BN substrate. We corroborate this surprising phenomenon by solving a tight-binding model with onsite Coulomb repulsion treated within coherent potential approximation, where hopping parameters are derived from density functional theory calculations based on the graphene/h-BN heterostructure. Our results indicate that both gapless and gapped states observed experimentally in graphene/h-BN heterostructures can be understood after a realistic value of the onsite Coulomb repulsion as well as different interlayer distances are taken into account. Finally, we propose ways to enhance the gapped state which is essential for potential application of graphene to next-generation electronics. Furthermore, we argue that band gap suppressed by many-body effect should happen in other van der Waals heterostructures. △ Less

Submitted 3 November, 2016; originally announced November 2016.

Comments: 9 pages, 8 figures

Journal ref: Phys. Rev. B 94, 195103 (2016)

Pore-scale simulations of drainage in granular materials: finite size effects and the representative elementary volume

Authors: Chao Yuan, Bruno Chareyre, Félix Darve

Abstract: A pore-scale model is introduced for two-phase flow in dense packings of polydisperse spheres. The model is developed as a component of a more general hydromechanical coupling framework based on the discrete element method, which will be elaborated in future papers. Here the emphasis is on the generation of a network of pores mapping the void space between spherical grains, and the definition of l… ▽ More A pore-scale model is introduced for two-phase flow in dense packings of polydisperse spheres. The model is developed as a component of a more general hydromechanical coupling framework based on the discrete element method, which will be elaborated in future papers. Here the emphasis is on the generation of a network of pores mapping the void space between spherical grains, and the definition of local criteria governing the primary drainage process. The pore space is decomposed by Regular Triangulation, from which a set of pores connected by throats are identified. A local entry capillary pressure is evaluated for each throat, based on the balance of capillary pressure and surface tension at equilibrium. The model reflects the possible entrapment of disconnected patches of the receding wetting phase. It is validated by a comparison with drainage experiments. A series of simulations are reported to illustrate size and boundary effects, key questions when studying small samples made of spherical particles be it in simulations or experiments. Repeated tests on samples of different sizes give evolution of water content which are not only scattered but also strongly biased for small sample sizes. More than 20,000 spheres are needed to reduce the bias on saturation below 0.02. Additional statistics are generated by subsampling a large sample of 64,000 spheres. They suggest that the minimal sampling volume for evaluating saturation is one hundred times greater that the sampling volume needed for measuring porosity with the same accuracy. This requirement in terms of sample size induces a need for efficient computer codes. The method described herein has a low algorithmic complexity in order to satisfy this requirement. It will be well suited to further developments toward coupled flow-deformation problems in which evolution of the microstructure require frequent updates of the pore network. △ Less

Submitted 5 January, 2016; originally announced January 2016.

Comments: to appear in Advances in Water Resources

Quantum tunneling time of a Bose-Einstein condensate traversing through a laser-induced potential barrier

Authors: Zhenglu Duan, Bixuan Fan, Chun-Hua Yuan, Jing Cheng, Shiyao Zhu, Weiping Zhang

Abstract: We theoretically study the effect of atomic nonlinearity on the tunneling time in the case of an atomic Bose-Einstein condensate (BEC) traversing the laser-induced potential barrier. The atomic nonlinearity is controlled to appear only in the region of the barrier by employing the Feshbach resonance technique to tune interatomic interaction in the tunneling process. Numerical simulation shows that… ▽ More We theoretically study the effect of atomic nonlinearity on the tunneling time in the case of an atomic Bose-Einstein condensate (BEC) traversing the laser-induced potential barrier. The atomic nonlinearity is controlled to appear only in the region of the barrier by employing the Feshbach resonance technique to tune interatomic interaction in the tunneling process. Numerical simulation shows that the atomic nonlinear effect dramatically changes the tunneling behavior of the BEC matter wave packet, and results in the violation of Hartman effect and the occurrence of negative tunneling time. △ Less

Submitted 1 June, 2010; originally announced June 2010.

Comments: 4 pages, 5 figures

Journal ref: Phys. Rev. A 81, 055602 (2010)

Microstructure and superconductivity of Ir-doped BaFe2As2 superconductor

Authors: X. L. Wang, H. Y. Shi, X. W. Yan, Y. C. Yuan, Z. -Y. Lu, X. Q. Wang, T. -S. Zhao*

Abstract: Polycrystalline samples with nominal composition of Ba(Fe1-xIrx)2As2 (x=0.10, 0.15, and 0.20) were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical resistivity, and magnetization measurements. XRD and SEM results showed that almost single phase samples were obtained. Bulk superconductivity with TC~28 K was observed in the x=0.10 sample. TC~28 K is… ▽ More Polycrystalline samples with nominal composition of Ba(Fe1-xIrx)2As2 (x=0.10, 0.15, and 0.20) were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical resistivity, and magnetization measurements. XRD and SEM results showed that almost single phase samples were obtained. Bulk superconductivity with TC~28 K was observed in the x=0.10 sample. TC~28 K is the highest superconducting critical temperature among the reported data for electron-doped AFe2As2-type (A=Ca, Sr, and Ba) superconductors. The upper critical field Hc2(0) reaches as high as 65 T for the x=0.10 sample. The underlying physics is discussed in connection with Co-doping case. △ Less

Submitted 21 December, 2009; originally announced December 2009.

Comments: 9 pages, 4 figures. Accepted for publication in Applied Physics Letters

Journal ref: Applied Physics Letters 96, 012507(2010)

Numerical Simulation of The Mechanical Properties of Nanoscale Metal Clusters Using The Atomistic-Continuum Mechanics Method

Authors: C. -Y. Chou, C. Yuan, Chung-Jung Wu, K. -N. Chiang

Abstract: A novel atomistic-continuum method (ACM) based on finite element method (FEM) is proposed to numerically simulate the nano-scaled Poisson's ratio and Young's modulus effect of Lithium (Li) body-centered cubic (BCC) structure. The potential energy between Li atoms is described by the Morse potential function [1]. The pre-force effect will be discussed due to the different Li lattice length betwee… ▽ More A novel atomistic-continuum method (ACM) based on finite element method (FEM) is proposed to numerically simulate the nano-scaled Poisson's ratio and Young's modulus effect of Lithium (Li) body-centered cubic (BCC) structure. The potential energy between Li atoms is described by the Morse potential function [1]. The pre-force effect will be discussed due to the different Li lattice length between experimental lattice constant and diatom distance from Morse function. Moreover, the size effect of the nano-scaled Li cluster will be introduced. △ Less

Submitted 14 August, 2007; originally announced August 2007.

Comments: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions)

Journal ref: Dans European Nano Systems Worshop - ENS 2005, Paris : France (2005)

Temperature Dependence of Resistivity of $Sr_2CoMoO_{6-δ}$ Films

Authors: C. L. Yuan, Z. Y. Zeng, Y. Zhu, P. P. Ong, Z. X. Shen, C. K. Ong

Abstract: We investigate the temperature dependence of the resistivity and magnetoresistance of a polycrystalline $Sr_2CoMoO_{6-δ}$ film deposited on (100)-$SrTiO_3$ substrate prepared by the pulsed laser deposition method. X-ray diffraction, Raman and magnetoresistance results demonstrate clearly the coexistence of a ferromagnetic metallic and an antiferromagnetic (or paramagnetic) insulating domain. Per… ▽ More We investigate the temperature dependence of the resistivity and magnetoresistance of a polycrystalline $Sr_2CoMoO_{6-δ}$ film deposited on (100)-$SrTiO_3$ substrate prepared by the pulsed laser deposition method. X-ray diffraction, Raman and magnetoresistance results demonstrate clearly the coexistence of a ferromagnetic metallic and an antiferromagnetic (or paramagnetic) insulating domain. Percolative transition between these two phases as the temperature varies, which is believed to induce a metal-insulator transition at around $T_C$, has been directly observed in our measurements of the temperature dependence of the sample resistivity. Thus we have provided new direct evidence that a phase separation scenario also exists in the ordered double-perovskite structure materials. △ Less

Submitted 23 July, 2003; v1 submitted 22 July, 2003; originally announced July 2003.