Showing 1–37 of 37 results for author: Xiong, L

Effects of analyst sentiment on volatility dynamics in financial market

Authors: Xiongfei Jiang, Tao Cen, Ling Bai, Lifu Jin, Jiu Zhang, Long Xiong

Abstract: Text emotions are extracted using natural language processing technique on a substantial corpus of analyst reports on the Chinese stock market. Subsequently, the text-based analyst sentiment indices are constructed. It is observed that both optimistic and pessimistic sentiments represent short-range memory. Optimistic and pessimistic sentiments are correlated with volatility positively and negativ… ▽ More Text emotions are extracted using natural language processing technique on a substantial corpus of analyst reports on the Chinese stock market. Subsequently, the text-based analyst sentiment indices are constructed. It is observed that both optimistic and pessimistic sentiments represent short-range memory. Optimistic and pessimistic sentiments are correlated with volatility positively and negatively, respectively. The analysis of transfer entropy reveals that past pessimistic sentiment affects future volatility. Further, we model the driving effect of analyst sentiment on volatility using a GARCH model. The results show that pessimistic sentiment is an explanatory factor for volatility, while optimistic sentiment is not. △ Less

Submitted 31 May, 2026; originally announced June 2026.

Comments: 13 pages, 4 figures, 3 tables

Is a team only as strong as its weakest link? Quantifying the short-board effect with AI Agents

Authors: Xin Xu, Jiu Zhang, Xiao-Ling Lei, Xiong-Fei Jiang, Long Xiong

Abstract: The short-board effect, analogous to Liebig's Law of the Minimum, postulates that the collective performance of a team is constrained by its weakest component. This principle has profound implications for the optimization of collaboration in a variety of contexts, including management, education, and organizational structures. Despite its theoretical significance, empirical validation remains elus… ▽ More The short-board effect, analogous to Liebig's Law of the Minimum, postulates that the collective performance of a team is constrained by its weakest component. This principle has profound implications for the optimization of collaboration in a variety of contexts, including management, education, and organizational structures. Despite its theoretical significance, empirical validation remains elusive due to challenges of assessing individual capabilities, controlling real-world variables, and data biases towards successful outcomes, as well as high employee turnover.To address this absence of knowledge, we employ multi-agents driven by large language models to simulate a teamwork with standard operating procedure, revealing the relationship between individual capability and collective team performance.In homogeneous team configurations, three capability regimes are observed, particularly the Sisyphus predicament state at the critical capability threshold characterized by extensive ineffective efforts and pseudo-high efficiency. Furthermore, with a single weak link quantifying the short-board effect, we highlight different impacts across core and non-core members on the team performance.More importantly, when the team exhibits multiple weak links, a cumulative product effect emerges, demonstrating that team performance is shaped by the aggregated impact of all weaknesses rather than the weakest link solely.This suggests that mitigation strategies should extend beyond the remediation of individual weak links.These findings rigorously elaborate the short-board theory and provide actionable insights to optimize team management, organizational operations, and supply chain resilience. △ Less

Submitted 8 May, 2026; originally announced May 2026.

Comments: 15 pages, 4 figures

A dispersal recolonisation 3D biofilm in vitro model based on co-assembled peptide amphiphiles and clinical wound fluid

Authors: Zhiquan Yu, Chenjia Zhao, Lingyun Xiong, Shanshan Su, Dawen Yu, Shilu Zhang, Yubin Ke, Hua Yang, Guo Zhang, Jiaming Sun, Nengqiang Guo, Yuanhao Wu

Abstract: Chronic wound infections are sustained by dynamic 3D biofilm cycles involving maturation, dispersal, and recolonisation, yet existing in vitro models fail to reproduce these temporal and structural complexities. Here, we report a strategy that co-assembles a designed protease-inhibitory peptide amphiphile (PA-GF) with patient-derived wound fluid (WF) to reconstruct the complete biofilm life cycle… ▽ More Chronic wound infections are sustained by dynamic 3D biofilm cycles involving maturation, dispersal, and recolonisation, yet existing in vitro models fail to reproduce these temporal and structural complexities. Here, we report a strategy that co-assembles a designed protease-inhibitory peptide amphiphile (PA-GF) with patient-derived wound fluid (WF) to reconstruct the complete biofilm life cycle in vitro. The PA-GF sequence incorporates an HWGF motif capable of binding and inhibiting matrix metalloproteinase-9 (MMP-9), thereby preserving the integrity of recolonised biofilms under proteolytic stress. Co-assembling with WF generated a living material that faithfully mimicked the biochemical and mechanical microenvironment of chronic wounds, supporting the formation of stable 3D biofilms capable of dispersal and recolonisation. Furthermore, we established a controllable polymicrobial infection model and validated its translational relevance through antibiotic susceptibility profiling and spatial microbiological analyses. Notably, the antibiotic response patterns of the PA/WF-derived biofilms closely mirrored those observed in a rat wound infection in vivo model. Collectively, our findings demonstrate that co-assembling living materials can recapitulate the nutritional composition, 3D architecture, and recolonisation dynamics of in vivo infectious biofilms, offering a physiologically relevant and customisable platform for investigating chronic wound infections and accelerating anti-biofilm drug discovery. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Unsupervised CP-UNet Framework for Denoising DAS Data with Decay Noise

Authors: Tianye Huang, Aopeng Li, Xiang Li, Jing Zhang, Sijing Xian, Qi Zhang, Mingkong Lu, Guodong Chen, Liangming Xiong, Xiangyun Hu

Abstract: Distributed acoustic sensor (DAS) technology leverages optical fiber cables to detect acoustic signals, providing cost-effective and dense monitoring capabilities. It offers several advantages including resistance to extreme conditions, immunity to electromagnetic interference, and accurate detection. However, DAS typically exhibits a lower signal-to-noise ratio (S/N) compared to geophones and is… ▽ More Distributed acoustic sensor (DAS) technology leverages optical fiber cables to detect acoustic signals, providing cost-effective and dense monitoring capabilities. It offers several advantages including resistance to extreme conditions, immunity to electromagnetic interference, and accurate detection. However, DAS typically exhibits a lower signal-to-noise ratio (S/N) compared to geophones and is susceptible to various noise types, such as random noise, erratic noise, level noise, and long-period noise. This reduced S/N can negatively impact data analyses containing inversion and interpretation. While artificial intelligence has demonstrated excellent denoising capabilities, most existing methods rely on supervised learning with labeled data, which imposes stringent requirements on the quality of the labels. To address this issue, we develop a label-free unsupervised learning (UL) network model based on Context-Pyramid-UNet (CP-UNet) to suppress erratic and random noises in DAS data. The CP-UNet utilizes the Context Pyramid Module in the encoding and decoding process to extract features and reconstruct the DAS data. To enhance the connectivity between shallow and deep features, we add a Connected Module (CM) to both encoding and decoding section. Layer Normalization (LN) is utilized to replace the commonly employed Batch Normalization (BN), accelerating the convergence of the model and preventing gradient explosion during training. Huber-loss is adopted as our loss function whose parameters are experimentally determined. We apply the network to both the 2-D synthetic and filed data. Comparing to traditional denoising methods and the latest UL framework, our proposed method demonstrates superior noise reduction performance. △ Less

Submitted 18 February, 2025; originally announced February 2025.

Comments: 13 pages, 8 figures

Simultaneous optical power delivery and distributed sensing through cross-band wavelength multiplexing over fiber link

Authors: Tianye Huang, Lu Guo, Xinyu Wang, Yao Chen, Jing Zhang, Ming Zhu, Mingkong Lu, Kaifu Chen, Hanlin Guo, Liangming Xiong, Xiangyun Hu, Perry Ping Shum

Abstract: Optical fibers offer significant advantages in both power delivery and distributed sensing. In remote areas where stable power supply is not easy to access, the distributed optical fiber sensing (DOFS) which offers long distance monitoring capability and the power-over-fiber (PoF) which can provide energy for connected electronics or other sensors are highly desired simultaneously. In this letter,… ▽ More Optical fibers offer significant advantages in both power delivery and distributed sensing. In remote areas where stable power supply is not easy to access, the distributed optical fiber sensing (DOFS) which offers long distance monitoring capability and the power-over-fiber (PoF) which can provide energy for connected electronics or other sensors are highly desired simultaneously. In this letter, the PoF-DOFS hybrid system is proposed and experimentally verified for the first time. By multiplexing the power channel and sensing channel with large wavelength separation, the cross-talk is greatly reduced. The results show that the Brillouin frequency shift under different temperature in the Brillouin optical time domain reflectometry remains unaffected by the high-power transmission background and the power delivery efficiency up to ~66% can be achieved over 1.3 km fiber link. This work paves the way for further research on PoF-DOFS hybrid system and gives a valuable solution for creating multi-parameter, multi-scale sensing network without the need for local power source. △ Less

Submitted 15 February, 2025; originally announced February 2025.

Comments: 12 pages,6 figures

Power-over-fiber and distributed acoustic sensing hybridization in single fiber channel

Authors: Jing Zhang, Yao Chen, Tianye Huang, Kaifu Chen, Hanlin Guo, Yongkang Huang, Lu Guo, Liangming Xiong, Perry Ping Shum

Abstract: The efficient and independent operation of power-over-fiber (PoF) and distributed acoustic sensing (DAS) has been demonstrated using standard single-mode fiber (SSMF). A transmission optical power efficiency (OPTE) of 6.67% was achieved over an 11.8 km fiber link, supporting both power delivery and distributed optical fiber sensing (DOFS). To minimize cross-talk, the system separates the power and… ▽ More The efficient and independent operation of power-over-fiber (PoF) and distributed acoustic sensing (DAS) has been demonstrated using standard single-mode fiber (SSMF). A transmission optical power efficiency (OPTE) of 6.67% was achieved over an 11.8 km fiber link, supporting both power delivery and distributed optical fiber sensing (DOFS). To minimize cross-talk, the system separates the power and sensing channels by a 40 THz bandwidth. In the experiment, the power and sensing light wavelengths are 1064 nm (continuous) and 1550 nm (pulsed), respectively. As the transmitted optical power increased from 0 W to 2.13 W, the DAS system successfully localized vibration sources and reconstructed phase information, confirming its ability to operate under high optical power. The reported scheme verifies the possibility of constructing the sensing-energy hybrid network based on conventional optical fiber with the advantages of flexibility and low cost. △ Less

Submitted 6 February, 2025; originally announced February 2025.

Comments: 11 pages, 6 figures

Integrating Graph Neural Networks and Many-Body Expansion Theory for Potential Energy Surfaces

Authors: Siqi Chen, Zhiqiang Wang, Xianqi Deng, Yili Shen, Cheng-Wei Ju, Jun Yi, Lin Xiong, Guo Ling, Dieaa Alhmoud, Hui Guan, Zhou Lin

Abstract: Rational design of next-generation functional materials relied on quantitative predictions of their electronic structures beyond single building blocks. First-principles quantum mechanical (QM) modeling became infeasible as the size of a material grew beyond hundreds of atoms. In this study, we developed a new computational tool integrating fragment-based graph neural networks (FBGNN) into the fra… ▽ More Rational design of next-generation functional materials relied on quantitative predictions of their electronic structures beyond single building blocks. First-principles quantum mechanical (QM) modeling became infeasible as the size of a material grew beyond hundreds of atoms. In this study, we developed a new computational tool integrating fragment-based graph neural networks (FBGNN) into the fragment-based many-body expansion (MBE) theory, referred to as FBGNN-MBE, and demonstrated its capacity to reproduce full-dimensional potential energy surfaces (FD-PES) for hierarchic chemical systems with manageable accuracy, complexity, and interpretability. In particular, we divided the entire system into basic building blocks (fragments), evaluated their single-fragment energies using a first-principles QM model and attacked many-fragment interactions using the structure-property relationships trained by FBGNNs. Our development of FBGNN-MBE demonstrated the potential of a new framework integrating deep learning models into fragment-based QM methods, and marked a significant step towards computationally aided design of large functional materials. △ Less

Submitted 3 November, 2024; originally announced November 2024.

Comments: Accepted as a Spotlight paper to NeurIPS 2024 AI4Mat Workshop. See https://openreview.net/forum?id=ra3CxVuhUf

Superluminal spacetime boundary, time reflection and quantum light generation from relativistic plasma mirrors

Authors: Chenhao Pan, Xinbing Song, Yang Cao, Li Xiong, Xiaofei Lan, Shaoyi Wang, Yuxin Leng, Yiming Pan

Abstract: A plasma mirror is an optical device for high-power, ultrashort-wavelength electromagnetic fields, utilizing a sheet of relativistic oscillating electrons to generate and manipulate light. In this work, we propose that the spatiotemporally varying plasma oscillation, induced by an ultra-high-intensity laser beam, functions as a "spacetime mirror" with significant potential for exploring quantum li… ▽ More A plasma mirror is an optical device for high-power, ultrashort-wavelength electromagnetic fields, utilizing a sheet of relativistic oscillating electrons to generate and manipulate light. In this work, we propose that the spatiotemporally varying plasma oscillation, induced by an ultra-high-intensity laser beam, functions as a "spacetime mirror" with significant potential for exploring quantum light. We find that the spacetime mirror exhibits several exotic features: (i) a superluminal spacetime boundary, (ii) time reflection and refraction, and (iii) quantum light sources with pair generation. Our theoretical and simulation results are in excellent agreement, and experimental verification is underway. Our work demonstrates the interplay with emerging fields such as time varying media, suggesting the plasma mirror as an ideal platform to study strong-field quantum optics at extremes. △ Less

Submitted 9 October, 2024; v1 submitted 2 October, 2024; originally announced October 2024.

Comments: 36 pages, 4 figures, SM file, 5 suppl. figures

Construction and Observation of Flexibly Controllable High-Dimensional Non-Hermitian Skin Effects

Authors: Qicheng Zhang, Yufei Leng, Liwei Xiong, Yuzeng Li, Kun Zhang, Liangjun Qi, Chunyin Qiu

Abstract: Non-Hermitian skin effect (NHSE) is one of the most fundamental phenomena in non-Hermitian physics. Although it is established that one-dimensional NHSE originates from the nontrivial spectral winding topology, the topological origin behind the higher-dimensional NHSE remains unclear so far. This poses a substantial challenge in constructing and manipulating high-dimensional NHSEs. Here, an intuit… ▽ More Non-Hermitian skin effect (NHSE) is one of the most fundamental phenomena in non-Hermitian physics. Although it is established that one-dimensional NHSE originates from the nontrivial spectral winding topology, the topological origin behind the higher-dimensional NHSE remains unclear so far. This poses a substantial challenge in constructing and manipulating high-dimensional NHSEs. Here, an intuitive bottom-to-top scheme to construct high-dimensional NHSEs is proposed, through assembling multiple independent one-dimensional NHSEs. Not only the elusive high-dimensional NHSEs can be effectively predicted from the well-defined one-dimensional spectral winding topologies, but also the high-dimensional generalized Brillouin zones can be directly synthesized from the one-dimensional counterparts. As examples, two two-dimensional nonreciprocal acoustic metamaterials are experimentally implemented to demonstrate highly controllable multi-polar NHSEs and hybrid skin-topological effects, where the sound fields can be frequency-selectively localized at any desired corners and boundaries. These results offer a practicable strategy for engineering high-dimensional NHSEs, which could boost advanced applications such as selective filters and directional amplifiers. △ Less

Submitted 31 May, 2024; originally announced June 2024.

Comments: Published in Advanced Materials

Journal ref: Advanced Materials, 2403108 (2024)

Interplay Between Single-Photon Ionization and the Auger Process in Argon Ion Formation

Authors: Linhao Xiong

Abstract: We explore the interactions between Argon and extreme ultraviolet (XUV) laser pulses across photon energies of 200 eV, 260 eV, and 315 eV, scrutinizing the influence of photon energy on Argon ion yields and unraveling the associated ionization pathways. Utilizing pulse durations of 10 fs and 30 fs, we spotlight a notable increase in Argon's ionization propensity with escalating laser intensities,… ▽ More We explore the interactions between Argon and extreme ultraviolet (XUV) laser pulses across photon energies of 200 eV, 260 eV, and 315 eV, scrutinizing the influence of photon energy on Argon ion yields and unraveling the associated ionization pathways. Utilizing pulse durations of 10 fs and 30 fs, we spotlight a notable increase in Argon's ionization propensity with escalating laser intensities, especially within the \(5 \times 10^{14}\, \text{W/cm}^2\) to \(1.2 \times 10^{16}\, \text{W/cm}^2\) range. While direct ionization predominated at 200 eV, the 260 eV and 315 eV spectra revealed complex interactions, prominently featuring the Auger process. A consistent overshadowing of odd-charged ions by even-charged Argon ions, particularly at 315 eV, paves the way for future research. The findings provide crucial insights into atomic interactions with intense light, establishing a groundwork for further exploration into similar atomic systems. △ Less

Submitted 12 April, 2024; originally announced April 2024.

Comments: 10 pages,7 figures

Topology reconstruction for asymmetric systems by isomorphic mapping or perturbation approximation

Authors: Yunlin Li, Jingguang Chen, Xingchao Qi, Langlang Xiong, Xianjun Wang, Yufu Liu, Fang Guan, Lei Shi, Xunya Jiang

Abstract: The systems without symmetries, e.g. the spatial and chiral symmetries, are generally thought to be improper for topological study and no conventional integral topological invariant can be well defined. In this work, with multi-band asymmetric Rice-Mele-like systems as examples, for the first time we show that the topology of all gaps can be reconstructed by two general methods and topological ori… ▽ More The systems without symmetries, e.g. the spatial and chiral symmetries, are generally thought to be improper for topological study and no conventional integral topological invariant can be well defined. In this work, with multi-band asymmetric Rice-Mele-like systems as examples, for the first time we show that the topology of all gaps can be reconstructed by two general methods and topological origin of many phenomena are revealed. A new integral topological invariant, i.e. the renormalized real-space winding number, can properly characterize the topology and bulk-edge correspondence of such systems. For the first method, an isomorphic mapping relationship between a Rice-Mele-like system and its chiral counterpart is set up, which accounts for the topology reconstruction in the half-filling gaps. For the second method, the Hilbert space of asymmetric systems could be reduced into degenerate subspaces by perturbation approximation, so that the topology in subspaces accounts for the topology reconstruction in the fractional-filling gaps. Surprisingly, the topology reconstructed by perturbation approximation exhibits extraordinary robustness since the topological edge states even exist far beyond the weak perturbation limit. We also show that both methods can be widely used for other asymmetric systems, e.g. the two-dimensional (2D) Rice-Mele systems and the superconductor systems. At last, for the asymmetric photonic systems, we predict different topological edge states by our topology-reconstruction theory and experimentally observe them in the laboratory, which agrees with each other very well. Our findings open a door for investigating new topological phenomena in asymmetric systems by various topological reconstruction methods which should greatly expand the category of topology study. △ Less

Submitted 24 March, 2024; v1 submitted 17 March, 2024; originally announced March 2024.

Scattering Singularity in Topological Dielectric Photonic Crystals

Authors: Langlang Xiong, Xunya Jiang, Guangwei Hu

Abstract: The exploration of topology in natural materials and metamaterials has garnered significant attention. Notably, the one-dimensional (1D) and two-dimensional (2D) Su-Schrieffer-Heeger (SSH) model, assessed through tight-binding approximations, has been extensively investigated in both quantum and classical systems, encompassing general and higher-order topology. Despite these advancements, a compre… ▽ More The exploration of topology in natural materials and metamaterials has garnered significant attention. Notably, the one-dimensional (1D) and two-dimensional (2D) Su-Schrieffer-Heeger (SSH) model, assessed through tight-binding approximations, has been extensively investigated in both quantum and classical systems, encompassing general and higher-order topology. Despite these advancements, a comprehensive examination of these models from the perspective of wave physics, particularly the scattering view, remains underexplored. In this study, we systematically unveil the origin of the 1D and 2D Zak phases stemming from the zero-scattering point, termed the scattering singularity in k-space. Employing an expanded plane wave expansion, we accurately compute the reflective spectrum of an infinite 2D photonic crystal (2D-PhC). Analyzing the reflective spectrum reveals the presence of a zero-scattering line in the 2D-PhC, considered the topological origin of the non-trivial Zak phase. Two distinct models, representing omnidirectional non-trivial cases and directional non-trivial cases, are employed to substantiate these findings. Our work introduces a novel perspective for characterizing the nature of non-trivial topological phases. The identification of the zero-scattering line not only enhances our understanding of the underlying physics but also provides valuable insights for the design of innovative devices. △ Less

Submitted 18 March, 2024; originally announced March 2024.

Comments: 8 pages, 4 figures

Enhancement of spin-orbit interaction and nearly perfect spin-conversion by 1D photonic crystal with the anisotropic defect layer

Authors: Xianjun Wang, Yufu Liu, Yunlin Li, Langlang Xiong, Xunya Jiang

Abstract: Although photon spin-orbit interaction (SOI) has been extensively studied, the vortex-conversion efficiency and the enhancement of spin Hall effect in abnormal modes in SOI remain to be investigated. Using an one-dimensional (1D) photonic crystal (PhC) system with the anisotropic defect layer(ADL), we firstly find that the generation efficiency of the vortex beam is close to 50\% when the number o… ▽ More Although photon spin-orbit interaction (SOI) has been extensively studied, the vortex-conversion efficiency and the enhancement of spin Hall effect in abnormal modes in SOI remain to be investigated. Using an one-dimensional (1D) photonic crystal (PhC) system with the anisotropic defect layer(ADL), we firstly find that the generation efficiency of the vortex beam is close to 50\% when the number of periodic layers of the PhC reaches 5. Secondly, We also discussed the case where linearly polarized light is obliquely incident on a defect state system, and find that the destructive interference between the normal mode and the abnormal mode reaches the maximum, resulting in the enhancement of the spin hall displacement, and the effect can be enhanced at any angle of incidence in this system. Finally, we found that in the defect mode, the mutual conversion of normal and abnormal mode spins can be regulated, and the conversion efficiency can be close to 100\%. △ Less

Submitted 24 February, 2024; originally announced February 2024.

Dual-polarization huge photonic spin Hall shift and deep-subwavelength sensing based on topological singularities in one-dimensional photonic crystals

Authors: Yufu Liu, Xianjun Wang, Yunlin Li, Haoran Zhang, Langlang Xiong, Xingchao Qi, Zhen Lai, Xuezhi Wang, Xunya Jiang

Abstract: Although several efforts have been taken to enhance the photonic spin Hall shift in deep-subwavelength region, according to effective medium theory, the fundamental confliction between near-zero reflection coefficient and near-zero incident angle still hinders the further application. Here, we reveal a fundamental breakdown of effective medium theory due to the existing of topological singularity… ▽ More Although several efforts have been taken to enhance the photonic spin Hall shift in deep-subwavelength region, according to effective medium theory, the fundamental confliction between near-zero reflection coefficient and near-zero incident angle still hinders the further application. Here, we reveal a fundamental breakdown of effective medium theory due to the existing of topological singularity in deep-subwavelength region in one-dimensional photonic crystals. We find that near the topological singularity, huge photonic spin Hall shift can be achieved for s-polarization and p-polarization. At the topological singularity, the reflected filed is split as dipole-like distribution with zero photonic spin Hall shift for both-polarizations, which is resulted from the interfere of the spin-maintained normal light and spin-flipped abnormal light. Based on the theoretical research, dual-polarizations thickness and dielectric constant sensing devices can be designed in deep-subwavelength region. Further more, by applying more complicated layered structure, multi-channels dual-polarizations detection and broadband dual-polarizations huge spin Hall shift platform can be designed. This work paves the way to exploring the topological properties and polarization control of photonic crystals and provides a prospective method for the design of multi-channels sensitive detection spin optical devices. △ Less

Submitted 20 February, 2024; originally announced February 2024.

Visualizing moiré ferroelectricity via plasmons and nano-photocurrent in graphene/twisted-WSe2 structures

Authors: Shuai Zhang, Yang Liu, Zhiyuan Sun, Xinzhong Chen, Baichang Li, S. L. Moore, Song Liu, Zhiying Wang, S. E. Rossi, Ran Jing, Jordan Fonseca, Birui Yang, Yinming Shao, Chun-Ying Huang, Taketo Handa, Lin Xiong, Matthew Fu, Tsai-Chun Pan, Dorri Halbertal, Xinyi Xu, Wenjun Zheng, P. J. Schuck, A. N. Pasupathy, C. R. Dean, Xiaoyang Zhu , et al. (6 additional authors not shown)

Abstract: Ferroelectricity, a spontaneous and reversible electric polarization, is found in certain classes of van der Waals (vdW) material heterostructures. The discovery of ferroelectricity in twisted vdW layers provides new opportunities to engineer spatially dependent electric and optical properties associated with the configuration of moiré superlattice domains and the network of domain walls. Here, we… ▽ More Ferroelectricity, a spontaneous and reversible electric polarization, is found in certain classes of van der Waals (vdW) material heterostructures. The discovery of ferroelectricity in twisted vdW layers provides new opportunities to engineer spatially dependent electric and optical properties associated with the configuration of moiré superlattice domains and the network of domain walls. Here, we employ near-field infrared nano-imaging and nano-photocurrent measurements to study ferroelectricity in minimally twisted WSe2. The ferroelectric domains are visualized through the imaging of the plasmonic response in a graphene monolayer adjacent to the moiré WSe2 bilayers. Specifically, we find that the ferroelectric polarization in moiré domains is imprinted on the plasmonic response of the graphene. Complementary nano-photocurrent measurements demonstrate that the optoelectronic properties of graphene are also modulated by the proximal ferroelectric domains. Our approach represents an alternative strategy for studying moiré ferroelectricity at native length scales and opens promising prospects for (opto)electronic devices. △ Less

Submitted 12 September, 2023; originally announced September 2023.

Comments: 19 pages, 3 figures

Journal ref: Nature Communications 14, 6200 (2023)

Experimental Characterization of Three-Band Braid Relations in Non-Hermitian Acoustic Systems

Authors: Qicheng Zhang, Luekai Zhao, Xun Liu, Xiling Feng, Liwei Xiong, Wenquan Wu, Chunyin Qiu

Abstract: The nature of complex eigenenergy enables unique band topology to the non-Hermitian (NH) lattice systems. Recently, there has been a fast growing interest in the elusive winding and braiding topologies of the NH single and double bands, respectively. Here, we explore the even more intricate NH multi-band topology and present the first experimental characterization of the three-band braid relations… ▽ More The nature of complex eigenenergy enables unique band topology to the non-Hermitian (NH) lattice systems. Recently, there has been a fast growing interest in the elusive winding and braiding topologies of the NH single and double bands, respectively. Here, we explore the even more intricate NH multi-band topology and present the first experimental characterization of the three-band braid relations by acoustic systems. Based on a concise tight-binding model, we design a ternary cavity-tube structure equipped with a highly controllable unidirectional coupler, through which the acoustic NH Bloch bands are experimentally reproduced in a synthetic dimension. We identify the NH three-band braid relations from both the perspectives of eigenvalues and eigenstates, including a noncommutative braid relation and a swappable braid relation. Our results could promote the understanding of NH Bloch band topology and pave the way toward designing new devices for manipulating acoustic states. △ Less

Submitted 14 December, 2022; originally announced December 2022.

Comments: 5 figures

Higher-order topological states in photonic Thue-Morse quasicrystals: quadrupole insulator and a new origin of corner states

Authors: Langlang Xiong, Yu Zhang, Yufu Liu, Yaoxian Zheng, Xunya Jiang

Abstract: Corner states (CSs) in higher-order topological insulators (HOTIs) have recently been of great interest in both crystals and quasicrystals. In contrast to electronic systems, HOTIs have not been found in photonic quasicrystals (PQCs). Here, we systemically study the higher-order topology in the two-dimensional Thue-Morse photonic quasicrystals (TM-PQCs). Not only the topological phase transition a… ▽ More Corner states (CSs) in higher-order topological insulators (HOTIs) have recently been of great interest in both crystals and quasicrystals. In contrast to electronic systems, HOTIs have not been found in photonic quasicrystals (PQCs). Here, we systemically study the higher-order topology in the two-dimensional Thue-Morse photonic quasicrystals (TM-PQCs). Not only the topological phase transition and the non-trivial CSs with fractional charge induced by multipole moments, but also a new type of CSs are found due to the complex structure of TM-PQCs near corners. The different origins of these CSs are also analyzed based on the tight-binding model. Our work opens the door to explore richer HOT physics beyond photonic crystals and the robustness of CSs in PQC shows the potential for applications. △ Less

Submitted 25 July, 2022; originally announced July 2022.

Atomically imprinted graphene plasmonic cavities

Authors: Brian S. Y. Kim, Aaron J. Sternbach, Min Sup Choi, Zhiyuan Sun, Francesco L. Ruta, Yinming Shao, Alexander S. McLeod, Lin Xiong, Yinan Dong, Anjaly Rajendran, Song Liu, Ankur Nipane, Sang Hoon Chae, Amirali Zangiabadi, Xiaodong Xu, Andrew J. Millis, P. James Schuck, Cory. R. Dean, James C. Hone, D. N. Basov

Abstract: Plasmon polaritons in van der Waals (vdW) materials hold promise for next-generation photonics. The ability to deterministically imprint spatial patterns of high carrier density in cavities and circuitry with nanoscale features underlies future progress in nonlinear nanophotonics and strong light-matter interactions. Here, we demonstrate a general strategy to atomically imprint low-loss graphene p… ▽ More Plasmon polaritons in van der Waals (vdW) materials hold promise for next-generation photonics. The ability to deterministically imprint spatial patterns of high carrier density in cavities and circuitry with nanoscale features underlies future progress in nonlinear nanophotonics and strong light-matter interactions. Here, we demonstrate a general strategy to atomically imprint low-loss graphene plasmonic structures using oxidation-activated charge transfer (OCT). We cover graphene with a monolayer of WSe$_2$, which is subsequently oxidized into high work-function WOx to activate charge transfer. Nano-infrared imaging reveals low-loss plasmon polaritons at the WOx/graphene interface. We insert WSe$_2$ spacers to precisely control the OCT-induced carrier density and achieve a near-intrinsic quality factor of plasmons. Finally, we imprint canonical plasmonic cavities exhibiting laterally abrupt doping profiles with single-digit nanoscale precision via programmable OCT. Specifically, we demonstrate technologically appealing but elusive plasmonic whispering-gallery resonators based on free-standing graphene encapsulated in WOx. Our results open avenues for novel quantum photonic architectures incorporating two-dimensional materials. △ Less

Submitted 25 June, 2022; originally announced June 2022.

Comments: 17 pages, 4 figures

Polarization-independent resonant lattice Kerker effect in phase-change metasurface

Authors: Lei Xiong, Xiaoqing Luo, Hongwei Ding, Yuanfu Lu, Guangyuan Li

Abstract: Resonant lattice Kerker effect in periodic resonators is one of the most interesting generalizations of the Kerker effect that relates to various fascinating functionalities such as scattering management and Huygens metasurfaces. However, so far this effect has been shown to be sensitive to the incident polarization, restricting its applications. Here, we report, for the first time, polarization-i… ▽ More Resonant lattice Kerker effect in periodic resonators is one of the most interesting generalizations of the Kerker effect that relates to various fascinating functionalities such as scattering management and Huygens metasurfaces. However, so far this effect has been shown to be sensitive to the incident polarization, restricting its applications. Here, we report, for the first time, polarization-independent resonant lattice Kerker effect in metasurfaces composed of periodic Ge$_2$Se$_2$Te$_5$ (GST) disks. For such a metasurface of square lattice, the spectrally overlap of the electric dipole and magnetic dipole surface lattice resonances can be realized by choosing an appropriate GST crystalline fraction regardless of the incident polarization. The operation wavelength and the required GST crystalline fraction can be conveniently tuned over large ranges since these parameters scale linearly with the disk size and the lattice period, greatly facilitating the design. Making use of the obtained resonant lattice Kerker effect, we realize a reconfigurable and polarization-independent lattice Huygens' metasurface with a dynamic phase modulation of close to $2π$ and high transmittance. This work will advance the engineering of the resonant lattice Kerker effect and promote its applications in phase modulation and wavefront control. △ Less

Submitted 4 July, 2022; v1 submitted 24 April, 2022; originally announced April 2022.

Comments: 21 pages, 7 figures

Topological properties of two-dimensional photonic square lattice without $C_4$ and $M_{x(y)}$ symmetries

Authors: Langlang Xiong, Yufu Liu, Yu Zhang, Yaoxian Zheng, Xunya Jiang

Abstract: Rich topological phenomena, edge states and two types of corner states, are unveiled in a two-dimensional square-lattice dielectric photonic crystal without both $C_4$ and $M_{x(y)}$ symmetries. Specifically, non-trivial type-I corner states, which do not exist in systems with $C_4$ and $M_{x(y)}$ since the degeneracy, are protected by non-zero quadrupole moment, no longer quantized to but less th… ▽ More Rich topological phenomena, edge states and two types of corner states, are unveiled in a two-dimensional square-lattice dielectric photonic crystal without both $C_4$ and $M_{x(y)}$ symmetries. Specifically, non-trivial type-I corner states, which do not exist in systems with $C_4$ and $M_{x(y)}$ since the degeneracy, are protected by non-zero quadrupole moment, no longer quantized to but less than $0.5$. Excellent properties, e.g. sub-wavelength localization and air-concentrated field distribution, are presented. Type-II corner states, induced by long-range interactions, are easier realized due to asymmetry. This work broadens the topological physics for the symmetries-broken systems and provides potential applications. △ Less

Submitted 18 March, 2022; originally announced March 2022.

The Design and Performance of Charged Particle Detector onboard the GECAM Mission

Authors: Y. B. Xu, X. L. Sun, S. Yang, X. Q. Li, W. X. Peng, K. Gong, X. H. Liang, Y. Q. Liu, D. Y. Guo, H. Wang, C. Y. Li, Z. H. An, J. J. He, X. J. Liu, S. L. Xiong, X. Y. Wen, Fan Zhang, D. L. Zhang, X. Y. Zhao, C. Y. Zhang, C. Cai, Z. Chang, G. Chen, C. Chen, Y. Y. Du , et al. (25 additional authors not shown)

Abstract: The Gravitational Wave highly energetic Electromagnetic Counterpart All-sky Monitor (GECAM) is dedicated to detecting gravitational wave gamma-ray bursts. It is capable of all-sky monitoring over and discovering gamma-ray bursts and new radiation phenomena. GECAM consists of two microsatellites, each equipped with 8 charged particle detectors (CPDs) and 25 gamma-ray detectors (GRDs). The CPD is us… ▽ More The Gravitational Wave highly energetic Electromagnetic Counterpart All-sky Monitor (GECAM) is dedicated to detecting gravitational wave gamma-ray bursts. It is capable of all-sky monitoring over and discovering gamma-ray bursts and new radiation phenomena. GECAM consists of two microsatellites, each equipped with 8 charged particle detectors (CPDs) and 25 gamma-ray detectors (GRDs). The CPD is used to measure charged particles in the space environment, monitor energy and flow intensity changes, and identify between gamma-ray bursts and space charged particle events in conjunction with GRD. CPD uses plastic scintillator as the sensitive material for detection, silicon photomultiplier (SiPM) array as the optically readable device, and the inlaid Am-241 radioactive source as the onboard calibration means. In this paper, we will present the working principle, physical design, functional implementation and preliminary performance test results of the CPD. △ Less

Submitted 9 December, 2021; originally announced December 2021.

Comments: accepted to RDTM

Inflight performance of the GECAM Gamma-ray and Charge particle Detectors

Authors: X. Q. Li, X. Y. Wen, S. L. Xiong, K. Gong, D. L. Zhang, Z. H. An, Y. B. Xu, Y. Q. Liu, C. Cai, Z. Chang, G. Chen, C. Chen, Y. Y. Du, M. Gao, R. Gao, D. Y. Guo, J. J. He, D. J. Hou, Y. G. Li, C. Li, C. Y. Li, G. Li, L. Li, Q. X. Li, X. F. Li , et al. (34 additional authors not shown)

Abstract: The GECAM mission consists of two identical microsatellites (GECAM-A and GECAM-B). Each satellite is equipped with 25 gamma-ray detectors (GRD) and 8 charged particle detectors (CPD). The main scientific objective of the GECAM mission is to detect gamma-ray bursts (GRBs) associated with the gravitational wave events produced by the merging of binary compact stars. After the launch on Dec. 10, 2020… ▽ More The GECAM mission consists of two identical microsatellites (GECAM-A and GECAM-B). Each satellite is equipped with 25 gamma-ray detectors (GRD) and 8 charged particle detectors (CPD). The main scientific objective of the GECAM mission is to detect gamma-ray bursts (GRBs) associated with the gravitational wave events produced by the merging of binary compact stars. After the launch on Dec. 10, 2020 , we carried out a series of on orbit tests. This paper introduces the test results of the GECAM-B satellite. According to the in-flight performance, the energy band for gamma-ray detection of GECAM-B is from about 7 keV to 3.5 MeV. GECAM-B can achieve prompt localization of GRBs. For the first time, GECAM-B realized a quasi-real-time transmission of trigger information using Beidou-3 RDSS. Keywords GECAM, gamma-ray burst, gravitational wave, GRD, CPD △ Less

Submitted 9 December, 2021; originally announced December 2021.

Comments: 16 pages, 8 figures

Active Tuning of Resonant Lattice Kerker Effect

Authors: Lei Xiong, Hongwei Ding, Yuanfu Lu, Guangyuan Li

Abstract: The Kerker effect has been generalized in nanophotonics and meta-optics, and has recently been of great interest by relating to various fascinating functionalities such as scattering management and perfect transmission, reflection or absorption. One of the most interesting generalizations is the resonant lattice Kerker effect in periodic nanostructures. However, its active tuning has not been expl… ▽ More The Kerker effect has been generalized in nanophotonics and meta-optics, and has recently been of great interest by relating to various fascinating functionalities such as scattering management and perfect transmission, reflection or absorption. One of the most interesting generalizations is the resonant lattice Kerker effect in periodic nanostructures. However, its active tuning has not been explored yet. Here, we report, for the first time, the active control of the resonant lattice Kerker effect in periodic Ge2Se2Te5 nanodisks. By changing the crystalline fraction, we show that the electric dipole lattice resonance (ED-LR), the magnetic dipole resonance (MDR), and thus the resonant lattice Kerker effect are all red-shifted. We therefore realize the transition from the ED-LR to the resonant lattice Kerker effect, which enables multilevel tuning of reflection, transmission and absorption with modulation depths above 86%. Taking advantage of the MDR redshifts, we also observe broadband and multilevel tuning of transmission with modulation depth of 87% over a broadband range of 588 nm. Our work establishes a new path for designing high-performance active nanophotonic devices. △ Less

Submitted 9 December, 2021; v1 submitted 4 November, 2021; originally announced November 2021.

Comments: 18 pages, 6 figures

Quality assurance test and Failure Analysis of SiPM Arrays of GECAM Satellites

Authors: D. L. Zhang, M. Gao, X. L. Sun, X. Q. Li, Z. H. An, X. Y. Wen, C. Cai, Z. Chang, G. Chen, C. Chen, Y. Y. Du, R. Gao, K. Gong, D. Y. Guo, J. J. He, D. J. Hou, Y. G. Li, C. Y. Li, G. Li, L. Li, X. F. Li, M. S. Li, X. H. Liang, X. J. Liu, Y. Q. Liu , et al. (23 additional authors not shown)

Abstract: The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) satellite consists of two small satellites. Each GECAM payload contains 25 gamma ray detectors (GRD) and 8 charged particle detectors (CPD). GRD is the main detector which can detect gamma-rays and particles and localize the Gamma-Ray Bursts (GRB),while CPD is used to help GRD to discriminate gamma-ray bursts an… ▽ More The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) satellite consists of two small satellites. Each GECAM payload contains 25 gamma ray detectors (GRD) and 8 charged particle detectors (CPD). GRD is the main detector which can detect gamma-rays and particles and localize the Gamma-Ray Bursts (GRB),while CPD is used to help GRD to discriminate gamma-ray bursts and charged particle bursts. The GRD makes use of lanthanum bromide (LaBr3) crystal readout by SiPM. As the all available SiPM devices belong to commercial grade, quality assurance tests need to be performed in accordance with the aerospace specifications. In this paper, we present the results of quality assurance tests, especially a detailed mechanism analysis of failed devices during the development of GECAM. This paper also summarizes the application experience of commercial-grade SiPM devices in aerospace payloads, and provides suggestions for forthcoming SiPM space applications. △ Less

Submitted 9 December, 2021; v1 submitted 1 September, 2021; originally announced September 2021.

Comments: 13 pages, 23 figures

Journal ref: RDTM-D-21-00057R4.2021.9.1

Mirror-backed dielectric metasurface sensor with ultrahigh figure of merit based on super-narrow Rayleigh anomaly

Authors: Yonghang Wang, Lei Xiong, Ming Tian, Guangyuan Li

Abstract: Plasmonic nanostructures with large local field enhancement have been extensively investigated for sensing applications. However, the quality factor and thus the sensing figure of merit are limited due to relatively high ohmic loss. Here we propose a novel plasmonic sensor with ultrahigh figure of merit based on super-narrow Rayleigh anomaly (RA) in a mirror-backed dielectric metasurface. Simulati… ▽ More Plasmonic nanostructures with large local field enhancement have been extensively investigated for sensing applications. However, the quality factor and thus the sensing figure of merit are limited due to relatively high ohmic loss. Here we propose a novel plasmonic sensor with ultrahigh figure of merit based on super-narrow Rayleigh anomaly (RA) in a mirror-backed dielectric metasurface. Simulation results show that the RA in such a metasurface can have a super-high quality factor of 16000 in the visible regime, which is an order of magnitude larger than the highest value of reported plasmonic nanostructures. We attribute this striking performance to the enhanced electric fields far away from the metal film. The super-high quality factor and the greatly enhanced field confined to the superstrate region make the mirror-backed dielectric metasurface an ideal platform for sensing. We show that the figure of merit of this RA-based metasurface sensor can be as high as 15930/RIU. Additionally, we reveal that RA-based plasmonic sensors share some typical characteristics, providing guidance for the structure design. We expect this work advance the development of high-performance plasmonic metasurface sensors. △ Less

Submitted 27 November, 2021; v1 submitted 26 August, 2021; originally announced August 2021.

Comments: 12 pages, 6 figures, 1 table

Narrow quadrupolar surface lattice resonances and band reversal in vertical metal-insulator-metal gratings

Authors: Xinyu Fang, Lei Xiong, Jianping Shi, Hongwei Ding, Guangyuan Li

Abstract: We report narrow quadrupolar surface lattice resonances (SLRs) under normal incidence, and the observation, for the first time, of the band reversal effect of SLRs supported by a vertical metal-insulator-metal nanograting, which is embedded in a homogeneous dielectric environment. Simulation results show that under normal incidence, quadrupolar SLR with linewidth of 1~nm and high quality factor of… ▽ More We report narrow quadrupolar surface lattice resonances (SLRs) under normal incidence, and the observation, for the first time, of the band reversal effect of SLRs supported by a vertical metal-insulator-metal nanograting, which is embedded in a homogeneous dielectric environment. Simulation results show that under normal incidence, quadrupolar SLR with linewidth of 1~nm and high quality factor of 979 can be excited in the near-infrared regime, and that under oblique incidence, out-of-plane dipolar SLRs of relatively large quality factors (>=150) can be launched. By varying the incidence angle, the SLR wavelength can be continuously tuned over an extremely broadband range of 750 nm, covering most of the near-infrared regime, and the quality factor decreases exponentially. Remarkably, the resonance lineshape can also be dynamically tuned from an asymmetric Fano-shaped dip to a peak, a dip/peak pair, and a perfect symmetric Lorentzian peak, suggesting the appearance of the band reversal effect. We expect the high-Q SLRs with broadband tunability and tunable lineshapes will find potential applications in enhanced nanoscale light-matter interactions in nanolasers, nonlinear optics and sensing. △ Less

Submitted 5 August, 2021; originally announced August 2021.

Comments: 11 pages, 6 figures

A General Principle: π-Conjugated Confinement Maximizes Band Gap of DUV NLO Materials

Authors: Lin Xiong, Li-Ming Wu, Ling Chen

Abstract: Current nonlinear optical materials face a conventional limitation on the tradeoff between band gap and birefringence, especially in the deep UV spectral region. To circumvent such a dilemma, we propose a general principle, a π-conjugated confinement, to partially decouple the inter group π-conjugated interactions with the separation of a non-π-conjugated group so as to maximize the band gap in co… ▽ More Current nonlinear optical materials face a conventional limitation on the tradeoff between band gap and birefringence, especially in the deep UV spectral region. To circumvent such a dilemma, we propose a general principle, a π-conjugated confinement, to partially decouple the inter group π-conjugated interactions with the separation of a non-π-conjugated group so as to maximize the band gap in comparison with those of simple π-conjugated salts, such as borates, carbonates. Meanwhile, to maintain a large optical anisotropy. We uncover that the π-conjugated confinement is a shared structural feature for all the known DUV NLO materials with favorable properties (45 compounds), and thus, it provides an essential design criterion. Guided by this principle, the carbonophosphate is predicted theoretically for the first time as a promising DUV candidate system, Sr3Y[PO4][CO3]3 and Na3X[PO4][CO3] (X = Ba, Sr, Ca, Mg) exhibit an enhanced birefringence that is 3-24 times larger than that of the simple phosphate, as well as an increased band gap that is 0.2-1.7 eV wider than that of the simple carbonate. Especially, the shortest SHG output of Sr3Y[PO4][CO3]3 is at λPM = 181 nm, being the shortest one among phosphates to date. △ Less

Submitted 23 April, 2021; originally announced April 2021.

Exciton emissions in bilayer WSe2 tuned by the ferroelectric polymer

Authors: Sixin Zhu, Dan Li, Jianlu Wang, Qiang Wang, Yongpeng Wu, Liang Xiong, Zhangfeng Jiang, Huihong Lin, Zhirui Gong, Qi Qin, Xingjun Wang

Abstract: In this work, a hybrid integration of few-layer transition metal dichalcogenides (TMDCs) and ferroelectric polymer is designed to achieve passive control of optical properties in-situ. The electrical polarization in ferroelectric P(VDF-TrFE) polymer can regulate the photoluminescence (PL) in few-layer TMDCs. The total PL intensity is substantially suppressed or enhanced under opposite polarization… ▽ More In this work, a hybrid integration of few-layer transition metal dichalcogenides (TMDCs) and ferroelectric polymer is designed to achieve passive control of optical properties in-situ. The electrical polarization in ferroelectric P(VDF-TrFE) polymer can regulate the photoluminescence (PL) in few-layer TMDCs. The total PL intensity is substantially suppressed or enhanced under opposite polarization in bilayer WSe2. This is because electrons transfer between valley K and Λ in the conduction band induced by the built-in electric field in P(VDF-TrFE) polymer. This charge transfer further changes the competing dynamics between direct and indirect exciton recombination path and overall optical radiation efficiency. We also illustrate that the engineered PL originates from external electric field dependent transferred electron effect. The theoretical result matches the experimental data well. This work demonstrates a device platform in which passive regulation is achieved using 2D TMDCs modulated by polarized ferroelectric materials. △ Less

Submitted 12 April, 2021; v1 submitted 3 March, 2021; originally announced March 2021.

Turbulence and heat transfer on a rotating, heated half soap bubble

Authors: X. Q. HE, A. D. Bragg, Y. L. Xiong, P. Fischer

Abstract: We use Direct Numerical Simulations to study the two-dimensional flow of a rotating, half soap bubble that is heated at its equator. The heating produces buoyancy and rotation generates a Coriolis forces in the fluid. However, due to the curved surface of the bubble, the buoyancy and Coriolis forces vary with latitude on the bubble, giving rise to rich flow behavior. We first explore the single-po… ▽ More We use Direct Numerical Simulations to study the two-dimensional flow of a rotating, half soap bubble that is heated at its equator. The heating produces buoyancy and rotation generates a Coriolis forces in the fluid. However, due to the curved surface of the bubble, the buoyancy and Coriolis forces vary with latitude on the bubble, giving rise to rich flow behavior. We first explore the single-point properties of the flow, including the Reynolds and Nusselt numbers, mean fields, and Reynolds stresses, all as a function of latitude. For a given Rayleigh number, we observe a non-monotonic dependence on the Rossby number Ro, and large scale mean circulations that are strongly influenced by rotation. We then consider quantities that reveal the multiscale nature of the flow, including spectrums and spectral fluxes of kinetic and thermal energy, and enstrophy, and structure functions of velocity and temperature. The fluxes show that just a for nonbuoyant two-dimensional turbulence on a flat surface, there is an upscale flux of kinetic energy at larger scales (fed by buoyancy injection of turbulent kinetic energy at smaller scales), and a downscale flux of enstrophy at smaller scales. The kinetic energy spectrum and velocity structure functions are well described by Bolgiano-Obukhov (BO) scaling at scales where the effects of rotation are weak. The temperature structure functions do not, however, satisfy BO scaling in general, due to strong intermittency in the temperature field. △ Less

Submitted 18 November, 2020; originally announced November 2020.

A low-energy sensitive compact gamma-ray detector based on LaBr3 and SiPM for GECAM

Authors: P. Lv, S. L. Xiong, X. L. Sun, J. G. Lv, Y. G. Li

Abstract: The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) project is the planned Chinese space telescope for detecting the X and gamma-ray counterpart. It consists of two micro-satellites in low earth orbit with the advantages of instantaneous full-sky coverage, low energy threshold down to 6 keV and can be achieved within a short period and small budget. Due to the li… ▽ More The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) project is the planned Chinese space telescope for detecting the X and gamma-ray counterpart. It consists of two micro-satellites in low earth orbit with the advantages of instantaneous full-sky coverage, low energy threshold down to 6 keV and can be achieved within a short period and small budget. Due to the limitation of size, weight and power consumption of micro-satellites, silicon photomultipliers (SiPMs) are used to replace the photomultiplier tubes (PMTs) to assemble a novel gamma-ray detector. A prototype of a SiPM array with LaBr3 crystal is built and tested, and it shows a high detection efficiency (70% at 5.9 keV) and an acceptable uniformity. The low-energy X-ray of 5.9 keV can be detected by a simply readout circuit, and the energy resolution is 6.5% (FWHM) at 662 keV. The design and performance of the detector are discussed in detail in this paper. △ Less

Submitted 13 September, 2018; v1 submitted 21 March, 2018; originally announced March 2018.

Comments: 9 pages, 10 figures, accepteded by JINST

The electromagnetic waves propagation in unmagnetized plasma media using parallelized finite-difference time-domain method

Authors: Lang-lang Xiong, Xi-min Wang, Song Liu, Zhi-yun Peng, Shuang-ying Zhong

Abstract: The finite-difference time-domain (FDTD) method has been commonly utilized to simulate the electromagnetic (EM) waves propagation in the plasma media. However, the FDTD method may bring about extra run-time on concerning computationally large and complicated EM problems. Fortunately, the FDTD method is easy to parallelize. Besides, GPU has been widely used for parallel computing due to its unique… ▽ More The finite-difference time-domain (FDTD) method has been commonly utilized to simulate the electromagnetic (EM) waves propagation in the plasma media. However, the FDTD method may bring about extra run-time on concerning computationally large and complicated EM problems. Fortunately, the FDTD method is easy to parallelize. Besides, GPU has been widely used for parallel computing due to its unique SPMD (Single Program Multiple Data) architecture. In this paper, we represent the parallel Runge-Kutta exponential time differencing scheme FDTD (RKETD) method for the unmagnetized plasma implemented on GPU. The detailed flowchart of parallel RKETD-FDTD method is described. The accuracy and acceleration performance of the proposed parallel RKETD-FDTD method implemented on GPU are substantiated by calculating the reflection and transmission coefficients for one-dimensional unmagnetized plasma slab. The results indicate that the numerical precision of the parallel RKETD-FDTD scheme is consistent with that of the code implemented on CPU. The computation efficiency is greatly improved compared with merely CPU-based serial RKETD-FDTD method. Moreover, the comparisons of the performance of CUDA-based GPU parallel program, OpenMP (Open Multi-Processing)-based CPU parallel program, and single-CPU serial program on the same host computer are done. Compared with the serial program, both parallel programs get good results, while GPU-based parallel program gains better result. △ Less

Submitted 12 April, 2018; v1 submitted 4 September, 2017; originally announced September 2017.

Comments: 12 pages,3 figures

Journal ref: Lang-lang Xiong, Xi-min Wang, Song Liu, Zhi-yun Peng, Shuang-ying Zhong, The electromagnetic waves propagation in unmagnetized plasma media using parallelized finite-difference time-domain method, Optik, Volume 166, August 2018, Pages 8-14

Giant Gating Tunability of Optical Refractive Index in Transition Metal Dichalcogenide Monolayers

Authors: Yiling Yu, Yifei Yu, Lujun Huang, Haowei Peng, Liwei Xiong, Linyou Cao

Abstract: We report that the refractive index of transition metal dichacolgenide (TMDC) monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by > 60% in the imaginary part and > 20% in the real part around exciton resonances using CMOS-compatible electrical gating. This giant tunablility is rooted in the dominance of excitonic effects in the refractive index of the monolayers and the strong s… ▽ More We report that the refractive index of transition metal dichacolgenide (TMDC) monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by > 60% in the imaginary part and > 20% in the real part around exciton resonances using CMOS-compatible electrical gating. This giant tunablility is rooted in the dominance of excitonic effects in the refractive index of the monolayers and the strong susceptibility of the excitons to the influence of injected charge carriers. The tunability mainly results from the effects of injected charge carriers to broaden the spectral width of excitonic interband transitions and to facilitate the interconversion of neutral and charged excitons. The other effects of the injected charge carriers, such as renormalizing bandgap and changing exciton binding energy, only play negligible roles. We also demonstrate that the atomically thin monolayers, when combined with photonic structures, can enable the efficiencies of optical absorption (reflection) tuned from 40% (60%) to 80% (20%) due to the giant tunability of refractive index. This work may pave the way towards the development of field-effect photonics in which the optical functionality can be controlled with CMOS circuits. △ Less

Submitted 27 May, 2017; originally announced May 2017.

Calibration of the Space-borne Compton Polarimeter POLAR flight model with 100% polarized X-ray beams

Authors: H. L. Xiao, W. Hajdas, P. Socha, R. Marcinkowski, B. B. Wu, T. W. Bao, J. Y. Chai, Y. W. Dong, M. N. Kong, L. Li, Z. H. Li, J. T. Liu, H. L. Shi, L. M. Song, J. C. Sun, R. J. Wang, Y. H. Wang, X. Wen, S. L. Xiong, J. Zhang, L. Y. Zhang, S. N. Zhang, X. F. Zhang, Y. J. Zhang, F. Cadoux , et al. (10 additional authors not shown)

Abstract: POLAR is space-borne detector designed for a precise measurement of gamma-ray polarization of the prompt emissions of Gamma-Ray Bursts in the energy range 50 keV - 500 keV. POLAR is a compact Compton polarimeter consisting of 40$\times$ 40 plastic scintillator bars read out by 25 multi-anode PMTs. In May 2015, we performed a series of tests of the POLAR flight model with 100\% polarized x-rays bea… ▽ More POLAR is space-borne detector designed for a precise measurement of gamma-ray polarization of the prompt emissions of Gamma-Ray Bursts in the energy range 50 keV - 500 keV. POLAR is a compact Compton polarimeter consisting of 40$\times$ 40 plastic scintillator bars read out by 25 multi-anode PMTs. In May 2015, we performed a series of tests of the POLAR flight model with 100\% polarized x-rays beams at the European Synchrotron Radiation Facility beam-line ID11 aming to study thresholds, crosstalk between channels and responses of POLAR flight model to polarized X-ray beams. In this paper we present the data analysis method and some analysis results. According the results, POLAR FM has good polarimetric capabilities. △ Less

Submitted 24 April, 2017; v1 submitted 20 April, 2017; originally announced April 2017.

Comments: The paper was withdrawn by authors because the work has not yet finshed

Gain factor and parameter settings optimization of the new gamma-ray burst polarimeter POLAR

Authors: X. F. Zhang, W. Hajdas, H. L. Xiao, X. Wen, B. B. Wu, T. W. Bao, T. Batsch, T. Bernasconi, F. Cadoux, I. Cernuda, J. Y. Chai, Y. W. Dong, N. Gauvin, J. J. He, M. Kole, M. N. Kong, C. Lechanoine-Leluc, L. Li, Z. H. Li, J. T. Liu, X. Liu, R. Marcinkowski, S. Orsi, M. Pohl, D. Rapin , et al. (16 additional authors not shown)

Abstract: As a space-borne detector POLAR is designed to conduct hard X-ray polarization measurements of gamma-ray bursts on the statistically significant sample of events and with an unprecedented accuracy. During its development phase a number of tests, calibrations runs and verification measurements were carried out in order to validate instrument functionality and optimize operational parameters. In thi… ▽ More As a space-borne detector POLAR is designed to conduct hard X-ray polarization measurements of gamma-ray bursts on the statistically significant sample of events and with an unprecedented accuracy. During its development phase a number of tests, calibrations runs and verification measurements were carried out in order to validate instrument functionality and optimize operational parameters. In this article we present results on gain optimization togeter with verification data obtained in the course of broad laboratory and environmental tests. In particular we focus on exposures to the $^{137}$Cs radioactive source and determination of the gain dependence on the high voltage for all 1600 detection channels of the polarimeter. Performance of the instrument is described in detail with respect to the dynamic range, energy resolution and temperature dependence. Gain optimization algorithms and response non-uniformity studies are also broadly discussed. Results presented below constitute important parts for development of the POLAR calibration and operation database. △ Less

Submitted 14 March, 2017; v1 submitted 12 March, 2017; originally announced March 2017.

Comments: There still some disagreement about one of the conclusions presented in the paper among all the authors

Fano resonance scattering in waveguide with an impedance boundary condition

Authors: Lei Xiong, Wenping Bi, Yves Aurégan

Abstract: Sound propagation in a waveguide lined with one section of locally reactive material is studied by resonance scattering approach. The objective is to understand the effects of mode coupling in the lined section on the transmission. It is shown that a transmission zero is present in the vicinity of a resonance peak when a numerically real resonance frequency of the open lined section (opened to inf… ▽ More Sound propagation in a waveguide lined with one section of locally reactive material is studied by resonance scattering approach. The objective is to understand the effects of mode coupling in the lined section on the transmission. It is shown that a transmission zero is present in the vicinity of a resonance peak when a numerically real resonance frequency of the open lined section (opened to infinities through the rigid parts of the waveguide) is crossed. The transmission zero and immediate resonance peak form a Fano resonance, it has been explained as an interaction between a resonance and the non-resonant background. The real resonance frequency and its corresponding trapped mode are formed by the interferences (couplings) between two neighbor modes with complex resonance frequencies. It is also linked to the avoided crossing of eigenvalues and the exceptional point. The scattering matrix is expressed in terms of a matrix $\mathsf{H_{eff}}$ which describes approximately the complex resonances in the open lined section. With the aid of the eigenvalues and eigenfunctions of matrix $\mathsf{H_{eff}}$, the traditional acoustic resonance scattering formula can be extended to describe the coupling effects between the open lined section and the rigid parts of the waveguide. △ Less

Submitted 18 November, 2015; originally announced November 2015.

One electron oxygen reduction in room temperature ionic liquids: A comparative study of Butler-Volmer and Symmetric Marcus-Hush theories using microdisc electrodes

Authors: Eden E. L. Tanner, Linhongjia Xiong, Edward O. Barnes, Richard G. Compton

Abstract: The voltammetry for the reduction of oxygen at a microdisc electrode is reported in two room temperature ionic liquids: 1-butyl-1-methylpyyrolidinium bis(trifluoromethylsulfonyl) imide ([Bmpyrr][NTf2]) and trihexyltetradecylphosphonium bis9trifluoromethylsulfonyl) imide ([P14,6,6,6][NTf2]) at 298 K. Simulated voltammograms using Butler-Volmer theory and Symmetric Marcus-Hush (SMH) theory were comp… ▽ More The voltammetry for the reduction of oxygen at a microdisc electrode is reported in two room temperature ionic liquids: 1-butyl-1-methylpyyrolidinium bis(trifluoromethylsulfonyl) imide ([Bmpyrr][NTf2]) and trihexyltetradecylphosphonium bis9trifluoromethylsulfonyl) imide ([P14,6,6,6][NTf2]) at 298 K. Simulated voltammograms using Butler-Volmer theory and Symmetric Marcus-Hush (SMH) theory were compared with experimental data. Butler-Volmer theory consistently provided experimental parameters with a higher level of certainty than SMH theory. A value of solvent reorganisation energy for oxygen reduction in ionic liquids was inferred for the first time as 0.4-0.5 eV, which is attributable to inner-sphere reorganisation with a negligible contribution from solvent reorganisation. The developed Butler-Volmer and Symmetric Marcus-Hush programs are also used to theoretically study the possibility of kinetically limited steady state currents, and to establish an approximate equivalence relationship between microdisc electrodes and spherical electrodes resting on a surface for steady state voltammetry for both Butler-Volmer and Symmetric Marcus-Hush theory. △ Less

Submitted 5 March, 2015; originally announced March 2015.

Journal ref: J. Electroanal. Chem. 727 (2014) 59-68

Double potential step chronoamperometry at a microband electrode: Theory and experiment

Authors: Edward O. Barnes, Linhongjia Xiong, Kristopher R. Ward, Richard G. Compton

Abstract: Numerical simulation is used to characterise double potential step chronoamperometry at a microband electrode for a simple redox process A + e- goes to B, under conditions of full support such that diffusion is the only active form of mass transport. The method is shown to be highly sensitive for the measurement of the diffusion coefficient of both A and B, and is applied to the one electron reduc… ▽ More Numerical simulation is used to characterise double potential step chronoamperometry at a microband electrode for a simple redox process A + e- goes to B, under conditions of full support such that diffusion is the only active form of mass transport. The method is shown to be highly sensitive for the measurement of the diffusion coefficient of both A and B, and is applied to the one electron reduction of decamethylferrocene (DMFc), DMFc - e- goes to DMFc+, in the room temperature ionic liquid 1-propyl-3-methylimidazolium bistrifluoromethylsulfonylimide. Theory and experiment are seen to be in excellent agreement and the following values of the diffusion coefficients were measured at 298 K: D_(DMFc) = 2.50 x 10^(-7) cm^(2) s^(-1) and D_(DMFc+) = 9.50 x 10^(-8) cm^(2) s^(-1). △ Less

Submitted 21 May, 2013; originally announced May 2013.

Journal ref: J. Electroanal. Chem., 701 (2013) 59-68