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Recent advances of interface engineering in inverted perovskite solar cells Shiqi Yu(余诗琪), Zhuang Xiong(熊壮), Zhenhan Wang(王振涵), Haitao Zhou(周海涛), Fei Ma(马飞), Zihan Qu(瞿子涵), Yang Zhao(赵洋), Xinbo Chu(楚新波), and Jingbi You(游经碧) Chin. Phys. B, 2022, 31 (10): 107307.   DOI: 10.1088/1674-1056/ac8e9f Abstract （339）   HTML （8）    PDF （8178KB）（1394）       Knowledge map    Perovskite solar cells (PSCs) have witnessed great achievement in the past decade. Most of previous researches focus on the n—i—p structure of PSCs with ultra-high efficiency. While the n—i—p devices usually used the unstable charge transport layers, such as the hygroscopic doped spiro-OMeTAD, which affect the long-term stability. The inverted device with the p—i—n structure owns better stability when using stable undoped organic molecular or metal oxide materials. There are significant progresses in inverted PSCs, most of them related to charge transport or interface engineering. In this review, we will mainly summarize the inverted PSCs progresses related to the interface engineering. After that, we prospect the future direction on inverted PSCs.

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Review of Raman spectroscopy of two-dimensional magnetic van der Waals materials Yu-Jia Sun(孙宇伽), Si-Min Pang(庞思敏), and Jun Zhang(张俊) Chin. Phys. B, 2021, 30 (11): 117104.   DOI: 10.1088/1674-1056/ac1e0f Abstract （530）   HTML （12）    PDF （3052KB）（1123）       Knowledge map    Ultrathin van der Waals (vdW) magnets provide a possibility to access magnetic ordering in the two-dimensional (2D) limit, which are expected to be applied in the spintronic devices. Raman spectroscopy is a powerful characterization method to investigate the spin-related properties in 2D vdW magnets, including magnon and spin-lattice interaction, which are hardly accessible by other optical methods. In this paper, the recent progress of various magnetic properties in 2D vdW magnets studied by Raman spectroscopy is reviewed, including the magnetic transition, spin-wave, spin-lattice interaction, symmetry tuning induced by spin ordering, and nonreciprocal magneto-phonon Raman scattering.

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Widely tunable single-photon source with high spectral-purity from telecom wavelength to mid-infrared wavelength based on MgO:PPLN Chang-Wei Sun(孙昌伟), Yu Sun(孙宇), Jia-Chen Duan(端家晨), Guang-Tai Xue(薛广太), Yi-Chen Liu(刘奕辰), Liang-Liang Lu(陆亮亮), Qun-Yong Zhang(张群永), Yan-Xiao Gong(龚彦晓), Ping Xu(徐平), and Shi-Ning Zhu(祝世宁) Chin. Phys. B, 2021, 30 (10): 100312.   DOI: 10.1088/1674-1056/ac20cb Abstract （912）   HTML （4）    PDF （1543KB）（701）       Knowledge map    By utilizing the extended phase-matching (EPM) method, we investigate the generation of single photons with high spectral-purity in a magnesium-doped periodically-poled lithium niobate (MgO:PPLN) crystal via the spontaneous parametric down-conversion (SPDC) process. By adjusting the temperature and pump wavelength, the wavelength of the single photons can be tuned from telecom to mid-infrared (MIR) wavelengths, for which the spectral-purity can be above 0.95 with high transmission filters. In experiments, we engineer a MgO:PPLN with poling period of 20.35 μ which emits the EPM photon pair centered at 1496.6 nm and 1644.0 nm and carry out the joint spectral intensity (JSI) and Glauber's second-order self-correlation measurements to characterize the spectral purity. The results are in good agreement with the numerical simulations. Our work may provide a valuable approach for the generation of spectrally pure single photons at a wide range of wavelengths which is competent for various photonic quantum technologies.

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Density functional theory investigation on lattice dynamics, elastic properties and origin of vanished magnetism in Heusler compounds CoMnVZ (Z= Al, Ga) Guijiang Li(李贵江), Enke Liu(刘恩克), Guodong Liu(刘国栋), Wenhong Wang(王文洪), and Guangheng Wu(吴光恒) Chin. Phys. B, 2021, 30 (8): 083103.   DOI: 10.1088/1674-1056/ac0a6a Abstract （815）   HTML （13）    PDF （1511KB）（660）       Knowledge map    The lattice dynamics, elastic properties and the origin of vanished magnetism in equiatomic quaternary Heusler compounds CoMnVZ (Z=Al, Ga) are investigated by first principle calculations in this work. Due to the similar constituent atoms in CoMnVAl and CoMnVGa compounds, they are both stable in LiMgPdSn-type structure with comparable lattice size, phonon dispersions and electronic structures. Comparatively, we find that CoMnVAl is more structurally stable than CoMnVGa. Meanwhile, the increased covalent bonding component in CoMnVAl enhances its mechanical strength and Vickers hardness, which leads to better comprehensive mechanical properties than those of CoMnVGa. Practically and importantly, structural and chemical compatibilities at the interface make non-magnetic semiconductor CoMnVAl and magnetic topological semimetals Co2MnAl/Ga more suitable to be grown in heterostructures. Owing to atomic preferential occupation in CoMnVAl/Ga, the localized atoms Mn occupy C (0.5, 0.5, 0.5) Wyckoff site rather than B (0.25, 0.25, 0.25) and D (0.75, 0.75, 0.75) Wyckoff sites in LiMgPdSn-type structure, which results in symmetric band filling and consequently drives them to be non-magnetic. Correspondingly, by tuning localized atoms Mn to occupy B (0.25, 0.25, 0.25) or/and D (0.75, 0.75, 0.75) Wyckoff sites in off-stoichiometric Co-Mn-V-Al/Ga compounds and keeping the total valence electrons as 24, newly compensated ferrimagnetic compounds are theoretically achieved. We hope that our work will provide more choices for spintronic applications.

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Numerical analysis of motional mode coupling of sympathetically cooled two-ion crystals Li-Jun Du(杜丽军), Yan-Song Meng(蒙艳松), Yu-Ling He(贺玉玲), and Jun Xie(谢军) Chin. Phys. B, 2021, 30 (7): 073702.   DOI: 10.1088/1674-1056/abfc3e Abstract （438）   HTML （2）    PDF （1029KB）（654）       Knowledge map    A two-ion pair in a linear Paul trap is extensively used in the research of the simplest quantum-logic system; however, there are few quantitative and comprehensive studies on the motional mode coupling of two-ion systems yet. This study proposes a method to investigate the motional mode coupling of sympathetically cooled two-ion crystals by quantifying three-dimensional (3D) secular spectra of trapped ions using molecular dynamics simulations. The 3D resonance peaks of the 40Ca+-27Al+ pair obtained by using this method were in good agreement with the 3D in- and out-of-phase modes predicted by the mode coupling theory for two ions in equilibrium and the frequency matching errors were lower than 2%. The obtained and predicted amplitudes of these modes were also qualitatively similar. It was observed that the strength of the sympathetic interaction of the 40Ca+-27Al+ pair was primarily determined by its axial in-phase coupling. In addition, the frequencies and amplitudes of the ion pair's resonance modes (in all dimensions) were sensitive to the relative masses of the ion pair, and a decrease in the mass mismatch enhanced the sympathetic cooling rates. The sympathetic interactions of the 40Ca+-27Al+ pair were slightly weaker than those of the 24Mg+-27Al+ pair, but significantly stronger than those of 9Be+-27Al+. However, the Doppler cooling limit temperature of 40Ca+ is comparable to that of 9Be+ but lower than approximately half of that of 24Mg+. Furthermore, laser cooling systems for 40Ca+ are more reliable than those for 24Mg+ and 9Be+. Therefore, 40Ca+ is probably the best laser-cooled ion for sympathetic cooling and quantum-logic operations of 27Al+ and has particularly more notable comprehensive advantages in the development of high reliability, compact, and transportable 27Al+ optical clocks. This methodology may be extended to multi-ion systems, and it will greatly aid efforts to control the dynamic behaviors of sympathetic cooling as well as the development of low-heating-rate quantum logic clocks.

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Thermoelectric generators and their applications: Progress, challenges, and future prospects Nassima Radouane Chin. Phys. B, 2023, 32 (5): 057307.   DOI: 10.1088/1674-1056/aca5fd Abstract （171）   HTML （2）    PDF （2763KB）（632）       Knowledge map    Our community currently deals with issues such as rising electricity costs, pollution, and global warming. Scientists work to improve energy harvesting-based power generators in order to reduce their impacts. The Seebeck effect has been used to illustrate the capacity of thermoelectric generators (TEGs) to directly convert thermal energy to electrical energy. They are also ecologically beneficial since they do not include chemical products, function quietly because they lack mechanical structures and/or moving components, and may be built using different fabrication technologies such as three-dimentional (3D) printing, silicon technology, and screen printing, etc. TEGs are also position-independent and have a long operational lifetime. TEGs can be integrated into bulk and flexible devices. This review gives further investigation of TEGs, beginning with a full discussion of their operating principle, kinds, materials utilized, figure of merit, and improvement approaches, which include various thermoelectric material arrangements and utilised technologies. This paper also discusses the use of TEGs in a variety of disciplines such as automobile and biomedical.

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Variational quantum simulation of thermal statistical states on a superconducting quantum processer Xue-Yi Guo(郭学仪), Shang-Shu Li(李尚书), Xiao Xiao(效骁), Zhong-Cheng Xiang(相忠诚), Zi-Yong Ge(葛自勇), He-Kang Li(李贺康), Peng-Tao Song(宋鹏涛), Yi Peng(彭益), Zhan Wang(王战), Kai Xu(许凯), Pan Zhang(张潘), Lei Wang(王磊), Dong-Ning Zheng(郑东宁), and Heng Fan(范桁) Chin. Phys. B, 2023, 32 (1): 010307.   DOI: 10.1088/1674-1056/aca7f3 Abstract （598）   HTML （11）    PDF （3465KB）（629）       Knowledge map    Quantum computers promise to solve finite-temperature properties of quantum many-body systems, which is generally challenging for classical computers due to high computational complexities. Here, we report experimental preparations of Gibbs states and excited states of Heisenberg $XX$ and $XXZ$ models by using a 5-qubit programmable superconducting processor. In the experiments, we apply a hybrid quantum-classical algorithm to generate finite temperature states with classical probability models and variational quantum circuits. We reveal that the Hamiltonians can be fully diagonalized with optimized quantum circuits, which enable us to prepare excited states at arbitrary energy density. We demonstrate that the approach has a self-verifying feature and can estimate fundamental thermal observables with a small statistical error. Based on numerical results, we further show that the time complexity of our approach scales polynomially in the number of qubits, revealing its potential in solving large-scale problems.

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Magnetic two-dimensional van der Waals materials forspintronic devices Yu Zhang(张雨), Hongjun Xu(许洪军), Jiafeng Feng(丰家峰), Hao Wu(吴昊), Guoqiang Yu(于国强), and Xiufeng Han(韩秀峰) Chin. Phys. B, 2021, 30 (11): 118504.   DOI: 10.1088/1674-1056/ac2808 Abstract （607）   HTML （3）    PDF （3012KB）（616）       Knowledge map    Magnetic two-dimensional (2D) van der Waals (vdWs) materials and their heterostructures attract increasing attention in the spintronics community due to their various degrees of freedom such as spin, charge, and energy valley, which may stimulate potential applications in the field of low-power and high-speed spintronic devices in the future. This review begins with introducing the long-range magnetic order in 2D vdWs materials and the recent progress of tunning their properties by electrostatic doping and stress. Next, the proximity-effect, current-induced magnetization switching, and the related spintronic devices (such as magnetic tunnel junctions and spin valves) based on magnetic 2D vdWs materials are presented. Finally, the development trend of magnetic 2D vdWs materials is discussed. This review provides comprehensive understandings for the development of novel spintronic applications based on magnetic 2D vdWs materials.

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Measuring Loschmidt echo via Floquet engineering in superconducting circuits Shou-Kuan Zhao(赵寿宽), Zi-Yong Ge(葛自勇), Zhong-Cheng Xiang(相忠诚), Guang-Ming Xue(薛光明), Hai-Sheng Yan(严海生), Zi-Ting Wang(王子婷), Zhan Wang(王战), Hui-Kai Xu(徐晖凯), Fei-Fan Su(宿非凡), Zhao-Hua Yang(杨钊华), He Zhang(张贺), Yu-Ran Zhang(张煜然), Xue-Yi Guo(郭学仪), Kai Xu(许凯), Ye Tian(田野), Hai-Feng Yu(于海峰), Dong-Ning Zheng(郑东宁), Heng Fan(范桁), and Shi-Ping Zhao(赵士平) Chin. Phys. B, 2022, 31 (3): 030307.   DOI: 10.1088/1674-1056/ac40f8 Abstract （785）   HTML （4）    PDF （1107KB）（604）       Knowledge map    The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.

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Gate-controlled magnetic transitions in Fe3GeTe2 with lithium ion conducting glass substrate Guangyi Chen(陈光毅), Yu Zhang(张玉), Shaomian Qi(齐少勉), and Jian-Hao Chen(陈剑豪) Chin. Phys. B, 2021, 30 (9): 097504.   DOI: 10.1088/1674-1056/ac1338 Abstract （783）   HTML （4）    PDF （806KB）（602）       Knowledge map    Since the discovery of magnetism in two dimensions, effective manipulation of magnetism in van der Waals magnets has always been a crucial goal. Ionic gating is a promising method for such manipulation, yet devices gated with conventional ionic liquid may have some restrictions in applications due to the liquid nature of the gate dielectric. Lithium-ion conducting glass-ceramics (LICGC), a solid Li+ electrolyte, could be used as a substrate while simultaneously acts as a promising substitute for ionic liquid. Here we demonstrate that the ferromagnetism of Fe3GeTe2 (FGT) could be modulated via LICGC. By applying a voltage between FGT and the back side of LICGC substrate, Li+ doping occurs and causes the decrease of the coercive field (Hc) and ferromagnetic transition temperature (Tc) in FGT nanoflakes. A modulation efficiency for Hc of up to ～ 24.6% under Vg = 3.5 V at T =100 K is achieved. Our results provide another method to construct electrically-controlled magnetoelectronics, with potential applications in future information technology.

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Fundamental study towards a better understanding of low pressure radio-frequency plasmas for industrial applications Yong-Xin Liu(刘永新), Quan-Zhi Zhang(张权治), Kai Zhao(赵凯), Yu-Ru Zhang(张钰如), Fei Gao(高飞),Yuan-Hong Song(宋远红), and You-Nian Wang(王友年) Chin. Phys. B, 2022, 31 (8): 085202.   DOI: 10.1088/1674-1056/ac7551 Abstract （457）   HTML （0）    PDF （11486KB）（575）       Knowledge map    Two classic radio-frequency (RF) plasmas, i.e., the capacitively and the inductively coupled plasmas (CCP and ICP), are widely employed in material processing, e.g., etching and thin film deposition, etc. Since RF plasmas are usually operated in particular circumstances, e.g., low pressures (mTorr-Torr), high-frequency electric field (13.56 MHz-200 MHz), reactive feedstock gases, diverse reactor configurations, etc., a variety of physical phenomena, e.g., electron resonance heating, discharge mode transitions, striated structures, standing wave effects, etc., arise. These physical effects could significantly influence plasma-based material processing. Therefore, understanding the fundamental processes of RF plasma is not only of fundamental interest, but also of practical significance for the improvement of the performance of the plasma sources. In this article, we review the major progresses that have been achieved in the fundamental study on the RF plasmas, and the topics include 1) electron heating mechanism, 2) plasma operation mode, 3) pulse modulated plasma, and 4) electromagnetic effects. These topics cover the typical issues in RF plasma field, ranging from fundamental to application.

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A review on the design of ternary logic circuits Xiao-Yuan Wang(王晓媛), Chuan-Tao Dong(董传涛), Zhi-Ru Wu(吴志茹), and Zhi-Qun Cheng(程知群) Chin. Phys. B, 2021, 30 (12): 128402.   DOI: 10.1088/1674-1056/ac248b Abstract （539）   HTML （5）    PDF （697KB）（575）       Knowledge map    A multi-valued logic system is a promising alternative to traditional binary logic because it can reduce the complexity, power consumption, and area of circuit implementation. This article briefly summarizes the development of ternary logic and its advantages in digital logic circuits. The schemes, characteristics, and application of ternary logic circuits based on CMOS, CNTFET, memristor, and other devices and processes are reviewed in this paper, providing some reference for the further research and development of ternary logic circuits.

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Discontinuous and continuous transitions of collective behaviors in living systems Xu Li(李旭), Tingting Xue(薛婷婷), Yu Sun(孙宇), Jingfang Fan(樊京芳), Hui Li(李辉), Maoxin Liu(刘卯鑫), Zhangang Han(韩战钢), Zengru Di(狄增如), and Xiaosong Chen(陈晓松) Chin. Phys. B, 2021, 30 (12): 128703.   DOI: 10.1088/1674-1056/ac3c3f Abstract （888）   HTML （9）    PDF （1918KB）（558）       Knowledge map    Living systems are full of astonishing diversity and complexity of life. Despite differences in the length scales and cognitive abilities of these systems, collective motion of large groups of individuals can emerge. It is of great importance to seek for the fundamental principles of collective motion, such as phase transitions and their natures. Via an eigen microstate approach, we have found a discontinuous transition of density and a continuous transition of velocity in the Vicsek models of collective motion, which are identified by the finite-size scaling form of order-parameter. At strong noise, living systems behave like gas. With the decrease of noise, the interactions between the particles of a living system become stronger and make them come closer. The living system experiences then a discontinuous gas-liquid like transition of density. The even stronger interactions at smaller noise make the velocity directions of the particles become ordered and there is a continuous phase transition of collective motion in addition.

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Reconstruction and functionalization of aerogels by controlling mesoscopic nucleation to greatly enhance macroscopic performance Chen-Lu Jiao(焦晨璐), Guang-Wei Shao(邵光伟), Yu-Yue Chen(陈宇岳), and Xiang-Yang Liu(刘向阳) Chin. Phys. B, 2023, 32 (3): 038103.   DOI: 10.1088/1674-1056/acb912 Abstract （640）   HTML （24）    PDF （7614KB）（556）       Knowledge map    This work presents a strategy for the mesoscopic engineering of hierarchically structured sodium alginate (SA) aerogels to enhance the macroscopic performance. The strategy was implemented by meso-functionalizing and reorganizing SA aerogels via controlled heterogeneous nucleation, in which microcrystalline cellulose-manganese dioxide (MCC-MnO2) nano-crystallites worked as template. Due to the short rod-like structure and abundant hydroxyl groups of MCC-MnO2, the organized mesostructure of SA aerogels was reconstructed during the assembly of SA molecule chains, which gave rise to a significant enhancement in macroscopic performance of SA areogels. For instance, the functionalized and reconstructed MCC-MnO2/SA aerogels acquired a more than 70% increase in mechanical strength with an excellent deformation recovery. Furthermore, an almost double enhancement of removal capacity for metal ions (i.e., Cu2+ and Pb2+) and organic dyes (i.e., congo red and methylene blue) was obtained for MnO2/SA aerogels, with an 87% repossession of the pollutants removal performance after 5 operation cycles.

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Solutions and memory effect of fractional-order chaotic system: A review Shaobo He(贺少波), Huihai Wang(王会海), and Kehui Sun(孙克辉) Chin. Phys. B, 2022, 31 (6): 060501.   DOI: 10.1088/1674-1056/ac43ae Abstract （422）   HTML （10）    PDF （13449KB）（555）       Knowledge map    Fractional calculus is a 300 years topic, which has been introduced to real physics systems modeling and engineering applications. In the last few decades, fractional-order nonlinear chaotic systems have been widely investigated. Firstly, the most used methods to solve fractional-order chaotic systems are reviewed. Characteristics and memory effect in those method are summarized. Then we discuss the memory effect in the fractional-order chaotic systems through the fractional-order calculus and numerical solution algorithms. It shows that the integer-order derivative has full memory effect, while the fractional-order derivative has nonideal memory effect due to the kernel function. Memory loss and short memory are discussed. Finally, applications of the fractional-order chaotic systems regarding the memory effects are investigated. The work summarized in this manuscript provides reference value for the applied scientists and engineering community of fractional-order nonlinear chaotic systems.

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Controlled vapor growth of 2D magnetic Cr2Se3 and its magnetic proximity effect in heterostructures Danliang Zhang(张丹亮), Chen Yi(易琛), Cuihuan Ge(葛翠环), Weining Shu(舒维宁), Bo Li(黎博), Xidong Duan(段曦东), Anlian Pan(潘安练), and Xiao Wang(王笑) Chin. Phys. B, 2021, 30 (9): 097601.   DOI: 10.1088/1674-1056/ac0cd9 Abstract （723）   HTML （8）    PDF （3458KB）（555）       Knowledge map    Two-dimensional (2D) magnetic materials have aroused tremendous interest due to the 2D confinement of magnetism and potential applications in spintronic and valleytronic devices. However, most of the currently 2D magnetic materials are achieved by the exfoliation from their bulks, of which the thickness and domain size are difficult to control, limiting the practical device applications. Here, we demonstrate the realization of thickness-tunable rhombohedral Cr2Se3 nanosheets on different substrates via the chemical vapor deposition route. The magnetic transition temperature at about 75 K is observed. Furthermore, van der Waals heterostructures consisting of Cr2Se3 nanosheets and monolayer WS2 are constructed. We observe the magnetic proximity effect in the heterostructures, which manifests the manipulation of the valley polarization in monolayer WS2. Our work contributes to the vapor growth and applications of 2D magnetic materials.

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Strong spin frustration and magnetism in kagomé antiferromagnets LnCu3(OH)6Br3 (Ln=Nd, Sm, and Eu) Jin-Qun Zhong(钟金群), Zhen-Wei Yu(余振伟), Xiao-Yu Yue(岳小宇), Yi-Yan Wang(王义炎), Hui Liang(梁慧), Yan Sun(孙燕), Dan-Dan Wu(吴丹丹), Zong-Ling Ding(丁宗玲), Jin Sun(孙进), Xue-Feng Sun(孙学峰), and Qiu-Ju Li(李秋菊) Chin. Phys. B, 2023, 32 (4): 047505.   DOI: 10.1088/1674-1056/acb9e8 Abstract （477）   HTML （159）    PDF （2462KB）（537）       Knowledge map    To study the effects of lanthanide ions on the geometrically frustrated antiferromagnets and their magnetic properties, we grew high-quality single crystals of $Ln$Cu$_{3}$(OH)$_{6}$Br$_{3}$ ($Ln={\rm Nd}$, Sm, and Eu) by hydrothermal method and studied their crystal structures and magnetic properties. The refinements of the crystal structure referred to the powder x-ray diffraction data show that $Ln$Cu$_{3}$(OH)$_{6}$Br$_{3}$ adopt a Kapellasite-type layer structure, which is isostructural to their chlorine analogue. Magnetic susceptibilities demonstrate that $Ln$Cu$_{3}$(OH)$_{6}$Br$_{3}$ have strong antiferromagnetic coupling and a pronounced magnetic frustration effect. Magnetization measurements indicate canted antiferromagnetic ordering of Cu$^{2+}$ ions around 16 K within the kagomé plane and weak ferromagnetic coupling. Moreover, shoulder-like anomalies in specific heat around 16 K could be a signature of emergent of magnetic ordering. The low-temperature negative magnetization and specific heat of $Ln$Cu$_{3}$(OH)$_{6}$Br$_{3}$ ($Ln={\rm Nd}$, Sm, and Eu) indicate that $Ln^{3+}$ ions induce more exotic magnetic ground state properties.

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Magneto-transport properties of thin flakes of Weyl semiconductor tellurium Nan Zhang(张南), Bin Cheng(程斌), Hui Li(李惠), Lin Li(李林), and Chang-Gan Zeng(曾长淦) Chin. Phys. B, 2021, 30 (8): 087304.   DOI: 10.1088/1674-1056/ac0a5e Abstract （792）   HTML （23）    PDF （7248KB）（534）       Knowledge map    As an elemental semiconductor, tellurium has recently attracted intense interest due to its non-trivial band topology, and the resulted intriguing topological transport phenomena. In this study we report systematic electronic transport studies on tellurium flakes grown via a simple vapor deposition process. The sample is self-hole-doped, and exhibits typical weak localization behavior at low temperatures. Substantial negative longitudinal magnetoresistance under parallel magnetic field is observed over a wide temperature region, which is considered to share the same origin with that in tellurium bulk crystals, i.e., the Weyl points near the top of valence band. However, with lowering temperature the longitudinal magnetoconductivity experiences a transition from parabolic to linear field dependency, differing distinctly from the bulk counterparts. Further analysis reveals that such a modulation of Weyl behaviors in this low-dimensional tellurium structure can be attributed to the enhanced inter-valley scattering at low temperatures. Our results further extend Weyl physics into a low-dimensional semiconductor system, which may find its potential application in designing topological semiconductor devices.

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Superconductivity in an intermetallic oxide Hf3Pt4Ge2O Chengchao Xu(徐程超), Hong Wang(王鸿), Huanfang Tian(田焕芳), Youguo Shi(石友国), Zi-An Li(李子安), Ruijuan Xiao(肖睿娟), Honglong Shi(施洪龙), Huaixin Yang(杨槐馨), and Jianqi Li(李建奇) Chin. Phys. B, 2021, 30 (7): 077403.   DOI: 10.1088/1674-1056/abfb53 Abstract （777）   HTML （1）    PDF （3238KB）（527）       Knowledge map    Discovery of a new superconductor with distinct crystal structure and chemistry often provides great opportunity for further expanding superconductor material base, and also leads to better understanding of superconductivity mechanisms. Here, we report the discovery of superconductivity in a new intermetallic oxide Hf3Pt4Ge2O synthesized through a solid-state reaction. The Hf3Pt4Ge2O crystallizes in a cubic structure (space group Fm-3m) with a lattice constant of a = 1.241 nm, whose stoichiometry and atomic structure are determined by electron microscopy and x-ray diffraction techniques. The superconductivity at 4.1 K and type-Ⅱ superconducting nature are evidenced by the electrical resistivity, magnetic susceptibility, and specific heat measurements. The intermetallic oxide Hf3Pt4Ge2O system demonstrates an intriguing structural feature that foreign oxygen atoms can be accommodated in the interstitial sites of the ternary intermetallic framework. We also successfully synthesized a series of Hf3Pt4Ge2O1+δ (-0.25 ≤ δ ≤ 0.5), and found the δ-dependent superconducting transition temperature Tc. The atomic structure and the electronic structure are also substantiated by first-principles calculations. Our results present an entirely new family of superconductors with distinct structural and chemical characteristics, and could attract research interest in further finding new superconductors and exploring novel physics pertaining to the 5d-electron in these intermetallic compound systems.

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Applications and functions of rare-earth ions in perovskite solar cells Limin Cang(苍利民), Zongyao Qian(钱宗耀), Jinpei Wang(王金培), Libao Chen(陈利豹), Zhigang Wan(万志刚), Ke Yang(杨柯), Hui Zhang(张辉), and Yonghua Chen(陈永华) Chin. Phys. B, 2022, 31 (3): 038402.   DOI: 10.1088/1674-1056/ac373a Abstract （513）   HTML （3）    PDF （4879KB）（512）       Knowledge map    The emerging perovskite solar cells have been recognized as one of the most promising new-generation photovoltaic technologies owing to their potential of high efficiency and low production cost. However, the current perovskite solar cells suffer from some obstacles such as non-radiative charge recombination, mismatched absorption, light induced degradation for the further improvement of the power conversion efficiency and operational stability towards practical application. The rare-earth elements have been recently employed to effectively overcome these drawbacks according to their unique photophysical properties. Herein, the recent progress of the application of rare-earth ions and their functions in perovskite solar cells were systematically reviewed. As it was revealed that the rare-earth ions can be coupled with both charge transport metal oxides and photosensitive perovskites to regulate the thin film formation, and the rare-earth ions are embedded either substitutionally into the crystal lattices to adjust the optoelectronic properties and phase structure, or interstitially at grain boundaries and surface for effective defect passivation. In addition, the reversible oxidation and reduction potential of rare-earth ions can prevent the reduction and oxidation of the targeted materials. Moreover, owing to the presence of numerous energetic transition orbits, the rare-earth elements can convert low-energy infrared photons or high-energy ultraviolet photons into perovskite responsive visible light, to extend spectral response range and avoid high-energy light damage. Therefore, the incorporation of rare-earth elements into the perovskite solar cells have demonstrated promising potentials to simultaneously boost the device efficiency and stability.