中国物理B

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Quantum simulation and quantum computation of noisy-intermediate scale

Kai Xu(许凯), and Heng Fan(范桁)

2022 (10): 100304-100304. doi: 10.1088/1674-1056/ac89de

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In the past years, great progresses have been made on quantum computation and quantum simulation. Increasing the number of qubits in the quantum processors is expected to be one of the main motivations in the next years, while noises in manipulation of quantum states may still be inevitable even the precision will improve. For research in this direction, it is necessary to review the available results about noisy multiqubit quantum computation and quantum simulation. The review focuses on multiqubit state generations, quantum computational advantage, and simulating physics of quantum many-body systems. Perspectives of near term noisy intermediate-quantum processors will be discussed.

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Ultrafast Coulomb explosion imaging of molecules and molecular clusters

Xiaokai Li(李孝开), Xitao Yu(余西涛), Pan Ma(马盼), Xinning Zhao(赵欣宁), Chuncheng Wang(王春成), Sizuo Luo(罗嗣佐), and Dajun Ding(丁大军)

2022 (10): 103304-103304. doi: 10.1088/1674-1056/ac89df

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Taking an image of their structure and a movie of their dynamics of small quantum systems have always been a dream of physicists and chemists. Laser-induced Coulomb explosion imaging (CEI) provides a great opportunity to make this dream a reality for small molecules or their aggregation —— clusters. The method is unique for identifying the atomic locations with ångstrom spatial resolution and capturing the structural evolution with a femtosecond time scale, in particular for imaging transient state products. This review summarizes the determination of three-dimensional equilibrium geometry of molecules and molecular cluster system through the reconstruction from the fragments momenta, and also shows that the dissociation dynamics on the complex potential energy surface can be tracked in real-time with the ultrafast CEI (UCEI). Furthermore, the detailed measurement and analysis procedures of the CEI, theoretical methods, exemplary results, and future perspectives of the technique are described.

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Momentum-space polarization fields in two-dimensional photonic-crystal slabs: Physics and applications

Wen-Zhe Liu(刘文哲), Lei Shi(石磊), Che-Ting Chan(陈子亭), and Jian Zi(资剑)

2022 (10): 104211-104211. doi: 10.1088/1674-1056/ac8ce5

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In addition to non-radiative guided modes, two-dimensional photonic-crystal slabs support guided resonant ones which can radiate into free space. From the polarization states of these guided resonances, a polarization field on a photonic band can be constructed in momentum space. Momentum-space polarization fields display complicated configurations and patterns with different types of polarization singularities inside, shedding new light on the manipulations of light flows. In this review, we summarize the recent research progress on momentum-space polarization fields and singularities in two-dimensional photonic-crystal slabs, focusing on their unique optical properties and potential applications as well.

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Advances and challenges in DFT-based energy materials design

Jun Kang(康俊), Xie Zhang(张燮), and Su-Huai Wei(魏苏淮)

2022 (10): 107105-107105. doi: 10.1088/1674-1056/ac89d7

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The growing worldwide energy needs call for developing novel materials for energy applications. Ab initio density functional theory (DFT) calculations allow the understanding and prediction of material properties at the atomic scale, thus, play an important role in energy materials design. Due to the fast progress of computer power and development of calculation methodologies, DFT-based calculations have greatly improved their predictive power, and are now leading to a paradigm shift towards theory-driven materials design. The aim of this perspective is to introduce the advances in DFT calculations which accelerate energy materials design. We first present state-of-the-art DFT methods for accurate simulation of various key properties of energy materials. Then we show examples of how these advances lead to the discovery of new energy materials for photovoltaic, photocatalytic, thermoelectric, and battery applications. The challenges and future research directions in computational design of energy materials are highlighted at the end.

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Recent advances of interface engineering in inverted perovskite solar cells

Shiqi Yu(余诗琪), Zhuang Xiong(熊壮), Zhenhan Wang(王振涵), Haitao Zhou(周海涛), Fei Ma(马飞), Zihan Qu(瞿子涵), Yang Zhao(赵洋), Xinbo Chu(楚新波), and Jingbi You(游经碧)

2022 (10): 107307-107307. doi: 10.1088/1674-1056/ac8e9f

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Perovskite solar cells (PSCs) have witnessed great achievement in the past decade. Most of previous researches focus on the n—i—p structure of PSCs with ultra-high efficiency. While the n—i—p devices usually used the unstable charge transport layers, such as the hygroscopic doped spiro-OMeTAD, which affect the long-term stability. The inverted device with the p—i—n structure owns better stability when using stable undoped organic molecular or metal oxide materials. There are significant progresses in inverted PSCs, most of them related to charge transport or interface engineering. In this review, we will mainly summarize the inverted PSCs progresses related to the interface engineering. After that, we prospect the future direction on inverted PSCs.

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Recent advances in quasi-2D superconductors via organic molecule intercalation

Mengzhu Shi(石孟竹), Baolei Kang(康宝蕾), Tao Wu(吴涛), and Xianhui Chen(陈仙辉)

2022 (10): 107403-107403. doi: 10.1088/1674-1056/ac8e9d

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Superconductivity at the 2D limit shows emergent novel quantum phenomena, including anomalously enhanced H_c2, quantum metallic states and quantum Griffiths singularity, which has attracted much attention in the field of condensed matter physics. In this article, we focus on new advances in quasi-2D superconductors in the bulk phase using an organic molecular electrochemical intercalation method. The enhanced superconductivity and emergent pseudogap behavior in these quasi-2D superconductors are summarized with a further prospect.

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Near-infrared photocatalysis based on upconversion nanomaterials

Xingyuan Guo(郭星原), Zhe Wang(王哲), Shengyan Yin(尹升燕), and Weiping Qin(秦伟平)

2022 (10): 108201-108201. doi: 10.1088/1674-1056/ac7556

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As the global energy crisis and environmental pollution problems become increasingly severe, it is important to develop new energy capture and pollution management methods. Among these new technologies, photocatalysis has garnered significant interest because of its significant application prospects in harnessing pollution-free solar energy to degrade organic pollutants. From a fundamental scientific and technical perspective, improved optical frequency is a key research topic that provides a useful framework for studying the optical processes impacted by the local photonic environment. This type of study is especially pertinent because plasmonics emphasizes nonlinearity. Thus, near-infrared (NIR) catalysis has received considerable attention. In this review, we aimed to provide an integrated framework for NIR photocatalysis. We briefly introduce photocatalysis based on upconversion (UC) materials, including the efficiency of UC materials and the bination and energy transfer process between the semiconductor and UC particles as well as photoelectric response photocontrolled-delivery and photodynamic therapy based on NIR-responsive materials.

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Dynamic stabilization of atomic ionization in a high-frequency laser field with different initial angular momenta

Di-Yu Zhang(张頔玉), Yue Qiao(乔月), Wen-Di Lan(蓝文迪), Jun Wang(王俊), Fu-Ming Guo(郭福明), Yu-Jun Yang(杨玉军), and Da-Jun Ding(丁大军)

2022 (10): 103202-103202. doi: 10.1088/1674-1056/ac892a

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We investigated the ionization of an atom with different orbital angular momenta in a high-frequency laser field by solving the time-dependent Schrödinger equation. The results showed that the ionization stabilization features changed with the relative direction between the angular momentum of the initial state and the vector field of the laser pulse. The ionization mechanism of the atom irradiated by a high frequency was explained by calculating the transition matrix and evolution of the time-dependent wave packet. This study can provide comprehensive understanding to improve atomic nonadiabatic ionization.

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Amplitude and rotation of the ellipticity of harmonicsfrom a linearly polarized laser field

Ping Li(李萍), Na Gao(高娜), Rui-Xian Yu(蔚瑞贤), Jun Wang(王俊), Su-Yu Li(李苏宇), Fu-Ming Guo(郭福明), and Yu-Jun Yang(杨玉军)

2022 (10): 103303-103303. doi: 10.1088/1674-1056/ac8ce8

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We simulate the dynamic response of H₂⁺ in a linearly polarized laser field by numerically solving the time-dependent Schrödinger equation. The elliptically polarized high-order harmonics generated by H₂⁺ irradiated by the linearly polarized laser field are systematically investigated. The result shows that the amplitude and rotation of the ellipticity of harmonics are affected by the alignment angle and internuclear distance of the molecule. Analyzing the change in forces acted on the ionized electrons and the trajectories of the electrons, the phenomena are found to be due to the change in the direction of the total Coulomb forces from the two nuclei felt by the recollided ionized electrons in the direction perpendicular to the laser polarization direction. Based on the influence law, we can select the harmonics with a specific frequency band under different alignment angles and then synthesize the isolated attosecond pulses with different rotations, which can be continuously converted from right-handed circular polarization, linear polarization, and left-handed circular polarization by changing the alignment angle. This study provides a new possible approach to the real-time detection of molecular states by using attosecond pulses and obtaining more optimized harmonics with molecular properties.

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Femtosecond laser-induced Cu plasma spectra at different laser polarizations and sample temperatures

Yitong Liu(刘奕彤), Qiuyun Wang(王秋云), Luyun Jiang(蒋陆昀), Anmin Chen(陈安民), Jianhui Han(韩建慧), and Mingxing Jin(金明星)

2022 (10): 105201-105201. doi: 10.1088/1674-1056/ac6864

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Laser-induced breakdown spectroscopy (LIBS) is a good technique for detecting and analyzing material elements due to the plasma emission produced by the high-power laser pulse. Currently, a significant topic of LIBS research is improving the emission intensity of LIBS. This study investigated the effect of laser-polarization on femtosecond laser-ablated Cu plasma spectra at different sample temperatures. The measured lines under circularly polarized lasers were higher than those under linearly and elliptically polarized lasers. The enhancement effect was evident at higher Cu temperatures when comparing the plasma spectra that have circular and linear polarizations for different target temperatures. To understand the influence of laser-polarization and sample temperature on signal intensity, we calculated the plasma temperature (PT) and electron density (ED) . The change in PT and ED was consistent with the change in the atomic lines as the laser polarization was being adjusted. When raising the Cu temperature, the PT increased while the ED decreased. Raising the Cu temperature whilst adjusting the laser-polarization is effective for improving the signal of femtosecond LIBS compared to raising the initial sample temperature alone or only changing the laser polarization.

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Pressure-induced phase transition in transition metal trifluorides

Peng Liu(刘鹏), Meiling Xu(徐美玲), Jian Lv(吕健), Pengyue Gao(高朋越), Chengxi Huang(黄呈熙), Yinwei Li(李印威), Jianyun Wang(王建云), Yanchao Wang(王彦超), and Mi Zhou(周密)

2022 (10): 106104-106104. doi: 10.1088/1674-1056/ac5887

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As a fundamental thermodynamic variable, pressure can alter the bonding patterns and drive phase transitions leading to the creation of new high-pressure phases with exotic properties that are inaccessible at ambient pressure. Using the swarm intelligence structural prediction method, the phase transition of TiF₃, from R—3c to the Pnma phase, was predicted at high pressure, accompanied by the destruction of TiF₆ octahedra and formation of TiF₈ square antiprismatic units. The Pnma phase of TiF₃, formed using the laser-heated diamond-anvil-cell technique was confirmed via high-pressure x-ray diffraction experiments. Furthermore, the in situ electrical measurements indicate that the newly found Pnma phase has a semiconducting character, which is also consistent with the electronic band structure calculations. Finally, it was shown that this pressure-induced phase transition is a general phenomenon in ScF₃, VF₃, CrF₃, and MnF₃, offering valuable insights into the high-pressure phases of transition metal trifluorides.

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Synthesis and superconductivity in yttrium superhydrides under high pressure

Yingying Wang(王莹莹), Kui Wang(王奎), Yao Sun(孙尧), Liang Ma(马良), Yanchao Wang(王彦超), Bo Zou(邹勃), Guangtao Liu(刘广韬), Mi Zhou(周密), and Hongbo Wang(王洪波)

2022 (10): 106201-106201. doi: 10.1088/1674-1056/ac872e

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Flourishing rare earth superhydrides are a class of recently discovered materials that exhibit near-room-temperature superconductivity at high pressures, ushering in a new era of superconductivity research at high pressures. Yttrium superhydrides drew the most attention among these superhydrides due to their abundance of stoichiometries and excellent superconductivities. Here, we carried out a comprehensive study of yttrium superhydrides in a wide pressure range of 140 GPa—300 GPa. We successfully synthesized a series of superhydrides with the compositions of YH₄, YH₆, YH₇, and YH₉, and reported superconducting transition temperatures of 82 K at 167 GPa, 218 K at 165 GPa, 29 K at 162 GPa, and 230 K at 300 GPa, respectively, as evidenced by sharp drops in resistance. The structure and superconductivity of YH₄ were taken as a representative example and were also examined using x-ray diffraction measurements and the superconductivity suppression under external magnetic fields, respectively. Clathrate YH₁₀, a candidate for room-temperature superconductor, was not synthesized within the study pressure and temperature ranges of up to 300 GPa and 2000 K. The current study established a detailed foundation for future research into room-temperature superconductors in polynary yttrium-based superhydrides.

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Effect of the codoping of N—H—O on the growth characteristics and defects of diamonds under high temperature and high pressure

Zhenghao Cai(蔡正浩), Bowei Li(李博维), Liangchao Chen(陈良超), Zhiwen Wang(王志文), Shuai Fang(房帅), Yongkui Wang(王永奎), Hongan Ma(马红安), and Xiaopeng Jia(贾晓鹏)

2022 (10): 108104-108104. doi: 10.1088/1674-1056/ac7866

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Diamond crystals were synthesized with different doping proportions of N—H—O at 5.5 GPa—7.1 GPa and 1370 °C—1450 °C. With the increase in the N—H—O doping ratio, the crystal growth rate decreased, the temperature and pressure conditions required for diamond nucleation became increasingly stringent, and the diamond crystallization process was affected. [111] became the dominant plane of diamonds; surface morphology became block-like; and growth texture, stacking faults, and etch pits increased. The diamond crystals had a two-dimensional growth habit. Increasing the doping concentration also increased the amount of N that entered the diamond crystals as confirmed via Fourier transform infrared spectroscopy. However, crystal quality gradually deteriorated as verified by the red-shifting of Raman peak positions and the widening of the Raman full width at half maximum. With the increase in the doping ratio, the photoluminescence property of the diamond crystals also drastically changed. The intensity of the N vacancy center of the diamond crystals changed, and several Ni-related defect centers, such as the NE1 and NE3 centers, appeared. Diamond synthesis in N—H—O-bearing fluid provides important information for deepening our understanding of the growth characteristics of diamonds in complex systems and the formation mechanism of natural diamonds, which are almost always N-rich and full of various defect centers. Meanwhile, this study proved that the type of defect centers in diamond crystals could be regulated by controlling the N—H—O impurity contents of the synthesis system.

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Design of vertical diamond Schottky barrier diode with junction terminal extension structure by using the n-Ga₂O₃/p-diamond heterojunction

Wang Lin(林旺), Ting-Ting Wang(王婷婷), Qi-Liang Wang(王启亮), Xian-Yi Lv(吕宪义), Gen-Zhuang Li(李根壮), Liu-An Li(李柳暗), Jin-Ping Ao(敖金平), and Guang-Tian Zou(邹广田)

2022 (10): 108105-108105. doi: 10.1088/1674-1056/ac7e37

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A novel junction terminal extension structure is proposed for vertical diamond Schottky barrier diodes (SBDs) by using an n-Ga₂O₃/p-diamond heterojunction. The depletion region of the heterojunction suppresses part of the forward current conduction path, which slightly increases the on-resistance. On the other hand, the reverse breakdown voltage is enhanced obviously because of attenuated electric field crowding. By optimizing the doping concentration, length, and depth of n-Ga₂O₃, the trade-off between on-resistance and breakdown voltage with a high Baliga figure of merit (FOM) value is realized through Silvaco technology computer-aided design simulation. In addition, the effect of the work functions of the Schottky electrodes is evaluated. The results are beneficial to realizing a high-performance vertical diamond SBD.

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Relationship between the spatial position of the seed and growth mode for single-crystal diamond grown with an enclosed-type holder

Wen-Liang Xie(谢文良), Xian-Yi Lv(吕宪义), Qi-Liang Wang(王启亮), Liu-An Li(李柳暗), and Guang-Tian Zou(邹广田)

2022 (10): 108106-108106. doi: 10.1088/1674-1056/ac7e35

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The relationship between the spatial position of the diamond seed and growth mode is investigated with an enclosed-type holder for single-crystal diamond growth using the microwave plasma chemical vapor deposition epitaxial method. The results demonstrate that there are three main regions by varying the spatial position of the seed. Due to the plasma concentration occurring at the seed edge, a larger depth is beneficial to transfer the plasma to the holder surface and suppress the polycrystalline diamond rim around the seed edge. However, the plasma density at the edge decreases drastically when the depth is too large, resulting in the growth of a vicinal grain plane and the reduction of surface area. By adopting an appropriate spatial location, the size of single-crystal diamond can be increased from 7 mm × 7 mm × 0.35 mm to 8.6 mm × 8.6 mm × 2.8 mm without the polycrystalline diamond rim.

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Up-conversion detection of mid-infrared light carrying orbital angular momentum

Zheng Ge(葛正), Chen Yang(杨琛), Yin-Hai Li(李银海), Yan Li(李岩), Shi-Kai Liu(刘世凯), Su-Jian Niu(牛素俭), Zhi-Yuan Zhou(周志远), and Bao-Sen Shi(史保森)

2022 (10): 104210-104210. doi: 10.1088/1674-1056/ac6eda

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Frequency up-conversion is an effective method of mid-infrared (MIR) detection by converting long-wavelength photons to the visible domain, where efficient detectors are readily available. Here, we generate MIR light carrying orbital angular momentum (OAM) from a difference frequency generation process and perform up-conversion on it via sum frequency conversion in a bulk quasi-phase-matching crystal. The maximum quantum conversion efficiencies from MIR to visible are 34.0%, 10.4%, and 3.5% for light with topological charges of 0, 1, and 2, respectively, achieved by utilizing an optimized strong pump light. We also verify the OAM conservation with a specially designed interferometer, and the results agree well with the numerical simulations. Our study opens up the possibilities for generating, manipulating, and detecting MIR light that carries OAM, and will have great potential for optical communications and remote sensing in the MIR regime.

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Observation of multiple charge density wave phases in epitaxial monolayer 1T-VSe₂ film

Junyu Zong(宗君宇), Yang Xie(谢阳), Qinghao Meng(孟庆豪), Qichao Tian(田启超), Wang Chen(陈望), Xuedong Xie(谢学栋), Shaoen Jin(靳少恩), Yongheng Zhang(张永衡), Li Wang(王利), Wei Ren(任伟), Jian Shen(沈健), Aixi Chen(陈爱喜), Pengdong Wang(王鹏栋), Fang-Sen Li(李坊森), Zhaoyang Dong(董召阳), Can Wang(王灿), Jian-Xin Li(李建新), and Yi Zhang(张翼)

2022 (10): 107301-107301. doi: 10.1088/1674-1056/ac5c3e

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As a special order of electronic correlation induced by spatial modulation, the charge density wave (CDW) phenomena in condensed matters attract enormous research interests. Here, using scanning—tunneling microscopy in various temperatures, we discover a hidden incommensurate stripe-like CDW order besides the ($sqrt{7}$ × $sqrt{3}$) CDW phase at low-temperature of 4 K in the epitaxial monolayer 1T-VSe₂} film. Combining the variable-temperature angle-resolved photoemission spectroscopic (ARPES) measurements, we discover a two-step transition of an anisotropic CDW gap structure that consists of two parts Δ₁ and Δ₂. The gap part Δ₁ that closes around ～ 150 K is accompanied with the vanish of the ($sqrt{7}$ × $sqrt{3}$) CDW phase. While another momentum-dependent gap part Δ₂ can survive up to ～ 340 K, and is suggested to the result of the incommensurate CDW phase. This two-step transition with anisotropic gap opening and the resulted evolution in ARPES spectra are corroborated by our theoretical calculation based on a phenomenological form for the self-energy containing a two-gap structure Δ₁ + Δ₂, which suggests different forming mechanisms between the ($sqrt{7}$ × $sqrt{3}$) and the incommensurate CDW phases. Our findings provide significant information and deep understandings on the CDW phases in monolayer 1T-VSe₂} film as a two-dimensional (2D) material.

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Sign reversal of anisotropic magnetoresistance and anomalous thickness-dependent resistivity in Sr₂CrWO₆/SrTiO₃ films

Chunli Yao(姚春丽), Tingna Shao(邵婷娜), Mingrui Liu(刘明睿), Zitao Zhang(张子涛), Weimin Jiang(姜伟民), Qiang Zhao(赵强), Yujie Qiao(乔宇杰), Meihui Chen(陈美慧), Xingyu Chen(陈星宇), Ruifen Dou(窦瑞芬), Changmin Xiong(熊昌民), and Jiacai Nie(聂家财)

2022 (10): 107302-107302. doi: 10.1088/1674-1056/ac6164

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High-quality Sr₂CrWO₆ (SCWO) films have been grown on SrTiO₃ (STO) substrate by pulsed laser deposition under low oxygen pressure. With decrease of the film thickness, a drastic conductivity increase is observed. The Hall measurements show that the thicker the film, the lower the carrier density. An extrinsic mechanism of charge doping due to the dominance of oxygen vacancies at SCWO/STO interfaces is proposed. The distribution and gradient of carrier concentration in SCWO films are considered to be related to this phenomenon. Resistivity behavior observed in these films is found to follow the variable range hopping model. It is revealed that with increase of the film thickness, the extent of disorder in the lattice increases, which gives a clear evidence of disorder-induced localization charge carriers in these films. Magnetoresistance measurements show that there is a negative magnetoresistance in SCWO films, which is considered to be caused by the magnetic scattering of magnetic elements Cr³⁺ and W⁵⁺. In addition, a sign reversal of anisotropic magnetoresistance (AMR) in SCWO film is observed for the first time, when the temperature varies across a characteristic value, T_M. Magnetization—temperature measurements demonstrate that this AMR sign reversal is caused by the direction transition of easy axis of magnetization from the in-plane ferromagnetic order at T > T_M to the out-of-plane at T < T_M.

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Near-field multiple super-resolution imaging from Mikaelian lens to generalized Maxwell's fish-eye lens

Yangyang Zhou(周杨阳), and Huanyang Chen(陈焕阳)

2022 (10): 104205-104205. doi: 10.1088/1674-1056/ac5d34

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Super-resolution imaging is vital for optical applications, such as high capacity information transmission, real-time bio-molecular imaging, and nanolithography. In recent years, technologies and methods of super-resolution imaging have attracted much attention. Different kinds of novel lenses, from the superlens to the super-oscillatory lens, have been designed and fabricated to break through the diffraction limit. However, the effect of the super-resolution imaging in these lenses is not satisfactory due to intrinsic loss, aberration, large sidebands, and so on. Moreover, these lenses also cannot realize multiple super-resolution imaging. In this research, we introduce the solid immersion mechanism to Mikaelian lens (ML) for multiple super-resolution imaging. The effect is robust and valid for broadband frequencies. Based on conformal transformation optics as a bridge linking the solid immersion ML and generalized Maxwell's fish-eye lens (GMFEL), we also discovered the effect of multiple super-resolution imaging in the solid immersion GMFEL.

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Enhanced single photon emission in silicon carbide with Bull's eye cavities

Xing-Hua Liu(刘兴华), Fang-Fang Ren(任芳芳), Jiandong Ye(叶建东), Shuxiao Wang(王书晓), Wei-Zong Xu(徐尉宗), Dong Zhou(周东), Mingbin Yu(余明斌), Rong Zhang(张荣), Youdou Zheng(郑有炓), and Hai Lu(陆海)

2022 (10): 104206-104206. doi: 10.1088/1674-1056/ac785f

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The authors demonstrate a Bull's eye cavity design that is composed of circular Bragg gratings and micropillar optical cavity in 4H silicon carbide (4H-SiC) for single photon emission. Numerical calculations are used to investigate and optimize the emission rate and directionality of emission. Thanks to the optical mode resonances and Bragg reflections, the radiative decay rates of a dipole embedded in the cavity center is enhanced by 12.8 times as compared to that from a bulk 4H-SiC. In particular, a convergent angular distribution of the emission in far field is simultaneously achieved, which remarkably boost the collection efficiency. The findings of this work provide an alternative architecture to manipulate light—matter interactions for achieving high-efficient SiC single photon sources towards applications in quantum information technologies.

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Spatiotemporal mode-locked multimode fiber laser with dissipative four-wave mixing effect

Ming-Wei Qiu(邱明伟), Chao-Qun Cai(蔡超群), and Zu-Xing Zhang(张祖兴)

2022 (10): 104207-104207. doi: 10.1088/1674-1056/ac6ee9

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The high degree of freedom and novel nonlinear phenomena of multimode fiber are attracting attention. In this work, we demonstrate a spatiotemporal mode-locked multimode fiber laser, which relies on microfiber knot resonance (MKR) via dissipative four-wave-mixing (DFMW) to achieve high-repetition-rate pulses. Apart from that, DFMW mode locking with switchable central wavelengths can also be obtained. It was further found that high pulse energy induced nonlinear effect of the dominant mode-locking mechanism transforming from DFMW to nonlinear Kerr beam cleaning effect (NL-KBC). The experimental results are valuable for further comprehending the dynamic characteristics of spatiotemporal mode-locked multimode fiber lasers, facilitating them much more accessible for applications.

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Phase-matched second-harmonic generation in hybrid polymer-LN waveguides

Zijie Wang(王梓杰), Bodong Liu(刘伯东), Chunhua Wang(王春华), and Huakang Yu(虞华康)

2022 (10): 104208-104208. doi: 10.1088/1674-1056/ac6edc

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Here we propose a hybrid polymer-LN waveguide for achieving phase-matched second-harmonic generation (SHG). From the aspect of super-mode theory, the geometric parameters of the hybrid semi-nonlinear waveguide were optimized to utilize both symmetric (even) and antisymmetric (odd) modes of the pump and SHG waves so as to facilitate phase matching with large modal overlap. Phase matching between a fundamental even (TE₀₀-like) mode at 1320 nm and a fundamental odd (TE₀₁-like) mode at 660 nm was found with a calculated modal overlap integral of 0.299, while utilizing the largest nonlinear coefficient d₃₃, and achieving an efficient calculated normalized conversion efficiency of 148% W^-1·cm^-2. Considering the fabrication feasibility of such hybrid waveguide with features including etchless, large dimension, and low structural sensitivity, we believe our findings would provide a useful reference for future on-chip efficient nonlinear conversion devices.

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Bound states in the continuum in metal—dielectric photonic crystal with a birefringent defect

Hongzhen Tang(唐宏珍), Peng Hu(胡鹏), Da-Jian Cui(崔大健), Hong Xiang(向红), and Dezhuan Han(韩德专)

2022 (10): 104209-104209. doi: 10.1088/1674-1056/ac6db6

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By using the difference of the band structure for the TE and TM waves in the metal—dielectric photonic crystals beyond the light cone and the birefringence of the anisotropic crystal, a one-dimensional photonic system is constructed to realize the bound states in the continuum (BICs). In addition to the BICs arising from the polarization incompatibility, the Friedrich—Wintgen BICs are also achieved when the leaking TM wave is eliminated due to the destructive interference of its ordinary and extraordinary wave components in the anisotropic crystal. A modified scheme favorable for practical application is also proposed. This scheme for BICs may help to suppress the radiation loss in the metal—dielectric photonic crystal systems.

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Quantum simulation of τ-anti-pseudo-Hermitian two-level systems

Chao Zheng(郑超)

2022 (10): 100301-100301. doi: 10.1088/1674-1056/ac8738

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Different from the Hermitian case, non-Hermitian (NH) systems have novel properties and strongly relate to open and dissipative quantum systems. In this work, we investigate how to simulate τ-anti-pseudo-Hermitian systems in a Hermitian quantum device using linear combinations of unitaries and duality quantum algorithm. Specifying the τ to time-reversal (T) and parity-time-reversal (PT) operators, we construct the two NH two-level systems, design quantum circuits including three qubits, and decide the quantum gates explicitly in detail. We also calculate the success probabilities of the simulation. Experimental implementation can be expected in small quantum simulator.

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Parallel optimization of underwater acoustic models: A survey

Zi-jie Zhu(祝子杰), Shu-qing Ma(马树青), Xiao-Qian Zhu(朱小谦), Qiang Lan(蓝强), Sheng-Chun Piao(朴胜春), and Yu-Sheng Cheng(程玉胜)

2022 (10): 104301-104301. doi: 10.1088/1674-1056/ac7ccc

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Underwater acoustic models are effective tools for simulating underwater sound propagation. More than 50 years of research have been conducted on the theory and computational models of sound propagation in the ocean. Unfortunately, underwater sound propagation models were unable to solve practical large-scale three-dimensional problems for many years due to limited computing power and hardware conditions. Since the mid-1980s, research on high performance computing for acoustic propagation models in the field of underwater acoustics has flourished with the emergence of high-performance computing platforms, enabling underwater acoustic propagation models to solve many practical application problems that could not be solved before. In this paper, the contributions of research on high-performance computing for underwater acoustic propagation models since the 1980s are thoroughly reviewed and the possible development directions for the future are outlined.

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Energy band and charge-carrier engineering in skutterudite thermoelectric materials

Zhiyuan Liu(刘志愿), Ting Yang(杨婷), Yonggui Wang(王永贵), Ailin Xia(夏爱林), and Lianbo Ma(马连波)

2022 (10): 107303-107303. doi: 10.1088/1674-1056/ac6ee8

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The binary CoSb₃ skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of CoSb₃ materials can be significantly reduced through phonon engineering, such as low-dimensional structure, the introduction of nano second phases, nanointerfaces or nanopores, which greatly improves their ZT values. The phonon engineering can optimize significantly the thermal transport properties of CoSb₃-based materials. However, the improvement of the electronic transport properties is not obvious, or even worse. Energy band and charge-carrier engineering can significantly improve the electronic transport properties of CoSb₃-based materials while optimizing the thermal transport properties. Therefore, the decoupling of thermal and electronic transport properties of CoSb₃-based materials can be realized by energy band and charge-carrier engineering. This review summarizes some methods of optimizing synergistically the electronic and thermal transport properties of CoSb₃ materials through the energy band and charge-carrier engineering strategies. Energy band engineering strategies include band convergence or resonant energy levels caused by doping/filling. The charge-carrier engineering strategy includes the optimization of carrier concentration and mobility caused by doping/filling, forming modulation doped structures or introducing nano second phase. These strategies are effective means to improve performance of thermoelectric materials and provide new research ideas of development of high-efficiency thermoelectric materials.

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Multiplexing technology based on SQUID for readout of superconducting transition-edge sensor arrays

Xinyu Wu(吴歆宇), Qing Yu(余晴), Yongcheng He(何永成), Jianshe Liu(刘建设), and Wei Chen(陈炜)

2022 (10): 108501-108501. doi: 10.1088/1674-1056/ac693c

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Multiplexing technologies based on superconducting quantum interference devices (SQUIDs) are crucial to cryogenic readout of superconducting transition-edge sensor (TES) arrays. Demands for large-scale TES arrays promote the development of multiplexing technologies towards large multiplexing factors and low readout noise. The development of multiplexing technologies also facilitates new applications of TES arrays in a wide range of frequencies. Here we summarize different types of SQUID-based multiplexing technologies including time-division multiplexing, code-division multiplexing, frequency-division multiplexing and microwave SQUID multiplexing. The advances and parameter constraints of each multiplexing technology are also discussed.

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Recent advances in two-dimensional layered and non-layered materials hybrid heterostructures

Haixin Ma(马海鑫), Yanhui Xing(邢艳辉), Boyao Cui(崔博垚), Jun Han(韩军), Binghui Wang(王冰辉), and Zhongming Zeng(曾中明)

2022 (10): 108502-108502. doi: 10.1088/1674-1056/ac5c36

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With the development of Moore's law, the future trend of devices will inevitably be shrinking and integration to further achieve size reduction. The emergence of new two-dimensional non-layered materials (2DNLMs) not only enriches the 2D material family to meet future development, but also stimulates the global enthusiasm for basic research and application technologies in the 2D field. Van der Waals (vdW) heterostructures, in which two-dimensional layered materials (2DLMs) are physically stacked layer by layer, can also occur between 2DLMs and 2DNLMs hybrid heterostructures, providing an alternative platform for nanoelectronics and optoelectronic applications. Here, we outline the recent developments of 2DLMs/2DNLMs hybrid heterostructures, with particular emphasis on major advances in synthetic methods and applications. And the categories and crystal structures of 2DLMs and 2DNLMs are also shown. We highlight some promising applications of the heterostructures in electronics, optoelectronics, and catalysis. Finally, we provide conclusions and future prospects in the 2D materials field.

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Experimental realization of two-dimensional single-layer ultracold gases of ⁸⁷Rb in an accordion lattice

Liangwei Wang(王良伟), Kai Wen(文凯), Fangde Liu(刘方德), Yunda Li(李云达), Pengjun Wang(王鹏军), Lianghui Huang(黄良辉), Liangchao Chen(陈良超), Wei Han(韩伟), Zengming Meng(孟增明), and Jing Zhang(张靖)

2022 (10): 103401-103401. doi: 10.1088/1674-1056/ac873c

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We experimentally realize two-dimensional (2D) single-layer ultracold gases of ⁸⁷Rb by dynamically tuning the periodicity of a standing wave, known as accordion lattice. In order to load ⁸⁷Rb Bose—Einstein condensate into single dark fringe node of the blue detuning optical lattice, we reduce the lattice periodicity from 26.7 μ to 3.5 μ with the help of an acousto-optic deflector (AOD) to compress the three-dimensional BEC adiabatically into a flat and uniform quasi-2D single-layer. We describe the experimental procedure of the atoms loading into the accordion lattice in detail and present the characteristics of the quasi-2D ultracold gases. This setup provides an important platform for studying in- and out-of equilibrium physics, phase transition and 2D topological matter.

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A minimal model for the auxetic response of liquid crystal elastomers

Bingyu Yu(於冰宇), Yuanchenxi Gao(高袁晨曦), Bin Zheng(郑斌), Fanlong Meng(孟凡龙), Yu Fang(方羽), Fangfu Ye(叶方富), and Zhongcan Ouyang(欧阳钟灿)

2022 (10): 104601-104601. doi: 10.1088/1674-1056/ac754e

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We develop a minimal phenomenological model to describe the auxetic response recently observed in liquid crystal elastomers, and further determine by theoretical calculation the critical condition required for the auxetic response to occur.

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Boosting the performance of crossed ZnO microwire UV photodetector by mechanical contact homo-interface barrier

Yinzhe Liu(刘寅哲), Kewei Liu(刘可为), Jialin Yang(杨佳霖), Zhen Cheng(程祯), Dongyang Han(韩冬阳), Qiu Ai(艾秋), Xing Chen(陈星), Yongxue Zhu(朱勇学), Binghui Li(李炳辉), Lei Liu(刘雷), and Dezhen Shen(申德振)

2022 (10): 106101-106101. doi: 10.1088/1674-1056/ac80b0

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One-dimensional (1D) micro/nanowires of wide band gap semiconductors have become one of the most promising blocks of high-performance photodetectors. However, in the axial direction of micro/nanowires, the carriers can transport freely driven by an external electric field, which usually produces large dark current and low detectivity. Here, an UV photodetector built from three cross-intersecting ZnO microwires with double homo-interfaces is demonstrated by the chemical vapor deposition and physical transfer techniques. Compared with the reference device without interface, the dark current of this ZnO double-interface photodetector is significantly reduced by nearly 5 orders of magnitude, while the responsivity decreases slightly, thereby greatly improving the normalized photocurrent-to-dark current ratio. In addition, ZnO double-interface photodetector exhibits a much faster response speed (～ 0.65 s) than the no-interface device (～ 95 s). The improved performance is attributed to the potential barriers at the microwire—microwire homo-interfaces, which can regulate the carrier transport. Our findings in this work provide a promising approach for the design and development of high-performance photodetectors.

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Identification of the phosphorus-doping defect in MgS as a potential qubit

Jijun Huang(黄及军), and Xueling Lei(雷雪玲)

2022 (10): 106102-106102. doi: 10.1088/1674-1056/ac7dbc

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The P_S defect is obtained by replacing one S atom with one P atom in the wide-bandgap semiconductor MgS. Based on first-principles calculations, the formation energy, defect levels, and electronic structure of the P_S defect in different charge states are evaluated. We predict that the neutral P_S⁰ and positively charged P_S⁺¹ are the plausible qubit candidates for the construction of quantum systems, since they maintain the spin conservation during optical excited transition. The zero-phonon lines at the P_S⁰ and P_S⁺¹ defects are 0.43 eV and 0.21 eV, respectively, which fall in the infrared band. In addition, the zero-field splitting parameter D of the P_S⁺¹ with spin-triplet is 2920 MHz, which is in the range of microwave, showing that the P_S⁺¹ defect can be manipulated by microwave. Finally, the principal values of the hyperfine tensor are examined, it is found that they decay exponentially with the distance from the defect site.

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Unusual thermodynamics of low-energy phonons in the Dirac semimetal Cd₃As₂

Zhen Wang(王振), Hengcan Zhao(赵恒灿), Meng Lyu(吕孟), Junsen Xiang(项俊森), Qingxin Dong(董庆新), Genfu Chen(陈根富), Shuai Zhang(张帅), and Peijie Sun(孙培杰)

2022 (10): 106501-106501. doi: 10.1088/1674-1056/ac8928

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By studying the thermal conductivity, specific heat, elastic modulus, and thermal expansion as a function of temperature for Cd₃As₂, we have unveiled a couple of important thermodynamic features of the low-energy phonons strongly interacting with Dirac electrons. The existence of soft optical phonons, as inferred from the extremely low thermal conductivity, is unambiguously confirmed by low-temperature specific heat revealing significant deviation from Debye's description. The estimated Debye temperature is small in the range of 100—200 K and varies significantly depending upon the measurement used in its experimental determination. The thermodynamic Grüneisen ratio γ reveals a remarkable reduction below about 100 K, an energy scale that is highly relevant to the Dirac states, towards negative values below about 10 K that are indicative of lattice instability.

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Observation of quadratic magnetoresistance in twisted double bilayer graphene

Yanbang Chu(褚衍邦), Le Liu(刘乐), Yiru Ji(季怡汝), Jinpeng Tian(田金朋), Fanfan Wu(吴帆帆), Jian Tang(汤建), Yalong Yuan(袁亚龙), Yanchong Zhao(赵岩翀), Xiaozhou Zan(昝晓州), Rong Yang(杨蓉), Kenji Watanabe, Takashi Taniguchi, Dongxia Shi(时东霞), Wei Yang(杨威), and Guangyu Zhang(张广宇)

2022 (10): 107201-107201. doi: 10.1088/1674-1056/ac6866

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Magnetoresistance ({MR}) provides rich information about Fermi surface, carrier scatterings, and exotic phases for a given electronic system. Here, we report a study of the magnetoresistance for the metallic states in twisted double bilayer graphene (TDBG). We observe quadratic magnetoresistance in both Moiré valence band (VB) and Moiré conduction band (CB). The scaling analysis shows validity of Kohler's rule in the Moiré valence band. On the other hand, the quadratic magnetoresistance appears near the halo structure in the Moiré conduction band, and it violates Kohler's rule, demonstrating the {MR} scaling related to band structure in TDBG. We also propose an alternative scaling near the halo structure. Further analysis implies that the observed quadratic magnetoresistance and alternative scaling in conduction band are related to the halo boundary. Our results may inspire investigation on {MR} in twisted 2D materials and provide new knowledge for {MR} study in condensed matter physics.

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Ac Josephson effect in Corbino-geometry Josephson junctions constructed on Bi₂Te₃ surface

Yunxiao Zhang(张云潇), Zhaozheng Lyu(吕昭征), Xiang Wang(王翔), Enna Zhuo(卓恩娜), Xiaopei Sun(孙晓培), Bing Li(李冰), Jie Shen(沈洁), Guangtong Liu(刘广同), Fanming Qu(屈凡明), and Li Lü(吕力)

2022 (10): 107402-107402. doi: 10.1088/1674-1056/ac89d4

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Recently, a Corbino-geometry type of Josephson junction constructed on the surface of topological insulators has been proposed for hosting and braiding Majorana zero modes. As a first step to test this proposal, we successfully fabricated Corbino-geometry Josephson junctions (JJs) on the surface of Bi₂Te₃ flakes. Ac Josephson effect with fractional Shapiro steps was observed in the Corbino-geometry JJs while the flux in the junction area was quantized. By analyzing the experimental data using the resistively shunted Josephson junction model, we found that the Corbino-geometry JJs exhibit a skewed current—phase relation due to its high transparency. The results suggest that Corbino-geometry JJs constructed on the surface of topological insulators may provide a promising platform for studying Majorana-related physics.

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Multiple modes of perpendicular magnetization switching scheme in single spin—orbit torque device

Tong-Xi Liu(刘桐汐), Zhao-Hao Wang(王昭昊), Min Wang(王旻), Chao Wang(王朝), Bi Wu(吴比), Wei-Qiang Liu(刘伟强), and Wei-Sheng Zhao(赵巍胜)

2022 (10): 107501-107501. doi: 10.1088/1674-1056/ac6ed9

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Spin—orbit torque (SOT) has been considered as one of the promising technologies for the next-generation magnetic random access memory (MRAM). So far, SOT has been widely utilized for inducing various modes of magnetization switching. However, it is a challenge that so many multiple modes of magnetization switching are integrated together. Here we propose a method of implementing both unipolar switching and bipolar switching of the perpendicular magnetization within a single SOT device. The mode of switching can be easily changed by tuning the amplitude of the applied current. We show that the field-like torque plays an important role in switching process. The field-like torque induces the precession of the magnetization in the case of unipolar switching, however, the field-like torque helps to generate an effective z-component torque in the case of bipolar switching. In addition, the influence of key parameters on the mode of switching is discussed, including the field-like torque strength, the bias field, and the current density. Our proposal can be used to design novel reconfigurable logic circuits in the near future.

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Peptide backbone-copper ring structure: A molecular insight into copper-induced amyloid toxicity

Jing Wang(王静), Hua Li(李华), Xiankai Jiang(姜先凯), Bin Wu(吴斌), Jun Guo(郭俊), Xiurong Su(苏秀榕), Xingfei Zhou(周星飞), Yu Wang(王宇), Geng Wang(王耿), Heping Geng(耿和平), Zheng Jiang(姜政), Fang Huang(黄方), Gang Chen(陈刚), Chunlei Wang(王春雷), Haiping Fang(方海平), and Chenqi Xu(许琛琦)

2022 (10): 108702-108702. doi: 10.1088/1674-1056/ac8920

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Copper ions can promote amyloid diseases that are associated with amyloid peptides, such as type 2 diabetes (T2D), Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). However, the underlying molecular mechanism remains obscure. Here we present that Cu²⁺ is able to specifically bind to the backbone of T2D-related human islet amyloid polypeptide (hIAPP) by forming a ring structure, which causes the reduction of Cu²⁺ to Cu⁺ to produce reactive oxygen species (ROS) and the modulation of hIAPP aggregation. Nuclear magnetic resonance spectroscopy showed that Cu²⁺ bound to the backbone of a turn region, His18—Ser21, which is critical for hIAPP aggregation. Ab initio calculations and x-ray absorption fine structure analyses revealed that Cu²⁺ simultaneously bound with both the amide nitrogen and carbonyl oxygen on the peptide backbone, resulting in a ring structure, and causing the reduction of Cu²⁺ to Cu⁺ to form a hIAPP-Cu⁺ complex. 2',7'-dichlorodihydrofluorescin diacetate fluorescence measurements further indicated that this complex led to enhanced ROS levels in rat insulinoma cells. Additionally, thioflavin T fluorescence and atomic force microscopy measurements denoted that the backbone-Cu ring structure largely modulated hIAPP aggregation, including the inhibition of hIAPP fibrillation and the promotion of peptide oligomerization. These findings shed new light on the molecular mechanism of Cu²⁺-induced amyloid toxicity involving both the enhancement of ROS and the modulation of hIAPP aggregation.

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Finite-time Mittag—Leffler synchronization of fractional-order complex-valued memristive neural networks with time delay

Guan Wang(王冠), Zhixia Ding(丁芝侠), Sai Li(李赛), Le Yang(杨乐), and Rui Jiao(焦睿)

2022 (10): 100201-100201. doi: 10.1088/1674-1056/ac7209

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Without dividing the complex-valued systems into two real-valued ones, a class of fractional-order complex-valued memristive neural networks (FCVMNNs) with time delay is investigated. Firstly, based on the complex-valued sign function, a novel complex-valued feedback controller is devised to research such systems. Under the framework of Filippov solution, differential inclusion theory and Lyapunov stability theorem, the finite-time Mittag—Leffler synchronization (FTMLS) of FCVMNNs with time delay can be realized. Meanwhile, the upper bound of the synchronization settling time (SST) is less conservative than previous results. In addition, by adjusting controller parameters, the global asymptotic synchronization of FCVMNNs with time delay can also be realized, which improves and enrich some existing results. Lastly, some simulation examples are designed to verify the validity of conclusions.

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Measurement-device-independent quantum secret sharing with hyper-encoding

Xing-Xing Ju(居星星), Wei Zhong(钟伟), Yu-Bo Sheng(盛宇波), and Lan Zhou(周澜)

2022 (10): 100302-100302. doi: 10.1088/1674-1056/ac70bb

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Quantum secret sharing (QSS) is a typical multi-party quantum communication mode, in which the key sender splits a key into several parts and the participants can obtain the key by cooperation. Measurement-device-independent quantum secret sharing (MDI-QSS) is immune to all possible attacks from measurement devices and can greatly enhance QSS's security in practical applications. However, previous MDI-QSS's key generation rate is relatively low. Here, we adopt the polarization-spatial-mode hyper-encoding technology in the MDI-QSS, which can increase single photon's channel capacity. Meanwhile, we use the cross-Kerr nonlinearity to realize the complete hyper-entangled Greenberger—Horne—Zeilinger state analysis. Both above factors can increase MDI-QSS's key generation rate by about 10³. The proposed hyper-encoded MDI-QSS protocol may be useful for future multiparity quantum communication applications.

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Quantum correlation and entropic uncertainty in a quantum-dot system

Ying-Yue Yang(杨颖玥), Li-Juan Li(李丽娟), Liu Ye(叶柳), and Dong Wang(王栋)

2022 (10): 100303-100303. doi: 10.1088/1674-1056/ac7295

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We explore the dynamical behaviors of the measurement uncertainty and quantum correlation for a vertical quantum-dot system in the presence of magnetic field, including electron-electron interaction and Coulomb-blocked systems. Stemming from the quantum-memory-assisted entropic uncertainty relation, the uncertainty of interest is associated with temperature and parameters related to the magnetic field. Interestingly, the temperature has two kinds of influences on the variation of measurement uncertainty with respect to the magnetic-field-related parameters. We also discuss the relation between the lower bound of Berta et al. and the quantum discord. It is found that there is a natural competition between the quantum discord and the entropy min_{Π_i^B}S_{Π_i^B}(ρ_A|B). Finally, we bring in two improved bounds to offer a more precise limit to the entropic uncertainty.

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Spin transfer nano-oscillator based on synthetic antiferromagnetic skyrmion pair assisted by perpendicular fixed magnetic field

Yun-Xu Ma(马云旭), Jia-Ning Wang(王佳宁), Zhao-Zhuo Zeng(曾钊卓), Ying-Yue Yuan(袁映月), Jin-Xia Yang(杨金霞), Hui-Bo Liu(刘慧博), Sen-Fu Zhang(张森富), Jian-Bo Wang(王建波), Chen-Dong Jin(金晨东), and Qing-Fang Liu(刘青芳)

2022 (10): 100501-100501. doi: 10.1088/1674-1056/ac6ee4

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As a microwave generator, spin transfer nano-oscillator (STNO) based on skyrmion promises to become one of the next-generation spintronic devices. However, there still exist a few limitations to the practical applications. In this paper, we propose a new STNO based on synthetic antiferromagnetic (SAF) skyrmion pair assisted by a perpendicular fixed magnetic field. It is found that the oscillation frequency of this kind of STNO can reach up to 5.0 GHz, and the multiple oscillation peak with higher frequency can be realized under a fixed out-of-plane magnetic field. Further investigation shows that the skyrmion stability is improved by bilayer antiferromagnetic coupling, which guarantees the stability process of skyrmion under higher spin-polarized current density. Our results provide the alternative possibilities for designing new skyrmion-based STNO to further improve the oscillation frequency, and realize the output of multiple frequency microwave signal.

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Fusionable and fissionable waves of (2+1)-dimensional shallow water wave equation

Jing Wang(王静), Xue-Li Ding(丁学利), and Biao Li(李彪)

2022 (10): 100502-100502. doi: 10.1088/1674-1056/ac70c0

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We investigate a (2+1)-dimensional shallow water wave equation and describe its nonlinear dynamical behaviors in physics. Based on the N-soliton solutions, the higher-order fissionable and fusionable waves, fissionable or fusionable waves mixed with soliton molecular and breather waves can be obtained by various constraints of special parameters. At the same time, by the long wave limit method, the interaction waves between fissionable or fusionable waves with higher-order lumps are acquired. Combined with the dynamic figures of the waves, the properties of the solution are deeply studied to reveal the physical significance of the waves.

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Extremely hidden multi-stability in a class of two-dimensional maps with a cosine memristor

Li-Ping Zhang(张丽萍), Yang Liu(刘洋), Zhou-Chao Wei(魏周超), Hai-Bo Jiang(姜海波), Wei-Peng Lyu(吕伟鹏), and Qin-Sheng Bi(毕勤胜)

2022 (10): 100503-100503. doi: 10.1088/1674-1056/ac7294

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We present a class of two-dimensional memristive maps with a cosine memristor. The memristive maps do not have any fixed points, so they belong to the category of nonlinear maps with hidden attractors. The rich dynamical behaviors of these maps are studied and investigated using different numerical tools, including phase portrait, basins of attraction, bifurcation diagram, and Lyapunov exponents. The two-parameter bifurcation analysis of the memristive map is carried out to reveal the bifurcation mechanism of its dynamical behaviors. Based on our extensive simulation studies, the proposed memristive maps can produce hidden periodic, chaotic, and hyper-chaotic attractors, exhibiting extremely hidden multi-stability, namely the coexistence of infinite hidden attractors, which was rarely observed in memristive maps. Potentially, this work can be used for some real applications in secure communication, such as data and image encryptions.

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Finite-time synchronization of uncertain fractional-order multi-weighted complex networks with external disturbances via adaptive quantized control

Hongwei Zhang(张红伟), Ran Cheng(程然), and Dawei Ding(丁大为)

2022 (10): 100504-100504. doi: 10.1088/1674-1056/ac686b

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The finite-time synchronization of fractional-order multi-weighted complex networks (FMCNs) with uncertain parameters and external disturbances is studied. Firstly, based on fractional calculus characteristics and Lyapunov stability theory, quantized controllers are designed to guarantee that FMCNs can achieve synchronization in a limited time with and without coupling delay, respectively. Then, appropriate parameter update laws are obtained to identify the uncertain parameters in FMCNs. Finally, numerical simulation examples are given to validate the correctness of the theoretical results.

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Periodic and chaotic oscillations in mutual-coupled mid-infrared quantum cascade lasers

Zhi-Wei Jia(贾志伟), Li Li(李丽), Yi-Yan Guo(郭一岩), An-Bang Wang(王安帮), Hong Han(韩红), Jin-Chuan Zhang(张锦川), Pu Li(李璞), Shen-Qiang Zhai(翟慎强), and Feng-Qi Liu(刘峰奇)

2022 (10): 100505-100505. doi: 10.1088/1674-1056/ac8f34

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Dynamic states in mutual-coupled mid-infrared quantum cascade lasers (QCLs) were numerically investigated in the parameter space of injection strength and detuning frequency based on the Lang—Kobayashi equations model. Three types of period-one states were found, with different periods of injection time delay τ_inj, 2τ_inj, and reciprocal of the detuning frequency. Besides, square-wave, quasi-period, pulse-burst and chaotic oscillations were also observed. It is concluded that external-cavity periodic dynamics and optical modes beating are the mainly periodic dynamics. The interaction of the two periodic dynamics and the high-frequency dynamics stimulated by strong injection induces the dynamic states evolution. This work helps to understand the dynamic behaviors in QCLs and shows a new way to mid-infrared wide-band chaotic laser.

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Molecule opacity study on low-lying states of CS

Rui Li(李瑞), Jiqun Sang(桑纪群), Xiaohe Lin(林晓贺), Jianjun Li(李建军), Guiying Liang(梁桂颖), and Yong Wu(吴勇)

2022 (10): 103101-103101. doi: 10.1088/1674-1056/ac834f

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CS molecule, which plays a key role in atmospheric and astrophysical circumstances, has drawn great attention for long time. Owing to its large state density, the detailed information of the electronic structure of CS is still lacking. In this work, the high-level MRCI+Q method is used to compute the potential energy curves, dipole moments and transition dipole moments of singlet and triplet states correlated with the lowest dissociation limit of CS, based on which high accurate vibration—rotation levels and spectroscopic constants of bound states are evaluated. The opacity of CS relevant to atmospheric circumstance is computed at a pressure of 100 atms for different temperatures. With the increase of temperature, band systems from different transitions mingle with each other, and band boundaries become blurred, which are originated from the increased population on vibrational excited states and electronic excited states at high temperature.

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Formation of high-density cold molecules via electromagnetic trap

Ya-Bing Ji(纪亚兵), Bin Wei(魏斌), Heng-Jiao Guo(郭恒娇), Qing Liu(刘青), Tao Yang(杨涛), Shun-Yong Hou(侯顺永), and Jian-Ping Yin(印建平)

2022 (10): 103201-103201. doi: 10.1088/1674-1056/ac720c

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Preparation and control of cold molecules are advancing rapidly, motivated by many exciting applications ranging from tests of fundamental physics to quantum information processing. Here, we propose a trapping scheme to create high-density cold molecular samples by using a combination of electric and magnetic fields. In our theoretical analysis and numerical calculations, a typical alkaline-earth monofluoride, MgF, is used to test the feasibility of our proposal. A cold MgF molecular beam is first produced via an electrostatic Stark decelerator and then loaded into the proposed electromagnetic trap, which is composed of an anti-Helmholtz coil, an octupole, and two disk electrodes. Following that, a huge magnetic force is applied to the molecular sample at an appropriate time, which enables further compressing of the spatial distribution of the cold sample. Molecular samples with both higher number density and smaller volume are quite suitable for the laser confinement and other molecular experiments such as cold collisions in the next step.

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Dynamics of molecular alignment steered by a few-cycle terahertz laser pulse

Qi-Yuan Cheng(程起元), Yu-Zhi Song(宋玉志), Deng-Wang Li(李登旺), Zhi-Ping Liu(刘治平), and Qing-Tian Meng(孟庆田)

2022 (10): 103301-103301. doi: 10.1088/1674-1056/ac6eeb

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The field-free alignment of molecule ClCN is investigated by using a terahertz few-cycle pulse (THz FCP) based on the time-dependent density matrix theory. It is shown that a high degree of molecular alignment can be obtained by changing the matching number of the THz FCPs in the adiabatic regime and the non-adiabatic regime. The matching number can affect both the maximum value of the alignment and the time at which it is achieved. It is also found that a higher degree of alignment can be achieved by using the THz FCP at lower intensity and there exists an optimal threshold of molecular alignment with the increase of the field amplitude. Also found is the frequency sensitive region in which the degree of maximum alignment can be enhanced greatly by modulating the center frequencies of different THz FCPs. The investigation demonstrates that comparing with a THz single-cycle pulse, a better result of the field-free alignment can be created by a THz FCP at a constant rotational temperature of molecule.

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Terahertz spectroscopy and lattice vibrational analysis of pararealgar and orpiment

Ya-Wei Zhang(张亚伟), Guan-Hua Ren(任冠华), Xiao-Qiang Su(苏晓强), Tian-Hua Meng(孟田华), and Guo-Zhong Zhao(赵国忠)

2022 (10): 103302-103302. doi: 10.1088/1674-1056/ac7cd3

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Terahertz time-domain spectroscopy (THz-TDS) is an effective nondestructive and noninvasive tool for investigating sulfur-containing pigments. Combined with Raman spectroscopy and vibrational mode analysis, it is significant for artifact identification and conservation. In this work, the terahertz absorption spectra of pararealgar (As₄S₄) and orpiment (As₂S₃) samples mixed with polytetrafluoroethylene (PTFE) are characterized in a range from 0.2 THz to 2.2 THz, and their distinctive peaks are observed, respectively. Meanwhile, qualitative analysis is also implemented by using Raman spectroscopy as a complementary technique. The lattice vibrations are simulated by using solid-state density functional theory (ss-DFT), illustrating different characteristic absorption peaks for specific crystalline structures and dynamic properties. This work provides a reliable database of sulfur-containing pigments for using the THz technology to actually analyze and diagnose cultural relics.

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Tunable second-order sideband effects in hybrid optomechanical cavity assisted with a Bose—Einstein condensate

Li-Wei Liu(刘利伟), Chun-Guang Du(杜春光), Guo-Heng Zhang(张国恒), Qiong Chen(陈琼), Yu-Qing Shi(石玉清), Pei-Yu Wang(王培煜), and Yu-Qing Zhang(张玉青)

2022 (10): 103701-103701. doi: 10.1088/1674-1056/ac6ed7

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We theoretically investigated a second-order optomechanical-induced transparency (OMIT) process of a hybrid optomechanical system (COMS), which a Bose—Einstein condensate (BEC) in the presence of atom—atom interaction trapped inside a cavity with a moving end mirror. The advantage of this hybrid COMS over a bare COMS is that the frequency of the second mode is controlled by the s-wave scattering interaction. Based on the traditional linearization approximation, we derive analytical solutions for the output transmission intensity of the probe field and the dimensionless amplitude of the second-order sideband (SS). The numerical results show that the transmission intensity of the probe field and the dimensionless amplitude of the SS can be controlled by the s-wave scattering frequency. Furthermore, the control field intensities, the effective detuning, the effective coupling strength of the cavity field with the Bogoliubov mode are used to control the transmission intensity of the probe field and the dimensionless amplitude of the SS.

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Single-beam leaky-wave antenna with wide scanning angle and high scanning rate based on spoof surface plasmon polariton

Huan Jiang(蒋欢), Xiang-Yu Cao(曹祥玉), Tao Liu(刘涛), Liaori Jidi(吉地辽日), and Sijia Li(李思佳)

2022 (10): 104101-104101. doi: 10.1088/1674-1056/ac5881

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We propose a single-beam leaky-wave antenna (LWA) with a wide-scanning angle and a high-scanning rate based on spoof surface plasmon polariton (SSPP) in this paper. The SSPP transmission line (TL) is etched with periodically arranged circular patches, which converts the slow-wave mode into the fast-wave region for radiation. The proposed LWA is designed, fabricated, and tested. The simulated results imply that the proposed LWA not only achieves a high radiation efficiency of about 81.4%, and a high scanning rate of 12.12, but also has a large scanning angle of 176° over a narrow operation bandwidth of 8.3—9.6 GHz (for |S₁₁|<-10 dB). In addition, the simulated average gain of the LWA can reach as high as 10.9 dBi. The measured scanning angle range is 175° in the operation band of 8.2—9.6 GHz, and the measured average gain is 10.6 dBi. The experimental results are consistent with the simulation, validating its performance. An antenna with high radiation efficiency, wide scanning angle range, and high scanning rate has great potential for application in radar and wireless communication systems.

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Circular dichroism spectra of α -lactose molecular measured by terahertz time-domain spectroscopy

Chun Wang(王春), Bo Wang(王博), Gaoshuai Wei(魏高帅), Jianing Chen(陈佳宁), and Li Wang(汪力)

2022 (10): 104201-104201. doi: 10.1088/1674-1056/ac6edb

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Researchers have long studied circular dichroism (CD) for its enormous prospects in life sciences. Many biomolecules have vibration modes in the terahertz region, and terahertz CD spectra are robust to detect biomolecular structures. However, few studies explore the terahertz CD spectra on even natural materials due to technical challenges in both fields. Here, we report a setup of home-built terahertz time-domain spectroscopy to measure the polarization states of terahertz waves. By carefully measuring the transmission Jones matrix, we obtain terahertz CD spectra of α -lactose tablets and D-glucose tablets. Our results show that the terahertz CD spectra are sensitive to vibrational motions in biochemical compounds, which will find wide applications in biosensing and biomedical diagnostics.

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Influences of nanoparticles and chain length on thermodynamic and electrical behavior of fluorine liquid crystals

Ines Ben Amor, Lotfi Saadaoui, Abdulaziz N. Alharbi, Talal M. Althagafi, and Taoufik Soltani

2022 (10): 104202-104202. doi: 10.1088/1674-1056/ac7293

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Hydrogen-bonded polar nematic liquid crystal series with the general formula nOBAF (n = 7—12) is studied. The mesomorphic characterization is demonstrated through differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The complexes with short alkyl chains (n=7, 8) present a wide nematic range and monotropic smectic F mesophase, whereas the longer alkyl chain (n=10—12) analogues show high melting and low clearing mesomorphic liquid crystals. The thermal range of the mesophase and the birefringence increase with chain length decreasing. Furthermore, the effect of the nanoparticles (LiNbO₃) on the thermal and the electrical behavior of 8OBAF are investigated. The presence of LiNbO₃ nanoparticles increases the conductivity and reduces the resistivity of the complex.

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Enhancement of the second harmonic generation from monolayer WS₂ coupled with a silica microsphere

Xiao-Zhuo Qi(祁晓卓), and Xi-Feng Ren(任希锋)

2022 (10): 104203-104203. doi: 10.1088/1674-1056/ac6868

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Monolayer transition metal dichalcogenides (TMDs) are widely used for integrated optical and photoelectric devices. Owing to their broken inversion symmetry, monolayer TMDs have a large second-order optical nonlinearity. However, the optical second-order nonlinear conversion efficiency of monolayer TMDs is still limited by the interaction length. In this work, we theoretically study the second harmonic generation (SHG) from monolayer tungsten sulfide (WS₂) enhanced by a silica microsphere cavity. By tuning the position, size, and crystal orientation of the material, second-order nonlinear coupling can occur between the fundamental pump mode and different second harmonic cavity modes, and we obtain an optimal SHG conversion efficiency with orders of magnitude enhancement. Our work demonstrates that the microsphere cavity can significantly enhance SHG from monolayer 2D materials under flexible conditions.

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Raman lasing and other nonlinear effects based on ultrahigh-Q CaF₂ optical resonator

Tong Xing(邢彤), Enbo Xing(邢恩博), Tao Jia(贾涛), Jianglong Li(李江龙), Jiamin Rong(戎佳敏), Yanru Zhou(周彦汝), Wenyao Liu(刘文耀), Jun Tang(唐军), and Jun Liu(刘俊)

2022 (10): 104204-104204. doi: 10.1088/1674-1056/ac8728

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The calcium fluoride (CaF₂) whispering gallery mode crystalline resonator is an excellent platform for nonlinear optical applications because of the decreasing in threshold caused by ultrahigh quality (Q) factor. In this paper, we achieved the observation of Raman lasing, first-order Raman comb, and second-order Raman lasing in a CaF₂ disk resonator with a diameter of 4.96 mm and an ultrahigh-Q of 8.43× 10⁸ at 1550-nm wavelength. We also observed thermal effects in CaF₂ disk resonator, and the threshold of thermo-optical oscillation is approximately coincident with Raman lasing, since the intracavity power increases rapidly when the power reaches the threshold, and higher input pump power results in longer thermal drift and higher Raman emission power. With a further increase in pump power, the optical frequency combs range is from 1520 nm to 1650 nm, with a wavelength interval of 4× m FSR. It is a promising candidate for optical communication, biological environment monitoring, spectral analysis, and microwave signal sources.

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Variational approximation methods for long-range force transmission in biopolymer gels

Haiqin Wang(王海钦), and Xinpeng Xu(徐新鹏)

2022 (10): 104602-104602. doi: 10.1088/1674-1056/ac720a

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The variational principle of minimum free energy (MFEVP) has been widely used in research of soft matter statics. The MFEVP can be used not only to derive equilibrium equations (including both bulk equations and boundary conditions), but also to develop direct variational methods (such as Ritz method) to find approximate solutions to these equilibrium equations. We apply these variational methods to study long-range force transmission in nonlinear elastic biopolymer gels. It is shown that the slow decay of cell-induced displacements measured experimentally for fibroblast spheroids in three-dimensional fibrin gels can be well explained by variational approximations based on the three-chain model of biopolymer gels.

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Experimental study of the influence of annular nozzle on acoustic characteristics of detonation sound wave generated by pulse detonation engine

Yang Kang(康杨), Ning Li(李宁), Xiao-Long Huang(黄孝龙), and Chun-Sheng Weng(翁春生)

2022 (10): 104701-104701. doi: 10.1088/1674-1056/ac80a9

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Acoustic characteristics of the detonation sound wave generated by a pulse detonation engine with an annular nozzle, including peak sound pressure, directivity, and A duration, are experimentally investigated while utilizing gasoline as fuel and oxygen-enriched air as oxidizer. Three annular nozzle geometries are evaluated by varying the ratio of inner cone diameter to detonation tube exit diameter from 0.36 to 0.68. The experimental results show that the annular nozzles have a significant effect on the acoustic characteristics of the detonation sound wave. The annular nozzles can amplify the peak sound pressure of the detonation sound wave at 90° while reducing it at 0° and 30°. The directivity angle of the detonation sound wave is changed by annular nozzles from 30° to 90°. The A duration of the detonation sound wave at 90° is also increased by the annular nozzles. These changes indicate that the annular nozzles have an important influence on the acoustic energy distribution of the detonation sound wave, which amplify the acoustic energy in a direction perpendicular to the tube axis and weaken it along the direction of the tube axis.

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Active thermophoresis and diffusiophoresis

Huan Liang(梁欢), Peng Liu(刘鹏), Fangfu Ye(叶方富), and Mingcheng Yang(杨明成)

2022 (10): 104702-104702. doi: 10.1088/1674-1056/ac754d

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Thermophoresis and diffusiophoresis respectively refer to the directed drift of suspended particles in solutions with external thermal and chemical gradients, which have been widely used in the manipulation of mesoscopic particles. We here study a phoretic-like motion of a passive colloidal particle immersed in inhomogeneous active baths, where the thermal and chemical gradients are replaced separately by activity and concentration gradients of the active particles. By performing simulations, we show that the passive colloidal particle experiences phoretic-like forces that originate from its interactions with the inhomogeneous active fluid, and thus drifts along the gradient field, leading to an accumulation. The results are similar to the traditional phoretic effects occurring in passive colloidal suspensions, implying that the concepts of thermophoresis and diffusiophoresis could be generalized into active baths.

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Analytical model for Rayleigh—Taylor instability in conical target conduction region

Zhong-Yuan Zhu(朱仲源), Yun-Xing Liu(刘云星), Ying-Jun Li(李英骏), and Jie Zhang(张杰)

2022 (10): 105202-105202. doi: 10.1088/1674-1056/ac8731

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This work builds an isobaric steady-state fluid analytical-physical model of the plasma conduction region in a conical target. The hydrodynamic instability in the double-cone ignition scheme^[21] for inertial confinement fusion (ICF) proposed by Zhang is studied with the built model. With this idealized model, the relevant parameters, such as density, temperature, and length of the plasma in the conduction region of the conical target under long-pulse conditions are given. The solution of the proposed analytical model dovetails with the trend of the numerical simulation. The model and results in this paper are beneficial for discussing how to attenuate Rayleigh—Taylor instability in ICF processes with conical and spherical targets.

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Evolution of the high-field-side radiation belts during the neon seeding plasma discharge in EAST tokamak

Ji-Chan Xu(许吉禅), Liang Wang(王亮), Guo-Sheng Xu(徐国盛), Yan-Min Duan(段艳敏), Ling-Yi Meng(孟令义), Ke-Dong Li(李克栋), Fang Ding(丁芳), Rui-Rong Liang(梁瑞荣), Jian-Bin Liu(刘建斌), and EAST Team

2022 (10): 105203-105203. doi: 10.1088/1674-1056/ac935a

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Divertor detachment achieved by injecting impurities or increasing density is always accompanied with various local radiation phenomena in the boundary or core plasma. This paper presents the formation and evolution of the high-field-side (HFS) radiation belts during the neon seeding plasma discharge in upper single null configuration with two directions of toroidal magnetic field in EAST tokamak. The neon mixed with deuterium seeding can induce the divertor detachment with strong radiation belts in the HFS scrape-off layer (SOL) region. With the increase of the radiation power, the plasma discharge will transit from H-mode to L-mode, and meanwhile the radiation belts move away from the near X-point to HFS SOL. When the radiation power is high enough, the radiation belts begin to move further to the other X-point along the HFS SOL, and even cause plasma disruption. The results indicate that the behavior of the radiation belts is related to the radiation power, plasma confinement performance and state of divertor detachment, which is useful for developing better feedback control methods to achieve high-performance radiative divertor operation mode.

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Lattice damage in InGaN induced by swift heavy ion irradiation

Ning Liu(刘宁), Li-Min Zhang(张利民), Xue-Ting Liu(刘雪婷), Shuo Zhang(张硕), Tie-Shan Wang(王铁山), and Hong-Xia Guo(郭红霞)

2022 (10): 106103-106103. doi: 10.1088/1674-1056/ac7ccd

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The microstructural responses of In_0.32Ga_0.68N and In_0.9Ga_0.1N films to 2.25 GeV Xe ion irradiation have been investigated using x-ray diffraction, Raman scattering, ion channeling and transmission electron microscopy. It was found that the In-rich In_0.9Ga_0.1N is more susceptible to irradiation than the Ga-rich In_0.32Ga_0.68N. Xe ion irradiation with a fluence of 7× 10¹¹ ions·cm^-2 leads to little damage in In_0.32Ga_0.68N but an obvious lattice expansion in In_0.9Ga_0.1N. The level of lattice disorder in In_0.9Ga_0.1N increases after irradiation, due to the huge electronic energy deposition of the incident Xe ions. However, no Xe ion tracks were observed to be formed, which is attributed to the very high velocity of 2.25 GeV Xe ions. Point defects and/or small defect clusters are probably the dominant defect type in Xe-irradiated In_0.9Ga_0.1N.

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First principles study of hafnium intercalation between graphene and Ir(111) substrate

Hao Peng(彭浩), Xin Jin(金鑫), Yang Song(宋洋), and Shixuan Du(杜世萱)

2022 (10): 106801-106801. doi: 10.1088/1674-1056/ac6941

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The intercalation of heteroatoms between graphene and metal substrates is a promising method for integrating epitaxial graphene with functional materials. Various elements and their oxides have been successfully intercalated into graphene/metal interfaces to form graphene-based heterostructures, showing potential applications in electronic devices. Here we theoretically investigate the hafnium intercalation between graphene and Ir(111). It is found that the penetration barrier of Hf atom is significantly large due to its large atomic radius, which suggests that hafnium intercalation should be carried out with low deposition doses of Hf atoms and high annealing temperatures. Our results show the different intercalation behaviors of a large-size atom and provide guidance for the integration of graphene and hafnium oxide in device applications.

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Kondo screening cloud in a superconductor with mixed s-wave and p-wave pairing states

Zhen-Zhen Huang(黄真真), Xiong-Tao Peng(彭雄涛), Wan-Sheng Wang(王万胜), and Jin-Hua Sun(孙金华)

2022 (10): 107101-107101. doi: 10.1088/1674-1056/ac7213

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We study the Kondo screening of a spin-1/2 magnetic impurity coupled to a superconductor, which is fabricated by combination of an s-wave superconductor, a ferromagnet and a semiconductor with Rashba spin—orbit coupling (RSOC). The proximity induced superconducting states include the s-wave and p-wave pairing components with the aids of RSOC, and the ferromagnet induces a Zeeman field which removes the spin degeneracy of the quasiparticles in the triplet states. Thus, the Kondo screening of magnetic impurity involves the orbital degrees of freedom, and is also affected by the Zeeman field. Using the variational method, we calculate the binding energy and the spin—spin correlation between the magnetic impurity and the electrons in the coexisting s-wave and p-wave pairing states. We find that Kondo singlet forms more easily with stronger RSOC, but Zeeman field in general decreases the binding energy. The spin—spin correlation decays fast in the vicinity of the magnetic impurity. Due to the RSOC, the spatial spin—spin correlation becomes highly anisotropic, and the Zeeman field can induce extra asymmetry to the off-diagonal components of the spin—spin correlation. Our study can offer some insights into the studies of extrinsic topological superconductors fabricated from the hybrid structures containing chains of magnetic impurities.

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Origin of the low formation energy of oxygen vacancies in CeO₂

Han Xu(许涵), Tongtong Shang(尚彤彤), Xuefeng Wang(王雪锋), Ang Gao(高昂), and Lin Gu(谷林)

2022 (10): 107102-107102. doi: 10.1088/1674-1056/ac7457

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Oxygen vacancies play a crucial role in determining the catalytic properties of Ce-based catalysts, especially in oxidation reactions. The design of catalytic activity requires keen insight into oxygen vacancy formation mechanisms. In this work, we investigate the origin of oxygen vacancies in CeO₂ from the perspective of electron density {via} high-energy synchrotron powder x-ray diffraction. Multipole refinement results indicate that there is no obvious hybridization between bonded Ce and O atoms in CeO₂. Subsequent quantitative topological analysis of the experimental total electron density reveals the closed-shell interaction behavior of the Ce—O bond. The results of first-principles calculation indicate that the oxygen vacancy formation energy of CeO₂ is the lowest among three commonly used redox catalysts. These findings indicate the relatively weak bond strength of the Ce—O bond, which induces a low oxygen vacancy formation energy for CeO₂ and thus promotes CeO₂ as a superior catalyst for oxidation reactions. This work provides a new direction for design of functional metal oxides with high oxygen vacancy concentrations.

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Improvement of femtosecond SPPs imaging by two-color laser photoemission electron microscopy

Chun-Lai Fu(付春来), Zhen-Long Zhao(赵振龙), Bo-Yu Ji(季博宇), Xiao-Wei Song(宋晓伟), Peng Lang(郎鹏), and Jing-Quan Lin(林景全)

2022 (10): 107103-107103. doi: 10.1088/1674-1056/ac6ede

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Clear imaging of surface plasmon polaritons (SPPs) is a prerequisite for SPPs-based applications. In this work, we demonstrate an improvement of near-field imaging of SPPs via directly comparing the visibility of the photoemission electron microscopy (PEEM) image of SPPs under one- and two-color laser excitation (also known as one- or two-color laser PEEM). By measuring the photoelectron yield and the contrast of the interference fringes of SPPs, we demonstrate that in addition to enhancing the photoemission yield, two-color laser PEEM can significantly improve the contrast between bright and dark fringes (nearly 4 times higher than that of one-color laser case). By recording the nonlinear order of the photoelectrons ejected from the bright and dark fringes, respectively, the underlying mechanism for the improved visibility is revealed. In addition, the influences of the polarization direction of 400-nm laser on the PEEM images of the SPPs with different wave vector directions are shown. These results can provide technical support for the development of SPPs-based communication devices and catalysis.

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Two-color laser PEEM imaging of horizontal and vertical components of femtosecond surface plasmon polaritons

Zhen-Long Zhao(赵振龙), Bo-Yu Ji(季博宇), Lun Wang(王伦), Peng Lang(郎鹏), Xiao-Wei Song(宋晓伟), and Jing-Quan Lin(林景全)

2022 (10): 107104-107104. doi: 10.1088/1674-1056/ac8921

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Explicit visualization of different components of surface plasmon polaritons (SPPs) propagating at dielectric/metal interfaces is crucial in offering chances for the detailed design and control of the functionalities of plasmonic nanodevices in the future. Here, we reported independent imaging of the vertical and horizontal components of SPPs launched from a rectangular trench in the gold film by a 400-nm laser-assisted near-infrared (NIR) femtosecond laser time-resolved photoemission electron microscopy (TR-PEEM). The experiments demonstrate that distinct imaging of different components of SPPs field can be easily achieved by introducing the 400-nm laser. It can circumvent the risk of sample damage and information loss of excited SPPs field that is generally confronted in the usual NIR laser TR-PEEM scheme. The underlying mechanism for realizing distinct imaging of different components of the SPPs field with two-color PEEM is revealed via measuring the double logarithmic dependence of photoemission yield with the 800-nm and 400-nm pulse powers of different polarizations. Moreover, it is found that the PEEM image quality of the vertical and horizontal components of the SPPs field is nearly independent of the 400-nm pulse polarization. These results pave a way for SPPs-based applications and offer a possible solution for drawing a space—time field of SPPs in three dimensions.

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Prediction of quantum anomalous Hall effect in CrI₃/ScCl₂ bilayer heterostructure

Yuan Gao(高源), Huiping Li(李慧平), and Wenguang Zhu(朱文光)

2022 (10): 107304-107304. doi: 10.1088/1674-1056/ac67cb

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Based on first-principles calculations, a two-dimensional (2D) van der Waals (vdW) bilayer heterostructure consisting of two topologically trivial ferromagnetic (FM) monolayers CrI₃ and ScCl₂ is proposed to realize the quantum anomalous Hall effect (QAHE) with a sizable topologically nontrivial band gap of 4.5 meV. Its topological nature is attributed to an interlayer band inversion between the monolayers and critically depends on the symmetry of the stacking configuration. We further demonstrate that the topologically nontrivial band gap can be increased nearly linearly by the application of a perpendicular external pressure and reaches 8.1 meV at 2.7 GPa, and the application of an external out-of-plane electric field can also modulate the band gap and convert the system back to topologically trivial via eliminating the band inversion. An effective model is developed to describe the topological phase evolution in this bilayer heterostructure. This work provides a new candidate system based on 2D vdW materials for realization of potential high-temperature QAHE with considerable controllability.

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Epitaxial Bi₂Sr₂CuOy thin films as p-type transparent conductors

Chen Zhou(周臣), Wang-Ping Cheng(程王平), Yuan-Di He(何媛娣), Cheng Shao(邵成), Ling Hu(胡令), Ren-Huai Wei(魏仁怀), Jing-Gang Qin(秦经刚), Wen-Hai Song(宋文海), Xue-Bin Zhu(朱雪斌), Chuan-Bing Cai(蔡传兵), and Yu-Ping Sun(孙玉平)

2022 (10): 107305-107305. doi: 10.1088/1674-1056/ac67ca

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Development of p-type transparent conducting thin films is tireless due to the trade-off issue between optical transparency and conductivity. The rarely concerned low normal state resistance makes Bi-based superconducting cuprates the potential hole-type transparent conductors, which have been realized in Bi₂Sr₂CaCu₂O_y thin films. In this study, epitaxial superconducting Bi₂Sr₂CuO_y and Bi₂Sr_1.8Nd_0.2CuO_y thin films with superior normal state conductivity are proposed as p-type transparent conductors. It is found that the Bi₂Sr_1.8Nd_0.2CuO_y thin film with thickness 15 nm shows an average visible transmittance of 65% and room-temperature sheet resistance of 650 Ω/sq. The results further demonstrate that Bi-based cuprate superconductors can be regarded as potential p-type transparent conductors for future optoelectronic applications.

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Transition metal anchored on C₉N₄ as a single-atom catalyst for CO₂ hydrogenation: A first-principles study

Jia-Liang Chen(陈嘉亮), Hui-Jia Hu(胡慧佳), and Shi-Hao Wei(韦世豪)

2022 (10): 107306-107306. doi: 10.1088/1674-1056/ac6158

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To alleviate the greenhouse effect and maintain the sustainable development, it is of great significance to find an efficient and low-cost catalyst to reduce carbon dioxide (CO₂) and generate formic acid (FA). In this work, based on the first-principles calculation, the catalytic performance of a single transition metal (TM) (TM = Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, Au, or Hg) atom anchored on C₉N₄ monolayer (TM@C₉N₄) for the hydrogenation of CO₂ to FA is calculated. The results show that single TM atom doping in C₉N₄ can form a stable TM@C₉N₄ structure, and Cu@C₉N₄ and Co@C₉N₄ show better catalytic performance in the process of CO₂ hydrogenation to FA (the corresponding maximum energy barriers are 0.41 eV and 0.43 eV, respectively). The partial density of states (PDOS), projected crystal orbital Hamilton population (pCOHP), difference charge density analysis and Bader charge analysis demonstrate that the TM atom plays an important role in the reaction. The strong interaction between the 3d orbitals of the TM atom and the non-bonding orbitals (1π_g) of CO₂ allows the reaction to proceed under mild conditions. In general, our results show that Cu@C₉N₄ and Co@C₉N₄ are a promising single-atom catalyst and can be used as the non-precious metals electrocatalyst for CO₂ hydrogenation to formic acid.

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Synthesis and properties of La_1-xSr_xNiO₃ and La_1-xSr_xNiO₂

Mengwu Huo(霍梦五), Zengjia Liu(刘增家), Hualei Sun(孙华蕾), Lisi Li(李历斯), Hui Lui(刘晖), Chaoxin Huang(黄潮欣), Feixiang Liang(梁飞翔), Bing Shen(沈冰), and Meng Wang(王猛)

2022 (10): 107401-107401. doi: 10.1088/1674-1056/ac7a1a

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Superconductivity has been realized in films of La_1-xSr_xNiO₂. Here we report synthesis and characterization of polycrystalline samples of La_1-xSr_xNiO₃ and La_1-xSr_xNiO₂ (0 ≤ x ≤ 0.2). Magnetization and resistivity measurements reveal that La_1-xSr_xNiO₃ are paramagnetic metal and La_1-xSr_xNiO₂ exhibit an insulating behavior. Superconductivity is not detected in bulk samples of La_1-xSr_xNiO₂. The absence of superconductivity in bulk La_1-xSr_xNiO₂ may be due to the generation of hydroxide during reduction, a small amount of nickel impurity, or incomplete reduction of apical oxygen. The effect of interface in films of La_1-xSr_xNiO₂ may also play a role for superconductivity.

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Terahertz magnetic resonance in MnCr₂O₄ under high magnetic field

Peng Zhang(张朋), Kaibo He(贺凯博), Zheng Wang(王铮), Shile Zhang(张仕乐), Jianming Dai(戴建明), and Fuhai Su(苏付海)

2022 (10): 107502-107502. doi: 10.1088/1674-1056/ac7f8b

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Terahertz (THz) time-domain spectroscopy (THz-TDS) of polycrystalline MnCr₂O₄ was performed at <9 T and low temperatures. A resonance absorption in the sub-THz range with linear blueshifts was observed as the magnetic field was increased from 4 T to 9 T. These magnetism-driven absorptions originated from a ferromagnetic resonance, which agrees with low-field electron spin resonance measurements and ferromagnetic resonance theory. The low-temperature g-factors of MnCr₂O₄ were also obtained using THz-TDS. This work provides new insights into the spin dynamics of chromite spinel compounds in the THz region.

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A novel natural surface-enhanced fluorescence system based on reed leaf as substrate for crystal violet trace detection

Hui-Ju Cao(曹会菊), Hong-Wen Cao(曹红文), Yue Li(李月), Zhen Sun(孙祯), Yun-Fan Yang(杨云帆), Ti-Feng Jiao(焦体峰), and Ming-Li Wang(王明利)

2022 (10): 107801-107801. doi: 10.1088/1674-1056/ac7215

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The preparation of surface-enhanced fluorescence (SEF) substrates is often influenced by experimental strategies and factors such as the morphology and size of the nanostructures. In this study, using the natural reed leaves (RLs) without any special pretreatment as the substrate, metal silver is modified by magnetron sputtering technology to prepare a stable and efficient SEF system. The abundant “hedgehog-like”protrusions on the RL substrate surface can generate high-density “hot spots”, thus enhancement factor (EF) is enhanced up to 3345 times. The stability and reproducibility are verified in many measurements. The contribution of the intervention of silver nanostructure to the radiation attenuation process of fluorescent molecules is analyzed with the aid of Jablonski diagrams. Three-dimensional (3D) finite difference time domain (FDTD) simulates the spatial electric field and “hot spots”distribution of the substrate. The “hedgehog-like”protrusion structure generates multiple “hot spots”, which produce an excellent local surface plasmon resonance (LSPR) effect and provide higher fluorescence signal. Finally, RL/Ag-35 substrate is used to detect crystal violet (CV), and the detection limit is as low as 10^-13 M. This “hedgehog-like”SEF substrate provides a new strategy for the trace detection of CV, which has a good practical application value.

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Characteristics of secondary electron emission from few layer graphene on silicon (111) surface

Guo-Bao Feng(封国宝), Yun Li(李韵), Xiao-Jun Li(李小军), Gui-Bai Xie(谢贵柏), and Lu Liu(刘璐)

2022 (10): 107901-107901. doi: 10.1088/1674-1056/ac76a9

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As a typical two-dimensional (2D) coating material, graphene has been utilized to effectively reduce secondary electron emission from the surface. Nevertheless, the microscopic mechanism and the dominant factor of secondary electron emission suppression remain controversial. Since traditional models rely on the data of experimental bulk properties which are scarcely appropriate to the 2D coating situation, this paper presents the first-principles-based numerical calculations of the electron interaction and emission process for monolayer and multilayer graphene on silicon (111) substrate. By using the anisotropic energy loss for the coating graphene, the electron transport process can be described more realistically. The real physical electron interactions, including the elastic scattering of electron—nucleus, inelastic scattering of the electron—extranuclear electron, and electron—phonon effect, are considered and calculated by using the Monte Carlo method. The energy level transition theory-based first-principles method and the full Penn algorithm are used to calculate the energy loss function during the inelastic scattering. Variations of the energy loss function and interface electron density differences for 1 to 4 layer graphene coating GoSi are calculated, and their inner electron distributions and secondary electron emissions are analyzed. Simulation results demonstrate that the dominant factor of the inhibiting of secondary electron yield (SEY) of GoSi is to induce the deeper electrons in the internal scattering process. In contrast, a low surface potential barrier due to the positive deviation of electron density difference at monolayer GoSi interface in turn weakens the suppression of secondary electron emission of the graphene layer. Only when the graphene layer number is 3, does the contribution of surface work function to the secondary electron emission suppression appear to be slightly positive.

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Effect of interface anisotropy on tilted growth of eutectics: A phase field study

Mei-Rong Jiang(姜美荣), Jun-Jie Li(李俊杰), Zhi-Jun Wang(王志军), and Jin-Cheng Wang(王锦程)

2022 (10): 108101-108101. doi: 10.1088/1674-1056/ac76af

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Interfacial energy anisotropy plays an important role in tilted growth of eutectics. However, previous studies mainly focused on the solid—solid interface energy anisotropy, and whether the solid—liquid interface energy anisotropy can significantly affect the tilted growth of eutectics still remains unclear. In this study, a multi-phase field model is employed to investigate both the effect of solid—liquid interfacial energy anisotropy and the effect of solid—solid interfacial energy anisotropy on tilted growth of eutectics. The findings reveal that both the solid—liquid interfacial energy anisotropy and the solid—solid interfacial energy anisotropy can induce the tilted growth of eutectics. The results also demonstrate that when the rotation angle is within a range of 30°—60°, the growth of tilted eutectics is governed jointly by the solid—solid interfacial energy anisotropy and the solid—liquid interfacial energy anisotropy; otherwise, it is mainly controlled by the solid—solid interfacial energy anisotropy. Further analysis shows that the unequal pinning angle at triple point caused by the adjustment of the force balance results in different solute-diffusion rates on both sides of triple point. This will further induce an asymmetrical concentration distribution along the pulling direction near the solid—liquid interface and the tilted growth of eutectics. Our findings not only shed light on the formation mechanism of tilted eutectics but also provide theoretical guidance for controlling the microstructure evolution during eutectic solidification.

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Accurate determination of anisotropic thermal conductivity for ultrathin composite film

Qiu-Hao Zhu(朱秋毫), Jing-Song Peng(彭景凇), Xiao Guo(郭潇), Ru-Xuan Zhang(张如轩), Lei Jiang(江雷), Qun-Feng Cheng(程群峰), and Wen-Jie Liang(梁文杰)

2022 (10): 108102-108102. doi: 10.1088/1674-1056/ac6ee5

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Highly anisotropic thermal conductive materials are of significance in thermal management applications. However, accurate determination of ultrathin composite thermal properties is a daunting task due to the tiny thermal conductance, severely hindering the further exploration of novel efficient thermal management materials, especially for size-confined environments. In this work, by utilizing a hybrid measuring method, we demonstrate an accurate determination of thermal properties for montmorillonite/reduced graphene oxide (MMT/rGO) composite film with a thickness range from 0.2 μ m to 2 μ m. The in-plane thermal conductivity measurement is realized by one-dimensional (1D) steady-state heat conduction approach while the cross-plane one is achieved via a modified 3ω method. As-measured thermal conductivity results are cross-checked with different methods and known materials, revealing the high measurement accuracy. A high anisotropic ratio of 60.5, independent of composite thickness, is observed in our measurements, further ensuring the negligible measurement error. Notably, our work develops an effective approach to the determination of ultrathin composite thermal conductivity, which may promote the development of ultrathin composites for potential thermal-related applications.

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High-sensitivity refractive index sensors based on Fano resonance in a metal-insulator-metal based arc-shaped resonator coupled with a rectangular stub

Shubin Yan(闫树斌), Hao Su(苏浩), Xiaoyu Zhang(张晓宇), Yi Zhang(张怡), Zhanbo Chen(陈展博), Xiushan Wu(吴秀山), and Ertian Hua(华尔天)

2022 (10): 108103-108103. doi: 10.1088/1674-1056/ac76ac

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A metal-insulator-metal (MIM)-based arc-shaped resonator coupled with a rectangular stub (MARS) structure is proposed. This structure can generate two tunable Fano resonances originating from two different mechanisms. The structure has the advantage of being sensitive to the refractive index, and this feature makes it favorable for application in various microsensors. The relationship between the structural parameters and Fano resonance is researched using the finite element method (FEM) based on the software COMSOL Multiphysics 5.4. The simulation reveals that the sensitivity reaches 1900 nm/refractive index unit (RIU), and the figure of merit (FOM) is 23.75.

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Broadband and high efficiency terahertz metasurfaces for anomalous refraction and vortex beam generation

Wen-Yu Li(李文宇), Ran Sun(孙然), Jing-Yu Liu(刘靖宇), Tian-Hua Meng(孟田华), and Guo-Zhong Zhao(赵国忠)

2022 (10): 108701-108701. doi: 10.1088/1674-1056/ac70bd

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The applications of metasurfaces are currently a highly active research field due to their extraordinary ability to manipulate electromagnetic waves. The ultra-thin characteristics of metasurfaces allow the miniaturization and integration of metasurface devices. However, these devices work typically under a low efficiency and narrow bandwidth condition. In this work, we design eight multilayered unit cells with similar amplitudes and a phase interval of π/4, which convert the polarization states of the terahertz (THz) waves between two orthogonal directions. The average cross-polarized transmission amplitudes of these cells are all around 0.9 in an ultra-broad frequency range from 0.5 THz to 1.4 THz. Furthermore, unit cells are used to construct both an ultra-thin anomalous refraction metalens and a vortex phase plate. Our simulation results show that the anomalous refraction for the transmitted linear polarization component is comparable to the theoretical prediction, and the maximum error is determined to be below 4.8%. The vortex phase plate can also generate an ideal terahertz vortex beam with a mode purity of 90% and more. The distributions of longitudinal electric field, intensity, and phase illustrate that the generated vortex beam has excellent propagation characteristics and a weak divergence. Simulations of the two types of metasurface devices, based on the eight unit cells, exhibit very high efficiencies in a wide bandwidth. Our research will assist in the improvement in the practical applications of metasurfaces. It also provides a reference for the design of high efficiency and broadband devices that are applied to other frequency ranges.

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Device simulation of quasi-two-dimensional perovskite/silicon tandem solar cells towards 30%-efficiency

Xiao-Ping Xie(谢小平), Qian-Yu Bai(白倩玉), Gang Liu(刘刚), Peng Dong(董鹏), Da-Wei Liu(刘大伟), Yu-Feng Ni(倪玉凤), Chen-Bo Liu(刘晨波), He Xi(习鹤), Wei-Dong Zhu(朱卫东), Da-Zheng Chen(陈大正), and Chun-Fu Zhang(张春福)

2022 (10): 108801-108801. doi: 10.1088/1674-1056/ac7292

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Perovskite/silicon (Si) tandem solar cells have been recognized as the next-generation photovoltaic technology with efficiency over 30% and low cost. However, the intrinsic instability of traditional three-dimensional (3D) hybrid perovskite seriously hinders the lifetimes of tandem devices. In this work, the quasi-two-dimensional (2D) (BA)₂(MA)_n-1Pb_nI_3n+1 (n=1, 2, 3, 4, 5) (where MA denotes methylammonium and BA represents butylammonium), with senior stability and wider bandgap, are first used as an absorber of semitransparent top perovskite solar cells (PSCs) to construct a four-terminal (4T) tandem devices with a bottom Si-heterojunction cell. The device model is established by Silvaco Atlas based on experimental parameters. Simulation results show that in the optimized tandem device, the top cell (n=4) obtains a power conversion efficiency (PCE) of 17.39% and the Si bottom cell shows a PCE of 11.44%, thus an overall PCE of 28.83%. Furthermore, by introducing a 90-nm lithium fluoride (LiF) anti-reflection layer to reduce the surface reflection loss, the current density (J_sc) of the top cell is enhanced from 15.56 mA/cm² to 17.09 mA/cm², the corresponding PCE reaches 19.05%, and the tandem PCE increases to 30.58%. Simultaneously, in the cases of n=3, 4, and 5, all the tandem PCEs exceed the limiting theoretical efficiency of Si cells. Therefore, the 4T quasi-2D perovskite/Si devices provide a more cost-effective tandem strategy and long-term stability solutions.

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Development of ZnTe film with high copper doping efficiency for solar cells

Xin-Lu Lin(林新璐), Wen-Xiong Zhao(赵文雄), Qiu-Chen Wu(吴秋晨), Yu-Feng Zhang(张玉峰), Hasitha Mahabaduge, and Xiang-Xin Liu(刘向鑫)

2022 (10): 108802-108802. doi: 10.1088/1674-1056/ac6b27

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Since a hole barrier was formed in back contact due to mismatch of work function, the back contact material for CdTe cell has been a significant research direction. The ZnTe:Cu is an ideal back contact material, which reduces the valence band discontinuity and can be used as the electron back reflection layer to inhibit interface recombination. The conductivity of ZnTe:Cu film is improved by applying RF-coupled DC sputtering and post-deposition heat treatment. The doping efficiency is computed as the ratio of free hole density and copper concentration, which can be correlated with performance for CdTe-based solar cell. The higher doping efficiency means that more copper atoms substitute for Zn sites in ZnTe lattices and less mobilized copper atoms remain which can enter into the CdTe absorber layer. Copper atoms are suspected as dominant element for CdTe-based cell degradation. After optimizing the ZnTe:Cu films, a systematic study is carried out to incorporate ZnTe:Cu film into CdTe solar cell. The EQE spectrum is kept relatively stable over the long wavelength range without decreasing. It is proved that the conduction band barrier of device with ZnTe:Cu/Au contact material has an effect on the EQE response, which works as free electron barrier and reduces the recombination rate of free carrier. According to the dark J—V data or the light J—V data in the linear region, the current indicates that the intercept gives the diode reverse saturation current. The results of ideality factor indicate that the dominant recombination occurs in the space charge region. In addition, the space charge density and depletion width of solar cell can be estimated by C—V profiling.

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Recombination-induced voltage-dependent photocurrent collection loss in CdTe thin film solar cell

Ling-Ling Wu(吴玲玲), Guang-Wei Wang(王光伟), Juan Tian(田涓), Dong-Ming Wang(王东明), and De-Liang Wang(王德亮)

2022 (10): 108803-108803. doi: 10.1088/1674-1056/ac728e

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Recently, the efficiency of CdTe thin film solar cell has been improved by using new type of window layer Mg_xZn_1-xO (MZO). However, it is hard to achieve such a high efficiency as expected. In this report a comparative study is carried out between the MZO/CdTe and CdS/CdTe solar cells to investigate the factors affecting the device performance of MZO/CdTe solar cells. The efficiency loss quantified by voltage-dependent photocurrent collection efficiency (η_C(V')) is 3.89% for MZO/CdTe and 1.53% for CdS/CdTe solar cells. The higher efficiency loss for the MZO/CdTe solar cell is induced by more severe carrier recombination at the MZO/CdTe p—n junction interface and in CdTe bulk region than that for the CdS/CdTe solar cell. Activation energy (E_a) of the reverse saturation current of the MZO/CdTe and CdS/CdTe solar cells are found to be 1.08 eV and 1.36 eV, respectively. These values indicate that for the CdS/CdTe solar cell the carrier recombination is dominated by bulk Shockley—Read—Hall (SRH) recombination and for the MZO/CdTe solar cell the carrier recombination is dominated by the p—n junction interface recombination. It is found that the tunneling-enhanced interface recombination is also involved in carrier recombination in the MZO/CdTe solar cell. This work demonstrates the poor device performance of the MZO/CdTe solar cell is induced by more severe interface and bulk recombination than that of the CdS/CdTe solar cell.

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