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    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
    Abstract264)      PDF (517KB)(300)      
    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.
    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
    Abstract223)      PDF (2793KB)(223)      
    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.
    Suppression of ion migration in perovskite materials by pulse-voltage method
    Xue-Yan Wang(王雪岩), Hu Wang(王虎), Luo-Ran Chen(陈烙然), Yu-Chuan Shao(邵宇川), and Jian-Da Shao(邵建达)
    Chin. Phys. B, 2021, 30 (11): 118104.   DOI: 10.1088/1674-1056/ac248d
    Abstract97)      PDF (1398KB)(71)      
    Hybrid halide perovskites have great potential for applications in optoelectronic devices. However, the typical ion migration in perovskite could lead to the non-repeatability of electrical measurement, instability of material, and degradation of device performance. The basic current-voltage behavior of perovskite materials is intricate due to the mixed electronic-ionic characteristic, which is still poorly understood in these semiconductors. Developing novel measurement schematic is a promising solution to obtain the intrinsic electrical performance without the interference of ion migration. Herein, we explore the pulse-voltage (PV) method on methylammonium lead tribromide single crystals to protect the device from the ion migration. A guideline is summarized through the analysis of measurement history and condition parameters. The influence of the ion migration on current-voltage measurement, such as repeatability and hysteresis loop, is under controlled. An application of the PV method is demonstrated on the activation energy of conductivity. The abruption of activation energy still exists near the phase transition temperature despite the ion migration is excluded by the PV method, introducing new physical insight on the current-voltage behavior of perovskite materials. The guideline on PV method will be beneficial for measuring halide perovskite materials and developing optoelectronic applications with new technique schematic.
    Realization of semiconducting Cu2Se by direct selenization of Cu(111)
    Yumu Yang(杨雨沐), Qilong Wu(吴奇龙), Jiaqi Deng(邓嘉琦), Jing Wang(王静), Yu Xia(夏雨), Xiaoshuai Fu(富晓帅), Qiwei Tian(田麒玮), Li Zhang(张力), Long-Jing Yin(殷隆晶), Yuan Tian(田园), Sheng-Yi Xie(谢声意), Lijie Zhang(张利杰), and Zhihui Qin(秦志辉)
    Chin. Phys. B, 2021, 30 (11): 116802.   DOI: 10.1088/1674-1056/ac0037
    Abstract119)      PDF (1904KB)(118)      
    Bulk group IB transition-metal chalcogenides have been widely explored due to their applications in thermoelectrics. However, a layered two-dimensional form of these materials has been rarely reported. Here, we realize semiconducting Cu2Se by direct selenization of Cu(111). Scanning tunneling microcopy measurements combined with first-principles calculations allow us to determine the structural and electronic properties of the obtained structure. X-ray photoelectron spectroscopy data reveal chemical composition of the sample, which is Cu2Se. The observed moiré pattern indicates a lattice mismatch between Cu2Se and the underlying Cu(111)-$\sqrt{3}$×$\sqrt{3}$ surface. Differential conductivity obtained by scanning tunneling spectroscopy demonstrates that the synthesized Cu2Se exhibits a band gap of 0.78 eV. Furthermore, the calculated density of states and band structure demonstrate that the isolated Cu2Se is a semiconductor with an indirect band gap of ~ 0.8 eV, which agrees quite well with the experimental results. Our study provides a simple pathway varying toward the synthesis of novel layered 2D transition chalcogenides materials.
    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
    Abstract438)      PDF (1543KB)(521)      
    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.
    LnCu3(OH)6Cl3 (Ln = Gd, Tb, Dy): Heavy lanthanides onspin-1/2 kagome magnets
    Ying Fu(付盈), Lianglong Huang(黄良龙), Xuefeng Zhou(周雪峰), Jian Chen(陈见), Xinyuan Zhang(张馨元), Pengyun Chen(陈鹏允), Shanmin Wang(王善民), Cai Liu(刘才), Dapeng Yu(俞大鹏), Hai-Feng Li(李海峰), Le Wang(王乐), and Jia-Wei Mei(梅佳伟)
    Chin. Phys. B, 2021, 30 (10): 100601.   DOI: 10.1088/1674-1056/ac1e20
    Abstract187)      PDF (1946KB)(155)      
    The spin-1/2 kagome antiferromagnets are key prototype materials for studying frustrated magnetism. Three isostructural kagome antiferromagnets LnCu3(OH)6Cl3 (Ln = Gd, Tb, Dy) have been successfully synthesized by the hydrothermal method. LnCu3(OH)6Cl3 adopts space group P3m1 and features the layered Cu-kagome lattice with lanthanide Ln3+ cations sitting at the center of the hexagons. Although heavy lanthanides (Ln = Gd, Tb, Dy) in LnCu3(OH)6Cl3 provide a large effective magnetic moment and ferromagnetic-like spin correlations compared to light-lanthanides (Nd, Sm, Eu) analogues, Cu-kagome holds an antiferromagnetically ordered state at around 17 K like YCu3(OH)6Cl3.
    Dual mechanisms of Bcl-2 regulation in IP3-receptor-mediated Ca2+ release: A computational study
    Hong Qi(祁宏), Zhi-Qiang Shi(史志强), Zhi-Chao Li(李智超), Chang-Jun Sun(孙长君), Shi-Miao Wang(王世苗), Xiang Li(李翔), and Jian-Wei Shuai(帅建伟)
    Chin. Phys. B, 2021, 30 (10): 108704.   DOI: 10.1088/1674-1056/ac1e0d
    Abstract152)      PDF (1927KB)(128)      
    Inositol 1,4,5-trisphosphate receptors (IP3R)-mediated calcium ion (Ca2+) release plays a central role in the regulation of cell survival and death. Bcl-2 limits the Ca2+ release function of the IP3R through a direct or indirect mechanism. However, the two mechanisms are overwhelmingly complex and not completely understood. Here, we convert the mechanisms into a set of ordinary differential equations. We firstly simulate the time evolution of Ca2+ concentration under two different levels of Bcl-2 for the direct and indirect mechanism models and compare them with experimental results available in the literature. Secondly, we employ one- and two-parameter bifurcation analysis to demonstrate that Bcl-2 can suppress Ca2+ signal from a global point of view both in the direct and indirect mechanism models. We then use mathematical analysis to clarify that the indirect mechanism is more efficient than the direct mechanism in repressing Ca2+ signal. Lastly, we predict that the two mechanisms restrict Ca2+ signal synergistically. Together, our study provides theoretical insights into Bcl-2 regulation in IP3R-mediated Ca2+ release, which may be instrumental for the successful development of therapies to target Bcl-2 for cancer treatment.
    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
    Abstract349)   HTML0)    PDF (806KB)(421)      
    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.
    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
    Abstract182)   HTML0)    PDF (1294KB)(256)      
    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.
    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
    Abstract154)   HTML0)    PDF (1879KB)(216)      
    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.
    Ultrafast structural dynamics using time-resolved x-ray diffraction driven by relativistic laser pulses
    Chang-Qing Zhu(朱常青), Jun-Hao Tan(谭军豪), Yu-Hang He(何雨航), Jin-Guang Wang(王进光), Yi-Fei Li(李毅飞), Xin Lu(鲁欣), Ying-Jun Li(李英骏), Jie Chen(陈洁), Li-Ming Chen(陈黎明), and Jie Zhang(张杰)
    Chin. Phys. B, 2021, 30 (9): 098701.   DOI: 10.1088/1674-1056/ac0baf
    Abstract201)   HTML0)    PDF (2226KB)(153)      
    Based on a femtosecond laser plasma-induced hard x-ray source with a high laser pulse energy (>100 mJ) at 10 Hz repetition rate, we present a time-resolved x-ray diffraction system on an ultrafast time scale. The laser intensity is at relativistic regime (2×1019 W/cm2), which is essential for effectively generating Kα source in high-Z metal material. The produced copper Kα radiation yield reaches to 2.5×108 photons/sr/shot. The multilayer mirrors are optimized for monochromatizating and two-dimensional beam shaping of Kα emission. Our experiment exhibits its ability of monitoring the transient structural changes in a thin film SrCoO2.5 crystal. It is demonstrated that this facility is a powerful tool to perform dynamic studies on samples and adaptable to the specific needs for different particular applications with high flexibility.
    Strain-dependent resistance and giant gauge factor in monolayer WSe2
    Mao-Sen Qin(秦茂森), Xing-Guo Ye(叶兴国), Peng-Fei Zhu(朱鹏飞), Wen-Zheng Xu(徐文正), Jing Liang(梁晶), Kaihui Liu(刘开辉), and Zhi-Min Liao(廖志敏)
    Chin. Phys. B, 2021, 30 (9): 097203.   DOI: 10.1088/1674-1056/ac11d2
    Abstract140)   HTML0)    PDF (949KB)(155)      
    We report the strong dependence of resistance on uniaxial strain in monolayer WSe2 at various temperatures, where the gauge factor can reach as large as 2400. The observation of strain-dependent resistance and giant gauge factor is attributed to the emergence of nonzero Berry curvature dipole. Upon increasing strain, Berry curvature dipole can generate net orbital magnetization, which would introduce additional magnetic scattering, decreasing the mobility and thus conductivity. Our work demonstrates the strain engineering of Berry curvature and thus the transport properties, making monolayer WSe2 potential for application in the highly sensitive strain sensors and high-performance flexible electronics.
    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
    Abstract408)   HTML0)    PDF (1511KB)(406)      
    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.
    Effective model for rare-earth Kitaev materials and its classical Monte Carlo simulation
    Mengjie Sun(孙梦杰), Huihang Lin(林慧航), Zheng Zhang(张政), Yanzhen Cai(蔡焱桢), Wei Ren(任玮), Jing Kang(康靖), Jianting Ji(籍建葶), Feng Jin(金峰), Xiaoqun Wang(王孝群), Rong Yu(俞榕), Qingming Zhang(张清明), and Zhengxin Liu(刘正鑫)
    Chin. Phys. B, 2021, 30 (8): 087503.   DOI: 10.1088/1674-1056/ac0a5d
    Abstract206)   HTML0)    PDF (2226KB)(210)      
    Recently, the family of rare-earth chalcohalides were proposed as candidate compounds to realize the Kitaev spin liquid (KSL) [Chin. Phys. Lett. 38 047502 (2021)]. In the present work, we firstly propose an effective spin Hamiltonian consistent with the symmetry group of the crystal structure. Then we apply classical Monte Carlo simulations to preliminarily study the model and establish a phase diagram. When approaching to the low temperature limit, several magnetic long range orders are observed, including the stripe, the zigzag, the antiferromagnetic (AFM), the ferromagnetic (FM), the incommensurate spiral (IS), the multi-Q, and the 120° ones. We further calculate the thermodynamic properties of the system, such as the temperature dependence of the magnetic susceptibility and the heat capacity. The ordering transition temperatures reflected in the two quantities agree with each other. For most interaction regions, the system is magnetically more susceptible in the ab-plane than in the c-direction. The stripe phase is special, where the susceptibility is fairly isotropic in the whole temperature region. These features provide useful information to understand the magnetic properties of related materials.
    CeAu2In4: A candidate of quasi-one-dimensional antiferromagnetic Kondo lattice
    Meng Lyu(吕孟), Hengcan Zhao(赵恒灿), Jiahao Zhang(张佳浩), Zhen Wang(王振), Shuai Zhang(张帅), and Peijie Sun(孙培杰)
    Chin. Phys. B, 2021, 30 (8): 087101.   DOI: 10.1088/1674-1056/ac0a60
    Abstract135)   HTML0)    PDF (1950KB)(118)      
    Needle-like single crystals of CeAu2In4 have been grown from In flux and characterized as a new candidate of quasi-one-dimensional Kondo lattice compound by crystallographic, magnetic, transport, and specific-heat measurements down to very low temperatures. We observe an antiferromagnetic transition at TN ≈ 0.9 K, a highly non-mean-field profile of the corresponding peak in specific heat, and a large Sommerfeld coefficient γ =369 mJ·mol-1·K-2. The Kondo temperature TK is estimated to be 1.1 K, being low and comparable to TN. While Fermi liquid behavior is observed deep into the magnetically ordered phase, the Kadowaki-Woods ratio is much reduced relative to the expected value for Ce compounds with Kramers doublet ground state. Markedly, this feature shares striking similarities to that of the prototypical quasi-one-dimensional compounds YbNi4P2 and CeRh6Ge4 with tunable ferromagnetic quantum critical point. Given the shortest Ce-Ce distance along the needle direction, CeAu2In4 appears to be an interesting model system for exploring antiferromagnetic quantum critical behaviors in a quasi-one-dimensional Kondo lattice with enhanced quantum fluctuations.
    Group velocity matters for accurate prediction of phonon-limited carrier mobility
    Qiao-Lin Yang(杨巧林), Hui-Xiong Deng(邓惠雄), Su-Huai Wei(魏苏淮), and Jun-Wei Luo(骆军委)
    Chin. Phys. B, 2021, 30 (8): 087201.   DOI: 10.1088/1674-1056/ac0133
    Abstract118)   HTML0)    PDF (828KB)(138)      
    First-principles approaches have recently been developed to replace the phenomenological modeling approaches with adjustable parameters for calculating carrier mobilities in semiconductors. However, in addition to the high computational cost, it is still a challenge to obtain accurate mobility for carriers with a complex band structure, e.g., hole mobility in common semiconductors. Here, we present a computationally efficient approach using isotropic and parabolic bands to approximate the anisotropy valence bands for evaluating group velocities in the first-principles calculations. This treatment greatly reduces the computational cost in two ways: relieves the requirement of an extremely dense κ mesh to obtain a smooth change in group velocity, and reduces the 5-dimensional integral to 3-dimensional integral. Taking Si and SiC as two examples, we find that this simplified approach reproduces the full first-principles calculation for mobility. If we use experimental effective masses to evaluate the group velocity, we can obtain hole mobility in excellent agreement with experimental data over a wide temperature range. These findings shed light on how to improve the first-principles calculations towards predictive carrier mobility in high accuracy.
    Signatures of strong interlayer coupling in γ-InSe revealed by local differential conductivity
    Xiaoshuai Fu(富晓帅), Li Liu(刘丽), Li Zhang(张力), Qilong Wu(吴奇龙), Yu Xia(夏雨), Lijie Zhang(张利杰), Yuan Tian(田园), Long-Jing Yin(殷隆晶), and Zhihui Qin(秦志辉)
    Chin. Phys. B, 2021, 30 (8): 087306.   DOI: 10.1088/1674-1056/abff32
    Abstract116)   HTML0)    PDF (5948KB)(146)      
    Interlayer coupling in layered semiconductors can significantly affect their optoelectronic properties. However, understanding the mechanisms behind the interlayer coupling at the atomic level is not straightforward. Here, we study modulations of the electronic structure induced by the interlayer coupling in the γ-phase of indium selenide (γ-InSe) using scanning probe techniques. We observe a strong dependence of the energy gap on the sample thickness and a small effective mass along the stacking direction, which are attributed to strong interlayer coupling. In addition, the moiré patterns observed in γ-InSe display a small band-gap variation and nearly constant local differential conductivity along the patterns. This suggests that modulation of the electronic structure induced by the moiré potential is smeared out, indicating the presence of a significant interlayer coupling. Our theoretical calculations confirm that the interlayer coupling in γ-InSe is not only of the van der Waals origin, but also exhibits some degree of hybridization between the layers. Strong interlayer coupling might play an important role in the performance of γ-InSe-based devices.
    Excess-iron driven spin glass phase in Fe1+yTe1-xSex
    Long Tian(田龙), Panpan Liu(刘盼盼), Tao Hong(洪涛), Tilo Seydel, Xingye Lu(鲁兴业), Huiqian Luo(罗会仟), Shiliang Li(李世亮), and Pengcheng Dai(戴鹏程)
    Chin. Phys. B, 2021, 30 (8): 087402.   DOI: 10.1088/1674-1056/ac0695
    Abstract103)   HTML0)    PDF (1310KB)(100)      
    The iron-chalcogenide superconductor FeTe1-xSex displays a variety of exotic features distinct from iron pnictides. Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x=0.5, the existence of a spin glass phase with short-range magnetic order in the doping range (x~0.1-0.3) has rarely been studied. Here, we use DC/AC magnetization and (quasi) elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe1.07Te0.8Se0.2 sample. The AC-frequency dependent spin-freezing temperature Tf generates a frequency sensitivity ΔTf(ω) /[Tf(ω) Δlog10ω]≈0.028 and the description of the critical slowing down with τ=τ0(Tf / TSG)-zv gives TSG≈22 K and zv≈10, comparable to that of a classical spin-glass system. We have also extended the frequency-dependent Tf to the smaller time scale using energy-resolution-dependent neutron diffraction measurements, in which the TN of the short-range magnetic order increases systematically with increasing energy resolution. By removing the excess iron through annealing in oxygen, the spin-freezing behavior disappears, and bulk superconductivity is realized. Thus, the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity.
    Stabilization of formamidinium lead iodide perovskite precursor solution for blade-coating efficient carbon electrode perovskite solar cells
    Yu Zhan(占宇), Weijie Chen(陈炜杰), Fu Yang(杨甫), and Yaowen Li(李耀文)
    Chin. Phys. B, 2021, 30 (8): 088803.   DOI: 10.1088/1674-1056/abfbcb
    Abstract136)   HTML0)    PDF (4217KB)(138)      
    Formamidinium lead triiodide (FAPbI3) is a research hotspot in perovskite photovoltaics due to its broad light absorption and proper thermal stability. However, quite a few researches focused on the stability of the FAPbI3 perovskite precursor solutions. Besides, the most efficient FAPbI3 layers are prepared by the spin-coating method, which is limited to the size of the device. Herein, the stability of FAPbI3 perovskite solution with methylammonium chloride (MACl) or cesium chloride (CsCl) additive is studied for preparing perovskite film through an upscalable blade-coating method. Each additive works well for achieving a high-quality FAPbI3 film, resulting in efficient carbon electrode perovskite solar cells (pero-SCs) in the ambient condition. However, the perovskite solution with MACl additive shows poor aging stability that no α-FAPbI3 phase is observed when the solution is aged over one week. While the perovskite solution with CsCl additive shows promising aging stability that it still forms high-quality pure α-FAPbI3 perovskite film even the solution is aged over one month. During the solution aging process, the MACl could be decomposed into methylamine which will form some unfavored intermediated phase inducing δ-phase FAPbI3. Whereas, replacing MACl with CsCl could effectively solve this issue. Our founding shows that there is a great need to develop a non-MACl FAPbI3 perovskite precursor solution for cost-effective preparation of pero-SCs.
    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
    Abstract338)   HTML0)    PDF (3238KB)(402)      
    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.
ISSN 1674-1056   CN 11-5639/O4

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