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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
    Abstract565)   HTML1)    PDF (1543KB)(583)      
    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.
    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
    Abstract422)   HTML0)    PDF (806KB)(488)      
    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.
    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
    Abstract436)   HTML0)    PDF (1107KB)(482)      
    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.
    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
    Abstract486)   HTML1)    PDF (1511KB)(466)      
    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.
    A double quantum dot defined by top gates in a single crystalline InSb nanosheet
    Yuanjie Chen(陈元杰), Shaoyun Huang(黄少云), Jingwei Mu(慕经纬), Dong Pan(潘东), Jianhua Zhao(赵建华), and Hong-Qi Xu(徐洪起)
    Chin. Phys. B, 2021, 30 (12): 128501.   DOI: 10.1088/1674-1056/abff2e
    Abstract470)   HTML0)    PDF (1960KB)(411)      
    We report on the transport study of a double quantum dot (DQD) device made from a freestanding, single crystalline InSb nanosheet. The freestanding nanosheet is grown by molecular beam epitaxy and the DQD is defined by the top gate technique. Through the transport measurements, we demonstrate how a single quantum dot (QD) and a DQD can be defined in an InSb nanosheet by tuning voltages applied to the top gates. We also measure the charge stability diagrams of the DQD and show that the charge states and the inter-dot coupling between the two individual QDs in the DQD can be efficiently regulated by the top gates. Numerical simulations for the potential profile and charge density distribution in the DQD have been performed and the results support the experimental findings and provide a better understanding of fabrication and transport characteristics of the DQD in the InSb nanosheet. The achieved DQD in the two-dimensional InSb nanosheet possesses pronounced benefits in lateral scaling and can thus serve as a new building block for the developments of quantum computation and quantum simulation technologies.
    A composite micromotor driven by self-thermophoresis and Brownian rectification
    Xin Lou(娄辛), Nan Yu(余楠), Ke Chen(陈科), Xin Zhou(周昕), Rudolf Podgornik, and Mingcheng Yang(杨明成)
    Chin. Phys. B, 2021, 30 (11): 114702.   DOI: 10.1088/1674-1056/ac2727
    Abstract407)   HTML0)    PDF (517KB)(388)      
    Brownian motors and self-phoretic microswimmers are two typical micromotors, for which thermal fluctuations play different roles. Brownian motors utilize thermal noise to acquire unidirectional motion, while thermal fluctuations randomize the self-propulsion of self-phoretic microswimmers. Here we perform mesoscale simulations to study a composite micromotor composed of a self-thermophoretic Janus particle under a time-modulated external ratchet potential. The composite motor exhibits a unidirectional transport, whose direction can be reversed by tuning the modulation frequency of the external potential. The maximum transport capability is close to the superposition of the drift speed of the pure Brownian motor and the self-propelling speed of the pure self-thermophoretic particle. Moreover, the hydrodynamic effect influences the orientation of the Janus particle in the ratched potential, hence also the performance of the composite motor. Our work thus provides an enlightening attempt to actively exploit inevitable thermal fluctuations in the implementation of the self-phoretic microswimmers.
    Solving quantum rotor model with different Monte Carlo techniques
    Weilun Jiang(姜伟伦), Gaopei Pan(潘高培), Yuzhi Liu(刘毓智), and Zi-Yang Meng(孟子杨)
    Chin. Phys. B, 2022, 31 (4): 040504.   DOI: 10.1088/1674-1056/ac4f52
    Abstract399)   HTML1)    PDF (1004KB)(361)      
    We systematically test the performance of several Monte Carlo update schemes for the (2+1)d XY phase transition of quantum rotor model. By comparing the local Metropolis (LM), LM plus over-relaxation (OR), Wolff-cluster (WC), hybrid Monte Carlo (HM), hybrid Monte Carlo with Fourier acceleration (FA) schemes, it is clear that among the five different update schemes, at the quantum critical point, the WC and FA schemes acquire the smallest autocorrelation time and cost the least amount of CPU hours in achieving the same level of relative error, and FA enjoys a further advantage of easily implementable for more complicated interactions such as the long-range ones. These results bestow one with the necessary knowledge of extending the quantum rotor model, which plays the role of ferromagnetic/antiferromagnetic critical bosons or Z2 topological order, to more realistic and yet challenging models such as Fermi surface Yukawa-coupled to quantum rotor models.
    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
    Abstract363)   HTML2)    PDF (1918KB)(359)      
    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.
    Electronic structures and topological properties of TeSe2 monolayers
    Zhengyang Wan(万正阳), Hao Huan(郇昊), Hairui Bao(鲍海瑞), Xiaojuan Liu(刘晓娟), and Zhongqin Yang(杨中芹)
    Chin. Phys. B, 2021, 30 (11): 117304.   DOI: 10.1088/1674-1056/ac2489
    Abstract430)   HTML4)    PDF (2793KB)(354)      
    The successfully experimental fabrication of two-dimensional Te monolayer films [Phys. Rev. Lett. 119 106101 (2017)] has promoted the researches on the group-VI monolayer materials. In this work, the electronic structures and topological properties of a group-VI binary compound of TeSe2 monolayers are studied based on the density functional theory and Wannier function method. Three types of structures, namely, α-TeSe2, β-TeSe2, and γ-TeSe2, are proposed for the TeSe2 monolayer among which the α-TeSe2 is found being the most stable. All the three structures are semiconductors with indirect band gaps. Very interestingly, the γ-TeSe2 monolayer becomes a quantum spin Hall (QSH) insulator with a global nontrivial energy gap of 0.14 eV when a 3.5% compressive strain is applied. The opening of the global band gap is understood by the competition between the decrease of the local band dispersion and the weakening of the interactions between the Se px, py orbitals and Te px, py orbitals during the process. Our work realizes topological states in the group-VI monolayers and promotes the potential applications of the materials in spintronics and quantum computations.
    Detection of influential nodes with multi-scale information
    Jing-En Wang(王静恩), San-Yang Liu(刘三阳), Ahmed Aljmiai, and Yi-Guang Bai(白艺光)
    Chin. Phys. B, 2021, 30 (8): 088902.   DOI: 10.1088/1674-1056/abff2d
    Abstract189)   HTML21)    PDF (17476KB)(346)      
    The identification of influential nodes in complex networks is one of the most exciting topics in network science. The latest work successfully compares each node using local connectivity and weak tie theory from a new perspective. We study the structural properties of networks in depth and extend this successful node evaluation from single-scale to multi-scale. In particular, one novel position parameter based on node transmission efficiency is proposed, which mainly depends on the shortest distances from target nodes to high-degree nodes. In this regard, the novel multi-scale information importance (MSII) method is proposed to better identify the crucial nodes by combining the network's local connectivity and global position information. In simulation comparisons, five state-of-the-art algorithms, i.e. the neighbor nodes degree algorithm (NND), betweenness centrality, closeness centrality, Katz centrality and the k-shell decomposition method, are selected to compare with our MSII. The results demonstrate that our method obtains superior performance in terms of robustness and spreading propagation for both real-world and artificial networks.
    Gauss quadrature based finite temperature Lanczos method
    Jian Li(李健) and Hai-Qing Lin(林海青)
    Chin. Phys. B, 2022, 31 (5): 050203.   DOI: 10.1088/1674-1056/ac5986
    Abstract337)   HTML4)    PDF (782KB)(334)      
    The finite temperature Lanczos method (FTLM), which is an exact diagonalization method intensively used in quantum many-body calculations, is formulated in the framework of orthogonal polynomials and Gauss quadrature. The main idea is to reduce finite temperature static and dynamic quantities into weighted summations related to one- and two-dimensional Gauss quadratures. Then lower order Gauss quadrature, which is generated from Lanczos iteration, can be applied to approximate the initial weighted summation. This framework fills the conceptual gap between FTLM and kernel polynomial method, and makes it easy to apply orthogonal polynomial techniques in the FTLM calculation.
    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
    Abstract252)   HTML2)    PDF (3052KB)(327)      
    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.
    Electronic structure and spin–orbit coupling in ternary transition metal chalcogenides Cu2TlX2 (X = Se, Te)
    Na Qin(秦娜), Xian Du(杜宪), Yangyang Lv(吕洋洋), Lu Kang(康璐), Zhongxu Yin(尹中旭), Jingsong Zhou(周景松), Xu Gu(顾旭), Qinqin Zhang(张琴琴), Runzhe Xu(许润哲), Wenxuan Zhao(赵文轩), Yidian Li(李义典), Shuhua Yao(姚淑华), Yanfeng Chen(陈延峰), Zhongkai Liu(柳仲楷), Lexian Yang(杨乐仙), and Yulin Chen(陈宇林)
    Chin. Phys. B, 2022, 31 (3): 037101.   DOI: 10.1088/1674-1056/ac3ecd
    Abstract307)   HTML1)    PDF (5919KB)(314)      
    Ternary transition metal chalcogenides provide a rich platform to search and study intriguing electronic properties. Using angle-resolved photoemission spectroscopy and ab initio calculation, we investigate the electronic structure of Cu$_{2}$Tl$X_{2}$ ($X=\text{Se, Te}$), ternary transition metal chalcogenides with quasi-two-dimensional crystal structure. The band dispersions near the Fermi level are mainly contributed by the Te/Se p orbitals. According to our ab-initio calculation, the electronic structure changes from a semiconductor with indirect band gap in Cu$_{2}$TlSe$_{2}$ to a semimetal in Cu$_{2}$TlTe$_{2}$, suggesting a band-gap tunability with the composition of Se and Te. By comparing ARPES experimental data with the calculated results, we identify strong modulation of the band structure by spin-orbit coupling in the compounds. Our results provide a ternary platform to study and engineer the electronic properties of transition metal chalcogenides related to large spin-orbit coupling.
    Revealing the A1g-type strain effect on superconductivity and nematicity in FeSe thin flake
    Zhaohui Cheng(程朝晖), Bin Lei(雷彬), Xigang Luo(罗习刚), Jianjun Ying(应剑俊), Zhenyu Wang(王震宇), Tao Wu(吴涛), and Xianhui Chen(陈仙辉)
    Chin. Phys. B, 2021, 30 (9): 097403.   DOI: 10.1088/1674-1056/ac1efa
    Abstract215)   HTML2)    PDF (1879KB)(308)      
    The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate. Recently, a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe1-xCox)2As2, suggesting a strong interplay between nematicity and superconductivity. Since the long-range spin order is absent in FeSe superconductor, whether a similar strain effect could be also observed or not is an interesting question. Here, by utilizing a flexible film as substrate, we successfully achieve a wide-range-strain tuning of FeSe thin flake, in which both the tensile and compressive strain could reach up to ~0.7%, and systematically study the strain effect on both superconducting and nematic transition (Tc and Ts) in the FeSe thin flake. Our results reveal a predominant A1g-type strain effect on Tc. Meanwhile, Ts exhibits a monotonic anti-correlation with Tc and the maximum Tc reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain. Finally, in comparison with the results in the underdoped Ba(Fe1-xCox)2As2, the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity. In addition, our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.
    First neutron Bragg-edge imaging experimental results at CSNS
    Jie Chen(陈洁), Zhijian Tan(谭志坚), Weiqiang Liu(刘玮强), Sihao Deng(邓司浩), Shengxiang Wang(王声翔), Liyi Wang(王立毅), Haibiao Zheng(郑海彪), Huaile Lu(卢怀乐), Feiran Shen(沈斐然), Jiazheng Hao(郝嘉政), Xiaojuan Zhou(周晓娟), Jianrong Zhou(周健荣), Zhijia Sun(孙志嘉), Lunhua He(何伦华), and Tianjiao Liang(梁天骄)
    Chin. Phys. B, 2021, 30 (9): 096106.   DOI: 10.1088/1674-1056/ac0da7
    Abstract249)   HTML1)    PDF (1294KB)(304)      
    The neutron Bragg-edge imaging is expected to be a new non-destructive energy-resolved neutron imaging technique for quantitatively two-dimensional or three-dimensional visualizing crystallographic information in a bulk material, which could be benefited from pulsed neutron source. Here we build a Bragg-edge imaging system on the General Purpose Powder Diffractometer at the China Spallation Neutron Source. The residual strain mapping of a bent Q235 ferrite steel sample has been achieved with a spectral resolution of 0.15% by the time-of-flight neutron Bragg-edge imaging on this system. The results show its great potential applications in materials science and engineering.
    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
    Abstract328)   HTML1)    PDF (3012KB)(297)      
    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.
    Intrinsic V vacancy and large magnetoresistance in V1-δSb2 single crystal
    Yong Zhang(张勇), Xinliang Huang(黄新亮), Jinglei Zhang(张警蕾), Wenshuai Gao(高文帅), Xiangde Zhu(朱相德), and Li Pi(皮雳)
    Chin. Phys. B, 2022, 31 (3): 037102.   DOI: 10.1088/1674-1056/ac3070
    Abstract203)   HTML1)    PDF (2105KB)(296)      
    The binary pnictide semimetals have attracted considerable attention due to their fantastic physical properties that include topological effects, negative magnetoresistance, Weyl fermions, and large non-saturation magnetoresistance. In this paper, we have successfully grown the high-quality V1-δSb2 single crystals by Sb flux method and investigated their electronic transport properties. A large positive magnetoresistance that reaches 477% under a magnetic field of 12 T at T = 1.8 K was observed. Notably, the magnetoresistance showed a cusp-like feature at the low magnetic fields and such feature weakened gradually as the temperature increased, which indicated the presence of a weak antilocalization effect (WAL). In addition, based upon the experimental and theoretical band structure calculations, V1-δSb2 is a research candidate for a flat band.
    Development of series SQUID array with on-chip filter for TES detector
    Wentao Wu(伍文涛), Zhirong Lin(林志荣), Zhi Ni(倪志), Peizhan Li(李佩展), Tiantian Liang(梁恬恬), Guofeng Zhang(张国峰), Yongliang Wang(王永良), Liliang Ying(应利良), Wei Peng(彭炜), Wen Zhang(张文), Shengcai Shi(史生才), Lixing You(尤立星), and Zhen Wang(王镇)
    Chin. Phys. B, 2022, 31 (2): 028504.   DOI: 10.1088/1674-1056/ac2b91
    Abstract286)   HTML3)    PDF (3471KB)(273)      
    A cold preamplifier based on superconducting quantum interference devices (SQUIDs) is currently the preferred readout technology for the low-noise transition edge sensor (TES). In this work, we have designed and fabricated a series SQUID array (SSA) amplifier for the TES detector readout circuit. In this SSA amplifier, each SQUID cell is composed of a first-order gradiometer formed using two equally large square washers, and an on-chip low pass filter (LPF) as a radio-frequency (RF) choke has been developed to reduce the Josephson oscillation interference between individual SQUID cells. In addition, a highly symmetric layout has been designed carefully to provide a fully consistent embedded electromagnetic environment and achieve coherent flux operation. The measured results show smooth V-Φ characteristics and a swing voltage that increases linearly with increasing SQUID cell number N. A white flux noise level as low as 0.28 μΦ0/Hz1/2 is achieved at 0.1 K, corresponding to a low current noise level of 7 pA/Hz1/2. We analyze the measured noise contribution at mK-scale temperatures and find that the dominant noise derives from a combination of the SSA intrinsic noise and the equivalent current noise of the room temperature electronics.
    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
    Abstract223)   HTML3)    PDF (3458KB)(266)      
    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.
    Defect calculations with quasiparticle correction: A revisited study of iodine defects in CH3NH3PbI3
    Ling Li(李玲) and Wan-Jian Yin(尹万健)
    Chin. Phys. B, 2022, 31 (1): 017103.   DOI: 10.1088/1674-1056/ac3505
    Abstract265)   HTML1)    PDF (4326KB)(259)      
    Defect levels in semiconductor band gaps play a crucial role in functionalized semiconductors for practical applications in optoelectronics; however, first-principle defect calculations based on exchange-correlation functionals, such as local density approximation, grand gradient approximation (GGA), and hybrid functionals, either underestimate band gaps or misplace defect levels. In this study, we revisited iodine defects in CH3NH3PbI3 by combining the accuracy of total energy calculations of GGA and single-electron level calculation of the GW method. The combined approach predicted neutral Im i to be unstable and the transition level of Im i(+1/-1) to be close to the valence band maximum. Therefore, Im i may not be as detrimental as previously reported. Moreover, Vm I may be unstable in the -1 charged state but could still be detrimental owing to the deep transition level of Vm I(+1/0). These results could facilitate the further understanding of the intrinsic point defect and defect passivation observed in CH3NH3PbI3.
ISSN 1674-1056   CN 11-5639/O4

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