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    Nikita M. Kondratiev, Valery E. Lobanov, Artem E. Shitikov, Ramzil R. Galiev, Dmitry A. Chermoshentsev, Nikita Yu. Dmitriev, Andrey N. Danilin, Evgeny A. Lonshakov, Kirill N. Min’kov, Daria M. Sokol, Steevy J. Cordette, Yi-Han Luo, Wei Liang, Junqiu Liu, Igor A. Bilenko
    Frontiers of Physics, 2023, 18(2): 21305.

    The stabilization and manipulation of laser frequency by means of an external cavity are nearly ubiquitously used in fundamental research and laser applications. While most of the laser light transmits through the cavity, in the presence of some back-scattered light from the cavity to the laser, the self-injection locking effect can take place, which locks the laser emission frequency to the cavity mode of similar frequency. The self-injection locking leads to dramatic reduction of laser linewidth and noise. Using this approach, a common semiconductor laser locked to an ultrahigh-Q microresonator can obtain sub-Hertz linewidth, on par with state-of-the-art fiber lasers. Therefore it paves the way to manufacture high-performance semiconductor lasers with reduced footprint and cost. Moreover, with high laser power, the optical nonlinearity of the microresonator drastically changes the laser dynamics, offering routes for simultaneous pulse and frequency comb generation in the same microresonator. Particularly, integrated photonics technology, enabling components fabricated via semiconductor CMOS process, has brought increasing and extending interest to laser manufacturing using this method. In this article, we present a comprehensive tutorial on analytical and numerical methods of laser self-injection locking, as well a review of most recent theoretical and experimental achievements.

    Yaofeng Li, Huilin Lai, Chuandong Lin, Demei Li
    Frontiers of Physics, 2022, 17(6): 63500.

    Kelvin−Helmholtz (KH) instability is a fundamental fluid instability that widely exists in nature and engineering. To better understand the dynamic process of the KH instability, the influence of the tangential velocity on the compressible KH instability is investigated by using the discrete Boltzmann method based on the nonequilibrium statistical physics. Both hydrodynamic and thermodynamic nonequilibrium (TNE) effects are probed and analyzed. It is found that, on the whole, the global density gradients, the TNE strength and area firstly increase and decrease afterwards. Both the global density gradient and heat flux intensity in the vertical direction are almost constant in the initial stage before a vortex forms. Moreover, with the increase of the tangential velocity, the KH instability evolves faster, hence the global density gradients, the TNE strength and area increase in the initial stage and achieve their peak earlier, and their maxima are higher for a larger tangential velocity. Physically, there are several competitive mechanisms in the evolution of the KH instability. (i) The physical gradients increase and the TNE effects are strengthened as the interface is elongated. The local physical gradients decrease and the local TNE intensity is weakened on account of the dissipation and/or diffusion. (ii) The global heat flux intensity is promoted when the physical gradients increase. As the contact area expands, the heat exchange is enhanced and the global heat flux intensity increases. (iii) The global TNE intensity reduces with the decreasing of physical gradients and increase with the increasing of TNE area. (iv) The nonequilibrium area increases as the fluid interface is elongated and is widened because of the dissipation and/or diffusion.

    Yuan Wang, Fayuan Zhang, Meng Zeng, Hongyi Sun, Zhanyang Hao, Yongqing Cai, Hongtao Rong, Chengcheng Zhang, Cai Liu, Xiaoming Ma, Le Wang, Shu Guo, Junhao Lin, Qihang Liu, Chang Liu, Chaoyu Chen
    Frontiers of Physics, 2023, 18(2): 21304.

    Topological states of matter possess bulk electronic structures categorized by topological invariants and edge/surface states due to the bulk-boundary correspondence. Topological materials hold great potential in the development of dissipationless spintronics, information storage and quantum computation, particularly if combined with magnetic order intrinsically or extrinsically. Here, we review the recent progress in the exploration of intrinsic magnetic topological materials, including but not limited to magnetic topological insulators, magnetic topological metals, and magnetic Weyl semimetals. We pay special attention to their characteristic band features such as the gap of topological surface state, gapped Dirac cone induced by magnetization (either bulk or surface), Weyl nodal point/line and Fermi arc, as well as the exotic transport responses resulting from such band features. We conclude with a brief envision for experimental explorations of new physics or effects by incorporating other orders in intrinsic magnetic topological materials.

    Mo Cheng, Junbo Yang, Xiaohui Li, Hui Li, Ruofan Du, Jianping Shi, Jun He
    Frontiers of Physics, 2022, 17(6): 63601.

    Two-dimensional (2D) semiconductors are emerging as promising candidates for the next-generation nanoelectronics. As a type of unique channel materials, 2D semiconducting transition metal dichalcogenides (TMDCs), such as MoS2 and WS2, exhibit great potential for the state-of-the-art field-effect transistors owing to their atomically thin thicknesses, dangling-band free surfaces, and abundant band structures. Even so, the device performances of 2D semiconducting TMDCs are still failing to reach the theoretical values so far, which is attributed to the intrinsic defects, excessive doping, and daunting contacts between electrodes and channels. In this article, we review the up-to-date three strategies for improving the device performances of 2D semiconducting TMDCs: (i) the controllable synthesis of wafer-scale 2D semiconducting TMDCs single crystals to reduce the evolution of grain boundaries, (ii) the ingenious doping of 2D semiconducting TMDCs to modulate the band structures and suppress the impurity scatterings, and (iii) the optimization design of interfacial contacts between electrodes and channels to reduce the Schottky barrier heights and contact resistances. In the end, the challenges regarding the improvement of device performances of 2D semiconducting TMDCs are highlighted, and the further research directions are also proposed. We believe that this review is comprehensive and insightful for downscaling the electronic devices and extending the Moore’s law.

    Yanming Hu, Yifan Fei, Xiao-Long Chen, Yunbo Zhang
    Frontiers of Physics, 2022, 17(6): 61505.

    The collisional dynamics of two symmetric droplets with equal intraspecies scattering lengths and particle number density for each component is studied by solving the corresponding extended Gross−Pitaevskii equation in two dimensions by including a logarithmic correction term in the usual contact interaction. We find the merging droplet after collision experiences a quadrupole oscillation in its shape and the oscillation period is found to be independent of the incidental momentum for small droplets. With increasing collision momentum the colliding droplets may separate into two, or even more, and finally into small pieces of droplets. For these dynamical phases we manage to present boundaries determined by the remnant particle number in the central area and the damped oscillation of the quadrupole mode. A stability peak for the existence of droplets emerges at the critical particle numberNc ≃ 48 for the quasi-Gaussian and flat-top shapes of the droplets.

    Guangqiang Mei, Pengfei Suo, Li Mao, Min Feng, Limin Cao
    Frontiers of Physics, 2023, 18(1): 13310.

    The quantum harmonic oscillator (QHO), one of the most important and ubiquitous model systems in quantum mechanics, features equally spaced energy levels or eigenstates. Here we present a new class of nearly ideal QHOs formed by hydrogenic substitutional dopants in an AlGaAs/GaAs heterostructure. On the basis of model calculations, we demonstrate that, when a δ-doping Si donor substitutes the Ga/Al lattice site close to AlGaAs/GaAs heterointerface, a hydrogenic Si QHO, characterized by a restoring Coulomb force producing square law harmonic potential, is formed. This gives rise to QHO states with energy spacing of ~8−9 meV. We experimentally confirm this proposal by utilizing gate tuning and measuring QHO states using an aluminum single-electron transistor (SET). A sharp and fast oscillation with period of ~7−8 mV appears in addition to the regular Coulomb blockade (CB) oscillation with much larger period, for positive gate biases above 0.5 V. The observation of fast oscillation and its behavior is quantitatively consistent with our theoretical result, manifesting the harmonic motion of electrons from the QHO. Our results might establish a general principle to design, construct and manipulate QHOs in semiconductor heterostructures, opening future possibilities for their quantum applications.

    Jian-Sheng Wang, Jiebin Peng, Zu-Quan Zhang, Yong-Mei Zhang, Tao Zhu
    Frontiers of Physics, 2023, 18(4): 43602.

    We review the description and modeling of transport phenomena among the electron systems coupled via scalar or vector photons. It consists of three parts. The first part is about scalar photons, i.e., Coulomb interactions. The second part is with transverse photons described by vector potentials. The third part is on ϕ = 0 or temporal gauge, which is a full theory of the electrodynamics. We use the nonequilibrium Green’s function (NEGF) formalism as a basic tool to study steady-state transport. Although with local equilibrium it is equivalent to the fluctuational electrodynamics (FE), the advantage of NEGF is that it can go beyond FE due to its generality. We have given a few examples in the review, such as transfer of heat between graphene sheets driven by potential bias, emission of light by a double quantum dot, and emission of energy, momentum, and angular momentum from a graphene nanoribbon. All of these calculations are based on a generalization of the Meir−Wingreen formula commonly used in electronic transport in mesoscopic systems, with materials properties represented by photon self-energy, coupled with the Keldysh equation and the solution to the Dyson equation.

    Weibin Zhang, Woochul Yang, Yingkai Liu, Zhiyong Liu, Fuchun Zhang
    Frontiers of Physics, 2022, 17(6): 63509.

    By high-throughput calculations, 13 thermally and environmentally stable Janus MA2Z4 monolayers were screened from 104 types of candidates. The 13 stable monolayers have very high charge carrier concentrations (×1015 cm−2), which are better than those of the well-known graphene and TaS2. Because of their excellent conductivity, the 6 monolayers with band gaps less than 0.5 eV are identified as potential electrode materials for hydrogen evolution reaction applications. For potential applications as photoelectric or photocatalytic materials, bandgaps (Eg-HSE) higher than 0.5 eV remained, which resulted in 7 potential candidates. Based on optical absorption analysis in the visible-light range, H-HfSiGeP4 and H-MoSiGeP4 have higher absorption ability and optical conductivity, which is quite impressive for optoelectronic, solar cell device, and photocatalysis applications. Additionally, the transmittance coefficient of Janus MA2Z4 monolayers is approximately 70%−80% in the visible-light range, which implies that these monolayers show good light transmittance. For potential applications as photocatalysts, the redox potential and charge effective mass analysis indicate that H-HfSiGeP4, H-MoSiGeP4, T-ScSiGeN4, and T-ZrSiGeN4 are suitable photocatalysts for CO2 reduction reactions. Using high-throughput identification, 13 types of new and stable Janus MA2Z4 monolayers were explored, and the basic properties and potential applications were investigated, which can reduce the time for experiments and provide basic data for the material genome initiative.

    Si Jia Li, Zhuo Yue Li, Guo Shai Huang, Xiao Bin Liu, Rui Qi Li, Xiang Yu Cao
    Frontiers of Physics, 2022, 17(6): 62501.

    Orbital angular momentum (OAM) is a phenomenon of vortex phase distribution in free space, which has attracted enormous attention in theoretical research and practical application of wireless communication systems due to its characteristic of infinitely orthogonal modes. However, traditional methods generating OAM beams are bound to complex structure, large device, multiple layers, complex feed networks, and limited beams in microwave range. Here, a digital coding transmissive metasurface (DCTMS) with a single layer substrate and the bi-symmetrical arrow is proposed and designed to generate multi-OAM-beam based on Pancharatnam−Berry (PB) phase principle. The 3-bit phase response can be realized by encoding the geometric phase into rotation angle of unit cell for DCTMS. Additionally, the phase compensation of the metasurface is introduced to achieve the beam focusing and the conversion from spherical wave to plane wave. According to the digital convolution theorem, the far-field patterns and near-field distributions of multi-OAM-beam withl= −2 modes are adequately demonstrated by DCTMS prototypes. The OAM efficiency and the purity are calculated to demonstrate the excellent multi-OAM-beam. The simulated and experimental results illustrate their performance of OAM beams. The designed DCTMS has profound application in multi-platform wireless communication systems and the multi-channel imaging systems.

    Bin Cheng, Xiu-Hao Deng, Xiu Gu, Yu He, Guangchong Hu, Peihao Huang, Jun Li, Ben-Chuan Lin, Dawei Lu, Yao Lu, Chudan Qiu, Hui Wang, Tao Xin, Shi Yu, Man-Hong Yung, Junkai Zeng, Song Zhang, Youpeng Zhong, Xinhua Peng, Franco Nori, Dapeng Yu
    Frontiers of Physics, 2023, 18(2): 21308.

    Quantum computers have made extraordinary progress over the past decade, and significant milestones have been achieved along the path of pursuing universal fault-tolerant quantum computers. Quantum advantage, the tipping point heralding the quantum era, has been accomplished along with several waves of breakthroughs. Quantum hardware has become more integrated and architectural compared to its toddler days. The controlling precision of various physical systems is pushed beyond the fault-tolerant threshold. Meanwhile, quantum computation research has established a new norm by embracing industrialization and commercialization. The joint power of governments, private investors, and tech companies has significantly shaped a new vibrant environment that accelerates the development of this field, now at the beginning of the noisy intermediate-scale quantum era. Here, we first discuss the progress achieved in the field of quantum computation by reviewing the most important algorithms and advances in the most promising technical routes, and then summarizing the next-stage challenges. Furthermore, we illustrate our confidence that solid foundations have been built for the fault-tolerant quantum computer and our optimism that the emergence of quantum killer applications essential for human society shall happen in the future.

    Zhen Ma, Shuai Li, Meng-Meng Xiao, Ya-Wen Zheng, Ming Lu, Haiwen Liu, Jin-Hua Gao, X. C. Xie
    Frontiers of Physics, 2023, 18(1): 13307.

    We report that the twisted few layer graphite (tFL-graphite) is a new family of moiré heterostructures (MHSs), which has richer and highly tunable moiré flat band structures entirely distinct from all the known MHSs. A tFL-graphite is composed of two few-layer graphite (Bernal stacked multilayer graphene), which are stacked on each other with a small twisted angle. The moiré band structure of the tFL-graphite strongly depends on the layer number of its composed two van der Waals layers. Near the magic angle, a tFL-graphite always has two nearly flat bands coexisting with a few pairs of narrowed dispersive (parabolic or linear) bands at the Fermi level, thus, enhances the DOS at EF . This coexistence property may also enhance the possible superconductivity as been demonstrated in other multiband superconductivity systems. Therefore, we expect strong multiband correlation effects in tFL-graphite. Meanwhile, a proper perpendicular electric field can induce several isolated nearly flat bands with nonzero valley Chern number in some simple tFL-graphites, indicating that tFL-graphite is also a novel topological flat band system.

    Xin Li, Guangcun Shan, Ruguang Ma, Chan-Hung Shek, Hongbin Zhao, Seeram Ramakrishna
    Frontiers of Physics, 2022, 17(6): 63501.

    MXene-based hydrogels have drawn considerable attention as flexible and wearable sensors. However, the application of MXene-based hydrogels after sensing failure has rarely been investigated, which is of great significance for expanding their engineering application. In this work, multifunctional mineral MXene hydrogels (MMHs) were synthesized via a simple method inspired by biomineralization. The prepared MMHs were stretchable, self-healable and conductive, and can be used to fabricate wearable tensile strain sensors showing a super-wide sensing range with excellent sensitivity. MMHs-based strain sensors were designed to be directly attached to the skin surface to detect tiny and large human motions. In addition, with the advantages of a large specific area, excellent hydrophilicity and abundant active adsorption sites for MXene nanosheets and hydrogels, dehydrated MMHs were used as highly efficient adsorbents for the removal of strontium ions from aqueous solutions. This work shows the great potential of MXene in promoting the development of next-generation functional materials.

    Linwei Sai, Li Fu, Qiuying Du, Jijun Zhao
    Frontiers of Physics, 2023, 18(1): 13306.

    Due to coexistence of huge number of structural isomers, global search for the ground-state structures of atomic clusters is a challenging issue. The difficulty also originates from the computational cost of ab initio methods for describing the potential energy surface. Recently, machine learning techniques have been widely utilized to accelerate materials discovery and molecular simulation. Compared to the commonly used artificial neural network, graph network is naturally suitable for clusters with flexible geometric environment of each atom. Herein we develop a cluster graph attention network (CGANet) by aggregating information of neighboring vertices and edges using attention mechanism, which can precisely predict the binding energy and force of silver clusters with root mean square error of 5.4 meV/atom and mean absolute error of 42.3 meV/Å, respectively. As a proof-of-concept, we have performed global optimization of medium-sized Agn clusters (n = 14−26) by combining CGANet and genetic algorithm. The reported ground-state structures for n = 14−21, have been successfully reproduced, while entirely new lowest-energy structures are obtained for n = 22−26. In addition to the description of potential energy surface, the CGANet is also applied to predict the electronic properties of clusters, such as HOMO energy and HOMO-LUMO gap. With accuracy comparable to ab initio methods and acceleration by at least two orders of magnitude, CGANet holds great promise in global search of lowest-energy structures of large clusters and inverse design of functional clusters.

    Jing Zhang, Zixiang Cui, Jie Liu, Chunjie Li, Haoyi Tan, Guangcun Shan, Ruguang Ma
    Frontiers of Physics, 2023, 18(1): 13603.

    Oxygen electrocatalysts are of great importance for the air electrode in zinc–air batteries (ZABs). Owing to large surface area, high electrical conductivity and ease of modification, two-dimensional (2D) materials have been widely studied as oxygen electrocatalysts for the rechargable ZABs. The elaborately modified 2D materials-based electrocatalysts, usually exhibit excellent performance toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which have attracted extensive interests of worldwide researchers. Given the rapid development of bifunctional electrocatalysts toward ORR and OER, the latest progress of non-noble electrocatalysts based on layered double hydroxides (LDHs), graphene, and MXenes are intensively reviewed. The discussion ranges from fundamental structure, synthesis, electrocatalytic performance of these catalysts, as well as their applications in the rechargeable ZABs. Finally, the challenges and outlook are provided for further advancing the commercialization of rechargeable ZABs.

    Junchao Hu, Xinglin Wen, Dehui Li
    Frontiers of Physics, 2023, 18(3): 33602.

    The optical properties of two-dimensional (2D) perovskites recently receive numerous research focus thanks to the strong quantum and dielectric confinement effects. In addition to the strong excitonic effect at room temperature, 2D perovskites also have appealing features that their optical properties can be flexibly tuned by alternating organic or inorganic layers. Particularly, 2D chiral perovskites and 2D perovskites based heterostructures are emerging as new platforms to extend their functionalities. To optimize performance of 2D perovskites-based optoelectronic devices, it is critical to understand the fundamentals and explore the strategies to engineer their optical properties. This review begins with an introduction to the excitons and self-trapped excitons of 2D perovskites. Subsequently, inorganic/organic layer effects on optical properties and 2D perovskites based heterostructures are discussed. We also discussed the nonlinear optical properties of 2D perovskite. We are looking forward to that this review can stimulate more efforts to understand and optimize the optical properties of 2D perovskites.

    Xudong Zhu, Yuqian Chen, Zheng Liu, Yulei Han, Zhenhua Qiao
    Frontiers of Physics, 2023, 18(2): 23302.

    We numerically study the general valley polarization and anomalous Hall effect in van der Waals (vdW) heterostructures based on monolayer jacutingaite family materials Pt2AX3 (A = Hg, Cd, Zn; X = S, Se, Te). We perform a systematic study on the atomic, electronic, and topological properties of vdW heterostructures composed of monolayer Pt2AX3 and two-dimensional ferromagnetic insulators. We show that four kinds of vdW heterostructures exhibit valley-polarized quantum anomalous Hall phase, i.e., Pt2HgS3/NiBr2, Pt2HgSe3/CoBr2, Pt2HgSe3/NiBr2, and Pt2ZnS3/CoBr2, with a maximum valley splitting of 134.2 meV in Pt2HgSe3/NiBr2 and sizable global band gap of 58.8 meV in Pt2HgS3/NiBr2. Our findings demonstrate an ideal platform to implement applications on topological valleytronics.

    Xiangli Qian, Huiying Sun, Tianlu Chen, Danzengluobu, Youliang Feng, Qi Gao, Quanbu Gou, Yiqing Guo, Hongbo Hu, Mingming Kang, Haijin Li, Cheng Liu, Maoyuan Liu, Wei Liu, Bingqiang Qiao, Xu Wang, Zhen Wang, Guangguang Xin, Yuhua Yao, Qiang Yuan, Yi Zhang
    Frontiers of Physics, 2022, 17(6): 64602.

    The High Altitude Detection of Astronomical Radiation (HADAR) experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique. It focuses the Cherenkov light emitted by extensive air showers through a large aperture water-lens system for observing very-high-energy γ-rays and cosmic rays. With the advantages of a large field-of-view (FOV) and low energy threshold, the HADAR experiment operates in a large-scale sky scanning mode to observe galactic sources. This study presents the prospects of using the HADAR experiment for the sky survey of TeV γ-ray sources from TeVCat and provids a one-year survey of statistical significance. Results from the simulation show that a total of 23 galactic point sources, including five supernova remnant sources and superbubbles, four pulsar wind nebula sources, and 14 unidentified sources, were detected in the HADAR FOV with a significance greater than 5 standard deviations (σ). The statistical significance for the Crab Nebula during one year of operation reached 346.0 σ and the one-year integral sensitivity of HADAR above 1 TeV was ~1.3%–2.4% of the flux from the Crab Nebula.

    Qirui Cui, Liming Wang, Yingmei Zhu, Jinghua Liang, Hongxin Yang
    Frontiers of Physics, 2023, 18(1): 13602.

    The two-dimensional (2D) magnets provide novel opportunities for understanding magnetism and investigating spin related phenomena in several atomic thickness. Multiple features of 2D magnets, such as critical temperatures, magnetoelectric/magneto-optic responses, and spin configurations, depend on the basic magnetic terms that describe various spins interactions and cooperatively determine the spin Hamiltonian of studied systems. In this review, we present a comprehensive survey of three types of basic terms, including magnetic anisotropy that is intimately related with long-range magnetic order, exchange coupling that normally dominates the spin interactions, and Dzyaloshinskii−Moriya interaction (DMI) that favors the noncollinear spin configurations, from the theoretical aspect. We introduce not only the physical features and origin of these crucial terms in 2D magnets but also many correlated phenomena, which may lead to the advance of 2D spintronics.

    Yue Chen, Zhengtao Liu, Ziyue Lin, Qiwen Jiang, Mingyang Du, Zihan Zhang, Hao Song, Hui Xie, Tian Cui, Defang Duan
    Frontiers of Physics, 2022, 17(6): 63502.

    The theoretical predictions and experimental synthesis of H3S and LaH10 superconductors with record high superconducting transition temperatures (Tc) have promoted the hydrogen-based superconducors to be a research hotspot in the field of solid-state physics. Here, we predict an unprecedented layered structure CaH15, with high Tc of 189 K at 200 GPa using ab initio calculations. As concerns the novel structure, one layer is made of a hydrogen nonagon, the other layer consists of a Ca atom and six H2 molecular units surrounding the Ca atom. This layered structure was also found in SrH15, YH15, and LaH15 at high pressures, each materials exhibit high Tc especially YH15 can reach above 200 K at 220 GPa. It represents the second class of layered superhydrides with high value of Tc after pentagraphene like HfH10.

    Guangcun Shan, Zejian Ding, Yury Gogotsi
    Frontiers of Physics, 2023, 18(1): 13604.
    Cui Kong, Jibing Liu, Hao Xiong
    Frontiers of Physics, 2023, 18(1): 12501.

    Nonreciprocal microwave devices, in which the transmission of waves is non-symmetric between two ports, are indispensable for the manipulation of information processing and communication. In this work, we show the nonreciprocal microwave transmission in a cavity magnonic system under the joint mechanism of phase modulation and magnon Kerr nonlinearity effect. In contrast to the schemes based on the standard phase modulation or magnon Kerr nonlinearity, we find that the joint mechanism enables the nonreciprocal transmission even at low power and makes us obtain a high nonreciprocal isolation ratio. Moreover, when two microwave modes are coupled to the magnon mode via a different coupling strength, the presented strong nonreciprocal response occurs, and it makes the nonreciprocal transmission manipulating by the magnetic field within a large adjustable range possible, which overcomes narrow operating bandwidths. This study may provide promising opportunities to realize nonreciprocal structures for wave transmission.

    Mucheng Guo, Shuping Liu, Weiye Sun, Miaomiao Ren, Fudong Wang, Manjin Zhong
    Frontiers of Physics, 2023, 18(2): 21303.

    Rare-earth doped crystals carry great prospect in developing ensemble-based solid state quantum memories for remote quantum communication and fast quantum processing applications. In recent years, with this system, remarkable quantum storage performances have been realized, and more exciting applications have been exploited, while the technical challenges are also significant. In this paper, we outlined the status quo in the development of rare-earth-based quantum memories from the point of view of different storage protocols, with a focus on the experimental demonstrations. We also analyzed the challenges and provided feasible solutions.

    Yafen Cai, Shuai Shi, Yijia Zhou, Jianhao Yu, Yali Tian, Yitong Li, Kuan Zhang, Chenhao Du, Weibin Li, Lin Li
    Frontiers of Physics, 2023, 18(1): 12302.

    Stabilizing important physical quantities to atom-based standards lies at the heart of modern atomic, molecular and optical physics, and is widely applied to the field of precision metrology. Of particular importance is the atom-based microwave field amplitude stabilizer, the so-called atomic candle. Previous atomic candles are realized with atoms in their ground state, and hence suffer from the lack of frequency band tunability and small stabilization bandwidth, severely limiting their development and potential applications. To tackle these limitations, we employ microwave-dressed Rydberg atoms to realize a novel atomic candle that features multi-band frequency tunability and large stabilization bandwidth. We demonstrate amplitude stabilization of microwave field from C-band to Ka-band, which could be extended to quasi-DC and terahertz fields by exploring abundant Rydberg levels. Our atomic candle achieves stabilization bandwidth of 100 Hz, outperforming previous ones by more than two orders of magnitude. Our simulation indicates the stabilization bandwidth can be further increased up to 100 kHz. Our work paves a route to develop novel electric field control and applications with a noise-resilient, miniaturized, sensitive and broadband atomic candle.

    Long-Yu Cheng, Fei Ming, Fa Zhao, Liu Ye, Dong Wang
    Frontiers of Physics, 2022, 17(6): 61504.

    In this work, we study the entropic uncertainty and quantum discord in two double-quantum-dot (DQD) system coupled via a transmission line resonator (TLR). Explicitly, the dynamics of the systemic quantum correlation and measured uncertainty are analysed with respect to a general X-type state as the initial state. Interestingly, it is found that the different parameters, including the eigenvalue α of the coherent state, detuning amount δ, frequency ω and the coupling constant g, have subtle effects on the dynamics of the entropic uncertainty, such as the oscillation period of the uncertainty. It is clear to reveal that the quantum discord and the lower bound of the entropic uncertainty are anti-correlated when the initial state of the system is the Werner-type state, while quantum discord and the lower bound of the entropic uncertainty are not anti-correlated when the initial state of the system is the Bell-diagonal state. Thereby, we claim that the current investigation would provide an insight into the entropic uncertainty and quantum correlation in DQDs system, and are basically of importance to quantum precision measurement in practical quantum information processing.

    Lei Shi, Hai-Zhou Lu
    Frontiers of Physics, 2023, 18(2): 21307.

    We review our most recent research on quantum transport, organizing the review according to the intensity of the magnetic field and focus mostly on topological semimetals and topological insulators. We first describe the phenomenon of quantum transport when a magnetic field is not present. We introduce the nonlinear Hall effect and its theoretical descriptions. Then, we discuss Coulomb instabilities in 3D higher-order topological insulators. Next, we pay close attention to the surface states and find a function to identify the axion insulator in the antiferromagnetic topological insulator MnBi2Te4. Under weak magnetic fields, we focus on the decaying Majorana oscillations which has the correlation with spin−orbit coupling. In the section on strong magnetic fields, we study the helical edge states and the one-sided hinge states of the Fermi-arc mechanism, which are relevant to the quantum Hall effect. Under extremely large magnetic fields, we derive a theoretical explanation of the negative magnetoresistance without a chiral anomaly. Then, we show how magnetic responses can be used to detect relativistic quasiparticles. Additionally, we introduce the 3D quantum Hall effect’s charge-density wave mechanism and compare it with the theory of 3D transitions between metal and insulator driven by magnetic fields.

    Tao Zhu, Yao Zhang, Xin Wei, Man Jiang, Hua Xu
    Frontiers of Physics, 2023, 18(3): 33601.

    Single-element two-dimensional (2D) tellurium (Te) which possesses an unusual quasi-one-dimensional atomic chain structure is a new member in 2D materials family. 2D Te possesses high carrier mobility, wide tunable bandgap, strong light-matter interaction, better environmental stability, and strong anisotropy, making Te exhibit tremendous application potential in next-generation electronic and optoelectronic devices. However, as an emerging 2D material, the research on fundamental property and device application of Te is still in its infancy. Hence, this review summarizes the most recent research progresses about the new star 2D Te and discusses its future development direction. Firstly, the structural features, basic physical properties, and various preparation methods of 2D Te are systemically introduced. Then, we emphatically summarize the booming development of 2D Te-based electronic and optoelectronic devices including field effect transistors, photodetectors and van der Waals heterostructure photodiodes. Finally, the future challenges, opportunities, and development directions of 2D Te-based electronic and optoelectronic devices are prospected.

    Jia-En Yang, Hang Xie
    Frontiers of Physics, 2022, 17(6): 63504.

    Topological edge states have crucial applications in the future nano spintronics devices. In this work, circularly polarized light is applied on the zigzag silicene-like nanoribbons resulting in the anisotropic chiral edge modes. An energy-dependent spin filter is designed based on the topological-insulator (TI) junctions with anisotropic chiral edge states. The resonance transmission has been observed in the TI junctions by calculating the local current distributions. And some strong Fabry−Perot resonances are found leading to the sharp transmission peaks. Whereas, the weak and asymmetric resonance corresponds to the broad transmission peaks. In addition, a qualitative relation between the resonant energy separation TR and group velocity vf is derived: TRhvfn/L, that indicated TR is proportional to vf and inversely proportional to the length L of the conductor. The different TR between the spin-up and spin-down cases results in the energy-resolved spin filtering effect. Moreover, the intensity of the circularly polarized light can modulate the group velocity vf. Thus, the intensity of circularly polarized light, as well as the conductor-length, play very vital roles in designing the energy-dependent spin filter. Since the transmission gap root in the Fabry−Perot resonances, the thermoelectric (TE) property can be enhanced by adjusting the gap. A schedule to enhance the TE performance in the TI-junction is proposed by modulating the electric field (Ez). The TE dependence on Ez in the nanojunction is investigated, where the appropriate Ez leads to a very high spin thermopower and spin figure of merit. These TI junctions have potential usages in the nano spintronics and thermoelectric devices.

    Yu-Long Hai, He-Jin Yan, Yong-Qing Cai
    Frontiers of Physics, 2023, 18(2): 23303.

    In our study, we constructed a series of inorganic nonmetallic ternary hydrides PSH6 by first-principles structural screening under pressure of 200 GPa. The structural stability under lower pressure are examined. Focusing on the structural stability, electronic and phonon properties, as well as the possible superconducting properties within the framework of Bardeen−Cooper−Schrieffer (BCS) theory, we show that PSH6 with space group \textcolor[RGB]12,108,100Pm3¯m possesses a superconducting transition temperature of 146 K at 130 GPa. In the pressure range of 100−200 GPa, our work suggests that the ternary phosphorus-sulfur-hydrogen would act as a promising compositional and elemental space for achieving high-temperature superconductivity.

    Lu Bo, Xiao-Fei Liu, Chuan Wang, Tie-Jun Wang
    Frontiers of Physics, 2023, 18(1): 12305.

    Chiral quantum optics is a new research area in light-matter interaction that depends on the direction of light propagation and offers a new path for the quantum regulation of light-matter interactions. In this paper, we study a spinning Kerr-type microresonator coupled with Λ-type atom ensembles, which are driven in opposite directions to generate asymmetric photon statistics. We find that a photon blockade can only be generated by driving the spinning resonator on right side without driving the spinning microresonator from the left side, resulting in chirality. The coupling strength between system modes can be precisely controlled by adjusting the detuning amount of the atomic pump field. Because of the splitting of the resonant frequency generated by the Fizeau drag, the destructive quantum interference generated in right side drive prevents the nonresonant transition path of state |1,0⟩ to state |2,0⟩. This direction-dependent chiral quantum optics is expected to be applied to chiral optical devices, single-photon sources and nonreciprocal quantum communications.

    Vitaly L. Galinsky, Lawrence R. Frank
    Frontiers of Physics, 2023, 18(4): 45301.

    Analytical expressions for scaling of brain wave spectra derived from the general nonlinear wave Hamiltonian form show excellent agreement with experimental “neuronal avalanche” data. The theory of the weakly evanescent nonlinear brain wave dynamics [Phys. Rev. Research 2, 023061 (2020); J. Cognitive Neurosci. 32, 2178 (2020)] reveals the underlying collective processes hidden behind the phenomenological statistical description of the neuronal avalanches and connects together the whole range of brain activity states, from oscillatory wave-like modes, to neuronal avalanches, to incoherent spiking, showing that the neuronal avalanches are just the manifestation of the different nonlinear side of wave processes abundant in cortical tissue. In a more broad way these results show that a system of wave modes interacting through all possible combinations of the third order nonlinear terms described by a general wave Hamiltonian necessarily produces anharmonic wave modes with temporal and spatial scaling properties that follow scale free power laws. To the best of our knowledge this has never been reported in the physical literature and may be applicable to many physical systems that involve wave processes and not just to neuronal avalanches.