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15 June 2023, Volume 32 Issue 7 Previous issue    Next issue

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TOPICIAL REVIEW—Plasma disruption

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Recent progress on deep learning-based disruption prediction algorithm in HL-2A tokamak Zongyu Yang(杨宗谕), Yuhang Liu(刘宇航), Xiaobo Zhu(朱晓博), Zhengwei Chen(陈正威), Fan Xia(夏凡), Wulyu Zhong(钟武律), Zhe Gao(高喆), Yipo Zhang(张轶泼), and Yi Liu(刘仪) Chin. Phys. B, 2023, 32 (7):  075202.  DOI: 10.1088/1674-1056/accb44 Abstract ( 157 )   HTML ( 7 )   PDF (6317KB) ( 165 )   Disruption prediction and mitigation is a crucial topic, especially for future large-scale tokamaks, due to disruption's concomitant harmful effects on the devices. On this topic, disruption prediction algorithm takes the responsibility to give accurate trigger signal in advance of disruptions, therefore the disruption mitigation system can effectively alleviate the harmful effects. In the past 5 years, a deep learning-based algorithm is developed in HL-2A tokamak. It reaches a true positive rate of 92.2%, a false positive rate of 2.5% and a total accuracy of 96.1%. Further research is implemented on the basis of this algorithm to solve three key problems, i.e., the algorithm's interpretability, real-time capability and transferability. For the interpretability, HL-2A's algorithm gives saliency maps indicating the correlation between the algorithm's input and output by perturbation analysis. The distribution of correlations shows good coherence with the disruption causes. For the transferability, a preliminary disruption predictor is successfully developed in HL-2M, a newly built tokamak in China. Although only 44 shots are used as the training set of this algorithm, it gives reasonable outputs with the help of data from HL-2A and J-TEXT. For the real-time capacity, the algorithm is accelerated to deal with an input slice within 0.3 ms with the help of some adjustments on it and TFLite framework. It is also implemented into the plasma control system and gets an accuracy of 89.0% during online test. This paper gives a global perspective on these results and discusses the possible pathways to make HL-2A's algorithm a more comprehensive solution for future tokamaks.

SPECIAL TOPIC—Plasma disruption

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Disruption prediction based on fusion feature extractor on J-TEXT Wei Zheng(郑玮), Fengming Xue(薛凤鸣), Zhongyong Chen(陈忠勇), Chengshuo Shen(沈呈硕), Xinkun Ai(艾鑫坤), Yu Zhong(钟昱), Nengchao Wang(王能超), Ming Zhang(张明),Yonghua Ding(丁永华), Zhipeng Chen(陈志鹏), Zhoujun Yang(杨州军), and Yuan Pan(潘垣) Chin. Phys. B, 2023, 32 (7):  075203.  DOI: 10.1088/1674-1056/acc7fc Abstract ( 145 )   HTML ( 7 )   PDF (2797KB) ( 72 )   Predicting disruptions across different tokamaks is necessary for next generation device. Future large-scale tokamaks can hardly tolerate disruptions at high performance discharge, which makes it difficult for current data-driven methods to obtain an acceptable result. A machine learning method capable of transferring a disruption prediction model trained on one tokamak to another is required to solve the problem. The key is a feature extractor which is able to extract common disruption precursor traces in tokamak diagnostic data, and can be easily transferred to other tokamaks. Based on the concerns above, this paper presents a deep feature extractor, namely, the fusion feature extractor (FFE), which is designed specifically for extracting disruption precursor features from common diagnostics on tokamaks. Furthermore, an FFE-based disruption predictor on J-TEXT is demonstrated. The feature extractor is aimed to extracting disruption-related precursors and is designed according to the precursors of disruption and their representations in common tokamak diagnostics. Strong inductive bias on tokamak diagnostics data is introduced. The paper presents the evolution of the neural network feature extractor and its comparison against general deep neural networks, as well as a physics-based feature extraction with a traditional machine learning method. Results demonstrate that the FFE may reach a similar effect with physics-guided manual feature extraction, and obtain a better result compared with other deep learning methods.

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Effect of tearing modes on the confinement of runaway electrons in Experimental Advanced Superconducting Tokamak Rui-Jie Zhou(周瑞杰) Chin. Phys. B, 2023, 32 (7):  075204.  DOI: 10.1088/1674-1056/acc3f8 Abstract ( 137 )   HTML ( 6 )   PDF (2152KB) ( 132 )   The effect of tearing modes on the confinement of runaway electrons is studied in Experimental Advanced Superconducting Tokamak (EAST). The general tendency of the radial diffusion coefficient of runaway electrons (REs) Dr is derived based on the time response relation between the tearing modes and runaway electrons. The results indicate that, the magnetic fluctuations of tearing modes will enhance the radial diffusion of runaway electrons when the magnetic island is small. Following the increasing of the magnetic fluctuations of the tearing modes, the formed large magnetic island may weaken the radial diffusion of runaway electrons. The results can be important to understand the confinement of runaway electrons when large magnetic islands exist in the plasma.

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Development of electromagnetic pellet injector for disruption mitigation of tokamak plasma Feng Li(李峰), Zhong-Yong Chen(陈忠勇), Sheng-Guo Xia(夏胜国), Wei Yan(严伟), Wei-Kang Zhang(张维康), Jun-Hui Tang(唐俊辉), You Li(李由), Yu Zhong(钟昱), Jian-Gang Fang(方建港), Fan-Xi Liu(刘凡溪),Gui-Nan Zou(邹癸南), Yin-Long Yu(喻寅龙), Zi-Sen Nie(聂子森), Zhong-He Jiang(江中和),Neng-Chao Wang(王能超), Yong-Hua Ding(丁永华), Yuan Pan(潘垣), and the J-TEXT team Chin. Phys. B, 2023, 32 (7):  075205.  DOI: 10.1088/1674-1056/acc7fb Abstract ( 167 )   HTML ( 242 )   PDF (1236KB) ( 148 )   Disruption remains to be a serious threat to large tokamaks like the International Thermonuclear Experimental Reactor (ITER). The injection speed of disruption mitigation systems (DMS) driven by high pressure gas is limited by the sound speed of the propellant gas. When extrapolating to ITER-like tokamaks, long overall reaction duration and shallow penetration depth due to low injection speed make it stricter for plasma control system to predict the impending disruptions. Some disruptions with a short warning time may be unavoidable. Thus, a fast time response and high injection speed DMS is essential for large scale devices. The electromagnetic pellet-injection (EMPI) system is a novel massive material injection system aiming to provide rapid and effective disruption mitigation. Based on the railgun concept, EMPI can accelerate the payload to over 1000 m/s and shorten the overall reaction time to a few milliseconds. To verify the injection ability and stability of the EMPI, the prototype injector EMPI-1 has been designed and assembled. The preliminary test has been carried out using a 5.9 g armature to propel a dummy pellet and the results suggest that the EMPI configuration has a great potential to be the DMS of the large scale fusion devices.

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Features of transport induced by ion-driven trapped-electron modes in tokamak plasmas Hui Li(李慧), Ji-Quan Li(李继全), Feng Wang(王丰), Qi-Bin Luan(栾其斌),Hong-En Sun(孙宏恩), and Zheng-Xiong Wang(王正汹) Chin. Phys. B, 2023, 32 (7):  075206.  DOI: 10.1088/1674-1056/acae7e Abstract ( 136 )   HTML ( 240 )   PDF (675KB) ( 118 )   As an obstacle in high-performance discharge in future fusion devices, disruptions may do great damages to the reactors through causing strong electromagnetic forces, heat loads and so on. The drift waves in tokamak are illustrated to play essential roles in the confinement performance as well. Depending on the plasma parameters and mode perpendicular wavelength, the mode phase velocity is either in the direction of electron diamagnetic velocity (namely, typical trapped electron mode) or in the direction of ion diamagnetic velocity (namely, the ubiquitous mode). Among them, the ubiquitous mode is directly investigated using gyro-fluid simulation associating with gyro-fluid equations for drift waves in tokamak plasmas. The ubiquitous mode is charactered by the short wavelength and propagates in ion diamagnetic direction. It is suggested that the density gradient is essential for the occurrence of the ubiquitous mode. However, the ubiquitous mode is also influenced by the temperature gradients and other plasma parameters including the magnetic shear and the fraction of trapped electrons. Furthermore, the ubiquitous mode may play essential roles in the turbulent transport. Meanwhile, the relevant parameters are scanned using a great number of electrostatic gyro-fluid simulations. The stability map is taken into consideration with the micro-instabilities contributing to the turbulent transport. The stability valley of the growth rates occurs with the assumption of the normalized temperature gradient equaling to the normalized density gradient.

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Comparison of different noble gas injections by massive gas injection on plasma disruption mitigation on Experimental Advanced Superconducting Tokamak Sheng-Bo Zhao(赵胜波), Hui-Dong Zhuang(庄会东), Jing-Sheng Yuan(元京升), De-Hao Zhang(张德皓),Li Li(黎立), Long Zeng(曾龙), Da-Long Chen(陈大龙), Song-Tao Mao(毛松涛), Ming Huang(黄明),Gui-Zhong Zuo(左桂忠), and Jian-Sheng Hu(胡建生) Chin. Phys. B, 2023, 32 (7):  075207.  DOI: 10.1088/1674-1056/acc1d6 Abstract ( 159 )   HTML ( 6 )   PDF (6952KB) ( 273 )   Massive gas injection (MGI) is a traditional plasma disruption mitigation method. This method directly injected massive gas into the pre-disruption plasma and had been developed on the Experimental Advanced Superconducting Tokamak (EAST). Different noble gas injection experiments, including He, Ne, and Ar, were performed to compare the mitigation effect of plasma disruption by evaluating the key parameters such as flight time, pre-thermal quench (pre-TQ), and current quench (CQ). The flight time was shorter for low atomic number (Z) gas, and the decrease in flight time by increasing the amount of gas was insignificant. However, both pre-TQ and CQ durations decreased considerably with the increase in gas injection amount. The effect of atomic mass on pre-TQ and CQ durations showed the opposite trend. The observed trend could help in controlling CQ duration in a reasonable area. Moreover, the analysis of radiation distribution with different impurity injections indicated that low Z impurity could reduce the asymmetry of radiation, which is valuable in mitigating plasma disruption. These results provided essential data support for plasma disruption mitigation on EAST and future fusion devices.

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Drift surface solver for runaway electron current dominant equilibria during the current quench Lu Yuan(袁露) and Di Hu(胡地) Chin. Phys. B, 2023, 32 (7):  075208.  DOI: 10.1088/1674-1056/acc1d7 Abstract ( 148 )   HTML ( 5 )   PDF (10727KB) ( 84 )   Runaway electron current generated during the current quench phase of tokamak disruptions could result in severe damage to future high performance devices. To control and mitigate such runaway electron current, it is important to accurately describe the runaway electron current dominated equilibrium, based on which further stability analysis could be carried out. In this paper, we derive a Grad-Shafranov-like equation solving for the axisymmetric drift surfaces of the runaway electrons instead of the magnetic flux surfaces for the simple case that all runaway electrons share the same parallel momentum. This new equilibrium equation is then numerically solved with simple rectangular wall with ITER-like and MAST-like geometry parameters. The deviation between the drift surfaces and the flux surfaces is readily obtained, and runaway electrons are found to be well confined even in regions with open field lines. The change of the runaway electron parallel momentum is found to result in a horizontal current center displacement without any changes in the total current or the external field. The runaway current density profile is found to affect the susceptibility of such displacement, with flatter profiles result in more displacement by the same momentum change. With up-down asymmetry in the external poloidal field, such displacement is accompanied by a vertical displacement of runaway electron current. It is found that this effect is more pronounced in smaller, compact device and weaker poloidal field cases. The above results demonstrate the dynamics of current center displacement caused by the momentum space change in the runaway electrons, and pave a way for more sophisticated runaway current equilibrium theory in the future with more realistic consideration on the runaway electron momentum distribution. This new equilibrium theory also provides foundation for future stability analysis of the runaway electron current.

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Runaway electron dynamics in Experimental Advanced Superconducting Tokamak helium plasmas Chen-Xi Luo(罗晨曦), Long Zeng(曾龙), Xiang Zhu(朱翔), Tian Tang(唐天), Zhi-Yong Qiu(仇志勇),Shi-Yao Lin(林士耀), Tao Zhang(张涛), Hai-Qing Liu(刘海庆), Tong-Hui Shi(石同辉), Bin Zhang(张斌),Rui Ding(丁锐), Wei Gao(高伟), Min-Rui Wang(王敏锐), Wei Gao(高伟), Ang Ti(提昂), Hai-Lin Zhao(赵海林), Tian-Fu Zhou(周天富), Jin-Ping Qian(钱金平), You-Wen Sun(孙有文), Bo Lv(吕波), Qing Zang(臧庆),Yin-Xian Jie(揭银先), Yun-Feng Liang(梁云峰), and Xiang Gao(高翔) Chin. Phys. B, 2023, 32 (7):  075209.  DOI: 10.1088/1674-1056/acac12 Abstract ( 139 )   HTML ( 233 )   PDF (3393KB) ( 179 )   The generation of runaway electrons (REs) is observed during the low-density helium ohmic plasma discharge in the Experimental Advanced Superconducting Tokamak (EAST). The growth rate of hard x-ray (HXR) is inversely proportional to the line-average density. Besides, the RE generation in helium plasma is higher than that in deuterium plasma at the same density, which is obtained by comparing the growth rate of HXR with the same discharge conditions. The potential reason is the higher electron temperature of helium plasma in the same current and electron density plateau. Furthermore, two Alfvén eigenmodes driven by REs have been observed. The frequency evolution of the mode is not fully satisfied with the Alfvén scaling and when extension of the Alfvén frequency is towards 0, the high frequency branch is ～ 50 kHz. The different spatial position of the two modes and the evolution of the helium concentration could be used to understand deviation between theoretical and experimental observation.

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Effect of the relative phase between pre-existing 2/1 and 3/1 magnetic islands on the suppression of runaway electrons on J-TEXT Jin-Yu Xiong(熊金玉), Zhong-He Jiang(江中和), Zi-Xiao Jiao(焦子啸), Zhen Li(李振),Yun-Feng Liang(梁云峰), Zhong-Yong Chen(陈忠勇), Yong-Hua Ding(丁永华), and J-TEXT Team Chin. Phys. B, 2023, 32 (7):  075210.  DOI: 10.1088/1674-1056/acc3f9 Abstract ( 143 )   HTML ( 4 )   PDF (1526KB) ( 70 )   In the experiments of actively triggering plasma disruption by massive gas injection, the externally applied resonant magnetic perturbation has been used to mitigate the hazard of runaway electron (RE). Motivated by the experiment of multimode coupling to suppress REs on J-TEXT, some typical simulation cases with non-ideal MHD with rotation-open discussion (NIMROD) code are carried out to explore the influential mechanism of different relative phases between m/n = 2/1 and m/n = 3/1 magnetic islands on the confinement of REs. Results show that the RE confinement is drastically affected by the relative phase between 2/1 and 3/1 magnetic islands. When the O point phase of 2/1 and 3/1 magnetic islands is toroidal 330°, REs can be effectively lost. The fitting curve of the remaining ratio of REs vs. the relative toroidal phase is predicted to approximate a sine-like function dependence. Further studies indicate that the phase difference between coexisting 2/1 and 3/1 islands can affect the radial transport of impurities. The loss of runaway electrons is closely related to the deposition effect of impurity. The impurity is easier to spread into the core region with smaller poloidal phase difference between the radial velocity of impurity and the impurity quantity of Ar.

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Prediction of multifaceted asymmetric radiation from the edge movement in density-limit disruptive plasmas on Experimental Advanced Superconducting Tokamak using random forest Wenhui Hu(胡文慧), Jilei Hou(侯吉磊), Zhengping Luo(罗正平), Yao Huang(黄耀), Dalong Chen(陈大龙),Bingjia Xiao(肖炳甲), Qiping Yuan(袁旗平), Yanmin Duan(段艳敏), Jiansheng Hu(胡建生),Guizhong Zuo(左桂忠), and Jiangang Li(李建刚) Chin. Phys. B, 2023, 32 (7):  075211.  DOI: 10.1088/1674-1056/acd2b0 Abstract ( 143 )   HTML ( 5 )   PDF (2814KB) ( 105 )   Multifaceted asymmetric radiation from the edge (MARFE) movement which can cause density limit disruption is often encountered during high density operation on many tokamaks. Therefore, identifying and predicting MARFE movement is meaningful to mitigate or avoid density limit disruption for the steady-state high-density plasma operation. A machine learning method named random forest (RF) has been used to predict the MARFE movement based on the density ramp-up experiment in the 2022's first campaign of Experimental Advanced Superconducting Tokamak (EAST). The RF model shows that besides Greenwald fraction which is the ratio of plasma density and Greenwald density limit, d$\beta_{\rm p}/$d$ t$, $H_{98}$ and d $W_{\rm mhd}/$d$t$ are relatively important parameters for MARFE-movement prediction. Applying the RF model on test discharges, the test results show that the successful alarm rate for MARFE movement causing density limit disruption reaches $\sim 85%$ with a minimum alarm time of $\sim 40 $ ms and mean alarm time of $\sim 700 $ ms. At the same time, the false alarm rate for non-disruptive and non-density-limit disruptive discharges can be kept below 5%. These results provide a reference to the prediction of MARFE movement in high density plasmas, which can help the avoidance or mitigation of density limit disruption in future fusion reactors.

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Stability impacts from the current and pressure profile modifications within finite sized island Yuxiang Sun(孙宇翔) and Di Hu(胡地) Chin. Phys. B, 2023, 32 (7):  075212.  DOI: 10.1088/1674-1056/acd369 Abstract ( 152 )   HTML ( 5 )   PDF (1646KB) ( 80 )   The stability (or instability) of finite sized magnetic island could play a significant role in disruption avoidance or disruption mitigation dynamics. Especially, various current and pressure profile modifications, such as the current drive and heating caused by electron cyclotron wave, or the radiative cooling and current expulsion caused by the shattered pellet injection could be applied within the island to modify its stability, thus changing the ensuing dynamics. In this study, we calculate the mode structure modification caused by such profile changes within the island using the perturbed equilibrium approach, thus obtain the change of stability criterion $\varDelta$' and assess the corresponding quasi-linear island stability. The positive helical current perturbation is found to always stabilize the island, while the negative one is found to do the opposite, in agreement with previous results. The pressure bump or hole within the island has a more complicated stability impact. In the small island regime, its contribution is monotonic, with pressure bump that tends to stabilize the island while pressure hole destabilizes it. This effect is relatively weak, though, due to the cancellation of the pressure term's odd parity contribution in the second derivatives of the mode structure. In the large island regime, such cancellation is broken due to the island asymmetry, and the pressure contribution to stability is manifested, which is non-monotonic. The stability analysis in this paper helps to more accurately clarify the expected island response in the presence of profile modifications caused by disruption avoidance or mitigation systems.

SPECIAL TOPIC—Smart design of materials and design of smart materials

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Enhanced mechanical and thermal properties of two-dimensional SiC and GeC with temperature and size dependence Lei Huang(黄磊), Kai Ren(任凯), Huanping Zhang(张焕萍), and Huasong Qin(覃华松) Chin. Phys. B, 2023, 32 (7):  076103.  DOI: 10.1088/1674-1056/acc78f Abstract ( 160 )   HTML ( 2 )   PDF (2748KB) ( 168 )   Two-dimensional materials with novel mechanical and thermal properties are available for sensors, photodetectors, thermoelectric, crystal diode and flexible nanodevices. In this investigation, the mechanical and thermal properties of pristine SiC and GeC are explored by molecular dynamics simulations. First, the fracture strength and fracture strain behaviors are addressed in the zigzag and armchair directions at 300 K. The excellent toughness of SiC and GeC is demonstrated by the maximal fracture strain of 0.43 and 0.47 in the zigzag direction, respectively. The temperature-tunable tensile strength of SiC and GeC is also investigated. Then, using non-equilibrium molecular dynamics (NEMD) calculations, the thermal performances of SiC and GeC are explored. In particular, the thermal conductivity of SiC and GeC shows a pronounced size dependence and reaches up to 85.67 W·m-1·K-1 and 34.37 W·m-1·K-1, respectively. The goal of our work is to provide a theoretical framework that can be used in the near future. This will enable us to design an efficient thermal management scheme for two-dimensional materials in electronics and optoelectronics.

DATA PAPER

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Absolute dielectronic recombination rate coefficients of highly charged ions at the storage ring CSRm and CSRe Zhongkui Huang(黄忠魁), Shuxing Wang(汪书兴), Weiqiang Wen(汶伟强), Hanbing Wang(汪寒冰), Wanlu Ma(马万路), Chongyang Chen(陈重阳), Chunyu Zhang(张春雨), Dongyang Chen(陈冬阳), Houke Huang(黄厚科), Lin Shao(邵林), Xin Liu(刘鑫), Xiaopeng Zhou(周晓鹏), Lijun Mao(冒立军), Jie Li(李杰), Xiaoming Ma(马晓明), Meitang Tang(汤梅堂), Jiancheng Yang(杨建成), Youjin Yuan(原有进), Shaofeng Zhang(张少锋), Linfan Zhu(朱林繁), and Xinwen Ma(马新文) Chin. Phys. B, 2023, 32 (7):  073401.  DOI: 10.1088/1674-1056/acbc69 Abstract ( 140 )   HTML ( 2 )   PDF (3175KB) ( 73 )   Dielectronic recombination (DR) is one of the dominant electron-ion recombination mechanisms for most highly charged ions (HCIs) in cosmic plasmas, and thus, it determines the charge state distribution and ionization balance therein. To reliably interpret spectra from cosmic sources and model the astrophysical plasmas, precise DR rate coefficients are required to build up an accurate understanding of the ionization balance of the sources. The main cooler storage ring (CSRm) and the experimental cooler storage ring (CSRe) at the Heavy-Ion Research Facility in Lanzhou (HIRFL) are both equipped with electron cooling devices, which provide an excellent experimental platform for electron-ion collision studies for HCIs. Here, the status of the DR experiments at the HIRFL-CSR is outlined, and the DR measurements with Na-like Kr25+ ions at the CSRm and CSRe are taken as examples. In addition, the plasma recombination rate coefficients for Ar12+, 14+, Ca14+, 16+, 17+, Ni19+, and Kr25+ ions obtained at the HIRFL-CSR are provided. All the data presented in this paper are openly available at https://doi.org/10.57760/sciencedb.j00113.00092.

INSTRUMENTATION AND MEASUREMENT

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Current sensor based on diamond nitrogen-vacancy color center Zi-Yang Shi(史子阳), Wei Gao(高伟), Qi Wang(王启), Hao Guo(郭浩), Jun Tang(唐军), Zhong-Hao Li(李中豪), Huan-Fei Wen(温焕飞), Zong-Min Ma(马宗敏), and Jun Liu(刘俊) Chin. Phys. B, 2023, 32 (7):  070704.  DOI: 10.1088/1674-1056/acc3fe Abstract ( 199 )   HTML ( 4 )   PDF (1692KB) ( 309 )   High precision current measurement is very important for the calibration of various high-precision equipment and the measurement of other precision detection fields. A new current sensor based on diamond nitrogen-vacancy (NV) color center magnetic measurement method is proposed to realize the accurate measurement of current. This new current method can greatly improve the accuracy of current measurement. Experiments show that the linearity of the current sensor based on diamond NV color center can reach up to 33 ppm, which is superior to other current sensors and solves the problem of low linearity. When the range of input current is 5-40 A, the absolute error of the calculated current is less than 51 μA, and the relative error is 2.42×10-6 at 40 A. Combined with the research content and results of the experiment, the application of the current sensor in the field of current precision measurement is prospected.

REVIEW

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Energy conversion materials for the space solar power station Xiao-Na Ren(任晓娜), Chang-Chun Ge(葛昌纯), Zhi-Pei Chen(陈志培), Irfan(伊凡), Yongguang Tu(涂用广), Ying-Chun Zhang(张迎春), Li Wang(王立), Zi-Li Liu(刘自立), and Yi-Qiu Guan(关怡秋) Chin. Phys. B, 2023, 32 (7):  078802.  DOI: 10.1088/1674-1056/acbdee Abstract ( 144 )   HTML ( 2 )   PDF (3747KB) ( 117 )   Since it was first proposed, the space solar power station (SSPS) has attracted great attention all over the world; it is a huge space system and provides energy for Earth. Although several schemes and abundant studies on the SSPS have been proposed and conducted, it is still not realized. The reason why SSPS is still an idea is not only because it is a giant and complex project, but also due to the requirement for various excellent space materials. Among the diverse required materials, we believe energy materials are the most important. Herein, we review the space energy conversion materials for the SSPS.

RAPID COMMUNICATION

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Anomalous non-Hermitian dynamical phenomenon on the quantum circuit Chenxiao Dong(董陈潇), Zhesen Yang(杨哲森), Jinfeng Zeng(曾进峰), and Jiangping Hu(胡江平) Chin. Phys. B, 2023, 32 (7):  070305.  DOI: 10.1088/1674-1056/acce9a Abstract ( 197 )   HTML ( 2 )   PDF (1171KB) ( 160 )   The anomalous non-Hermitian dynamical phenomenon with the non-Hermitian skin effect (NHSE) attracts wide attention due to its novel physics and promising applications. Here, we propose a new type of non-unitary discrete-time quantum walk system demonstrating the NHSE and anomalous non-Hermitian dynamical phenomena, including the dynamical chiral phenomenon, the funneling phenomenon on the domain wall, and the anomalous reflection on the phase impurity. Furthermore, we design the quantum circuit experiments of these quantum walk systems and numerically simulate them with quantum noises to verify the robustness of the non-Hermitian dynamical phenomenon on the noisy intermediate-scale quantum (NISQ) devices. Our work paves the way for implementing the non-Hermitian dynamical phenomenon on the quantum circuit.

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Periodic electron oscillation in coupled two-dimensional lattices Hot! Yan-Yan Lu(陆艳艳), Chao Wang(王超), Jin-Yi Jiang(将金益), Jie Liu(刘洁), and Jian-Xin Zhong(钟建新) Chin. Phys. B, 2023, 32 (7):  070306.  DOI: 10.1088/1674-1056/acce93 Abstract ( 374 )   HTML ( 13 )   PDF (1670KB) ( 412 )   We study the time evolution of electron wavepacket in the coupled two-dimensional (2D) lattices with mirror symmetry, utilizing the tight-binding Hamiltonian framework. We show analytically that the wavepacket of an electron initially located on one atomic layer in the coupled 2D square lattices exhibits a periodic oscillation in both the transverse and longitudinal directions. The frequency of this oscillation is determined by the strength of the interlayer hopping. Additionally, we provide numerical evidence that a damped periodic oscillation occurs in the coupled 2D disordered lattices with degree of disorder W, with the decay time being inversely proportional to the square of W and the frequency change being proportional to the square of W, which is similar to the case in the coupled 1D disordered lattices. Our numerical results further confirm that the periodic and damped periodic electron oscillations are universal, independent of lattice geometry, as demonstrated in AA-stacked bilayer and tri-layer graphene systems. Unlike the Bloch oscillation driven by electric fields, the periodic oscillation induced by interlayer coupling does not require the application of an electric field, has an ultrafast periodicity much shorter than the electron decoherence time in real materials, and can be tuned by adjusting the interlayer coupling. Our findings pave the way for future observation of periodic electron oscillation in material systems at the atomic scale.

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Circuit quantum electrodynamics with a quadruple quantum dot Ting Lin(林霆), Hai-Ou Li(李海欧), Gang Cao(曹刚), and Guo-Ping Guo(郭国平) Chin. Phys. B, 2023, 32 (7):  070307.  DOI: 10.1088/1674-1056/accd57 Abstract ( 148 )   HTML ( 3 )   PDF (1216KB) ( 111 )   In this theoretical work, we describe a mechanism for the coupling between a plane structure consisting of four quantum dots and a resonator. We systematically study the dependence of the quadruple coupling strength and the qubit decoherence rate and point out the optimized operating position of the hybrid system. According to the transmission given by the input-output theory, the signatures in the resonator spectrum are predicted. Furthermore, based on the parameters already achieved in previous works, we prove that the device described in this paper can achieve the strong coupling limit, i.e., this approach can be used for system extension under the existing technical conditions. Our results show an effective and promotable approach to couple quantum dot structures in plane with the resonator and propose a meaningful extension method.

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Neural network analytic continuation for Monte Carlo: Improvement by statistical errors Hot! Kai-Wei Sun(孙恺伟) and Fa Wang(王垡) Chin. Phys. B, 2023, 32 (7):  070705.  DOI: 10.1088/1674-1056/accd4c Abstract ( 221 )   HTML ( 4 )   PDF (2228KB) ( 245 )   This study explores the use of neural network-based analytic continuation to extract spectra from Monte Carlo data. We apply this technique to both synthetic and Monte Carlo-generated data. The training sets for neural networks are carefully synthesized without "data leakage". We find that the training set should match the input correlation functions in terms of statistical error properties, such as noise level, noise dependence on imaginary time, and imaginary time-displaced correlations. We have developed a systematic method to synthesize such training datasets. Our improved algorithm outperforms the widely used maximum entropy method in highly noisy situations. As an example, our method successfully extracted the dynamic structure factor of the spin-1/2 Heisenberg chain from quantum Monte Carlo simulations.

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Temperature-free mass tracking of a levitated nanoparticle Hot! Yuan Tian(田原), Yu Zheng(郑瑜), Lyu-Hang Liu(刘吕航), Guang-Can Guo(郭光灿), and Fang-Wen Sun(孙方稳) Chin. Phys. B, 2023, 32 (7):  074207.  DOI: 10.1088/1674-1056/accb4c Abstract ( 176 )   HTML ( 4 )   PDF (904KB) ( 207 )   Mass measurement is an essential analytical tool in the characterization of materials. Here we present a method for measuring the mass of an individual nanoparticle which has a fg-level mass. This method enables a temperature-independent mass measurement with the assistance of a sinusoidal electrostatic driving force. With this approach, we successfully track the change in properties of an optically levitated nanoparticle, such as mass, temperature, and electric charge, with air pressure. An abrupt change in the mass of silica nanoparticles is found to violate the Zhuravlev model. This method can be utilized to extend the mass analysis of materials, such as thermogravimetric analysis, to individual micro- or nano-particles.

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Electronic states of domain walls in commensurate charge density wave ground state and mosaic phase in 1T-TaS2 Hot! Yan Li(李彦), Yao Xiao(肖遥), Qi Zheng(郑琦), Xiao Lin(林晓), Li Huang(黄立), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2023, 32 (7):  077101.  DOI: 10.1088/1674-1056/accd4f Abstract ( 281 )   HTML ( 5 )   PDF (2110KB) ( 282 )   Domain walls (DWs) in the charge-density-wave (CDW) Mott insulator 1T-TaS2 have unique localized states, which play an important role in exploring the electronic properties of the material. However, the electronic states in DWs in 1T-TaS2 have not been clearly understood, mostly due to the complex structures, phases, and interlayer stacking orders in the DW areas. Here, we explored the electronic states of DWs in the large-area CDW phase and mosaic phase of 1T-TaS2 by scanning tunneling spectroscopy. Due to the different densities of DWs, the electronic states of DWs show distinct features in these phases. In the large area CDW phase, both the domain and the DWs (DW1, DW2, DW4) have zero conductance at the Fermi level; while in the mosaic phase, they can be metallic or insulating depending on their environments. In areas with a high density of DWs, some electronic states were observed both on the DWs and within the domains, indicating delocalized states over the whole region. Our work contributes to further understanding of the interplay between CDW and electron correlations in 1T-TaS2.

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Negative magnetoresistance in Dirac semimetal Cd3As2 with in-plane magnetic field perpendicular to current Hao-Nan Cui(崔浩楠), Guang-Yu Zhu(祝光宇), Jian-Kun Wang(王建坤), Jia-Jie Yang(杨佳洁), Wen-Zhuang Zheng(郑文壮), Ben-Chuan Lin(林本川), Zhi-Min Liao(廖志敏), Shuo Wang(王硕), and Da-Peng Yu(俞大鹏) Chin. Phys. B, 2023, 32 (7):  077305.  DOI: 10.1088/1674-1056/accd50 Abstract ( 145 )   HTML ( 2 )   PDF (1282KB) ( 87 )   Topological insulators and semimetals have exotic surface and bulk states with massless Dirac or Weyl fermions, demonstrating microscopic transport phenomenon based on relativistic theory. Chiral anomaly induced negative magnetoresistance (negative MR) under parallel magnetic field and current has been used as a probable evidence of Weyl fermions in recent years. Here we report a novel negative MR result with mutually perpendicular in-plane magnetic field and current in Cd3As2 nanowires. The negative MR has a considerable value of -16% around 1.5 K and could persist to room temperature of 300 K with value of -1%. The gate tuning and angle dependence of the negative MR demonstrate the mechanism of the observed negative MR is different from the chiral anomaly. Percolating current paths induced by charge puddles and disorder might be involved to produce such considerable negative MR. Our results indicate the negative MR effect in topological semimetals involves synergistic effects of many mechanisms besides chiral anomaly.

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Optimization of large-area YBa2Cu3O7-δ thin films by pulsed laser deposition for planar microwave devices Hot! Pei-Yu Xiong(熊沛雨), Fu-Cong Chen(陈赋聪), Zhong-Pei Feng(冯中沛), Jing-Ting Yang(杨景婷), Yu-Dong Xia(夏钰东), Yue-Feng Yuan(袁跃峰), Xu Wang(王旭), Jie Yuan(袁洁), Yun Wu(吴云), Jing Shi(石兢), and Kui Jin(金魁) Chin. Phys. B, 2023, 32 (7):  077402.  DOI: 10.1088/1674-1056/accb4d Abstract ( 198 )   HTML ( 3 )   PDF (2326KB) ( 237 )   This paper presents high quality YBa2Cu3O7-δ (YBCO) thin films on LaAlO3 substrate for microwave devices prepared by pulsed laser deposition (PLD). The double-sided YBCO films cover a large area and have been optimized for key parameters relevant to microwave device applications, such as surface morphology and surface resistance (Rs). This was achieved by improving the target quality and increasing the oxygen pressure during deposition, respectively. To evaluate the suitability of the YBCO films for microwave devices, a pair of microwave filters based on microstrip fabricated on films from this work and a commercial company were compared. The results show that the YBCO films in this work could completely meet the requirements for microwave devices.

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A novel calculation strategy for optimized prediction of the reduction of electrochemical window at anode Hot! Guochen Sun(孙国宸), Jian Gao(高健), and Hong Li(李泓) Chin. Phys. B, 2023, 32 (7):  078201.  DOI: 10.1088/1674-1056/accd51 Abstract ( 170 )   HTML ( 2 )   PDF (827KB) ( 142 )   The reduction of the electrochemical window (EW) of electrolytes plays a significant role in assessing their compatibility with the anode in lithium-ion batteries. However, the accurate calculation of the reduction of EW is still challenging due to missing the solvation effects, condensation effects, kinetic factors, and the passivation on anodes. The theoretical prediction of the intrinsic and apparent EW is confirmed by a comprehensive experimental analysis of ethylene carbonate-dimethyl carbonate (EC-DMC) electrolytes, combining linear sweep voltammetry (LSV) and gas chromatography-mass spectrometry (GC-MS). The proposed novel kinetic normal distribution theory model can quantitatively explain the current density from LSV and affirm acetaldehyde (MeCHO) as one of the primary reduction products of EC. The solvent effect restricts the intrinsic EW of EC-DMC without lithium salt to 2.6 V (vs. Li+/Li) arising from the Marcus-Gerischer theory and the passivation of MeCHO on the anode broadens the apparent EW to 0.3 V (vs. Li+/Li) arising from the normal distribution of the lowest unoccupied molecular orbital (LUMO) for MeCHO produced by thermal motion. In addition, the passivation on the anode depends intensively on the lithium salt, resulting in more complicated influences on the apparent EW.

GENERAL

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Interaction solutions and localized waves to the (2+1)-dimensional Hirota-Satsuma-Ito equation with variable coefficient Xinying Yan(闫鑫颖), Jinzhou Liu(刘锦洲), and Xiangpeng Xin(辛祥鹏) Chin. Phys. B, 2023, 32 (7):  070201.  DOI: 10.1088/1674-1056/acb9f2 Abstract ( 155 )   HTML ( 2 )   PDF (3208KB) ( 126 )   This article investigates the Hirota-Satsuma-Ito equation with variable coefficient using the Hirota bilinear method and the long wave limit method. The equation is proved to be Painlevé integrable by Painlevé analysis. On the basis of the bilinear form, the forms of two-soliton solutions, three-soliton solutions, and four-soliton solutions are studied specifically. The appropriate parameter values are chosen and the corresponding figures are presented. The breather waves solutions, lump solutions, periodic solutions and the interaction of breather waves solutions and soliton solutions, etc. are given. In addition, we also analyze the different effects of the parameters on the figures. The figures of the same set of parameters in different planes are presented to describe the dynamical behavior of solutions. These are important for describing water waves in nature.

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Soliton propagation for a coupled Schrödinger equation describing Rossby waves Li-Yang Xu(徐丽阳), Xiao-Jun Yin(尹晓军), Na Cao(曹娜) and Shu-Ting Bai(白淑婷) Chin. Phys. B, 2023, 32 (7):  070202.  DOI: 10.1088/1674-1056/acb9e5 Abstract ( 157 )   HTML ( 2 )   PDF (4449KB) ( 102 )   We study a coupled Schrödinger equation which is started from the Boussinesq equation of atmospheric gravity waves by using multiscale analysis and reduced perturbation method. For the coupled Schrödinger equation, we obtain the Manakov model of all-focusing, all-defocusing and mixed types by setting parameters value and apply the Hirota bilinear approach to provide the two-soliton and three-soliton solutions. Especially, we find that the all-defocusing type Manakov model admits bright-bright soliton solutions. Furthermore, we find that the all-defocusing type Manakov model admits bright-bright-bright soliton solutions. Therefrom, we go over how the free parameters affect the Manakov model's all-focusing type's two-soliton and three-soliton solutions' collision locations, propagation directions, and wave amplitudes. These findings are useful for setting a simulation scene in Rossby waves research. The answers we have found are helpful for studying physical properties of the equation in Rossby waves.

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Rapid stabilization of stochastic quantum systems in a unified framework Jie Wen(温杰), Fangmin Wang(王芳敏), Yuanhao Shi(史元浩), Jianfang Jia(贾建芳), and Jianchao Zeng(曾建潮) Chin. Phys. B, 2023, 32 (7):  070203.  DOI: 10.1088/1674-1056/acb9f3 Abstract ( 120 )   HTML ( 4 )   PDF (1859KB) ( 81 )   Rapid stabilization of general stochastic quantum systems is investigated based on the rapid stability of stochastic differential equations. We introduce a Lyapunov-LaSalle-like theorem for a class of nonlinear stochastic systems first, based on which a unified framework of rapidly stabilizing stochastic quantum systems is proposed. According to the proposed unified framework, we design the switching state feedback controls to achieve the rapid stabilization of single-qubit systems, two-qubit systems, and N-qubit systems. From the unified framework, the state space is divided into two state subspaces, and the target state is located in one state subspace, while the other system equilibria are located in the other state subspace. Under the designed state feedback controls, the system state can only transit through the boundary between the two state subspaces no more than two times, and the target state is globally asymptotically stable in probability. In particular, the system state can converge exponentially in (all or part of) the state subspace where the target state is located. Moreover, the effectiveness and rapidity of the designed state feedback controls are shown in numerical simulations by stabilizing GHZ states for a three-qubit system.

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Angle robust transmitted plasmonic colors with different surroundings utilizing localized surface plasmon resonance Xufeng Gao(高旭峰), Qi Wang(王琦), Shijie Zhang(张世杰), Ruijin Hong(洪瑞金), and Dawei Zhang(张大伟) Chin. Phys. B, 2023, 32 (7):  070204.  DOI: 10.1088/1674-1056/ac921e Abstract ( 131 )   HTML ( 2 )   PDF (2054KB) ( 126 )   Color filters in different surroundings inherently suffer from angular sensitivity, which hinders their practical applications. Here, we present an angle-insensitive plasmonic filter that can produce different color responses to different surrounding environments. The color filters are based on a two-dimensional periodically and randomly distributed silver nanodisk array on a silica substrate. The proposed plasmonic color filters not only produce bright colors by altering the diameter of the Ag nanodisk, but also achieve continuous color palettes by changing the surrounding environment. Due to the weak coupling between the metallic nanodisks, the plasmonic color filters can enable good incident angle-insensitive properties (up to 30°). The strategy presented here could exhibit robust and promising applicability in anti-counterfeiting and imaging technologies.

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An improved ISR-WV rumor propagation model based on multichannels with time delay and pulse vaccination Yafang Dong(董雅芳), Liangán Huo(霍良安), Xiaoxiao Xie(谢笑笑), and Ming Li(李明) Chin. Phys. B, 2023, 32 (7):  070205.  DOI: 10.1088/1674-1056/acd2be Abstract ( 117 )   HTML ( 2 )   PDF (1555KB) ( 24 )   The rapid development of the Internet has broadened the channels of dissemination of information, it has also led to the rapid and widespread propagation of rumors, which can have a serious negative impact socially. In this paper, an improved ISR-WV rumor propagation model integrating multichannels is proposed by considering the system's time delay, and the influence of different channels of propagation on the dynamic process is further analyzed. Moreover, the basic reproduction number R0 , rumor-free equilibrium, and rumor-prevailing equilibrium, as well as their stability, are deduced. Then, an optimal control problem with pulse vaccination is designed. Finally, the validity of the model and theoretical results is verified by numerical simulations and a practical application. The results show that the rumor propagation threshold R0 is more sensitive to the rate of the propagation of the information base channel. The shorter the thinking time τ1 required for the ignorant to react after obtaining the information, the larger the final scale of propagation. Under this condition, the time delay τ2 spent by a spreader in producing a video is negatively related to the final scale of the propagation; conversely, a longer τ1 implies that the person tends to more cognizant, which can suppress the spread of rumors. Under this condition, τ2 has little effect on the final scale of propagation. In addition, the results also prove that timely implementation of the pulse vaccination control strategy of popular science education can effectively control the propagation of rumors and reduce their negative impact.

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Orientation determination of nitrogen-vacancy center in diamond using a static magnetic field Yangpeng Wang(王杨鹏), Rujian Zhang(章如健), Yan Yang(杨燕), Qin Wu(吴琴), Zhifei Yu(于志飞), and Bing Chen(陈冰) Chin. Phys. B, 2023, 32 (7):  070301.  DOI: 10.1088/1674-1056/acc0f7 Abstract ( 138 )   HTML ( 2 )   PDF (1149KB) ( 132 )   Nitrogen-vacancy (NV) centers in a bulk diamond are often employed to realize measurement of multiple physical quantities, which depends on orientation information of NV axis. We report a fast and effective method to determine the orientation of NV axis with the aid of a static magnetic field. By measuring the optically detected magnetic resonance spectra, we can precisely extract the polar angle information between the NV axis and the known magnetic field. Combining with the polar angle information of different kinds of NV centers, we employ the Nelder-Mead algorithm to get the optimal solution of the orientation of NV axis. This method is simple and efficient, and is easily applied in NV-based quantum sensing.

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Quantum homomorphic broadcast multi-signature based on homomorphic aggregation Xin Xu(徐鑫) and Ai-Han Yin(殷爱菡) Chin. Phys. B, 2023, 32 (7):  070302.  DOI: 10.1088/1674-1056/acac0e Abstract ( 146 )   HTML ( 2 )   PDF (528KB) ( 88 )   Quantum multi-signature has attracted extensive attention since it was put forward. Beside its own improvement, related research is often combined with other quantum signature. However, this type of quantum signature has one thing in common, that is, the generation and verification of signature depend heavily on the shared classical secret key. In order to increase the reliability of signature, the homomorphic aggregation technique is applied to quantum multi-signature, and then we propose a quantum homomorphic multi-signature protocol. Unlike previous quantum multi-signature protocols, this protocol utilizes homomorphic properties to complete signature generation and verification. In the signature generation phase, entanglement swapping is introduced, so that the individual signatures of multiple users are aggregated into a new multi-signature. The original quantum state is signed by the shared secret key to realize the verification of the signature in the verification phase. The signature process satisfies the homomorphic property, which can improve the reliability of the signature.

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First-order quantum phase transition and entanglement in the Jaynes-Cummings model with a squeezed light Chun-Qi Tang(汤椿琦) and Li-Tuo Shen(沈利托) Chin. Phys. B, 2023, 32 (7):  070303.  DOI: 10.1088/1674-1056/acb9f0 Abstract ( 147 )   HTML ( 4 )   PDF (2176KB) ( 51 )   We study the quantum phase transition and entanglement in the Jaynes-Cummings model with squeezed light, utilize a special transformation method to obtain the analytical ground state of the model within the near-resonance regime, and numerically verify the validity of the analytical ground state. It is found that the ground state exhibits a first-order quantum phase transition at the critical point linearly induced by squeezed light, and the ground state entanglement reaches its maximum when the qubit-field coupling strength is large enough at the critical point.

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A new method of constructing adversarial examples for quantum variational circuits Jinge Yan(颜金歌), Lili Yan(闫丽丽), and Shibin Zhang(张仕斌) Chin. Phys. B, 2023, 32 (7):  070304.  DOI: 10.1088/1674-1056/ac9b32 Abstract ( 148 )   HTML ( 5 )   PDF (725KB) ( 123 )   A quantum variational circuit is a quantum machine learning model similar to a neural network. A crafted adversarial example can lead to incorrect results for the model. Using adversarial examples to train the model will greatly improve its robustness. The existing method is to use automatic differentials or finite difference to obtain a gradient and use it to construct adversarial examples. This paper proposes an innovative method for constructing adversarial examples of quantum variational circuits. In this method, the gradient can be obtained by measuring the expected value of a quantum bit respectively in a series quantum circuit. This method can be used to construct the adversarial examples for a quantum variational circuit classifier. The implementation results prove the effectiveness of the proposed method. Compared with the existing method, our method requires fewer resources and is more efficient.

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Efficient semi-quantum secret sharing protocol using single particles Ding Xing(邢丁), Yifei Wang(王艺霏), Zhao Dou(窦钊), Jian Li(李剑),Xiubo Chen(陈秀波), and Lixiang Li(李丽香) Chin. Phys. B, 2023, 32 (7):  070308.  DOI: 10.1088/1674-1056/ace159 Abstract ( 150 )   HTML ( 1 )   PDF (495KB) ( 78 )   Semi-quantum secret sharing (SQSS) is a branch of quantum cryptography which only requires the dealer to have quantum capabilities, reducing the difficulty of protocol implementation. However, the efficiency of the SQSS protocol still needs to be further studied. In this paper, we propose a semi-quantum secret sharing protocol, whose efficiency can approach 100% as the length of message increases. The protocol is based on single particles to reduce the difficulty of resource preparation. Particle reordering, a simple but effective operation, is used in the protocol to improve efficiency and ensure security. Furthermore, our protocol can share specific secrets while most SQSS protocols could not. We also prove that the protocol is secure against common attacks.

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Variational quantum semi-supervised classifier based on label propagation Yan-Yan Hou(侯艳艳), Jian Li(李剑), Xiu-Bo Chen(陈秀波), and Chong-Qiang Ye(叶崇强) Chin. Phys. B, 2023, 32 (7):  070309.  DOI: 10.1088/1674-1056/acb9fb Abstract ( 150 )   HTML ( 2 )   PDF (707KB) ( 22 )   Label propagation is an essential semi-supervised learning method based on graphs, which has a broad spectrum of applications in pattern recognition and data mining. This paper proposes a quantum semi-supervised classifier based on label propagation. Considering the difficulty of graph construction, we develop a variational quantum label propagation (VQLP) method. In this method, a locally parameterized quantum circuit is created to reduce the parameters required in the optimization. Furthermore, we design a quantum semi-supervised binary classifier based on hybrid Bell and Z bases measurement, which has a shallower circuit depth and is more suitable for implementation on near-term quantum devices. We demonstrate the performance of the quantum semi-supervised classifier on the Iris data set, and the simulation results show that the quantum semi-supervised classifier has higher classification accuracy than the swap test classifier. This work opens a new path to quantum machine learning based on graphs.

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Improving source-in-the-middle continuous-variable quantum key distribution using a heralded hybrid linear amplifier Lei-Xin Wu(伍磊鑫), Yan-Yan Feng(冯艳艳), and Jian Zhou(周健) Chin. Phys. B, 2023, 32 (7):  070310.  DOI: 10.1088/1674-1056/ac9b39 Abstract ( 125 )   HTML ( 2 )   PDF (907KB) ( 139 )   A hybrid linear amplifier is inserted at the output of the source-in-the-middle distribution protocol to overcome the shortcomings of the transmission distance. The modified protocol aims to maintain a high key rate for long-distance transmission under high noise. It has the potential to significantly broaden the application range of the continuous variable quantum key distribution protocol. The effects of amplifier parameters and noise on the modified protocol are analyzed in detail with regard to applying it to a practical system. To make the simulation more realistic, the effect of finite size on the new protocol is taken into account. It will serve as a guideline for the future use of hybrid linear amplifiers. Different parameters can be adjusted to achieve the best performance for key rates of different quantum channels.

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Transition from isotropic to polar state of self-driven eccentric disks Jinghan Wang(王静晗), Tianliang Xu(许天亮), Jingxi He(何景熙), Kang Chen(陈康), and Wende Tian(田文得) Chin. Phys. B, 2023, 32 (7):  070501.  DOI: 10.1088/1674-1056/accd4d Abstract ( 153 )   HTML ( 2 )   PDF (2338KB) ( 68 )   Inspired by the eccentricity design of self-driven disks, we propose a computational model to study the remarkable behavior of this kind of active matter via Langevin dynamics simulations. We pay attention to the effect of rotational friction coefficient and rotational noise on the phase behavior. A homogeneous system without rotational noise exhibits a sharp discontinuous transition of orientational order from an isotropic to a polar state with the increase of rotational friction coefficient. When there is rotational noise, the transition becomes continuous. The formation of polar state originates from the effective alignment effect due to the mutual coupling of the positional and orientational degrees of freedom of each disk. The rotational noise could weaken the alignment effect and cause the large spatial density inhomogeneity, while the translational noise homogenizes the system. Our model makes further conceptual progress on how the microscopic interaction among self-driven agents yields effective alignment.

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Vibrational resonance in globally coupled bistable systems under the noise background Jiangling Liu(刘江令), Chaorun Li(李朝润), Hailing Gao(高海玲), and Luchun Du(杜鲁春) Chin. Phys. B, 2023, 32 (7):  070502.  DOI: 10.1088/1674-1056/acc05f Abstract ( 148 )   HTML ( 3 )   PDF (846KB) ( 41 )   Effects of system size, coupling strength, and noise on vibrational resonance (VR) of globally coupled bistable systems are investigated. The power spectral amplifications obtained by the three methods all show that the VR exists over a wide range of parameter values. The increase in system size induces and enhances the VR, while the increase in noise intensity suppresses and eventually eliminates the VR. Both the stochastic resonance and the system size resonance can coexist with the VR in different parameter regions. This research has potential applications to the weak signal detection process in stochastic multi-body systems.

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Turing/Turing-like patterns: Products of random aggregation of spatial components Jian Gao(高见), Xin Wang(王欣), Xinshuang Liu(刘心爽), and Chuansheng Shen(申传胜) Chin. Phys. B, 2023, 32 (7):  070503.  DOI: 10.1088/1674-1056/acc0f9 Abstract ( 140 )   HTML ( 1 )   PDF (6816KB) ( 29 )   Turing patterns are typical spatiotemporal ordered structures in various systems driven far from thermodynamic equilibrium. Turing's reaction-diffusion theory, containing a long-range inhibiting agent and a local catalytic agent, has provided an explanation for the formation of some patterns in nature. Numerical, experimental and theoretical studies about Turing/Turing-like patterns have been generally focused on systems driven far from thermodynamic equilibrium. The local dynamics of these systems are commonly very complex, which brings great difficulties to understanding of formation of patterns. Here, we investigate a type of Turing-like patterns in a near-equilibrium thermodynamic system experimentally and theoretically, and put forward a new formation mechanism and a quantitative method for Turing/Turing-like patterns. Specifically, we observe a type of Turing-like patterns in starch solutions, and study the effect of concentration on the structure of patterns. The experimental results show that, with the increase of concentration, patterns change from spots to inverse spots, and labyrinthine stripe patterns appear in the region of intermediate concentration. We analyze and model the formation mechanism of these patterns observed in experiments, and the simulation results agree with the experimental results. Our conclusion indicates that the random aggregation of spatial components leads to formation of these patterns, and the proportion of spatial components determines the structures. Our findings shed light on the formation mechanism for Turing/Turing-like patterns.

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Symmetry phases of asymmetric simple exclusion processes on two lanes with an intersection Bo Tian(田波), Wan-Qiang Wen(文万强), A-Min Li(李阿敏), and Ping Xia(夏萍) Chin. Phys. B, 2023, 32 (7):  070504.  DOI: 10.1088/1674-1056/acc058 Abstract ( 126 )   HTML ( 2 )   PDF (578KB) ( 80 )   This paper studies two-lane asymmetric simple exclusion processes (ASEPs) with an intersection. In the upstream segments of the intersection, one particle can move to the next site with rate 1 if the site is empty, and the other particle can move forward with rate p in the sites of downstream segments. The parameter p can represent the rate of slowing of motion, and the parameter is introduced to investigate spontaneous symmetry breaking (SSB) phenomenon. Extensive Monte Carlo simulations are carried out. It is shown that three symmetric phases exist and the SSB does not exist in the system. Simple mean field approach in which correlation of sites is ignored is firstly adopted to analyze the system, and the system is divided into four independent segments. It is found that the analytical results deviate from the simulation ones, especially when p is small. In addition, the inexsitence of SSB can only be explained qualitatively. Motivated by this, we carry out the cluster mean field analysis in which correlation of five sites is considered. It is shown that densities of the two upstream segments are equal, which demonstrates that the SSB does not exist. It is also shown that, as expected, the cluster mean field analysis performs much better than the simple mean field analysis.

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Influence of the initial parameters on soliton interaction in nonlinear optical systems Xinyi Zhang(张昕仪) and Ye Wu(吴晔) Chin. Phys. B, 2023, 32 (7):  070505.  DOI: 10.1088/1674-1056/ace1da Abstract ( 172 )   HTML ( 2 )   PDF (1573KB) ( 134 )   In nonlinear optical systems, optical solitons have the transmission properties of reducing error rate, improving system security and stability, and have important research significance in future research on all optical communication. This paper uses the bilinear method to obtain the two-soliton solutions of the nonlinear Schrödinger equation. By analyzing the relevant physical parameters in the obtained solutions, the interaction between optical solitons is optimized. The influence of the initial conditions on the interactions of the optical solitons is analyzed in detail, the reason why the interaction of the optical solitons is sensitive to the initial condition is discussed, and the interactions of the optical solitons are effectively weakened. The relevant results are beneficial for reducing the error rate and promoting the communication quality of the system.

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Fixed-time group consensus of second-order multi-agent systems based on event-triggered control Xiaoshuai Wu(武肖帅), Fenglan Sun(孙凤兰), Wei Zhu(朱伟), and Jürgen Kurths Chin. Phys. B, 2023, 32 (7):  070701.  DOI: 10.1088/1674-1056/acb9ee Abstract ( 193 )   HTML ( 5 )   PDF (1023KB) ( 254 )   The problem of fixed-time group consensus for second-order multi-agent systems with disturbances is investigated. For cooperative-competitive network, two different control protocols, fixed-time group consensus and fixed-time event-triggered group consensus, are designed. It is demonstrated that there is no Zeno behavior under the designed event-triggered control. Meanwhile, it is proved that for an arbitrary initial state of the system, group consensus within the settling time could be obtained under the proposed control protocols by using matrix analysis and graph theory. Finally, a series of numerical examples are propounded to illustrate the performance of the proposed control protocol.

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ESR-PINNs: Physics-informed neural networks with expansion-shrinkage resampling selection strategies Jianan Liu(刘佳楠), Qingzhi Hou(侯庆志), Jianguo Wei(魏建国), and Zewei Sun(孙泽玮) Chin. Phys. B, 2023, 32 (7):  070702.  DOI: 10.1088/1674-1056/acc1d5 Abstract ( 145 )   HTML ( 3 )   PDF (3330KB) ( 40 )   Neural network methods have been widely used in many fields of scientific research with the rapid increase of computing power. The physics-informed neural networks (PINNs) have received much attention as a major breakthrough in solving partial differential equations using neural networks. In this paper, a resampling technique based on the expansion-shrinkage point (ESP) selection strategy is developed to dynamically modify the distribution of training points in accordance with the performance of the neural networks. In this new approach both training sites with slight changes in residual values and training points with large residuals are taken into account. In order to make the distribution of training points more uniform, the concept of continuity is further introduced and incorporated. This method successfully addresses the issue that the neural network becomes ill or even crashes due to the extensive alteration of training point distribution. The effectiveness of the improved physics-informed neural networks with expansion-shrinkage resampling is demonstrated through a series of numerical experiments.

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Asymmetric magnetoimpedance effect and dipolar interactions of FINEMET/SiO2/FePd composite ribbons Yong-Bin Guo(郭永斌), Dao Wang(王岛), Zhong-Min Wang(王忠民), Lei Ma(马垒), and Zhen-Jie Zhao(赵振杰) Chin. Phys. B, 2023, 32 (7):  070703.  DOI: 10.1088/1674-1056/acad6e Abstract ( 128 )   HTML ( 2 )   PDF (1819KB) ( 88 )   The dipolar interactions are investigated through the asymmetric magneto-impedance in FINEMET/SiO2/FePd composite ribbons. The interface between the hard (FePd layer) phase and soft (FINEMET ribbon) phase is coherent by SiO2 layer in FINEMET/SiO2/FePd composite ribbons, which effectively induces dipolar interactions. The contribution of dipolar interaction to the bias field (Hb) by asymmetrical giant magneto-impedance and magnetic properties is analyzed. The results show that Hb response decreases with the increase of the SiO2 layer thickness, indicating that the linear region near-zero field can be tuned by the thickness of SiO2 layer. These results allow the GMI ratio (58%) and characteristic frequency (500 kHz) to be optimized. The transverse and longitudinal magnetic domain structures of FINEMET ribbon and FePd film are confirmed, respectively. The composite ribbons with high GMI ratio and low frequency can be applied to linear magnetic sensors.

ATOMIC AND MOLECULAR PHYSICS

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Saturated absorption spectrum of cesium micrometric-thin cell with suppressed crossover spectral lines Junlong Han(韩俊龙), Bowen Wang(王博闻), Junhe Zheng(郑俊鹤), Shuyuan Chen(陈书源),Wei Xiao(肖伟), Teng Wu(吴腾), Hong Guo(郭弘), and Xiang Peng(彭翔) Chin. Phys. B, 2023, 32 (7):  073201.  DOI: 10.1088/1674-1056/acc802 Abstract ( 140 )   HTML ( 3 )   PDF (1091KB) ( 122 )   Micrometric-thin cells (MCs) with alkali vapor atoms have been valuable for research and applications of hyperfine Zeeman splitting and atomic magnetometers under strong magnetic fields. We theoretically and experimentally study the saturated absorption spectra using a 100-μ cesium MC, where the pump and probe beams are linearly polarized with mutually perpendicular polarizations, and the magnetic field is along the pump beam. Because of the distinctive thin chamber of the MC, crossover spectral lines in saturated absorption spectra are largely suppressed leading to clear splittings of hyperfine Zeeman transitions in experiments, and the effect of spatial magnetic field gradient is expected to be reduced. A calculation method is proposed to achieve good agreements between theoretical calculations and experimental results. This method successfully explains the suppression of crossover lines in MCs, as well as the effects of magnetic field direction, propagation and polarization directions of the pump/probe beam on saturated absorption spectrum. The saturated absorption spectrum with suppressed crossover lines is used for laser frequency stabilization, which may provide the potential value of MCs for high spatial resolution strong-field magnetometry with high sensitivity.

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Elliptically polarized high-order harmonic generation in nitrogen molecules with cross-linearly polarized two-color laser fields Chunyang Zhai(翟春洋), Yinmeng Wu(吴银梦), Lingling Qin(秦玲玲), Xiang Li(李翔), Luke Shi(史璐珂), Ke Zhang(张可), Shuaijie Kang(康帅杰), Zhengfa Li(李整法), Yingbin Li(李盈傧), Qingbin Tang(汤清彬), and Benhai Yu(余本海) Chin. Phys. B, 2023, 32 (7):  073301.  DOI: 10.1088/1674-1056/acad70 Abstract ( 166 )   HTML ( 1 )   PDF (1606KB) ( 127 )   Circularly and elliptically polarized high-order harmonics have unique advantages when used in studying the chiral and magnetic features of matter. Here, we studied the polarization properties of high-order harmonics generated from alignment nitrogen molecules driven by cross-linearly polarized two-color laser fields. Through adjusting various laser parameters and targets, such as the relative phase, the crossing angle, the intensity ratio of the driving fields, and the molecular alignment angle, we obtained highly elliptically polarized high-order harmonics with the same helicity in a wide spectral range. This provides a possible effective way to generate elliptically polarized attosecond pulses. Finally, we showed the probability of controlling the spectral range of elliptically polarized harmonics.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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High efficiency and high transmission asymmetric polarization converter with chiral metasurface in visible and near-infrared region Yuhang Gao(高雨航), Yu Tian(田宇), Qingguo Du(杜庆国), Yuanli Wang(王原丽), Qin Fu(付琴), Qiang Bian(卞强), Zhengying Li(李政颖), Shuai Feng(冯帅), and Fangfang Ren(任芳芳) Chin. Phys. B, 2023, 32 (7):  074201.  DOI: 10.1088/1674-1056/acb9eb Abstract ( 135 )   HTML ( 2 )   PDF (1474KB) ( 163 )   Polarization manipulation of light is of great importance because it could promote development of wireless communications, biosensing, and polarization imaging. In order to use natural light more efficiently, it is highly demanded to design and fabricate high performance asymmetric polarization converters which could covert the natural light to one particular linearly polarized light with high efficiency. Traditionally, polarizers could be achieved by controllers with crystals and polymers exhibiting birefringence. However, the polarizers are bulky in size and the theoretical conversion efficiency of the polarizers is limited to 0.5 with unpolarized light incidence. In this paper, we propose a polarization converter which could preserve high transmission for one linearly polarized light and convert the orthogonal linearly polarized light to its cross-polarized with high transmittance based on a multi-layer chiral metasurface. Theoretical results show that normally incident y-polarized light preserves high transmittance for the wavelength range from 685 nm to 800 nm while the orthogonal normally incident x-polarized light is efficiently converted to the y-polarized light with high transmittance from 725 nm to 748 nm. Accordingly, for unpolarized light incidence, transmittance larger than 0.5 has been successfully achieved in a broadband wavelength range from 712 nm to 773 nm with a maximum transmittance of 0.58 at 732 nm.

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Optical encryption scheme based on spread spectrum ghost imaging Jin-Fen Liu(刘进芬), Yue Dong(董玥), Le Wang(王乐), and Sheng-Mei Zhao(赵生妹) Chin. Phys. B, 2023, 32 (7):  074202.  DOI: 10.1088/1674-1056/acbf27 Abstract ( 115 )   HTML ( 1 )   PDF (688KB) ( 79 )   An optical encryption (OE) scheme based on the spread spectrum ghost imaging (SSGI), named as SSGI-OE, is proposed to obtain a high security with a smaller key. In the scheme, the randomly selected row number of a Hadamard matrix of order N is used as the secure key, and shared with the authorized user, Bob, through a private channel. Each corresponding row vector of the order-N Hadamard matrix is then used as the direct sequence code to modulate a speckle pattern for the ghost imaging system, and an image is encrypted with the help of the SSGI. The measurement results from the bucket detector, named as ciphertext, are then transmitted to Bob through a public channel. The illuminating speckle patterns are also shared with Bob by the public channel. With the correct secure key, Bob could reconstruct the image with the aid of the SSGI system, whereas the unauthorized user, Eve, could not obtain any useful information of the encrypted image. The numerical simulations and experimental results show that the proposed scheme is feasible with a higher security and a smaller key. For the 32×32 pixels image, the number of bits sent from Alice to Bob by using SSGI-OE (M=1024, N=2048) scheme is only 0.0107 times over a computational ghost imaging optical encryption scheme. When the eavesdropping ratio (ER) is less than 40%, the eavesdropper cannot acquire any information of the encrypted image. The extreme circumstance for the proposed SSGI-OE scheme is also discussed, where the eavesdropper begins to extract the information when ER is up to 15%.

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Single-frequency linearly polarized Q-switched fiber laser based on Nb2GeTe4 saturable absorber Si-Yu Chen(陈思雨), Hai-Qin Deng(邓海芹), Wan-Ru Zhang(张万儒), Yong-Ping Dai(戴永平), Tao Wang(王涛), Qiang Yu(俞强), Can Li(李灿), Man Jiang(姜曼), Rong-Tao Su(粟荣涛), Jian Wu(吴坚), and Pu Zhou(周朴) Chin. Phys. B, 2023, 32 (7):  074203.  DOI: 10.1088/1674-1056/acad6d Abstract ( 149 )   HTML ( 1 )   PDF (999KB) ( 91 )   We report a single-frequency linearly polarized Q-switched fiber laser based on an Nb2GeTe4 saturable absorber (SA). The Nb2GeTe4 SA triggers passive Q-switching of the laser, and an un-pumped Yb-doped fiber together with a 0.08-nm-bandwidth polarization-maintaining fiber Bragg grating (FBG) acts as an ultra-narrow bandwidth filter to realize single-longitudinal-mode (SLM) oscillation. The devices used in the laser are all kept polarized, so as to ensure linearly polarized laser output. Stable SLM linearly polarized Q-switching operation at 1064.6 nm is successfully achieved, producing a laser with a shortest pulse width of 1.36 μ s, a linewidth of 28.4 MHz, a repetition rate of 28.3 kHz-95.9 kHz, and a polarization extinction ratio of about 30 dB. It is believed that the single-frequency linearly polarized pulsed fiber laser studied in this paper has great application value in gravitational wave detection, beam combining, nonlinear frequency conversion, and other fields.

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High power, widely tunable femtosecond MgO:PPLN optical parametric oscillator Jinfang Yang(杨金芳), Chong Wang(王翀), Weijun Ling(令维军), Jingwen Xue(薛婧雯), Xiaojuan Du(杜晓娟), Wenting Wang(王文婷), Yuxiang Zhao(赵玉祥), Feiping Lu(路飞平), Xiangbing Li(李向兵), Jiajun Song(宋贾俊), Zhaohua Wang(王兆华), and Zhiyi Wei(魏志义) Chin. Phys. B, 2023, 32 (7):  074204.  DOI: 10.1088/1674-1056/accd59 Abstract ( 144 )   HTML ( 1 )   PDF (1005KB) ( 234 )   We demonstrate a high power, widely tunable femtosecond MgO-doped periodically poled lithium niobate (MgO:PPLN) optical parametric oscillator (OPO) at 151 MHz, pumped by a Kerr-lens mode-locked Yb:KGW laser. With a maximum pump power of 7 W, the OPO is capable of delivering as high as 2.2 W of the signal centered around 1500 nm with tunable signal spectrum ranges of 1377 nm-1730 nm at an extraction efficiency of 31.4%, which exhibits a long-term passive power stability better than 0.71% rms over 4 h. The maximum idler bandwidths of 185 nm at 3613 nm are obtained across the idler tuning ranges of 2539 nm-4191 nm. By compensating intracavity dispersion, the signal has the shortest pulse duration of 170 fs at 1428 nm.

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High-performance chiral all-optical OR logic gate based on topological edge states of valley photonic crystal Xiaorong Wang(王晓蓉), Hongming Fei(费宏明), Han Lin(林瀚), Min Wu(武敏), Lijuan Kang(康丽娟), Mingda Zhang(张明达), Xin Liu(刘欣), Yibiao Yang(杨毅彪), and Liantuan Xiao(肖连团) Chin. Phys. B, 2023, 32 (7):  074205.  DOI: 10.1088/1674-1056/accb41 Abstract ( 174 )   HTML ( 1 )   PDF (1405KB) ( 138 )   For all-optical communication and information processing, it is necessary to develop all-optical logic gates based on photonic structures that can directly perform logic operations. All-optical logic gates have been demonstrated based on conventional waveguides and interferometry, as well as photonic crystal structures. Nonetheless, any defects in those structures will introduce high scattering loss, which compromises the fidelity and contrast ratio of the information process. Based on the spin-valley locking effect that can achieve defect-immune unidirectional transmission of topological edge states in valley photonic crystals (VPCs), we propose a high-performance all-optical logic OR gate based on a VPC structure. By tuning the working bandwidth of the two input channels, we prevent interference between the two channels to achieve a stable and high-fidelity output. The transmittance of both channels is higher than 0.8, and a high contrast ratio of 28.8 dB is achieved. Moreover, the chirality of the logic gate originated from the spin-valley locking effect allows using different circularly polarized light as inputs, representing "1" or "0", which is highly desired in quantum computing. The device's footprint is 18 μm×12 μm, allowing high-density on-chip integration. In addition, this design can be experimentally fabricated using current nanofabrication techniques and will have potential applications in optical communication, information processing, and quantum computing.

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Thermometry utilizing stored short-wavelength spin waves in cold atomic ensembles Xingchang Wang(王兴昌), Jianmin Wang(王建民), Ying Zuo(左瀛), Liang Dong(董亮), Georgios A Siviloglou, and Jiefei Chen(陈洁菲) Chin. Phys. B, 2023, 32 (7):  074206.  DOI: 10.1088/1674-1056/accb4f Abstract ( 143 )   HTML ( 1 )   PDF (1359KB) ( 84 )   Temperature, as a measure of thermal motion, is a significant parameter characterizing a cold atomic ensemble optical quantum memory. In a cold gas, storage lifetime strongly depends on its temperature and is associated with the spin wave decoherence. Here we experimentally demonstrate a new spin wave thermometry method relying on this direct dependence. The short-wavelength spin waves resulting from the counter-propagating configuration of the control and the probe laser beams make this thermometry highly suitable for probing in situ the atomic motion in elongated clouds as the ones used in quantum memories. Our technique is realized with comparable precision for memories that rely on electromagnetically induced transparency as well as far-detuned Raman storage.

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Enhanced and controllable reflected group delay based on Tamm surface plasmons with Dirac semimetals Qiwen Zheng(郑棋文), Wenguang Lu(卢文广), Jiaqing Xu(胥加青),Yunyang Ye(叶云洋), Xinmin Zhao(赵新民), and Leyong Jiang(蒋乐勇) Chin. Phys. B, 2023, 32 (7):  074208.  DOI: 10.1088/1674-1056/aca205 Abstract ( 120 )   HTML ( 3 )   PDF (1258KB) ( 59 )   The reflected group delay from a multilayer structure comprising a one-dimensional photonic crystal coated with a bulk Dirac semimetal (BDS) separated by a spacer layer is investigated theoretically. It is shown that the group delay of the reflected beam in this structure can be significantly negatively enhanced and switched from negative to positive. The enhanced group delay originates from the steep phase change caused by the excitation of the optical Tamm state at the interface between the BDS and spacer layer. Moreover, positive and negative group delays can be actively tuned through the Fermi energy and the relaxation time of the BDS. We believe that this enhanced and tunable delay scheme has important research significance for the fabrication of optical delay devices.

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Fractional Noether theorem and fractional Lagrange equation of multi-scale mechano-electrophysiological coupling model of neuron membrane Peng Wang(王鹏) Chin. Phys. B, 2023, 32 (7):  074501.  DOI: 10.1088/1674-1056/ac9cbe Abstract ( 123 )   HTML ( 3 )   PDF (495KB) ( 81 )   Noether theorem is applied to a variable order fractional multiscale mechano-electrophysiological model of neuron membrane dynamics. The variable orders fractional Lagrange equation of a multiscale mechano-electrophysiological model of neuron membrane dynamics is given. The variable orders fractional Noether symmetry criterion and Noether conserved quantities are given. The forms of variable orders fractional Noether conserved quantities corresponding to Noether symmetry generators solutions of the model under different conditions are discussed in detail, and it is found that the expressions of variable orders fractional Noether conserved quantities are closely dependent on the external nonconservative forces and material parameters of the neuron.

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Dynamic evolution of low-viscosity fuel particle distribution driven by constant flow Zhong-Kun Yang(杨仲坤), Gao-Jun An(安高军), Xi-Meng Xu(徐曦萌), Zhe Zheng(郑哲), Yong-Xu Wang(王永旭), Li-Feng Xie(解立峰), Dan Zhang(张丹), and Bin Li(李斌) Chin. Phys. B, 2023, 32 (7):  074701.  DOI: 10.1088/1674-1056/acc8c2 Abstract ( 121 )   HTML ( 3 )   PDF (2788KB) ( 75 )   The effects of mass concentration and injection pressure on the atomization characteristics of low-viscosity fuel spray are studied in a constant-volume chamber. Microscopic spray parameters are measured by laser diffraction at different axial and radial positions downstream of the nozzle. The results show that the atomization effect is inhibited linearly with the increase of mass concentration. The increase of injection pressure promotes the droplet breakup. However, the trend gradually weakens and becomes more noticeable at high concentrations. Comparing with the concentration, the influence of the injection pressure on the atomization characteristics is dominant. Although low concentration and high injection pressure can promote the droplet breakup, they also increase the probability of droplet collision, resulting in droplet aggregation. This is more evident in low-viscosity fuels. The droplet size increases in the axial direction owing to the aggregation. However, the diameter decreases in the radial direction owing to the outward deflection of small droplets caused by air turbulence and entrainment. In addition, the high-velocity airflow significantly promotes the droplet breakup near the nozzle and spray axis regions and inhibits the aggregation effect. However, the lower-viscosity fuels keep smaller droplet sizes and better atomization in the whole spraying process, which is easier to realize than the higher-viscosity fuels. Overall, low concentration, high injection pressure, and low viscosity of fuel have beneficial effects on the droplet breakup. This is very important for improving the atomization effect of fuel.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Experimental research based on a C-band compact transit-time oscillator with a novel diode loading an embedded soft magnetic material and shielding structure Yufang He(何宇放), Juntao He(贺军涛), Junpu Ling(令钧溥), Lei Wang(王蕾), and Lili Song(宋莉莉) Chin. Phys. B, 2023, 32 (7):  075201.  DOI: 10.1088/1674-1056/ac8ce4 Abstract ( 124 )   HTML ( 3 )   PDF (3660KB) ( 150 )   In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field, a novel diode with an embedded soft magnetic and shielding structure is proposed. The soft magnetic material is designed to enhance the local magnetic field in the diode region. Moreover, the diode applies a shielding structure which can reduce the radial electric field. From simulation research, it is found that the emission and transmission quality of the electron beam with low magnetic field is greatly improved when loading this diode. Through simulation research, it is verified that the diode can increase the conversion efficiency of the transit-time oscillator (TTO) from 30% to 36.7%. In our experimental study, under the conditions of a diode voltage of 540 kV and a current of 10.5 kA, the output microwave power is 1.51 GW when loading the novel diode and the microwave frequency is 4.27 GHz when an external guiding magnetic field of 0.3 T is applied. The corresponding conversion efficiency is improved from 20.0% to 26.6%, which is 6.6% higher than that of a device loaded with a conventional diode. Our experiments have verified that this novel diode can effectively improve the conversion efficiency of high-power microwave sources operating with low magnetic field, and contribute to the miniaturization and compactness of high-power microwave devices.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Analysis of displacement damage effects on the charge-coupled device induced by neutrons at Back-n in the China Spallation Neutron Source Yuan-Yuan Xue(薛院院), Zu-Jun Wang(王祖军), Wei Chen(陈伟), Xiao-Qiang Guo(郭晓强), Zhi-Bin Yao(姚志斌), Bao-Ping He(何宝平), Xu Nie(聂栩), Shankun Lai(赖善坤), Gang Huang(黄港), Jiang-Kun Sheng(盛江坤), Wu-Ying Ma(马武英), and Shi-Long Gou(缑石龙) Chin. Phys. B, 2023, 32 (7):  076101.  DOI: 10.1088/1674-1056/acac07 Abstract ( 121 )   HTML ( 1 )   PDF (2269KB) ( 75 )   Displacement damage effects on the charge-coupled device (CCD) induced by neutrons at the back-streaming white neutron source (Back-n) in the China Spallation Neutron Source (CSNS) are analyzed according to an online irradiation experiment. The hot pixels, random telegraph signal (RTS), mean dark signal, dark current and dark signal non-uniformity (DSNU) induced by Back-n are presented. The dark current is calculated according to the mean dark signal at various integration times. The single-particle displacement damage and transient response are also observed based on the online measurement data. The trends of hot pixels, mean dark signal, DSNU and RTS degradation are related to the integration time and irradiation fluence. The mean dark signal, dark current and DSNU2 are nearly linear with neutron irradiation fluence when nearly all the pixels do not reach saturation. In addition, the mechanisms of the displacement damage effects on the CCD are demonstrated by combining the experimental results and technology computer-aided design (TCAD) simulation. Radiation-induced traps in the space charge region of the CCD will act as generation/recombination centers of electron-hole pairs, leading to an increase in the dark signal.

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Assessing high-energy x-ray and proton irradiation effects on electrical properties of P-GaN and N-GaN thin films Aoxue Zhong(钟傲雪), Lei Wang(王磊), Yun Tang(唐蕴), Yongtao Yang(杨永涛), Jinjin Wang(王进进), Huiping Zhu(朱慧平), Zhenping Wu(吴真平), Weihua Tang(唐为华), and Bo Li(李博) Chin. Phys. B, 2023, 32 (7):  076102.  DOI: 10.1088/1674-1056/accb8a Abstract ( 141 )   HTML ( 2 )   PDF (584KB) ( 127 )   The effects of ionizing and displacement irradiation of high-energy x-ray and 2-MeV proton on GaN thin films were investigated and compared in this study. The electrical properties of both P-GaN and N-GaN, separated from power devices, were gauged for fundamental analysis. It was found that the electrical properties of P-GaN were improved as a consequence of the disruption of the Mg-H bond induced by high-dose x-ray irradiation, as indicated by the Hall and circular transmission line model. Specifically, under a 100-Mrad(Si) x-ray dose, the specific contact resistance ρc of P-GaN decreased by 30%, and the hole carrier concentration increased significantly. Additionally, the atom displacement damage effect of a 2-MeV proton of 1×1013 p/cm2 led to a significant degradation of the electrical properties of P-GaN, while those of N-GaN remained unchanged. P-GaN was found to be more sensitive to irradiation than N-GaN thin film. The effectiveness of x-ray irradiation in enhancing the electrical properties of P-GaN thin films was demonstrated in this study.

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New MgO-H2O compounds at extreme conditions Lanci Guo(郭兰慈) and Jurong Zhang(张车荣) Chin. Phys. B, 2023, 32 (7):  076201.  DOI: 10.1088/1674-1056/ace035 Abstract ( 132 )   HTML ( 2 )   PDF (905KB) ( 42 )   The reaction of water and other materials has been the central topic under high-pressure physics research, because the Earth, super-Earth, Uranus, Neptune and other planets contain a great amount of water inside. However, the reaction between star-rich MgO and water under ultra-high pressure remains still poorly understood. Here, using ab initio evolutionary structure prediction researches of the structures of MgO-H2O system at 300 GPa-600 GPa, we find that (MgO)2H2O and MgO(H2O)2 could become stable. The (MgO)2H2O compounds may be an important component of super-Earth and the ice-rock boundary of Uranus and Neptune. Furthermore, it may be the reservoir under high pressure before the forming of the Earth's core or other super-Earths. The current findings could expand our knowledge and improve our understanding of the evolution and composition of planets.

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Anion type-dependent confinement effect on glass transitions of solutions of LiTFSI and LiFSI Jinbing Zhang(张晋兵), Fengping Wang(王凤平), Zexian Cao(曹则贤), and Qiang Wang(王强) Chin. Phys. B, 2023, 32 (7):  076401.  DOI: 10.1088/1674-1056/acca0d Abstract ( 133 )   HTML ( 1 )   PDF (717KB) ( 106 )   We present findings on the effect of nanometer-sized silica-based pores on the glass transition of aqueous solutions of lithium bis(trifluoromethane)sulfonimide (LiTFSI) and lithium difluorosulfimide (LiFSI), respectively. Our experimental results demonstrate a clear dependence of the confinement effect on the anion type, particularly for water-rich solutions, in which the precipitation of crystalized ice under cooling process induces the formation of freeze-concentrated phase confined between pore wall and core ice. As this liquid layer becomes thinner, the freeze-concentrated phase experiences glass transition at increasingly higher temperatures in solutions of LiTFSI. However, differently, for solutions of LiFSI and LiCl, this secondary confinement has a negligible effect on the glass transition of solutions confined wherein. These different behaviors emphasize the obvious difference in the dynamic properties' response of LiTFSI and LiFSI solutions to spatial confinement and particularly to the presence of the hydrophilic pore wall.

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Structure and stability of nitrogen hydrate in a single-walled carbon nanotube under external electric fields Chi Xu(徐驰), Jiaxian Li(厉嘉贤), Min Wei(韦敏), Xiaoyan Zhou(周晓艳), and Hangjun Lu(陆杭军) Chin. Phys. B, 2023, 32 (7):  076402.  DOI: 10.1088/1674-1056/accd4a Abstract ( 121 )   HTML ( 1 )   PDF (1495KB) ( 109 )   The effects of an external electric field on the structure and stability of the nitrogen hydrate confined in a single-walled carbon nanotube (CNT) were studied by using molecular dynamics (MD) simulations. It was found that the structure of the nitrogen hydrate, the occupancy and distribution of the nitrogen molecules inside the nanotube depend sensitively on the direction of the external electric field. A parallel electric field can destabilize the nitrogen hydrate and cause the release of nitrogen molecules from the ice nanotube of the hydrate. While a vertical electric field can redistribute the nitrogen molecules from the core to the shell of the hydrate. The occupancy of the nitrogen molecules of the hydrate follows a sigmoid-like function as the direction of the electric field changes. Our findings may aid in the development of methods to control gas release and encapsulation by using electric fields.

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Transport properties of CrP Xuebo Zhou(周学博), Ping Zheng(郑萍), Wei Wu(吴伟), Yu Sui(隋郁), and Jianlin Luo(雒建林) Chin. Phys. B, 2023, 32 (7):  076501.  DOI: 10.1088/1674-1056/acc80c Abstract ( 151 )   HTML ( 1 )   PDF (1033KB) ( 58 )   CrP has many exotic physical properties due to a four-fold degenerate band crossing at the Y point of the Brillouin zone, which is protected by the nonsymmorphic symmetry of the space group. We carried out the heat capacity, electrical and thermal transport measurements on CrP and extracted the electron thermal conductivity. Due to the difference in energy and momentum relaxation time during electron-phonon inelastic scattering, the normalized Lorentz number decreases below about 160 K. Below 25.6 K, the normalized Lorentz number begins to recover, which is due to the dominance of elastic scattering between electrons and defects at low temperatures.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Topological properties of tetratomic Su-Schrieffer-Heeger chains with hierarchical long-range hopping Guan-Qiang Li(李冠强), Bo-Han Wang(王博涵), Jing-Yu Tang(唐劲羽), Ping Peng(彭娉), and Liang-Wei Dong(董亮伟) Chin. Phys. B, 2023, 32 (7):  077102.  DOI: 10.1088/1674-1056/aca7ef Abstract ( 127 )   HTML ( 1 )   PDF (2042KB) ( 141 )   We propose a new generalized Su-Schrieffer-Heeger model with hierarchical long-range hopping based on a one-dimensional tetratomic chain. The properties of the topological states and phase transition, which depend on the cointeraction of the intracell and intercell hoppings, are investigated using the phase diagram of the winding number. It is shown that topological states with large positive/negative winding numbers can readily be generated in this system. The properties of the topological states can be verified by the ring-type structures in the trajectory diagram of the complex plane. The topological phase transition is strongly related to the opening (closure) of an energy bandgap at the center (boundaries) of the Brillouin zone. Finally, the non-zero-energy edge states at the ends of the finite system are revealed and matched with the bulk-boundary correspondence.

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Anomalous Josephson effect between d-wave superconductors through a two-dimensional electron gas with both Rashba spin-orbit coupling and Zeeman splitting Bin-Hao Du(杜彬豪), Mou Yang(杨谋), and Liang-Bin Hu(胡梁宾) Chin. Phys. B, 2023, 32 (7):  077201.  DOI: 10.1088/1674-1056/accc7f Abstract ( 128 )   HTML ( 1 )   PDF (640KB) ( 49 )   Based on the Bogoliubov-de Gennes equation and the extended McMillan's Green's function formalism, we study theoretically the Josephson effect between two d-wave superconductors bridged by a ballistic two-dimensional electron gas with both Rashba spin-orbit coupling and Zeeman splitting. We show that due to the interplay of Rashba spin-orbit coupling and Zeeman splitting and d-wave pairing, the current-phase relation in such a heterostructure may exhibit a series of novel features and can change significantly as some relevant parameters are tuned. In particular, anomalous Josephson current may occur at zero phase bias under various different situations if both time reversal symmetry and inversion symmetry of the system are simultaneously broken, which can be realized by tuning some relevant parameters of the system, including the relative orientations and the strengths of the Zeeman field and the spin-orbit field in the bridge region, the relative orientations of the a axes in two superconductor leads, or the relative orientations between the Zeeman field in the bridge region and the a axes in the superconductor leads. We show that both the magnitude and the direction of the anomalous Josephson current may depend sensitively on these relevant parameters.

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Controlled crossover of electron transport in graphene nanoconstriction: From Coulomb blockade to electron interference Wei Yu(余炜), Xiao Guo(郭潇), Yuwen Cai(蔡煜文), Xiaotian Yu(俞晓天), and Wenjie Liang(梁文杰) Chin. Phys. B, 2023, 32 (7):  077202.  DOI: 10.1088/1674-1056/accf67 Abstract ( 130 )   HTML ( 2 )   PDF (1263KB) ( 72 )   The ability to control transport behaviors in nanostructure is crucial for usage as a fundamental research platform as well as a practical device. In this study, we report a gate-controlled crossover of electron transport behaviors using graphene nanoconstrictions as a platform. The observed transport properties span from Coulomb blockade-dominated single electron transmission to electron-wave interference-dominated quantum behavior. Such drastic modulation is achieved by utilizing a single back gate on a graphene nanoconstriction structure, where the size of nanostructure in the constriction and coupling strength of it to the electrodes can be tuned electrically. Our results indicate that electrostatic field by gate voltage upon the confined nanostructure defines both the size of the nanoconstriction as well as its interaction to electrodes. Increasing gate voltage raises Fermi level to cross the energy profile in the nanoconstriction, resulting in decreased energy barriers which affect the size of nanoconstriction and transmissivity of electrons. The gate-tunable nanoconstriction device can therefore become a potential platform to study quantum critical behaviors and enrich electronic and spintronic devices.

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Diamond/c-BN van der Waals heterostructure with modulated electronic structures Su-Na Jia(贾素娜), Gao-Xian Li(李高贤), Nan Gao(高楠), Shao-Heng Cheng(成绍恒), and Hong-Dong Li(李红东) Chin. Phys. B, 2023, 32 (7):  077301.  DOI: 10.1088/1674-1056/acac10 Abstract ( 138 )   HTML ( 0 )   PDF (1993KB) ( 28 )   The structural and electronic properties of (100), (110), and (111) diamond/cubic boron nitride (c-BN) heterostructures are systematically investigated by first principles calculation. The interface between diamond and c-BN shows the weak van der Waals interactions, which is confirmed by the interface distance and interface binding energy. The diamond/c-BN structures are the direct bandgap semiconductors with moderate bandgap values ranging from 0.647 eV to 2.948 eV. This work helps to promote the application of diamond in electronic and optoelectronic devices.

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Narrowed Si0.7Ge0.3 channel FinFET with subthreshold swing of 64 mV/Dec using cyclic self-limited oxidation and removal process Hao-Yan Liu(刘昊炎), Yong-Liang Li(李永亮), and Wen-Wu Wang(王文武) Chin. Phys. B, 2023, 32 (7):  077302.  DOI: 10.1088/1674-1056/acad71 Abstract ( 145 )   HTML ( 1 )   PDF (825KB) ( 20 )   A narrowed Si0.7Ge0.3 channel fin field-effect transistor (FinFET) device is demonstrated in detail by using an accurate cyclic wet treatment process. The Si0.7Ge0.3 fin/per side of 0.63 nm in thickness can be accurately removed in each cycle by utilizing a self-limited oxidation with 40% HNO3 solution in 40 s and oxidation removal can be achieved with 1% HF solution in 10 s. As a result, after the dummy gate removal, the fin width of Si0.7Ge0.3 can be narrowed from 20 nm to 8 nm by utilizing 10 cycles of this wet treatment process. Compared with the conventional Si0.7Ge0.3 FinFET under a similar process, the narrowed Si0.7Ge0.3 channel FinFET can realize a strong gate control capability by using this newly developed wet treatment process, because its subthreshold slope can be reduced by 24%, improving from 87 mV/dec to 64 mV/dec.

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First-principles study of non-radiative carrier capture by defects at amorphous-SiO2/Si(100) interface Haoran Zhu(祝浩然), Weifeng Xie(谢伟锋), Xin Liu(刘欣), Yang Liu(刘杨), Jinli Zhang(张金利), and Xu Zuo(左旭) Chin. Phys. B, 2023, 32 (7):  077303.  DOI: 10.1088/1674-1056/ac9fc2 Abstract ( 139 )   HTML ( 1 )   PDF (1766KB) ( 104 )   Defects have a significant impact on the performance of semiconductor devices. Using the first-principles combined with one-dimensional static coupling theory approach, we have calculated the variation of carrier capture coefficients with temperature for the interfacial defects $P_{\rm b0}$ and $P_{\rm b1}$ in amorphous-SiO$_2$/Si(100) interface. It is found that the geometrical shapes of $P_{\rm b0}$ and $P_{\rm b1}$ defects undergo large deformations after capturing carriers to form charged defects, especially for the Si atoms containing a dangling bond. The hole capture coefficients of neutral $P_{\rm b0}$ and $P_{\rm b1}$ defects are largest than the other capture coefficients, indicating that these defects have a higher probability of forming positively charged centres. Meanwhile, the calculated results of non-radiative recombination coefficient of these defects show that both $P_{\rm b0}$ and $P_{\rm b1}$ defects are the dominant non-radiative recombination centers in the interface of a-SiO$_2$/Si(100).

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Epitaxial growth of trilayer graphene moiré superlattice Yalong Yuan(袁亚龙), Yanbang Chu(褚衍邦), Cheng Hu(胡成), Jinpeng Tian(田金朋), Le Liu(刘乐), Fanfan Wu(吴帆帆), Yiru Ji(季怡汝), Jiaojiao Zhao(赵交交), Zhiheng Huang(黄智恒), Xiaozhou Zan(昝晓洲), Luojun Du(杜罗军), Kenji Watanabe, Takashi Taniguchi, Dongxia Shi(时东霞), Zhiwen Shi(史志文), Wei Yang(杨威), and Guangyu Zhang(张广宇) Chin. Phys. B, 2023, 32 (7):  077304.  DOI: 10.1088/1674-1056/accdc8 Abstract ( 192 )   HTML ( 1 )   PDF (1929KB) ( 148 )   The graphene-based moiré superlattice has been demonstrated as an exciting system for investigating strong correlation phenomenon. However, the fabrication of such moiré superlattice mainly relies on transfer technology. Here, we report the epitaxial growth of trilayer graphene (TLG) moiré superlattice on hexagonal boron nitride (hBN) by a remote plasma-enhanced chemical vapor deposition method. The as-grown TLG/hBN shows a uniform moiré pattern with a period of ～ 15 nm by atomic force microscopy (AFM) imaging, which agrees with the lattice mismatch between graphene and hBN. By fabricating the device with both top and bottom gates, we observed a gate-tunable bandgap at charge neutral point (CNP) and displacement field tunable satellite resistance peaks at half and full fillings. The resistance peak at half-filling indicates a strong electron-electron correlation in our grown TLG/hBN superlattice. In addition, we observed quantum Hall states at Landau level filling factors ν = 6, 10, 14, ..., indicating that our grown trilayer graphene has the ABC stacking order. Our work suggests that epitaxy provides an easy way to fabricate stable and reproducible two-dimensional strongly correlated electronic materials.

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Multiple surface states, nontrivial band topology, and antiferromagnetism in GdAuAl4Ge2 Chengcheng Zhang(张成成), Yuan Wang(王渊), Fayuan Zhang(张发远), Hongtao Rong(戎洪涛), Yongqing Cai(蔡永青), Le Wang(王乐), Xiao-Ming Ma(马小明), Shu Guo(郭抒), Zhongjia Chen(陈仲佳), Yanan Wang(王亚南), Zhicheng Jiang(江志诚), Yichen Yang(杨逸尘), Zhengtai Liu(刘正太), Mao Ye(叶茂), Junhao Lin(林君浩), Jiawei Mei(梅佳伟), Zhanyang Hao(郝占阳), Zijuan Xie(谢子娟), and Chaoyu Chen(陈朝宇) Chin. Phys. B, 2023, 32 (7):  077401.  DOI: 10.1088/1674-1056/acca0e Abstract ( 155 )   HTML ( 0 )   PDF (3847KB) ( 87 )   Magnetic topological states of matter provide a fertile playground for emerging topological physics and phenomena. The current main focus is on materials whose magnetism stems from 3d magnetic transition elements, e.g., MnBi$_{{2}}$Te$_{4}$, Fe$_{{3}}$Sn$_{{2}}$, and Co$_{3}$Sn$_{{2}}$S$_{2}$. In contrast, topological materials with the magnetism from rare earth elements remain largely unexplored. Here we report rare earth antiferromagnet GdAuAl$_{{4}}$Ge$_{{2}}$ as a candidate magnetic topological metal. Angle resolved photoemission spectroscopy (ARPES) and first-principles calculations have revealed multiple bulk bands crossing the Fermi level and pairs of low energy surface states. According to the parity and Wannier charge center analyses, these bulk bands possess nontrivial $Z_{{2}}$ topology, establishing a strong topological insulator state in the nonmagnetic phase. Furthermore, the surface band pairs exhibit strong termination dependence which provides insight into their origin. Our results suggest GdAuAl$_{{4}}$Ge$_{2}$ as a rare earth platform to explore the interplay between band topology, magnetism and f electron correlation, calling for further study targeting on its magnetic structure, magnetic topology state, transport behavior, and microscopic properties.

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Improvement of the microstructure and magnetic properties of (La,Ce)-Fe-B nanocrystalline ribbons Li-Yu Lian(连李昱), Xiao-Wei Zhang(张晓伟), Ying Liu(刘颖), Jun Li(李军), and Ren-Quan Wang(王仁全) Chin. Phys. B, 2023, 32 (7):  077501.  DOI: 10.1088/1674-1056/acd8ae Abstract ( 130 )   HTML ( 0 )   PDF (5826KB) ( 43 )   The obstacles of inferior microstructure and poor magnetic properties of (La,Ce)-Fe-B type magnets stand in the way of expanding their applications. In this work, (La,Ce)-Fe-B melt-spun ribbons were prepared with different La/Ce ratios and rare earth contents. The microstructure and magnetic properties of these ribbons were investigated. With the La/Ce ratio increased, the fraction of the CeFe2 phase decreased and the β -La phase segregated among matrix grains, which deteriorated the coercivity of the ribbons. Reducing the rare earth content effectively suppressed the β -La phase and improved the proportion of the matrix phase in the ribbons. Here, the optimal alloy composite (La15Ce85)14Fe80B6 has been obtained with modified microstructure and inhibited secondary phases. Good ribbon performance was tested, with Hcj =4.51 kOe, Br =6.29 kG and (BH)max = 6.81 MGOe.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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GPU parallel computation of dendrite growth competition in forced convection using the multi-phase-field-lattice Boltzmann model Zi-Hao Gao(高梓豪), Chang-Sheng Zhu(朱昶胜), and Cang-Long Wang(王苍龙) Chin. Phys. B, 2023, 32 (7):  078101.  DOI: 10.1088/1674-1056/acbc68 Abstract ( 118 )   HTML ( 0 )   PDF (4521KB) ( 79 )   A graphics-processing-unit (GPU)-parallel-based computational scheme is developed to realize the competitive growth process of converging bi-crystal in two-dimensional states in the presence of forced convection conditions by coupling a multi-phase field model and a lattice Boltzmann model. The elimination mechanism in the evolution process is analyzed for the three conformational schemes constituting converging bi-crystals under pure diffusion and forced convection conditions, respectively, expanding the research of the competitive growth of columnar dendrites under melt convection conditions. The results show that the elimination mechanism for the competitive growth of converging bi-crystals of all three configurations under pure diffusion conditions follows the conventional Walton-Chalmers model. When there is forced convection with lateral flow in the liquid phase, the anomalous elimination phenomenon of unfavorable dendrites eliminating favorable dendrites occurs in the grain boundaries. In particular, the anomalous elimination phenomenon is relatively strong in conformation 1 and conformation 2 when the orientation angle of unfavorable dendrites is small, and relatively weak in conformation 3. Moreover, the presence of convection increases the tip growth rate of both favorable and unfavorable dendrites in the grain boundary. In addition, the parallelization of the multi-phase-field-lattice Boltzmann model is achieved by designing the parallel computation of the model on the GPU platform concerning the computer-unified-device-architecture parallel technique, and the results show that the parallel computation of this model based on the GPU has absolute advantages, and the parallel acceleration is more obvious as the computation area increases.

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Induced dipole dominant giant electrorheological fluid Rong Shen(沈容), Kunquan Lu(陆坤权), Zhaohui Qiu(邱昭晖), and Xiaomin Xiong(熊小敏) Chin. Phys. B, 2023, 32 (7):  078301.  DOI: 10.1088/1674-1056/accd4e Abstract ( 125 )   HTML ( 0 )   PDF (1953KB) ( 135 )   Traditional dielectric electrorheological fluid (ER) is based on the interaction of dielectric particle polarization, and the yield stress is low, which cannot meet the application requirements. The giant ER (GER) effect is caused by orientations and interactions of polar molecules adsorbed on the particle surfaces. Despite the high yield stress, these polar molecules are prone to wear and fall off, resulting in a continuous reduction in shear stress of GER liquid, which is also not suitable for application. Here we introduce a new type of ER fluid called induced dipole dominant ER fluid (ID-ER), of which the particles contain oxygen vacancies or conductor microclusters both prepared by high energy ball milling (HEBM) technique. In the electric field $E$, oxygen vacancies or conductor microclusters form induced dipoles. Because the local electric field $E_{\rm loc}$ in the gaps between particles can be two to three orders of magnitude larger than $E,$ the induced dipole moments must be large. The strong interactions of these induced dipoles make the yield stress of the ID-ER fluid reaching more than 100 kPa. Since there are oxygen vacancies or conductor microclusters everywhere in the particles, the particles will not lose the function due to surface wear during use. The experimental results show that the ID-ER fluid possesses the advantages of high shear stress, low current density, short response time, good temperature stability, long service life, and anti-settlement, etc. The comprehensive performance is much better than the existing ER materials, and also the preparation method is simple and easy to repeat, thus it should be a new generation of ER fluid suitable for practical applications.

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Two-dimensional horizontal visibility graph analysis of human brain aging on gray matter Huang-Jing Ni(倪黄晶), Ruo-Yu Du(杜若瑜), Lei Liang(梁磊), Ling-Ling Hua(花玲玲), Li-Hua Zhu(朱丽华), and Jiao-Long Qin(秦姣龙) Chin. Phys. B, 2023, 32 (7):  078501.  DOI: 10.1088/1674-1056/acc7f7 Abstract ( 155 )   HTML ( 0 )   PDF (2062KB) ( 128 )   Characterizing the trajectory of the healthy aging brain and exploring age-related structural changes in the brain can help deepen our understanding of the mechanism of brain aging. Currently, most structural magnetic resonance imaging literature explores brain aging merely from the perspective of morphological features, which cannot fully utilize the gray-scale values containing important intrinsic information about brain structure. In this study, we propose the construction of two-dimensional horizontal visibility graphs based on the pixel intensity values of the gray matter slices directly. Normalized network structure entropy (NNSE) is then introduced to quantify the overall heterogeneities of these graphs. The results demonstrate a decrease in the NNSEs of gray matter with age. Compared with the middle-aged and the elderly, the larger values of the NNSE in the younger group may indicate more homogeneous network structures, smaller differences in importance between nodes and thus a more powerful ability to tolerate intrusion. In addition, the hub nodes of different adult age groups are primarily located in the precuneus, cingulate gyrus, superior temporal gyrus, inferior temporal gyrus, parahippocampal gyrus, insula, precentral gyrus and postcentral gyrus. Our study can provide a new perspective for understanding and exploring the structural mechanism of brain aging.

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Model and data of optically controlled tunable capacitor in silicon single-photon avalanche diode Mei-Ling Zeng(曾美玲), Yang Wang(汪洋), Xiang-Liang Jin(金湘亮), Yan Peng(彭艳), and Jun Luo(罗均) Chin. Phys. B, 2023, 32 (7):  078502.  DOI: 10.1088/1674-1056/aca080 Abstract ( 121 )   HTML ( 1 )   PDF (904KB) ( 137 )   This paper reports the photocapacitance effect of silicon-based single-photon avalanche diodes (SPADs), and the frequency scattering phenomenon of capacitance. The test results of the small-signal capacitance-voltage method show that light can cause the capacitance of a SPAD device to increase under low-frequency conditions, and the photocapacitance exhibits frequency-dependent characteristics. Since the devices are fabricated based on the standard bipolar-CMOS-DMOS process, this study attributes the above results to the interfacial traps formed by Si-SiO2, and the illumination can effectively reduce the interfacial trap lifetime, leading to changes in the junction capacitance inside the SPAD. Accordingly, an equivalent circuit model considering the photocapacitance effect is also proposed in this paper. Accurate analysis of the capacitance characteristics of SPAD has important scientific significance and application value for studying the energy level distribution of device interface defect states and improving the interface quality.

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High-performance vertical GaN field-effect transistor with an integrated self-adapted channel diode for reverse conduction Siyu Deng(邓思宇), Dezun Liao(廖德尊), Jie Wei(魏杰), Cheng Zhang(张成),Tao Sun(孙涛), and Xiaorong Luo(罗小蓉) Chin. Phys. B, 2023, 32 (7):  078503.  DOI: 10.1088/1674-1056/ac8ce6 Abstract ( 134 )   HTML ( 0 )   PDF (1597KB) ( 246 )   A vertical GaN field-effect transistor with an integrated self-adapted channel diode (CD-FET) is proposed to improve the reverse conduction performance. It features a channel diode (CD) formed between a trench source on the insulator and a P-type barrier layer (PBL), together with a P-shield layer under the trench gate. At forward conduction, the CD is pinched off due to depletion effects caused by both the PBL and the metal-insulator-semiconductor structure from the trench source, without influencing the on-state characteristic of the CD-FET. At reverse conduction, the depletion region narrows and thus the CD turns on to achieve a very low turn-on voltage ($V_{\rm F}$), preventing the inherent body diode from turning on. Meanwhile, the PBL and P-shield layer can modulate the electric field distribution to improve the off-state breakdown voltage (${\rm BV}$). Moreover, the P-shield not only shields the gate from a high electric field but also transforms part of $C_{\rm GD}$ to $C_{\rm GS}$ so as to significantly reduce the gate charge ($Q_{\rm GD}$), leading to a low switching loss ($E_{\rm switch}$). Consequently, the proposed CD-FET achieves a low $V_{\rm F}$ of 1.65 V and a high ${\rm BV}$ of 1446 V, and $V_{\rm F}$, $Q_{\rm GD}$ and $E_{\rm switch}$ of the CD-FET are decreased by 49%, 55% and 80%, respectively, compared with those of a conventional metal-oxide-semiconductor field-effect transistor (MOSFET).

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High on-state current p-type tunnel effect transistor based on doping modulation Jiale Sun(孙佳乐), Yuming Zhang(张玉明), Hongliang Lu(吕红亮), Zhijun Lyu(吕智军),Yi Zhu(朱翊), Yuche Pan(潘禹澈), and Bin Lu(芦宾) Chin. Phys. B, 2023, 32 (7):  078504.  DOI: 10.1088/1674-1056/ac9cbb Abstract ( 142 )   HTML ( 0 )   PDF (663KB) ( 54 )   To solve the problem of the low on-state current in p-type tunnel field-effect transistors (p-TFETs), this paper analyzes the mechanism of adjusting the tunneling current of a TFET device determined by studying the influence of the peak position of ion implantation on the potential of the p-TFET device surface and the width of the tunneling barrier. Doping-regulated silicon-based high on-state p-TFET devices are designed and fabricated, and the test results show that the on-state current of the fabricated devices can be increased by about two orders of magnitude compared with the current of other devices with the same structure. This method provides a new idea for the realization of high on-state current TFET devices.

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Lightweight and highly robust memristor-based hybrid neural networks for electroencephalogram signal processing Peiwen Tong(童霈文), Hui Xu(徐晖), Yi Sun(孙毅), Yongzhou Wang(汪泳州), Jie Peng(彭杰),Cen Liao(廖岑), Wei Wang(王伟), and Qingjiang Li(李清江) Chin. Phys. B, 2023, 32 (7):  078505.  DOI: 10.1088/1674-1056/ac9cbc Abstract ( 161 )   HTML ( 0 )   PDF (1448KB) ( 165 )   Memristor-based neuromorphic computing shows great potential for high-speed and high-throughput signal processing applications, such as electroencephalogram (EEG) signal processing. Nonetheless, the size of one-transistor one-resistor (1T1R) memristor arrays is limited by the non-ideality of the devices, which prevents the hardware implementation of large and complex networks. In this work, we propose the depthwise separable convolution and bidirectional gate recurrent unit (DSC-BiGRU) network, a lightweight and highly robust hybrid neural network based on 1T1R arrays that enables efficient processing of EEG signals in the temporal, frequency and spatial domains by hybridizing DSC and BiGRU blocks. The network size is reduced and the network robustness is improved while ensuring the network classification accuracy. In the simulation, the measured non-idealities of the 1T1R array are brought into the network through statistical analysis. Compared with traditional convolutional networks, the network parameters are reduced by 95% and the network classification accuracy is improved by 21% at a 95% array yield rate and 5% tolerable error. This work demonstrates that lightweight and highly robust networks based on memristor arrays hold great promise for applications that rely on low consumption and high efficiency.

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Method of simulating hybrid STT-MTJ/CMOS circuits based on MATLAB/Simulink Min-Hui Ji(冀敏慧), Xin-Miao Zhang(张欣苗), Meng-Chun Pan(潘孟春), Qing-Fa Du(杜青法), Yue-Guo Hu(胡悦国), Jia-Fei Hu(胡佳飞), Wei-Cheng Qiu(邱伟成), Jun-Ping Peng(彭俊平), Zhu Lin(林珠), and Pei-Sen Li(李裴森) Chin. Phys. B, 2023, 32 (7):  078506.  DOI: 10.1088/1674-1056/acad69 Abstract ( 134 )   HTML ( 0 )   PDF (1745KB) ( 165 )   The spin-transfer-torque (STT) magnetic tunneling junction (MTJ) device is one of the prominent candidates for spintronic logic circuit and neuromorphic computing. Therefore, building a simulation framework of hybrid STT-MTJ/CMOS (complementary metal-oxide-semiconductor) circuits is of great value for designing a new kind of computing paradigm based on the spintronic devices. In this work, we develop a simulation framework of hybrid STT-MTJ/CMOS circuits based on MATLAB/Simulink, which is mainly composed of a physics-based STT-MTJ model, a controlled resistor, and a current sensor. In the proposed framework, the STT-MTJ model, based on the Landau-Lifshitz-Gilbert-Slonczewsk (LLGS) equation, is implemented using the MATLAB script. The proposed simulation framework is modularized design, with the advantage of simple-to-use and easy-to-expand. To prove the effectiveness of the proposed framework, the STT-MTJ model is benchmarked with experimental results. Furthermore, the pre-charge sense amplifier (PCSA) circuit consisting of two STT-MTJ devices is validated and the electrical coupling of two spin-torque oscillators is simulated. The results demonstrate the effectiveness of our simulation framework.

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Stability of connected and automated vehicles platoon considering communications failures Run-Kun Liu(刘润坤), Hai-Yang Yu(于海洋), Yi-Long Ren(任毅龙), and Zhi-Yong Cui(崔志勇) Chin. Phys. B, 2023, 32 (7):  078801.  DOI: 10.1088/1674-1056/acb0bc Abstract ( 134 )   HTML ( 0 )   PDF (1622KB) ( 100 )   As a form of a future traffic system, a connected and automated vehicle (CAV) platoon is a typical nonlinear physical system. CAVs can communicate with each other and exchange information. However, communication failures can change the platoon system status. To characterize this change, a dynamic topology-based car-following model and its generalized form are proposed in this work. Then, a stability analysis method is explored. Finally, taking the dynamic cooperative intelligent driver model (DC-IDM) for example, a series of numerical simulations is conducted to analyze the platoon stability in different communication topology scenarios. The results show that the communication failures reduce the stability, but information from vehicles that are farther ahead and the use of a larger desired time headway can improve stability. Moreover, the critical ratio of communication failures required to ensure stability for different driving parameters is studied in this work.

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Optimization of communication topology for persistent formation in case of communication faults Guo-Qiang Wang(王国强), He Luo(罗贺), Xiao-Xuan Hu(胡笑旋), and Jian-Wei Tai(台建玮) Chin. Phys. B, 2023, 32 (7):  078901.  DOI: 10.1088/1674-1056/acb0c0 Abstract ( 120 )   HTML ( 0 )   PDF (735KB) ( 19 )   To address the optimization problem of communication topology for persistent formation in the case of communication faults such as link interruption, transmitter failure, and receiver failure a two-stage model including fast reconstruction of communication topology and re-optimization of communication topology is constructed. Then, a fast reconstruction algorithm of communication topology for persistent formation (FRA-CT-PF), based on optimally rigid graph, arc addition operation, and path reversal operation, is proposed, which can quickly generate a feasible reconstructed communication topology after communication faults, thus ensuring the safety of the agents and maintaining the formation shape of persistent formation. Furthermore, a re-optimization algorithm of communication topology for persistent formation (ROA-CT-PF), based on agent position exchange, is proposed, which can further obtain a reoptimized communication topology to minimize the formation communication cost while still maintaining the formation shape of persistent formation. The time complexities of these two algorithms are also analyzed. Finally, the effectiveness of the above algorithms is verified by numerical experiments. Compared with existing algorithms, FRA-CT-PF can always obtain feasible reconstructed communication topology in much less time under all communication fault scenarios, and ROA-CT-PF can obtain a reoptimized communication topology to further reduce the formation communication cost in a shorter time.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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First-principles calculations of high pressure and temperature properties of Fe7C3 Li-Li Fan(范莉莉), Xun Liu(刘勋), Chang Gao(高畅), Zhong-Li Liu(刘中利), Yan-Li Li(李艳丽), and Hai-Jun Huang(黄海军) Chin. Phys. B, 2023, 32 (7):  079101.  DOI: 10.1088/1674-1056/acb915 Abstract ( 120 )   HTML ( 0 )   PDF (875KB) ( 118 )   Eckstrom-adcock iron carbide (Fe7C3) is considered to be the main constituent of the Earth's inner core due to its low shear wave velocity. However, the crystal structure of Fe7C3 remains controversial and its thermoelastic properties are not well constrained at high temperature and pressure. Based on the first-principles simulation method, we calculate the relative phase stability, equation of state, and sound velocity of Fe7C3 under core condition. The results indicate that the orthorhombic phase of Fe7C3 is stable under the core condition. While Fe7C3 does reproduce the low shear wave velocity and high Poisson's ratio of the inner core, its compressional wave velocity and density are 12% higher and 6% lower than those observed in seismic data, respectively. Therefore, we argue that carbon alone cannot completely explain the thermal properties of the inner core and the inclusion of other light elements may be required.

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Monte Carlo calculation of the exposure of Chinese female astronauts to earth's trapped radiation on board the Chinese Space Station Yipan Guo(郭义盼), Fazhi Yan(闫发智), Meihua Fang(方美华),Zhao Zhang(张昭), Wei Cheng(成巍), and Bing Guo(郭兵) Chin. Phys. B, 2023, 32 (7):  079401.  DOI: 10.1088/1674-1056/aca600 Abstract ( 144 )   HTML ( 1 )   PDF (1604KB) ( 98 )   With the development of China's crewed space mission, the space radiation risk for astronauts is increasingly prominent. This paper describes a simulation of the radiation doses experienced by a Chinese female voxel phantom on board the Chinese Space Station (CSS) performed using the Monte Carlo N-Particle (MCNP) software. The absorbed dose, equivalent dose, and effective dose experienced by the voxel phantom and its critical organs are discussed for different levels of shielding of the Tianhe core module. The risk of space-radiation exposure is then assessed by comparing these doses with the current risk limits in China (the skin dose limit for short-term low-earth-orbit missions) and the NASA figures (National Council on Radiation Protection and Measurements Report No. 98) for female astronauts. The results obtained can be used to guide and optimize the radiation protection provided for manned space missions.