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Oct. 2021, Volume 16 Issue 5

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Nanostructures have been designed using basic blocks with totally different dimensional, like MXene quantum dots (QDs) loaded on 2D nanosheets. QDs offer abundant active edging sites but suffer from severe aggregation if no constraint is applied. 2D presents large surface area, high conductivity and strong capacity to fix QDs. As a result, such heterojunction brings unique physics and promising catalysis for hydrogen production. For more details, please refer to the article entitled “A DFT study of Ti3C2O2 MXenes quantum dots supported on single layer graphene: Electronic structure an hydrogen evolution performance” by Qingquan Kong, Xuguang An, Lin Huang, Xiaolian Wang, Wei Feng, Siyao Qiu, Qingyuan Wang, Chenghua Sun, Front. Phys. 16(5), 53506 (2021). [Photo credit: Qingquan Kong at Chengdu University.]
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Aug. 2021, Volume 16 Issue 4

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Compared with traditional plasmonic-based surface-enhanced Raman scattering (SERS) substrates, plasmon-free SERS substrates, as new frontiers, have attracted tremendous attention for their abundant sources, excellent chemical stability, superior biocompatibility, good signal uniformity, and unique selectivity to target molecules. Recently, researchers have made great progress in fabricating novel plasmon-free SERS substrates and exploring new enhancement strategies to improve their sensitivity. This review summarizes the recent developments of plasmon-free SERS substrates and specially focuses on the enhancement mechanisms and the enhancement strategies. Moreover, the promising applications, current challenges, and future research opportunities in plasmon-free SERS substrates are discussed. For more details, please refer to the article entitled “The origin of ultrasensitive SERS sensing beyond plasmonics” by Leilei Lan, et al., Front. Phys. 16(4), 43300 (2021). [Photo credit: Teng Qiu at Southeast University.]
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Jun. 2021, Volume 16 Issue 3

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Heterojunction is featured with an interface between two different components. Due to their unequal electronic structures, like Fermi energy, band gap, and band edges, charge transfer and interfacial charge separations are often resulted. This offers large space for rational design of advanced heterojunctions towards various applications, such as solar cells, catalysts and transistors. The special topic on Heterojunction and Its Applications (Ed. Chenghua Sun) collects some articles on this topic, covering the applications in photocatalysis, solar cells, hydrogen production, hydrogen storage, etc. [Photo credits: Lin Ju at Anyang Normal University.]
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Apr. 2021, Volume 16 Issue 2

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Relative high signal uncertainty severely hindered the improvement the quantification performance for laser-induced breakdown spectroscopy (LIBS). However, due to lack of enough diagnostic technology and violent evolution nature of the laser-induced inhomogeneous plasma, the mechanism of uncertainty generation of LIBS always remains unclear. Based on previous understanding that morphological fluctuation of plasma is the main source of LIBS signal uncertainty, here the authors propose the mechanism leading to plasma morphology fluctuation: the frontier part of plasma was pushed back by the counter-balance force in shockwave generation and the bounced back part crash with the lower part, exaggerating tiny disturb into large fluctuation. For more details, please refer to the article entitled “Mechanism of signal uncertainty generation for laser-induced breakdown spectroscopy” by Yang-Ting Fu, et al., Front. Phys. 16(2), 22502 (2021). [Photo credits: Zhe Wang at Tsinghua University.]
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Feb. 2021, Volume 16 Issue 1

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Zeeman deceleration is widely used for cooling of atoms and molecules. However, further cooling of molecules to ultracold temperature following Zeeman deceleration is always hindered by the low density of the decelerated molecular packet provided by the traditional Zeeman decelerator. Here the authors propose an experimentally viable scheme, which employs a moving magnetic trap to bring a large density of lithium atom and methyl radical into standstill, enabling cold collision studies of the mixed atomic and molecular species inside a magnetic trap, allowing for the investigation of sympathetic cooling of methyl radical by laser-coolable lithium atoms. For more details, please refer to the article entitled “Simultaneous Zeeman deceleration of polyatomic free radical with lithium atoms” by Yang Liu and Le Luo, Front. Phys. 16(1), 12504 (2021). [Photo credits: Yang Liu at Sen Yet-Sen University.]
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Dec. 2020, Volume 15 Issue 6

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The Greenberger–Horne–Zeilinger (GHZ) serves as a fundamental resource for quantum applications. Always O(n) nonlinear sources are set for the generation of an n-qubit GHZ state, with strict coherence conditions. Here the authors propose an ultra-integrated scalable scheme to increase the size of GHZ states without increasing the number of optical elements, based on the frequency combs and graph theory. Frequency combs from just three on-chip micro-ring resonators can efficiently construct arbitrary GHZ states. Moreover, frequency-labeled photons of the final state lie in a single path that have significant potentials for long-distance quantum tasks. For more details, please refer to the article entitled “On-chip multiphoton Greenberger–Horne–Zeilinger state based on integrated frequency combs” by Pingyu Zhu, et al., Front. Phys. 15(6), 61501 (2020). [Photo credits: Ping Xu at National University of Defense Technology.]

Oct. 2020, Volume 15 Issue 5

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Asymmetric transmission, enabling one-way wave propagation with highly different transmission efficiency, has been widely explored in metasurface-based systems. In most cases, these metasurfaces are designed with multiple meta-atoms to improve the resolutions of local phase profiles, which can also pose challenges for design complexities, sample fabrication and intrinsic absorption. Here the authors proposed and studied a dual-layer binary metagrating, in which only a common coiling-up space structure is designed to achieve acoustic asymmetric transmission. Owing to the artful design of binary structures, asymmetric beam splitting is demonstrated in the proposed dual-layer metagrating with appropriate space (air gap), as schematically displayed in the cover. When the space is closed, symmetric beam splitting can be obtained. The working principle is explained from the gap-induced diffraction channel transition, and it could be extended to other physical systems, such as electromagnetic waves, elastic waves and water waves, leading to more functional devices with simplified design. For more details, please refer to the article entitled “Controllably asymmetric beam splitting via gap-induced diffraction channel transition in dual-layer binary metagratings” by Yang-Yang Fu, et al., Front. Phys. 15(5), 52502 (2020). [Photo credits: Yang-Yang Fu at Nanjing University of Aeronautics and Astronautics.]

Aug. 2020, Volume 15 Issue 4

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Quantum computers are promising in dealing with hard problems. However, due to the decoherence effect, quantum gates are very fragile. Thus, realizing robust quantum gates is the ultimate goal of quantum manipulation. Notably, geometric phases are intrinsic noise-resilient, and thus fast geometric quantum gates are ideal building blocks for quantum computers. It is predicted that modern superconducting quantum chips can readily support fast geometric quantum computation. It is also shown that the optimal control technique can be incorporated into the proposal to further improve the gate robustness. Therefore, this work provides a promising step towards fault-tolerant solid-state quantum computation. For more details, please refer to the article entitled “Nonadiabatic geometric quantum computation with optimal control on superconducting circuits” by Jing Xu, et al., Front. Phys. 15(4), 41503 (2020).
[Photo credits: Fei-Yan Lin at South China Normal University.]

Jun. 2020, Volume 15 Issue 3

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Single atom catalysts (SACs) show their unique advantages in various catalytic reactions. Graphitic carbon nitride (g-C3N4) is not only an excellent supporting material for single atom, but also an excellent photocatalyst. g-C3N4 based single-atom photocatalysts, due to their high catalysis activity, selectivity, and stability, become a hotspot in the field of photocatalysis. The preparation strategies, characterizations, and photocatalytic mechanism need further exploration and development. In the review entitled “Graphitic carbon nitride based single-atom photocatalysts”, the authors summarize the recent progress in g-C3N4-based single-atom photocatalysts, the significant roles of single atoms and catalysis mechanism. Moreover, the challenges and perspectives for exploring high-efficient g-C3N4-based single-atom photocatalysts are presented. For more details,please refer to the article entitled "Graphitic carbon nitride based single-atom photocatalysts" by Junwei Fu, et al., Front. Phys. 15(3), 33201 (2020).

Apr. 2020, Volume 15 Issue 2

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The phase behavior of water is a topic of perpetual interest due to its remarkable anomalous properties and importance to biology, material science, geoscience, nanoscience, etc. It is predicted confined water at interface can exist in large amounts of crystalline or amorphous states. The confined water layers at a hydrophobic/hydrophobic interface were investigated by advanced atomic force microscopy (AFM). The intercalated water molecules present themselves as two phases, low-density liquid (LDL, solid-like) and high-density liquid (HDL, liquid-like), according to their specific mechanical properties detected with two multifrequency-atomic force microscopy (MF-AFM) modes. For more details, please refer to the article entitled “Real-space visualization of intercalated water phases at the hydrophobic graphene interface with atomic force microscopy” by Zhi-Yue Zheng, et al., Front. Phys. 15(2), 23601 (2020). [Photo credits: Rui Xu at Renmin University of China.]

Feb. 2020, Volume 15 Issue 1

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Perovskite oxides thin films exhibit diverse properties and are of prime importance to multi-functional integrated electronic devices, where a burst of strategies are proposed to manipulate their intimate couplings and uncover new functionalities. A non-destructive low-energy hydrogen plasma implantation experiment has been performed in strongly correlated SrCrO3 thin films for proton incorporation here. Protons accumulate largely at the interfacial region near the substrate and induce the band-filling controlled Mott transition from metallic SrCrO3 to insulating HSrCrO2 phases. Our experimental results open a new strategy to manipulate the interplay between different collective phenomena in strongly correlated systems and may provide the opportunities to design novel proton-based multifunctional materials. For more details, please refer to the article entitled “Modulation of the electronic states of perovskite SrCrO3 thin films through protonation via low-energy hydrogen plasma implantation approaches” by Meng Wu, et al., Front. Phys. 15(1), 13601 (2020). [Photo credits: Meng Wu & Hui-Qiong Wang at Xiamen University.]

Dec. 2019, Volume 14 Issue 6

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On August 17, 2017, humankind for the first time detected a gravitational wave source due to a binary neutron star merger. It was followed by a short duration gamma-ray burst 1.7 seconds afterwards. Bing Zhang discussed the astrophysical origin of this 1.7-second delay, which holds the key to unveil the mystery of the formation, propagation, and emission of the relativistic jet launched from such a system. For more details, please refer to the article “The delay time of gravitational wave - gamma-ray burst associations” by Bing Zhang, Front. Phys. 14(6), 64402 (2019). [Photo credits: National Science Foundation/LIGO/Sonoma State University/A. Simonnet.]

Oct. 2019, Volume 14 Issue 5

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Artificial and periodically modulated optical structure realizes the possibility for tailoring the diffraction and dispersion properties of light. Electromagnetically induced grating (EIG) is constructed by replacing the traveling wave field of electromagnetically induced transparency with a standing-wave field, the atomic coherence of medium is modulated periodically in the space and the weak probe field can be diffracted into high order patterns. Compared with the traditional grating, the EIG configuration can be easily constructed and flexibly tuned, thus the properties of light propagation can be directly controlled. Here, a controllable electromagnetically induced grating is experimentally realized in a coherent rubidium ensemble. Such a controllable periodic structure can provide a powerful tool for studying the control of light dynamics, pave the way for realizing new optical device. For more details, please refer to the article “Controllable electromagnetically induced grating in a cascade-type atomic system” by Jin-Peng Yuan, Chao-Hua Wu, Yi-Hong Li, Li-Rong Wang, Yun Zhang, Lian-Tuan Xiao, and Suo-Tang Jia, Front. Phys. 14(5), 52603 (2019). [Photo credits: Jin-Peng Yuan & Li-Rong Wang]

Aug. 2019, Volume 14 Issue 4

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As an efficient initiating mechanism of turbulence and mixing of fluids, the Kelvin-Helmholtz instability (KHI) plays crucial roles in both scientific research and engineering applications, such as high-energy-density physics, geophysics and astrophysics, inertial confinement fusion, and combustion. Although it has been investigated extensively over the past decades, the kinetic modeling, the thermodynamic nonequilibrium (TNE) effects, and the understanding of complex fields of KHI, are still open problems. Recently, an easily implementable kinetic discrete Boltzmann model (DBM) is designed to quantitatively investigate the often-overlooked TNE effects of KHI, via tracking the evolution of non-equilibrium measures and morphological functionals. The core idea that the authors convey is, DBM also provides a set of handy and effective tools to describe, measure, and analyze the most relevant TNE behaviors, besides presenting the same results of corresponding hydrodynamic equations. For more details, please refer to the article “Nonequilibrium and morphological characterizations of Kelvin–Helmholtz instability in compressible flows ” by Yan-Biao Gan, Ai-Guo Xu, Guang-Cai Zhang, Chuan-Dong Lin, Hui-Lin Lai, and Zhi-Peng Liu, Front. Phys. 14(4), 43602 (2019). [Photo credits: Yan-Biao Gan, Ai-Guo Xu, and Ding Yuan at Harbin Institute of Technology, Shenzhen. Sun image: Courtesy of NASA/SDO and the AIA science teams.]

Jun. 2019, Volume 14 Issue 3

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Borophene, the lightest two-dimensional material, shows highly anisotropic atomic structures, electronic properties, thermal conductivity, optical, and surface ion transport properties. Both the free-standing and metal substrate supported borophenes have high structural diversity. Furthermore, the distinction between borophene crystal and boron vacancy defect is blurry, due to the ultralow boron vacancy defect formation energy. This phenomenon is completely different from other two-dimensional materials. Due to the small atomic mass of boron, borophene has very high Li/Na/K/Mg/Ca/Al storage capacity as the anode materials for alkali metal ion batteries. Ultra-fast ion migration is observed on the 2-Pmmn phase of borophene due to the unique corrugated structure. Borophene shows vast application prospect in alkali metal ion batteries, Li-S batteries, hydrogen storage, and catalytic reaction. For more details, please refer to the article “Review of borophene and its potential applications” by Zhi-Qiang Wang, et al., Front. Phys. 14(3), 33403. [Photo credits: Zhi-Qiang Wang]

Apr. 2019, Volume 14 Issue 2

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The optomechanical system (OMS) can be used to couple the mechanical, optical, and electric degree of freedom. Although single-cavity OMS is much interesting, the integrated optomechanical systems provide a platform for on-chip optical architectures with added versatility, which may be useful in optical information processing and quantum communication. Therefore, we need some OptoMechanics Technology Computer-Aided Design (OMTCAD) toolbox, which is the main function of OMPY (OptoMechanics by PYthon). Combined with OMPY and typical first principles codes, such as VASP or RESCU, the absorption properties of some complex OMSs utilizing novel materials can be investigated, which should be of much important for quantum computation and quantum information based on OMSs in future. For more details, please refer to the article “Optomechanical properties of a degenerate nonperiodic cavity chain” by Miao-Miao Zhao, Zhuo Qian, Bang-Pin Hou &Yong-Hong Zhao, Front. Phys. 14(2), 22601. [Photo credits: Yong-Hong Zhao]

Feb. 2019, Volume 14 Issue 1

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Graphene is an ideal 2D material system bridging electronic and photonic devices. It also breaks the fundamental speed and size limits by electronics and photonics, respectively. Graphene offers multiple functions of signal transmission, emission, modulation, and detection in a broad band, high speed, compact size, and low loss. Here, the authors have a brief view of graphene based functional devices at microwave, terahertz, and optical frequencies. Their fundamental physics and computational models were discussed as well. For more details, please refer to the article “Graphene based functional devices: A short review” by Rong Wang, et al., Front. Phys. 14(1), 13603 (2019). [Photo credits: Rong Wang & Wei E. I. Sha]

Dec. 2018, Volume 13 Issue 6

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In honor of professor Akito Arima's 88 year-old birthday, an International Symposium on Simplicity, Symmetry, and Beauty of Atomic Nuclei will be held in Shanghai from September 25–28, 2018. Taking advantage of this opportunity, the Editorial Office of the Journal Frontiers of Physics, together with main organizers of this Symposium, Jie Meng, Takaharu Otsuka, and Yu-Min Zhao, invited 13 scientists from China, Europe, Japan, and USA to contribute papers for the present Volume. The Editorial Board of Journal Frontiers of Physics and the organizers of this Symposium would like to present this Volume as our birthday gift to Akito.

Oct. 2018, Volume 13 Issue 5

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The authors present a series of invisibility concentrators with simplified material parameters beyond transformation optics. One of them can achieve the perfect invisible effect at frequencies of Fabry–Pérot resonances, while others have very small scattering. The required materials are feasible in practice. Analytical calculations and numerical simulations confirm the functionalities of these devices. For more details, please refer to the article “Perfect invisibility concentrator with simplified material parameters” by M. Zhou, L. Xu, L. Zhang, J. Wu, Y. Li, and H. Chen, Front. Phys. 13(5), 134101 (2018), and “Blueprints for real-world invisibility” by Philip Ball, Front. Phys. 13 (5), 134102 (2018). [Photo Credits: Lin Xu & Huanyang Chen, Xiamen University]

Aug. 2018, Volume 13 Issue 4

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Ultrathin GeAsSe and SnSbTe sheets own desirable electronic and optical properties. Monolayer GeAsSe and SnSbTe sheets can be easily exfoliated from the bulk crystals due to the weak interlayer binding energies. These sheets are energetically favorable and show excellent dynamical and thermal stability. Importantly, monolayer GeAsSe and SnSbTe possess moderate direct band gaps and superior hole mobility up to 20 000 cm2.V-1.s-1, and meanwhile exhibit notable absorption in the visible region. The appropriate band edge positions ensure that layered GeAsSe and SnSbTe materials are promising photocatalysts for water splitting. For more details, please refer to the article “Monolayered semiconducting GeAsSe and SnSbTe with ultrahigh hole mobility” by Yu Guo, Nan Gao, Yizhen Bai, Jijun Zhao, and Xiao Cheng Zeng. [Photo credits: Jijun Zhao, Dalian University of Technology]

Jun. 2018, Volume 13 Issue 3

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Since the discovery of graphene in 2004, many other 2D materials with unique properties and promising applications have been developed, which directly resulted in this special topic on Two-Dimensional Nanomaterials (Eds. Changzheng Wu & Xiaojun Wu).. Besides experimental investigations, computational/theoretical studies also played an important role in 2D materials research. In the cover are the newly predicted aluminum monoxide (AlO) nanosheets and several important and representative 2D materials. We believe that the joint efforts in experimental and theoretical communities will lead to more outstanding 2D materials, and the energetic puppy (mascot of 2018) will be running even faster in a more prosperous materials world. [Photo credits: Zhongfang Chen, University of Puerto Rico, San Juan PR 00923, USA]

Apr. 2018, Volume 13 Issue 2

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The search for and study of exotic quantum states in novel low-dimensional quantum materials have triggered extensive research in recent years. In our recent paper, we proposed that the realization of ferromagnetism in the newly discovered two-dimensional quantum material C3N under charge carrier injection, such as electric field gating or hydrogen doping. These theoretical findings not only demonstrate that the emergence of magnetism may stem from the itinerant electron mechanism rather than the effects of local magnetic impurities, but also open a new avenue to designing field-effect transistor devices for possible realization of an insulator-ferromagnetism transition by tuning an external electric field. For more details, please refer to the article “Exotic ferromagnetism in the two-dimensional quantum material C3N” by Wen-Cheng Huang, Wei Li, and Xiaosong Liu, Front. Phys. 13(2), 137104 (2018). [Photo credits: Wei Li & Xiaosong Liu]

Feb. 2018, Volume 13 Issue 1

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The special topic edited by F. Mallamace, R. Car & Limei Xu reports eleven contributions jointly written by lecturers and students attending the 2016 “Ettore Majorana” Erice International School on Water and Water Systems. These papers focus on the study of water and its solutions from a molecular perspective, water being a complex system at the intersection of Physics, Chemistry, Biology and Materials Science. On these bases it requires sophisticated experimental techniques and advanced statistical physics methods. The proposed special topic is organized to provide a broad field overview, including the recent ideas, as far as critical discussions, of the challenging problems proposed by the water physics that are currently attracting the researchers’ attention. [Photoed in Jiuzhaigou National Park. Photo credits: Zhong-Jie Deng & Hui-Jing Huang]

Dec. 2017, Volume 12 Issue 6

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As a universal concept in nonlinear science, synchronization has been broadly interested and extensively studied over the past decades. Whereas numerical and theoretical studies have unveiled abundant synchronization phenomena in coupled oscillators, few of them have been replicated in experiments, due to the sensitivity the synchronization dynamics to the noise perturbations and parameter mismatches. In the work by Jing Zhang, et al., the authors designed a new experimental setup to explore the synchronization patterns in asymmetrically coupled metronomes. By varying the initial conditions and coupling parameter, different synchronous patterns are generated and identified based on the audio signals. In particular, a new type of synchronous pattern, namely the in-phase delay synchronization state (IPDS), is reported for the first time, which is rooted in the breaking of the system symmetry. By a theoretical model, the authors also conducted a detailed analysis on the basin and transition properties of the patterns, which, together with the experimental findings, give a complete picture on the synchronization behaviors in coupled metronomes. For more details, please refer to the article “Synchronization of coupled metronomes on two layers” by Jing Zhang, Yi-Zhen Yu, and Xin-Gang Wang, Front. Phys. 12(6), 120508 (2017). [Photo credits: Xin-Gang Wang, Shaanxi Normal University]

Oct. 2017, Volume 12 Issue 5

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A Tuneable near to mid-infrared pump, terahertz (THz) probe spectroscopy in reflection geometry has been constructed in Professor Nan-Lin Wang’s laboratory, International Center for Quantum Materials, Peking University. The setup is capable of exciting the bulk materials with pump pulses ranging from 1.2 μm to 15 μm (shown in color yellow), and detecting the transient photoinduced subtle changes of reflected electric field at the frequency of 0.25-2.5 THz (shown in color red) at different temperatures. A two-output optical parametric amplifier and GaSe crystal are used for generating pump pulses, and ZnTe crystals are used for THz generation and electro-optic sampling (shown in color green). This kind of spectroscopy has been proven as a powerful tool for light control of different orders in strongly correlated materials. For more details, please refer to the article “Tunable near- to mid-infrared pump terahertz probe spectroscopy in reflection geometry” by S. J. Zhang, et al., Front. Phys. 12(5), 127802 (2017). [Photo credits: S. J. Zhang, Peking University]

Aug. 2017, Volume 12 Issue 4

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Graphene based all-carbon nano-junction is structurally stable and mechanically flexible. It has been extensively recognized as a good candidate of nanoscale electronic and spin-electronic device. Jian-Wei Li et al. investigated the electronic and thermal electronic transport properties of kinds of graphene based all-carbon nano-junctions using first principles method. Huge TMR roughly equal to 105 was found for these structures. In addition, thermally induced spin up current and spin down current flow along opposite direction in these systems, which indicates a thermally induced pure spin currents can be obtained in these structures. For more details, please refer to the article “Spin-resolved quantum transport in graphene-based nanojunctions” by Jian-Wei Li, et al., Front. Phys. 12(4), 126501 (2017). [Photo credits: Jian-Wei Li & Bin Wang, Shenzhen University, China]

Jun. 2017, Volume 12 Issue 3

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The physics of huge magnetoresistance in WTe2 requires full analysis of multiple elecctronic components. Xing-Chen Pan et al. combined magnetotransport and angle-resolved photoemission spectroscopy to study the electronic structures of WTe2. By analyzing the magnetoresistance and Hall data with mobility spectrum method, the authors demonstrated perfect electron-hole balance in pristine WTe2. Furthermore, transport experiments under ultra-high magnetic field observed a transition from parabolic magnetoresistance to linear magnetoresistance. This material is recently paid more attention as a new type-II topological Weyl semimetal candidate. For more details, please refer to the article “Carrier balance and linear magnetoresistance in type-II Weyl semimetal WTe2” by Xing-Chen Pan, et al., Front. Phys. 12(3), 127203 (2017). [Photo credits: Xing-Chen Pan & Fengqi Song, Nanjing University, China]

Apr. 2017, Volume 12 Issue 2

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In this article a general review of the status of dark matter is given, including the observational evidence, possible candidates, various searches of dark matter, etc. To assist readers from the particle physics community, several topics in cosmology which are relevant to the discussion of dark matter are also given in varying details. For instance, the freezing-out of massive particles is discussed, and some of the key expressions are derived, in detail. Some of the useful formulae and constants are given in three appendices. This article is intended to be self-contained. For more details, please refer to the article “A survey of dark matter and related topics in cosmology” by Bing-Lin Young, Front. Phys. 12(2), 121201 (2017). [Photo: The Hubble image of the CL0024+17 (ZwCL0024+1652) galaxy cluster. Credit: NASA, ESA, M. J. Jee and H. Ford, Johns Hopkins University.]

Dec. 2016, Volume 11 Issue 6

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Ultra-strong shock waves are of fundamental interest to astrophysics,inertial confinement fusion and compressible turbulences. A number of physicalor chemical transitions, such as phase transitions, reactions, dissociation andionization, are intrigued in a small region at the vicinity of the shock front,which has a thickness of several mean free paths. Non-equilibrium moleculardynamics simulations of ultra-strong shock waves in dense helium are carriedout as an example to illustrate the dynamics and microscopic structures of theshock front. For more details, please refer to the article “Molecular dynamicssimulations of microscopic structure of ultra strong shock waves in densehelium” by Hao Liu, et al., Front. Phys. 11(6), 115206 (2016). [Photo credits:Hao Liu and Wei Kang, Center for Applied Physics and Technology, PekingUniversity] ho

Oct. 2016, Volume 11 Issue 5

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Simulations with more fundamental physics did not help

The success of tokamak fusion reactors like ITER depends on the burning plasma having a very hot edge with good confinement. Current tokamaks can easily get into this high performance operation (H-mode). The hot edge lifts the core to the high temperatures. However if not enough heating power is supplied to the tokamak plasma, it falls into low performance operation (L-mode) with a high-level of turbulent transport and a cold edge. A long-standing problem for theory based simulations:  What quantitatively accounts for this high-level of turbulent transport in the L-mode cold edge?
Standard “gyrokinetic” simulations and models average over the fast “gyro-orbit” motion. They account very well for the low turbulence transport in the hot tokamak core. However they significantly underpredict the observed cold L-mode edge transport.  Is some process or mechanism being left out of the standard gyrokinetic simulations?  Or is there a breakdown in the standard gyrokinetic approximation of averaging over the fast “gyro-orbit” motion when the turbulence level is high?
We started to do computer simulations with more fundamental and exact physics to definitively answer the last questions. The new and more expensive “cyclokinetic” simulations follow the fast ion gyro-orbit motion without any averaging approximation.  As required, the less fundamental gyrokinetic simulations recover the more fundamental cyclokinetic simulations when the gyro-orbit motion is fast enough compared to the slow turbulent motion. This is very much like Newton’s theory of gravity recovers Einstein’s when the gravitational forces are weak enough. However when the turbulence level is very high, as in the tokamak cold edge, and the gyro-orbit is not fast enough, the cyclokinetic transport is found to be lower than gyrokinetic transport. The mystery remains:  what is being left out of standard gyrokinetic simulations that would account for the missing L-mode near edge transport?
For more detailed information, please refer to the article “Cyclokinetic models and simulations for high-frequency turbulence in fusion plasmas” by Zhao Deng, R. E. Waltz, and Xiaogang Wang, Front. Phys. 11(5), 115203 (2016). [Photo credits: Zhao Deng]

Aug. 2016, Volume 11 Issue 4

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The concept of open quantum system is of fundamental importance to many fields of modern physics. In particular, the energy dissipation and particle exchange between the system of primary interest and surrounding environment are the keys to many fascinating quantum phenomena. In the special topic “Progress in Open Quantum Systems: Fundamentals and Applications”, several state-of-the-art quantum dissipation theory methods are introduced. The usefulness and practicality of these methods are highlighted through a wide range of applications including energy transfer, electron and heat transport, and exciton diffusion. [Photo credits: Xiao Zheng, University of Science and Technology of China; Yun-An Yan, Guizhou Education University]

Jun. 2016, Volume 11 Issue 3

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In recent years, spin-orbit coupled ultracold atomic gases have become a major focus of research. By dressing atoms with suitably tailored laser light, motional and internal degrees of freedom can be coupled, resulting in the generation of artificial gauge fields, spin-orbit coupling, and the breaking of Galilean symmetry. Interesting dispersion relations can be engineered and studied in detail, such as double-well potentials in momentum space featuring regions of negative mass and roton-like minima. The systems can further be combined with optical lattices, providing a vast ground for the investigation of intriguing quantum dynamics.
In this review, we highlight some of the progress made in this field.  We examine the experimental accessibility of all relevant spin-orbit-coupling parameters, and further discuss the fundamental properties and applications of spin-orbit-coupled Bose-Einstein condensates (BECs) over a wide range of physical situations.  Both experimental as well as theoretical progress is highlighted. For more detailed information, please refer to the article “Properties of spin–orbit-coupled Bose–Einstein condensates” by Yongping Zhang, Maren Elizabeth Mossman, Thomas Busch, Peter Engels, and Chuanwei Zhang, Front. Phys. 11(3), 118103 (2016). [Photo credits: Mossman and Engels, WSU; Background image courtesy of Bob Hubner, WSU]

Apr. 2016, Volume 11 Issue 2

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Noble metallic nanostructures exhibit special optical properties resulting from the excitation of surface plasmons. Among the various metallic nanostructures, nanorods have attracted particular attention because of their shape-dependent and highly tunable plasmonic properties. Recently, two novel quasi-one-dimensional silver nanostructures, nanorice and nanocarrot, with shapes deviating from cylindrical nanorod were synthesized. In this issue a review article provides an overview of recent progress in the syntheses and the studies of plasmonic properties of these two novel nanostructures. For more detailed information, please refer to the article “Deviating from the nanorod shape: Shape-dependent plasmonic properties of silver nanorice and nanocarrot structures” by Hong-Yan Liang, Hong Wei, and Hong-Xing Xu, Front. Phys. 11(2), 117301 (2016). [Photo credits: Zhi-Li Jia & Hong Wei, Institute of Physics, Chinese Academy of Sciences]

Feb. 2016, Volume 11 Issue 1

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The special topic on Potential Physics at a Super τ-Charm Factory provides detailed discussions on important topics in τ-charm physics that will be explored in the future at a possible super-tau-charm factory, which will operate in the 2 GeV to 7.0 GeV energy range. Both theoretical and experimental issues are  covered, including extensive reviews of recent theoretical and experimental developments. Among the subjects covered are: probes of hadronic states and structure of hadrons, charmed meson and charmed baryon decays, tau physics, and possible new physics search at low energy. This renaissance has been driven in part by the experimental reports of neutral D mixing and the discovery of charmonium-like XYZ states at both B factories and BESIII, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related X(1835) meson state at BESII. [Photo credits: K.A. Olive, et al. (Particle Data Group), Chin. Phys. C, 38, 090001 (2014) & Hai-Bo Li, Institute of High Energy Physics, Chinese Academy of Sciences]

Dec. 2015, Volume 10 Issue 6

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The spin-orbit coupling is a well-known mechanism from astronomical systems to finite nuclei, and the Spin Hall Effect is a general transport phenomenon for particles with spin. The nucleon spin dynamics in intermediate-energy heavy-ion collisions has been investigated to extract detailed properties of nuclear spin-orbit interaction and nuclear tensor force, which are important components of nuclear force and crucial in understanding the shell structure of nuclei and a lot of interesting physics. The studies on this topic will hopefully stimulate more experimental efforts on measuring spin-dependent observables proposed by transport model calculations. The cover picture shows the density evolution in heavy-ion collisions: density (first row), spin polarization (second row), density gradient (third row), and current gradient (fourth row). For more detailed information, please refer to the article “Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions” by Jun Xu, et al., Front. Phys. 10(6), 102501 (2015). [Photo credits: Jun Xu, Shanghai Institute of Applied Physics, Chinese Academy of Sciences]

Oct. 2015, Volume 10 Issue 5

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As an important topic in condensed matter physics, strongly correlated system has attracted researchers close attentions for couple of decades. Especially, the investigation on the quantum phase transitions in strongly correlated systems is one of the most important topics for the discovery of new phases in condensed matter physics. We adopt the combination of the dynamical mean field theory and the continuous-time quantum Monte Carlo method to investigate the quantum phase transition in two-dimensional strongly correlated systems. Many splendid quantum phases that have been discovered in our work are presented in our present paper. For more detailed information, please refer to the article "Quantum phase transitions in two-dimensional strongly correlated fermion systems" by An Bao et al., Front. Phys. 10(5), 106401 (2015) [Photo credits: An Bao, Tsinghua University & Inner Mongolia University of Science & Technology]

Aug. 2015, Volume 10 Issue 4

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Gravity is the most mysterious force. By assuming a thermodynamic origin for gravity, we can calculate the vacuum temperature field that is created by the presence of matter. The attractive gravitational force between classical objects results naturally as macroscopic systems progress from non-equilibrium to equilibrium states. In particular, we predict repulsive gravitational force for a quantum wave packet, which may be relevant to the dark energy. For more details, please refer to the article “Repulsive gravitational effect of a quantum wave packet and experimental scheme with superfluid helium” by Hongwei Xiong, Front. Phys. 10, 100401 (2015). [Photo credits: Jiaming Fang, Zhejiang University of Technology]

Jun. 2015, Volume 10 Issue 3

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MXene is a new family of 2D transition metal carbides, nitrides and carbonitrides, exfoliated from layered MAX phases, where M, A, and X represent early d transition metals, main-group sp elements, and C or/and N, respectively. MXene is generally prepared by selectively removing A layers from the corresponding MAX phases with etchant solutions. The distinctive properties and promising applications of MXene sheets make them strong candidates for alternatives of graphene, which would attract more people step into this emerging area and find more surprise. For more details, please refer to the article “Recent advances in MXene: Preparation, properties and applications” by Jin-Cheng Lei, Xu Zhang, and Zhen Zhou, Front. Phys. 10, 107303 (2015). [Photo credits: Zhen Zhou, Nankai University]

Apr. 2015, Volume 10 Issue 2

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Bismuth-based skutterudite is a new topological insulator, in which the bands involved in the topological band-inversion process are d- and p-orbitals, which is distinctive with usual topological insulators, for instance in Bi2Se3 and BiTeI the bands involved in the topological band-inversion process are only p-orbitals. The present of large d-electronic states (primarily the eg states) makes the electronic interaction in this topological insulator much stronger than that in other conventional topological insulators. For more details, please refer to the article “Tunable topological quantum states in three- and two-dimensional materials” by Ming Yang, Xiao-Long Zhang, and Wu-Ming Liu, Front. Phys. 10, 108102 (2015). [Photo credits: Ming Yang, Institute of Physics, Chinese Academy of Sciences]

Feb. 2015, Volume 10 Issue 1

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The quasiparticle scattering interference phenomenon characterized by the peaks in the local density of states is studied within the renormalized mean field theory based on the Hubbard model. It is shown that the quasiparticle scattering interference pattern in the presence of single point-like impurity is strongly energy dependent due to the dominant d-wave symmetry gap. The present theoretical results mainly capture qualitative features of the quasiparticle scattering interference phenomenon in cuprate superconductors, showing that the quasiparticle scattering interference phenomenon is very closely related to the presence of impurity. More details could be found in the article “Quasiparticle scattering interference in the renormalized Hubbard model” by Shu-Hua Wang, Huai-Song Zhao, and Feng Yuan, Front. Phys. 10, 107401 (2015). [Photo credits: Feng Yuan, College of Physics, Qingdao University, China]

Dec. 2014, Volume 9 Issue 6

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A long-standing debate in transport modeling of nano junctions has eventually come to the end. The cover illustrates a recently confirmed atomic model of the famous Au-1,4-Benzenedithiol (BDT)-Au molecular junction where the H atom of the thiol group remains attached after the molecule-lead contact formed. A Non-equilibrium Green’s Function combined with density functional theory (NEGF-DFT) calculation well reproduces the experimental values with this model, demonstrating the reliability of the theory again and standing out the importance of interfacial geometry in transport modeling. For more details, please refer to article “Correlation of interfacial bonding mechanism and equilibrium conductance of molecular junctions” by Zhan-Yu Ning, Jing-Si Qiao, Wei Ji, and Hong Guo, pp 780-788. [Photo credits: Jing-Si Qiao and Wei Ji, Renmin University of China]

Oct. 2014, Volume 9 Issue 5

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A well-controlled single atom provides an idea quantum qubit and quantum node for quantum information processing. The cover illustrates the setup of trapping single Cesium atoms in a micro-size 1064 nm red-detuned optical tweezer and the corresponding state manipulation as a qubit in Shanxi University. In the experiment the qubit is encoded in Cesium “clock states” and the Rabi flopping is realized via a two-photon Raman process. For more details, please refer to the article “Quantum state manipulation of single-Cesium-atom qubit in a micro-optical trap” by Zhi-Hui Wang, Gang Li, Ya-Li Tian, and Tian-Cai Zhang, pp 539-570. [Photo credits: Tian-Cai Zhang, Shanxi University]

Aug. 2014, Volume 9 Issue 4

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A Peltier nano cooling device is proposed based on the self-doping properties of curved graphene nanoribbons, without need of gating or chemical doping. Its cooling power can be reversibly tuned by applying uniaxial pressure to the device. Upon application of a current through the GNR, heat is pumped from the junctions near the bottom of the structure to the junctions near the top. With a cooling power on the order of kW/cm2, on par with the best cooling devices based on using standard superlattice structures, the proposed cooling device helps pave the way toward designing graphene electronics which use 3D geometry rather than patterning and gating to control devices. For more details, please refer to the article “Tunable nano Peltier cooling device from geometric effects using a single graphene nanoribbon” by Wan-Ju Li, Dao-Xin Yao, and E. W. Carlson, pp 472–476. [Photo credits: Dao-Xin Yao, Sun Yat-Sen University; Wan-Ju Li and E. W. Carlson, Purdue University]

Jun. 2014, Volume 9 Issue 3

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Silicon is an attractive material for anodes in next-generation Li batteries, because it possesses ten times the theoretical capacity of the state-of-the-art carbonaceous counterpart. The cover illustrates the five generations of nanostructured Si anodes developed in Yi Cui’s laboratory: nanowires, core-shell nanowires, hollow nanospheres, double-walled nanotubes, and yolk-shell nanoparticles. These nanoscale structure designs have increased the capacity, prolonged the cycle life, and enhanced the Coulombic efficiency, by preventing fracture of Si, and stabilizing its interface with electrolyte. For more details, please refer to the article “Nanomaterials for electrochemical energy storage” by Nian Liu, et al., pp 323–350. [Photo credits: Nian Liu, Stanford University]

Apr. 2014, Volume 9 Issue 2

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The amplitudes of different pairing gap components induced by J1, J2 with J2'=0 at electron doping =0.51.sNNN is the s wave resulting from NNN AFM coupling, sx2+y2 and dx2-y2 from NN AFM coupling.The pairing strength of sNNN is peaked around the doping level x = 0.5, which is consistent with experimental observation. sNNN is also very robust against spin-orbital coupling. Moreover, it can be distinguished from conventional s-wave pairing by measuring and comparing superconducting gaps of different Fermi surfaces. For more details, please refer to the article “Pairing symmetry in layered BiS2 compounds driven by electron–electron correlation” by Yi Liang et al., pp 194–199. [Photo credits: Yi Liang, Institute of Physics, Chinese Academy of Sciences]

Feb. 2014, Volume 9 Issue 1

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High vacuum tip enhanced Raman spectroscopy (HV-TERS), one of the most recent advances in nanoscale analysis, is a high sensitivity and high spatial resolution optical analytical technique. It was found that in-situ plasmon driven chemical reaction can be investigated by HV-TERS. The temperature of localized area can be obtained by the clearly Stokes and anti-Stokes HV-TERS peaks. The nonlinear effects in HV-TERS, including IR active mode, Fermi Resonance and Hyper Raman, are also found. Those findings hold great promise for ultrasensitive detection and significantly extend the physical and chemical analysis for single molecule. For more details, please refer to the article “High-vacuum tip enhanced Raman spectroscopy” by Zheng-Long Zhang et al., pp 17–24. [Photo credits: Meng-Tao Sun, Institute of Physics, Chinese Academy of Sciences]

Dec. 2013, Volume 8 Issue 6

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High-energy astrophysics is one of the most active branches in the contemporary astrophysics. It studies astrophysical objects that emit X-ray and γ-ray photons, such as accreting super-massive and stellar-size black holes, and various species of neutron stars. With the operations of many space-borne and ground-based observational facilities, high-energy astrophysics has enjoyed rapid development in the past decades. It is foreseen that the field will continue to advance rapidly in the coming decade, with possible ground-breaking discoveries of astrophysical sources in the high-energy neutrino and gravitational wave channels. This Special Issue of Frontiers of Physics is dedicated to a systematic survey of the field of high-energy astrophysics as it stands in 2013. The Cover images show an artist’s impression on some high-energy astrophysical phenomena: an accreting black hole (top inset, credit: http://www.nasa.gov), a neutron star (bottom inset, credit: http://www.dailygalaxy.com), and an energetic jet launched from a black hole or a neutron star (the main image, credit: http://en.wikipedia.org).

Oct. 2013, Volume 8 Issue 5

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The current issue is dedicated to celebrating Centennial Physics at Peking University. The cover picture in the background shows the Western Gate of Peking University, and four small images are taken from four papers in the current issue respectively. For more detailed information, please refer to the current issue. [Photo credits: Ya-Nan Song, School of Physics, Peking University]

Aug. 2013, Volume 8 Issue 4

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China Jinping underground Laboratory (CJPL) is the deepest underground laboratory in the world. It is located in the central portion of one of the transport tunnels of a giant hydrodynamic engineering project at the huge Jinping Mountain area of Sichuan province, southwest of China. The rock covering thickness of CJPL is about 2400 m where the cosmic muon flux is about is about 60 /(m2﹒year). This provides a very promising environment for DM search. Inside CJPL,China Dark matter EXperiment (CDEX) employs a point-contact germanium (PCGe) detector whose energy threshold is less than 500 eV to search for WIMPs of mass below 10 GeV. The detector mass of the first phase CEDX-1 is 1 kg and that of second phase CDEX-10 is 10 kg. The ultimate goal of the CDEX Collaboration is to set up a ton-scale mass Ge detectors based on the PCGe detector and LAr active shielding and cooling systems. For more detailed information, please refer to the article “Introduction to the CDEX experiment” by Ke-Jun Kang, et al. [CDEX Collaboration], pp 412–437. [Photo credits: Qing Wang, Tsinghua University, China]

Jun. 2013, Volume 8 Issue 3

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Dark solitons are localized defects in defocusing systems, and manifest themselves in repulsive Bose–Einstein condensate as a notch in the condensate density and a phase jump across the center. Ring dark solitons are candidates for observing long-time behaviors of 2D dark solitons, and their relevant explorations in the Bose–Einstein condensate began in 2003. It was shown that deeper ring dark solitons inclined to suffer snaking instabilities with a lifetime less than 20 milliseconds. In spinor Bose–Einstein condensates, however, ring dark solitons show more favorable stability comparing to that in scalar Bose–Einstein condensates. The deepest ring dark soliton can enjoy a lifetime of more than 40 milliseconds before decaying into four vortex and anti-vortex pairs. In addition, it can be found that the ring dark soliton in 87Rb condensate lives about 12 milliseconds longer than that in 23Na condensate, and this should be ascribed to the different spin-dependent interactions for these two kinds of condensates. The following dynamics of the vortex and anti-vortex pairs shows periodical oscillations, which is a common characteristic between 23Na and 87Rb condensates. For more detailed information, please refer to the article “Ground states, solitons and spin textures in spin-1 Bose–Einstein condensates” by Shu-Wei Song et al., pp 302–318. [Photo credits: Shu-Wei Song, Institute of Physics, CAS]

Apr. 2013, Volume 8 Issue 2

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Simulation of turbulent thermonuclear combustion in a Chandrasekhar-mass white dwarf (density shown in blue): The subsonic deflagration flame (temperature shown in red/yellow/white) was initiated at the center of the star in a large number of ignition sparks. Due to buoyancy instability, uprising plumes of burning material form and shear flows at their edges generate turbulence that accelerates the flame. The result is a disruption of the star in a thermonuclear supernova explosion. Further details on this model can be found in F. K. Röpke et al., Astrophys. J., 2007, 668: 1132-1139. [Photo credits: F. K. Röpke, Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Germany]

Feb. 2013, Volume 8 Issue 1

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The electric transport properties of low-dimensional systems have attracted tremendous interests due to their applications in microelectronics and novel nanodevices. Ultra-thin metal films on semiconductor substrates have been a playground for the study of electronic transport properties of low dimensional materials. However, the experimental measurements on the electric transport of such systems are still challenging since they only survive in UHV environments due to high chemical activity. Besides, surface-sensitive methods are required to avoid the substrate effects that could be coupled with the transport of the metal systems atop. We develop the micro-four-point-probe method integrated with standard low-temperature scanning tunneling microscope, which allows the vibration-proof environments and a broad temperature range (4-300 K) for transport measurements. Both the high-resolution characterizations of the surface structure and in situ measurements of the electric transport are realized in a broad temperature range. Taking the Ag/Si(111)-(√3×√3)R30o interface as the prototype of two-dimensional metals, the metal-insulator transition is studied in detail. The surface structure characterizations show hexagonal patterns at room temperature, which supports the model of inequivalent triangle structure. A metal-insulator transition occurs at ~115 K. The low temperature transport measurements clearly reveal the strong localization characteristics of the insulating phase. For more detailed information, please refer to the article “Strong localization across the metal-insulator transition at the Ag/Si(111)-(√3 ×√3)R30o interface” by Yuan-Yuan Tang and Jian-Dong Guo, pp 44–49. [Photo credits: Jian-Dong Guo, Institute of Physics, CAS]

Dec. 2012, Volume 7 Issue 6

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Laser-induced plasma and laser-induced breakdown spectroscopy (LIBS): fast spectroscopic images showing the expansion of a plasma induced by a ns-laser pulse on an aluminum target in an argon ambient gas (left) and surface elemental maps of a marble (middle Sr and right Mg) with LIBS. The front cover, up left: structure of a plasma induced from a polymer material (polyethylene) in the air ambient with C2 molecule in yellow, CN radical in red and N atom in bleu; Up right: typical LIBS setup; Bottom left: time evolution of the emission spectrum from an Al plasma; Bottom right: elemental maps (Al and Si) of a speleothem. For more detailed information, please refer to the special topic on LIBS in this issue. [Photo credits: Vincent Motto-Ros and Jin Yu, Université Lyon 1, France]

Oct. 2012, Volume 7 Issue 5

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Intensive investigations have been devoted to synthesizing and characterizing silver nanoparticles in recent years because of their rich optical properties raised by the surface plasmon resonances in the visible spectral range. Branched silver nanostructures have attracted people’s interests for their high surface to volume ratios and fancy shapes. These unique properties make them the promising candidates for both catalysts and substrates in surface-enhanced Raman scattering. In this issue the researchers from Institute of Physics, Chinese Academy of Sciences, report a facile method to prepare novel branched silver nanowire structures and demonstrate that these structures are efficient for the surface-enhanced Raman scattering application. For more detailed information, please refer to the article "A facile synthesis of branched silver nanowire structures and its applications in surface-enhanced Raman scattering" by Feng-Zi Cong et al., pp 521-526. [Photo credits: Xiao-Rui Tian, Institute of Physics, Chinese Academy of Sciences]

Aug. 2012, Volume 7 Issue 4

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Multiferroelectric tunnel junctions (MFTJs), consisting of two ferromagnetic (FM) electrodes separated by a nanoscale ferroelectric (FE) barrier, exploiting the capability to control FM and FE orders via external electric and magnetic fields simultaneously, have potential applications not only in multi-state data storage due to the coexsistence of tunneling magnetoresistance and tunneling electroresistance effects, but also in electric field controlled spintronics as a result of the interfacial magnetoelectric coupling effect. For a long time, the ferroelectricity has been thought to survive only in thicker samples, limiting its use in tunnel barrier. Until recently, with the development of several characterization techniques, e.g., piezoresponse force microscopy, the ferroelectricity of perovskite ferroelectric oxide was confirmed to persist down to the nanometer scale, which makes it possible to use perovskite ferroelectrics as tunnel barriers. More details could be found in the article "Multiferroic tunnel junctions" by Yue-Wei Yin et al., pp 380-385. [Photo credits: Dr. Yue-Wei Yin at Pennsylvania State University & University of Science and Technology of China]

Jun. 2012, Volume 7 Issue 3

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The recent research on semiconductor quantum dots follows naturally the evolution of semiconductor technology from transistors based on bulk silicon and lasers based on bulk gallium arsenide to field effect transistors and quantum-well lasers. Semiconductor quantum dots are a natural step forward in allowing for the control of material composition in three dimensions and at the nanoscale with atomic precision. Simultaneously, the recent isolation of a single, atomically thick carbon graphene layer opened a new field of nanoelectronics based on carbon. Since graphene is a semimetal and does not have a gap, size quantization opens an energy gap and turns graphene into a semiconductor. However, the gap in graphene quantum dots, unlike in semiconductor quantum dots, can be tuned from zero to perhaps even the gap of the benzene ring. The researchers from the National Research Council of Canada will present a review of their recent work towards the understanding of electronic and optical properties of semiconductor and graphene quantum dots. More details could be found in the article "Electronic and optical properties of semiconductor and graphene quantum dots" by Wei-dong Sheng et al., pp 328-352. [Photo credits: Wei-dong Sheng at Fudan University, China, and Pawel Hawrylak at National Research Council of Canada]

Apr. 2012, Volume 7 Issue 2

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Linearly dispersive surface state of topological insulator Bi2Te3 measured by angle resolved photoemission spectroscopy, forming a single Dirac fermion. The crystal structure of Bi2Te3 is illustrated below. Topological insulators represent a new state of quantum matter with a bulk insulting gap and odd number of relativistic Dirac fermions on the surface. In the simplest case, the surface state consists of a single Dirac cone, with one quarter the degrees of freedom of graphene. The mathematical structure of a topological insulator is relevant to important issues under investigation by the quantum information processing community. It has the novelty of dissipationless edge state transport of reminiscent of quantum hall system but without external magnetic field. Moreover, with a surface magnetic layer the electrodynamics of the topological insulator is described by an additional topological term in Maxwell’s equation, leading to striking quantum phenomena such as an image magnetic monopole induced by an electric charge. More details could be found in the article "Studies on the electronic structures of three-dimensional topological insulators by angle resolved photoemission spectroscopy" by Yulin Chen, pp 175-192. [Photo credits: Yulin Chen at University of Oxford, UK]

Feb. 2012, Volume 7 Issue 1

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The robust quantum coherence and high controllability of Bose condensed atoms have led to many exciting advances in the field of quantum interferometry. Due to the atom-atom collisions, the systems of Bose condensed atoms are intrinsic nonlinear systems. In general, inter-particle interactions can be used to generate quantum entanglement and quantum entanglement can be utilized to enhance measurement precision. Therefore, it is important to control and exploit the nonlinear dynamics of Bose condensed atoms for the implementation of quantum metrology. The cover picture shows the matter-wave interference of repulsive atomic Bose-Einstein condensates in a one-dimensional harmonic trap, in which dark solitons are gradually generated. More details could be found in the review article "Nonlinear quantum interferometry with Bose condensed atoms" by Chaohong Lee et al., pp 109-130. [Photo credits: Chaohong Lee, School of Physics and Engineering, Sun Yat-Sen University, China]

Dec. 2011, Volume 6 Issue 4

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Fermi surface of (Tl, Rb)xFe2-ySe2 superconductor as revealed by high resolution angle-resolved photoemission spectroscopy. Two electron-like Fermi surface sheets are observed around the central point while one electron-like Fermi surface sheet is observed around the zone corner M point which is actually composed of two degenerate Fermi surface sheets. Such Fermi surface topology is distinct from that of other iron-based superconductors. It provides key insight on understanding the pairing mechanism in the iron-based superconductors. More details could be found in the article “Structural, magnetic and electronic properties of the iron-chalcogenide AxFe2-ySe2 (A=K, Cs, Rb, and Tl, etc.) superconductors” by Dai-xiang Mou, Lin Zhao, and Xing-jiang Zhou, pp 410-428. [Photo credits: Xing-jiang Zhou, Institute of Physics, Chinese Academy of Sciences, China]

Sep. 2011, Volume 6 Issue 3

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The recent achievements in fabricating nanostructured graphene devices have led to number of exciting advances in the field of carbon-based mesoscopic physics and quantum transport. As an important example, graphene quantum dots are promising candidates for future implementation of spin-based qubits with long spin coherence times exceeding values known from today’s III-V material quantum dots. The two limiting factors — spin-orbit interactions and hyperfine splitting — that lower spin lifetimes in these materials are expected to be far less prominent in graphene leading to more reliable devices. On the way to these systems a number of technological challenges have still to be overcome, such as for example well-behaving tunneling barriers and controllable confinement potentials. These efforts not only will bridge molecular and solid state physics but they will open also the door to many more interesting details of confined quasi-particles in graphene allowing to make use of the special graphene material properties in future mesoscopic devices. More details could be found in the article “Transport in graphene nanostructures” by Christoph Stampfer et al., pp 271-293. [Photo credits: Christoph Stampfer, RWTH Aachen University, Germany]

Jun. 2011, Volume 6 Issue 2

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Hydrogen has been considered the best substitute for fossil fuels in future, as it is clean and renewable. Currently, one of the main obstacles of hydrogen economy is the efficient storage, which should have high gravimetric and volumetric density, fast kinetics. However, no existing materials meet all the industry requirements. The interactions between hydrogen and materials are either too weak in physical adsorption or too strong in chemical adsorption. The rational design of materials for hydrogen storage is crucial to hydrogen economy. A group from Peking University has suggested a novel porous structure, which has large pores as well as exposed transition metal sites composed of tripyrrylmethane molecules decorated with Ti atoms. It has been shown that each Ti can adsorb three H2 molecules with average binding energy of 0.172 eV/H2, which is promising for the adsorption and release of H2 under ambient condition. More details can be found in the article “Tripyrrylmethane based 2D porous structure for hydrogen storage” by Xiao ZHOU (周啸) et al. pp 220-223. [Photo credits: Jian ZHOU (周健), College of Engineering, Peking University]

Mar. 2011, Volume 6 Issue 1

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The experimental achievement of ultracold atomic Bose-Einstein condensates (BEC) has led to a broad of exciting advances in the past decade. As a spectacular example, the emerging field of quantum superchemistry (QS) or collective non-Arrhenius reaction of matter waves has attracted great interests in recent years, from the simplest atom-dimer conversion, to the assembly of complex molecules and even to the bimolecular reaction A2+B→AB+A (experimentally observed in 2010). Many surprising QS effects, such as super-selectivity rule in multi-channel dissociation, double-slit-like interference in assembling trimers, and vacuum-noise effect in triggering reaction, have been revealed in this fascinating new wonderland. Novel applications are also expected, e.g. quantum memory via an atom-molecule dark state, and laser-controlled phase transition in a spin gas. Matter-wave QS thereby provides a promising bridge between atomic, molecular and optical physics (AMO), chemical physics and quantum information science. More details could be found in the article “Quantum superchemistry of de Broglie waves: New wonderland at ultracold temperature” by Hui JING (景辉), Ya-jing JIANG (蒋亚静), and Yuan-gang DENG (邓元刚), pp 15-45 [Photo credits: Hui JING (景辉), Henan Normal University, China].

Dec. 2010, Volume 5 Issue 4

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The ability to move individual atoms with the tip of a scanning microscope is a powerful first step towards building complex molecular machines at the atomic scale. For practical applications of such molecular machinery, it must be possible to construct it easily and at low cost, on a large-scale. The key satisfying these requirements is to find molecular systems that assemble themselves into the desired shapes and functions on tailor-made surfaces. Prof. Hong-jun GAO and his colleagues form the Institute of Physics of CAS demonstrate that single molecular rotors can be constructed by evaporating tetra-tert-butyl zinc phthalocyanine molecules on an Au(111) surface. The molecules adsorb by attaching to a single gold adatom off-center. Furthermore, these single molecular rotors self-assemble into large scale ordered arrays on Au(111) surfaces. A fixed rotation axis off center is an important step towards the eventual fabrication of molecular motors or generators. More details could be found in the article "Understanding formation of molecular rotor array on Au(111) surface " by Shi-xuan DU (杜世萱) et al., pp 380-386 [Photo credits: Shi-xuan DU (杜世萱), Institute of Physics, Chinese Academy of Sciences].

Sep. 2010, Volume 5 Issue 3

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In recent years, metamaterials has stimulated the interest of many researchers due to their many important applications, such as negative refraction, super-imaging, and invisible cloak. According to the well known effective-media model, the coupling interactions between the elements in metamaterials are somewhat ignored; therefore, the effective properties of metamaterials can be viewed as the "averaged effect' of the resonance property of the individual elements. However, the coupling interaction between elements should always exist when they are arranged into metamaterials. Sometimes, especially when the elements are very close, this coupling effect is not negligible, and will have a substantial effect on the metamaterials’ properties. The cover picture shows a particularly interesting and typical coupled metamaterials whose unit cell is composed of two identical split-ring resonators. The inductive interaction between these two magnetic "atoms" introduces the split the resonance, which strongly depends on the separation distance between the resonators. More details could be found in the article "Hybridization effect in coupled metamaterials" by Hui LIU (刘辉), Tao LI (李涛), Shu-ming WANG (王漱明) and Shi-ning ZHU (祝世宁), pp 277-290 [Photo credits: Tao LI(李涛) and Hui LIU (刘辉), Nanjing University, China].

Jun. 2010, Volume 5 Issue 2

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The Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory was the first one that consisted of two independent rings. It was designed to operate at high luminosity over a wide range of beam energies and with particle species ranging from polarized proton to heavy ions. From central gold-gold collisions at the top center-of-mass energy of 200 GeV per nucleon-nucleon pair, thousands of particles were produced (see cover figure). With several years of data taking, it was concluded that RHIC had created a strongly interacting, hot and dense matter with partonic degrees of freedom - the Quark Gluon Plasma. Such a matter is believed to have existed for a few microseconds after the big bang. The goal of the second phase of RHIC is to understand the properties of the matter, such as its colored degrees of freedom and its equation of state. The physics of RHIC is reviewed by Dr. Li-juan RUAN (阮丽娟) in the article"Relativistic Heavy-Ion Collider (RHIC) physics overview" , pp 205-214. [Photo credits: the STAR Collaboration, Brookhaven National Laboratory, USA]

Mar. 2010, Volume 5 Issue 1

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Over the last decades, digital information processing progressed at an enormous speed. It already becomes an indispensable resource both in science and in society. However, for some computational problems, no efficient algorithms are known yet. If quantum mechanical systems are used for information process, an exponential speedup will be obtained for some of these problems instead of today's classical computers. Among the many different physical systems that have been proposed as carriers of quantum information, nuclear and electronic spins have so far been the most successful candidates. The main challenge remains to be the combination of the spins into scalable quantum registers with hundreds or thousands of spins. The picture shows a particularly interesting candidate: the information would be stored in the nuclear spin of nitrogen or phosphorus atoms (blue spheres), which are stored in the center of C60 molecules. The molecules form nanometer-sized traps for the neutral atoms and thus make it possible to arrange them in predefined patterns, e.g. as rows on a silicon surface. More details could be found in the article "Spin qubits for quantum simulations" by Xin-hua PENG (彭新华) and Dieter SUTER, pp 1-25. [Photo credits: Prof. Dieter SUTER (Fakultät Physik, Technische Universität Dortmund, Germany)]

Dec. 2009, Volume 4 Issue 4

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Fermi surface of iron-based superconductor, Ba0.6K0.4 Fe2As2 (Tc=35 K), measured by high resolution angle-resolved photoemission spectroscopy (ARPES). Near the center Γ(0,0) point, two hole-like Fermi surface sheets are observed while near the corner M(β,β) point, two strong Fermi spots are observed. The two Fermi surface sheets near the Γ point show different superconducting gap: the inner one shows larger gap (10―12 meV) while the outer one has a smaller gap (7―8 meV). No gap node is observed on both Fermi surface sheets which is consistent with s-wave superconducting gap symmetry. Superconducting gap opening is also observed at the M(π,π) point with a gap size of 10 meV. The two Fermi surface spots near the M point are gapped below Tc but the gap persists above Tc. The rich and detailed superconducting gap information will provide key insights in understanding pairing mechanism in the iron-based superconductors. Please refer to the article “Band structure, Fermi surface and superconducting gap in FeAs-based superconductors revealed by angle-resolved photoemission spectroscopy” by Professor Xing-jiang ZHOU (周兴江) et al., pp 427―432, in this issue. [Photo credits: Prof. Xing-jiang ZHOU (周兴江) (Institute of Physics, Chinese Academy of Sciences, China)]

Sep. 2009, Volume 4 Issue 3

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Molecular orbitals for the symmetrical organic molecule 9,10-bis((2'-para-mercaptophenyl)-ethinyl)-anthracene show that the para position sulfur substituted molecules (top two: HOMO left and LUMO right) are extensive facilitating current to flow, while the meta position sulfur substituted ones (down two: LUMO up and HOMO down) are localized leading the current insensitive to bias. The distance between the sulfur atom and the gold electrode surface is 0.2 nm. The numerical results present that the molecular transport behavior is sensitive to its configurations and provide an opportunity to improve the conduction ability of the molecular devices. The electronic structures are calculated by the density functional theory B3PW91 gradient-corrected correlation functional with LanL2DZ basis set, with consideration of the Darwin relativistic effect. Please refer to the article “The first-principles calculation of molecular conduction” by Professor Hao CHEN (陈灏), pp 327―336, in this issue. [Photo credits: Prof. Hao CHEN (陈灏) (Fudan University, China)]

Jun. 2009, Volume 4 Issue 2

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The cover image shows an optical atomic clock which will be used as a promising frequency standard in the near future. The key part of this clock is ultracold atoms generating an ultrastable frequency. This clock will have an error no more than one second even running as long as the existing time of the Universe. Using this clock, scientists can measure gravitational red-shifts and time variation of fine-structure constant in the laboratory as well as testing the general relativity theory and seeking the new physics. Furthermore, this clock can be employed to explore the deep space and significantly improve the accuracy and resolution of the global positioning system, and even look for the origin of the Universe and the new definition of one second. Please refer to the article “Laser cooling and trapping of ytterbium atoms” by Professor Xin-ye XU et al., pp 160―164, in this issue, which will tell you how to make cold atoms for an optical atomic clock. [Photo credits: Prof. Xin-ye XU (徐信业) (ECNU, China)]

Mar. 2009, Volume 4 Issue 1

Cover Illustration
The BES-III (Beijing Sprectrometer III) detector, a general purpose solenoidal high performance detector located at the Beijing Electron-Positron Collider (BEPC-II), is designed to study the tau-charm physics at the center of mass energy of 2.0 to 4.6 GeV. It is 11 m long, 6 m wide, 9 m high and a total weight of about 700 ton, and consists of a drift chamber (MDC) which has a small cell structure filled with a helium-based gas, an electromagnetic calorimeter (EMC) made of CsI(Tl) crystals, time-of-flight counters (TOF) for particle identification made of plastic scintillators, a muon system made of Resistive Plate Chambers (RPC) and a super conducting magnet. The detector was finally installed into the assigned position in 2008 and has already been operated to collect data. The cover image shows the cross-section of BES-III. Please refer to the article “Charm physics — A field full of challenges and opportunities” by Professor Xue-qian LI et al. in this issue for details. [Photo credits: Prof. Xue-qian LI (李学潜) (Nankai University, China)]