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Absence of BCS-BEC crossover in FeSe0.45Te0.55 superconductor Junjie Jia(贾俊杰), Yadong Gu(谷亚东), Chaohui Yin(殷超辉), Yingjie Shu(束英杰), Yiwen Chen(陈逸雯), Jumin Shi(史聚民), Xing Zhang(张杏), Hao Chen(陈浩), Taimin Miao(苗泰民), Xiaolin Ren(任晓琳), Bo Liang(梁波), Wenpei Zhu(朱文培), Neng Cai(蔡能), Fengfeng Zhang(张丰丰), Shenjin Zhang(张申金), Feng Yang(杨峰), Zhimin Wang(王志敏), Qinjun Peng(彭钦军), Zuyan Xu(许祖彦), Hanqing Mao(毛寒青), Guodong Liu(刘国东), Zhian Ren(任治安), Lin Zhao(赵林), and Xing-Jiang Zhou(周兴江) Chin. Phys. B, 2024, 33 (7): 077404.   DOI: 10.1088/1674-1056/ad51f9 Abstract （50）      PDF （11205KB）（40）       Knowledge map    In iron-based superconductor Fe(Se,Te), a flat band-like feature near the Fermi level was observed around the Brillouin zone center in the superconducting state. It is under debate whether this is the evidence on the presence of the BCS-BEC [Bardeen-Cooper-Schrieffer (BCS), Bose-Einstein condensation (BEC)] crossover in the superconductor. High-resolution laser-based angle-resolved photoemission measurements are carried out on high quality single crystals of FeSe$_{0.45}$Te$_{0.55}$ superconductor to address the issue. By employing different polarization geometries, we have resolved and isolated the d$_{yz}$ band and the topological surface band, making it possible to study their superconducting behaviors separately. The d$_{yz}$ band alone does not form a flat band-like feature in the superconducting state and the measured dispersion can be well described by the BCS picture. We find that the flat band-like feature is formed from the combination of the d$_{yz}$ band and the topological surface state band in the superconducting state. These results reveal the origin of the flat band-like feature and rule out the presence of BCS-BEC crossover in Fe(Se,Te) superconductor.

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Observation of parabolic electron bands on superconductor LaRu2As2 Xingtai Zhou(周兴泰), Geng Li(李更), Lulu Pan(潘禄禄), Zichao Chen(陈子超), Meng Li(李萌), Yanhao Shi(时延昊), Haitao Yang(杨海涛), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2024, 33 (7): 077401.   DOI: 10.1088/1674-1056/ad4d63 Abstract （47）      PDF （1196KB）（20）       Knowledge map    Ru-based superconductor LaRu$_{2}$As$_{2}$ has been discovered exhibiting the highest critical temperature of $\sim 7.8 $ K among iron-free transition metal pnictides with the ThCr$_{2}$Si$_{2}$-type crystal structure. However, microscopic research on this novel superconducting material is still lacking. Here, we utilize scanning tunneling microscopy/spectroscopy to uncover the superconductivity and surface structure of LaRu$_{2}$As$_{2}$. Two distinct terminating surfaces are identified on the cleaved crystals, namely, the As surface and the La surface. Atomic missing line defects are observed on the La surface. Both surfaces exhibit a superconducting gap of $\sim 1.0 $ meV. By employing quasiparticle interference techniques, we observe standing wave patterns near the line defects on the La atomic plane. These patterns are attributed to quasiparticle scattering from two electron type parabolic bands.

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Coevolution of superconductivity and Hall coefficient with anisotropic lattice shrinkage in compressed KCa2Fe4As4F2 Jinyu Han(韩金宇), Wenshan Hong(洪文山), Shu Cai(蔡树), Jinyu Zhao(赵金瑜), Jing Guo(郭静), Yazhou Zhou(周亚洲), Pengyu Wang(王鹏玉), Lixin Cao(曹立新), Huiqian Luo(罗会仟), Shiliang Li(李世亮), Qi Wu(吴奇), and Liling Sun(孙力玲) Chin. Phys. B, 2024, 33 (7): 077402.   DOI: 10.1088/1674-1056/ad4d65 Abstract （40）      PDF （2821KB）（11）       Knowledge map    The stability of superconductivity in superconductors is widely recognized to be determined by various factors, including charge, spin, orbit, lattice, and other related degrees of freedom. Here, we report our findings on the pressure-induced coevolution of superconductivity and Hall coefficient in KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$, an iron-based superconductor possessing a hybrid crystal structure combining KFe$_{2}$As$_{2}$ and CaFeAsF. Our investigation, involving high-pressure resistance, Hall effect and x-ray diffraction (XRD) measurements, allows us to observe the connection of the superconductivity and Hall coefficient with the anisotropic lattice shrinkage. We find that its ambient-pressure tetragonal (T) phase presents a collapse starting at around 18 GPa, where the sign of the Hall coefficient ($R_{\rm H}$) changes from positive to negative. Upon further compression, both superconducting transition temperature ($T_{\rm c}$) and $R_{\rm H}$ exhibit a monotonous decrease. At around 41 GPa, the superconductivity is completely suppressed ($T_{\rm c}=0$), where the parameter $a$ begins to decline again and the Hall coefficient remains nearly unchanged. Our experiment results clearly demonstrate that the pressure-induced anisotropic lattice collapse plays a crucial role in tuning the interplay among multiple degrees of freedom in the superconducting system and, correspondingly, the stability of the superconductivity.

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Moiré superlattices arising from growth induced by screw dislocations in layered materials Fuyu Tian(田伏钰), Muhammad Faizan, Xin He(贺欣), Yuanhui Sun(孙远慧), and Lijun Zhang(张立军) Chin. Phys. B, 2024, 33 (7): 077403.   DOI: 10.1088/1674-1056/ad4cdc Abstract （30）      PDF （2683KB）（9）       Knowledge map    Moiré superlattices (MSLs) are modulated structures produced from homogeneous or heterogeneous two-dimensional layers stacked with a twist angle and/or lattice mismatch. Enriching the methods for fabricating MSL and realizing the unique emergent properties are key challenges in its investigation. Here we recommend that the spiral dislocation driven growth is another optional method for the preparation of high quality MSL samples. The spiral structure stabilizes the constant out-of-plane lattice distance, causing the variations in electronic and optical properties. Taking SnS$_{2}$ MSL as an example, we find prominent properties including large band gap reduction ($\sim 0.4 $ eV) and enhanced optical activity. First-principles calculations reveal that these unusual properties can be ascribed to the locally enhanced interlayer interaction associated with the Moiré potential modulation. We believe that the spiral dislocation driven growth would be a powerful method to expand the MSL family and broaden their scope of application.

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Critical behavior of quasi-two-dimensional ferromagnet Cr1.04Te2 Wei Niu(钮伟), Qin-Xin Song(宋沁心), Shi-Qi Chang(常世琦), Min Wang(王敏), Kui Yuan(袁奎), Jia-Cheng Gao(高嘉程), Shuo Wang(王硕), Zhen-Dong Wang(王振东), Kai-Fei Liu(刘凯斐), Ping Liu(刘萍), Yong-Bing Xu(徐永兵), Xiao-Qian Zhang(张晓倩), and Yong Pu(普勇) Chin. Phys. B, 2024, 33 (7): 077506.   DOI: 10.1088/1674-1056/ad4cd8 Abstract （36）      PDF （1779KB）（8）       Knowledge map    The self-intercalation of Cr into pristine two-dimensional (2D) van der Waals ferromagnetic CrTe$_{2}$, which forms chromium tellurides (Cr$_{x}$Te$_{2}$), has garnered interest due to their remarkable magnetic characteristics and the wide variety of chemical compositions available. Here, comprehensive basic characterization and magnetic studies are conducted on quasi-2D ferromagnetic Cr$_{1.04}$Te$_{2}$ crystals. Measurements of the isothermal magnetization curves are conducted around the critical temperature to systematically investigate the critical behavior. Specifically, the critical exponents $\beta = 0.2399$, $\gamma = 0.859$, and $\delta = 4.3498$, as well as the Curie temperature $T_{\rm C} = 249.56$,K, are determined using various methods, including the modified Arrott plots, the Kouvel-Fisher method, the Widom scaling method, and the critical isotherm analysis. These results indicate that the tricritical mean-field model accurately represents the critical behavior of Cr$_{1.04}$Te$_{2}$. A magnetic phase diagram with tricritical phenomenon is thus constructed. Further investigations confirm that the critical exponents obtained conform to the scalar equation near $T_{\rm C}$, indicating their self-consistency and reliability. Our work sheds light on the magnetic properties of quasi-2D Cr$_{1.04}$Te$_{2}$, broadening the scope of the van der Waals crystals for developments of future spintronic devices operable at room temperature.

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Cryo-EM combined with image deconvolution to determine ZIF-8 crystal structure Kang Wu(吴抗), Baisong Yang(杨柏松), Wenhua Xue(薛文华), Dapeng Sun(孙大鹏), Binghui Ge(葛炳辉), and Yumei Wang(王玉梅) Chin. Phys. B, 2024, 33 (7): 076802.   DOI: 10.1088/1674-1056/ad48f8 Abstract （52）      PDF （27545KB）（14）       Knowledge map    Metal-organic frameworks (MOFs) are crystalline porous materials with tunable properties, exhibiting great potential in gas adsorption, separation and catalysis.[1,2]It is challenging to visualize MOFs with transmission electron microscopy (TEM) due to their inherent instability under electron beam irradiation. Here, we employ cryo-electron microscopy (cryo-EM) to capture images of MOF ZIF-8, revealing inverted-space structural information at a resolution of up to about 1.7 Å and enhancing its critical electron dose to around 20 $e^-$/Å$^{2}$. In addition, it is confirmed by electron-beam irradiation experiments that the high voltage could effectively mitigate the radiolysis, and the structure of ZIF-8 is more stable along the [100] direction under electron beam irradiation. Meanwhile, since the high-resolution electron microscope images are modulated by contrast transfer function (CTF) and it is difficult to determine the positions corresponding to the atomic columns directly from the images. We employ image deconvolution to eliminate the impact of CTF and obtain the structural images of ZIF-8. As a result, the heavy atom Zn and the organic imidazole ring within the organic framework can be distinguished from structural images.

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Controlling the dynamic behavior of decentralized cluster through centralized approaches Daming Yuan(袁大明), Peilong Wang(王培龙), Peng Wang(王鹏), Xingyu Ma(马星宇), Chuyun Wang(汪楚云), Jing Wang(王璟), Huaicheng Chen(陈怀城), Gao Wang(王高), and Fangfu Ye(叶方富) Chin. Phys. B, 2024, 33 (6): 060702.   DOI: 10.1088/1674-1056/ad3dd0 Abstract （285）      PDF （3679KB）（254）       Knowledge map    How to control the dynamic behavior of large-scale artificial active matter is a critical concern in experimental research on soft matter, particularly regarding the emergence of collective behaviors and the formation of group patterns. Centralized systems excel in precise control over individual behavior within a group, ensuring high accuracy and controllability in task execution. Nevertheless, their sensitivity to group size may limit their adaptability to diverse tasks. In contrast, decentralized systems empower individuals with autonomous decision-making, enhancing adaptability and system robustness. Yet, this flexibility comes at the cost of reduced accuracy and efficiency in task execution. In this work, we present a unique method for regulating the centralized dynamic behavior of self-organizing clusters based on environmental interactions. Within this environment-coupled robot system, each robot possesses similar dynamic characteristics, and their internal programs are entirely identical. However, their behaviors can be guided by the centralized control of the environment, facilitating the accomplishment of diverse cluster tasks. This approach aims to balance the accuracy and flexibility of centralized control with the robustness and task adaptability of decentralized control. The proactive regulation of dynamic behavioral characteristics in active matter groups, demonstrated in this work through environmental interactions, holds the potential to introduce a novel technological approach and provide experimental references for studying the dynamic behavior control of large-scale artificial active matter systems.

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Field induced Chern insulating states in twisted monolayer-bilayer graphene Zhengwen Wang(王政文), Yingzhuo Han(韩英卓), Kenji Watanabe, Takashi Taniguchi, Yuhang Jiang(姜宇航), and Jinhai Mao(毛金海) Chin. Phys. B, 2024, 33 (6): 067301.   DOI: 10.1088/1674-1056/ad3b8a Abstract （159）      PDF （1262KB）（188）       Knowledge map    Unraveling the mechanism underlying topological phases, notably the Chern insulators (ChIs) in strong correlated systems at the microscopy scale, has captivated significant research interest. Nonetheless, ChIs harboring topological information have not always manifested themselves, owing to the constraints imposed by displacement fields in certain experimental configurations. In this study, we employ density-tuned scanning tunneling microscopy (DT-STM) to investigate the ChIs in twisted monolayer-bilayer graphene (tMBG). At zero magnetic field, we observe correlated metallic states. While under a magnetic field, a metal-insulator transition happens and an integer ChI is formed emanating from the filling index $ s = 3$ with a Chern number $C = 1$. Our results underscore the pivotal role of magnetic fields as a powerful probe for elucidating topological phases in twisted Van der Waals heterostructures.

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Relationship between disorder, magnetism and band topology in Mn(Sb1-xBix)2Te4 single crystals Ming Xi(席明) and Hechang Lei(雷和畅) Chin. Phys. B, 2024, 33 (6): 067503.   DOI: 10.1088/1674-1056/ad3dd8 Abstract （112）      PDF （919KB）（163）       Knowledge map    We investigate the evolution of magnetic properties as well as the content and distribution of Mn for Mn(Sb$_{1-x}$Bi$_{x}$)$_{2}$Te$_{4}$ single crystals grown by large-temperature-gradient chemical vapor transport method. It is found that the ferromagnetic MnSb$_{2}$Te$_{4}$ changes to antiferromagnetism with Bi doping when $x \ge 0.25$. Further analysis implies that the occupations of Mn ions at Sb/Bi site Mn$_{\rm Sb/Bi}$ and Mn site Mn$_{\rm Mn}$ have a strong influence on the magnetic ground states of these systems. With the decrease of Mn$_{\rm Mn}$ and increase of Mn$_{\rm Sb/Bi}$, the system will favor the ferromagnetic ground state. In addition, the rapid decrease of $T_{\rm C/N}$ with increasing Bi content when $x \le 0.25$ and the insensitivity of $T_{\rm N}$ to $x$ when $x > 0.25$ suggest that the main magnetic interaction may change from the Ruderman-Kittel-Kasuya-Yosida type at low Bi doping region to the van-Vleck type in high Bi doped samples.

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Unveiling the pressure-driven metal-semiconductor-metal transition in the doped TiS2 Jiajun Chen(陈佳骏), Xindeng Lv(吕心邓), Simin Li(李思敏), Yaqian Dan(但雅倩), Yanping Huang(黄艳萍), and Tian Cui(崔田) Chin. Phys. B, 2024, 33 (6): 067104.   DOI: 10.1088/1674-1056/ad4325 Abstract （109）      PDF （1175KB）（130）       Knowledge map    Conventional theories expect that materials under pressure exhibit expanded valence and conduction bands, leading to increased electrical conductivity. Here, we report the electrical properties of the doped 1$T$-TiS$_{2}$ under high pressure by electrical resistance investigations, synchrotron x-ray diffraction, Raman scattering and theoretical calculations. Up to 70GPa, an unusual metal-semiconductor-metal transition occurs. Our first-principles calculations suggest that the observed anti-Wilson transition from metal to semiconductor at 17GPa is due to the electron localization induced by the intercalated Ti atoms. This electron localization is attributed to the strengthened coupling between the doped Ti atoms and S atoms, and the Anderson localization arising from the disordered intercalation. At pressures exceeding 30.5GPa, the doped TiS$_{2}$ undergoes a re-metallization transition initiated by a crystal structure phase transition. We assign the most probable space group as $P$2$_{1}$2$_{1}$2$_{1}$. Our findings suggest that materials probably will eventually undergo the Wilson transition when subjected to sufficient pressure.

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One memristor-one electrolyte-gated transistor-based high energy-efficient dropout neuronal units Yalin Li(李亚霖), Kailu Shi(时凯璐), Yixin Zhu(朱一新), Xiao Fang(方晓), Hangyuan Cui(崔航源), Qing Wan(万青), and Changjin Wan(万昌锦) Chin. Phys. B, 2024, 33 (6): 068401.   DOI: 10.1088/1674-1056/ad39d6 Abstract （71）      PDF （923KB）（74）       Knowledge map    Artificial neural networks (ANN) have been extensively researched due to their significant energy-saving benefits. Hardware implementations of ANN with dropout function would be able to avoid the overfitting problem. This letter reports a dropout neuronal unit (1R1T-DNU) based on one memristor-one electrolyte-gated transistor with an ultralow energy consumption of 25pJ/spike. A dropout neural network is constructed based on such a device and has been verified by MNIST dataset, demonstrating high recognition accuracies ($> 90$%) within a large range of dropout probabilities up to 40%. The running time can be reduced by increasing dropout probability without a significant loss in accuracy. Our results indicate the great potential of introducing such 1R1T-DNUs in full-hardware neural networks to enhance energy efficiency and to solve the overfitting problem.

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Semiclassical approach to spin dynamics of a ferromagnetic S=1 chain Chengchen Li(李承晨), Yi Cui(崔祎), Weiqiang Yu(于伟强), and Rong Yu(俞榕) Chin. Phys. B, 2024, 33 (6): 067501.   DOI: 10.1088/1674-1056/ad3c32 Abstract （70）      PDF （1107KB）（85）       Knowledge map    Motivated by recent experimental progress on the quasi-one-dimensional quantum magnet NiNb$_2$O$_6$, we study the spin dynamics of an $S=1$ ferromagnetic Heisenberg chain with single-ion anisotropy by using a semiclassical molecular dynamics approach. This system undergoes a quantum phase transition from a ferromagnetic to a paramagnetic state under a transverse magnetic field, and the magnetic response reflecting this transition is well described by our semiclassical method. We show that at low temperature the transverse component of the dynamical structure factor depicts clearly the magnon dispersion, and the longitudinal component exhibits two continua associated with single- and two-magnon excitations, respectively. These spin excitation spectra show interesting temperature dependence as effects of magnon interactions. Our findings shed light on the experimental detection of spin excitations in a large class of quasi-one-dimensional magnets.

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Layered kagome compound Na2Ni3S4 with topological flat band Junyao Ye(叶君耀), Yihao Lin(林益浩), Haozhe Wang(王浩哲), Zhida Song(宋志达), Ji Feng(冯济), Weiwei Xie(谢韦伟), and Shuang Jia(贾爽) Chin. Phys. B, 2024, 33 (5): 057103.   DOI: 10.1088/1674-1056/ad3431 Abstract （312）   HTML （17）    PDF （2643KB）（297）       Knowledge map    We report structural and electronic properties of Na$_2$Ni$_3$S$_4$, a quasi-two-dimensional compound composed of alternating layers of [Ni$_3$S$_4$]$^{2-}$ and Na$^{+}$. The compound features a remarkable Ni-based kagome lattice with a square planar configuration of four surrounding S atoms for each Ni atom. Magnetization and electrical measurements reveal a weak paramagnetic insulator with a gap of about 0.5 eV.Our band structure calculation highlights a set of topological flat bands of the kagome lattice derived from the rotated d$_{xz}$-orbital with $C_\mathrm{3}$ + $T$ symmetry in the presence of crystal-field splitting.

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Nonreciprocal transport in the superconducting state of the chiral crystal NbGe2 Yonglai Liu(刘永来), Xitong Xu(许锡童), Miao He(何苗), Haitian Zhao(赵海天), Qingqi Zeng(曾庆祺), Xingyu Yang(杨星宇), Youming Zou(邹优鸣), Haifeng Du(杜海峰), and Zhe Qu(屈哲) Chin. Phys. B, 2024, 33 (5): 057402.   DOI: 10.1088/1674-1056/ad334b Abstract （167）   HTML （12）    PDF （2451KB）（188）       Knowledge map    Due to the lack of inversion, mirror or other roto-inversion symmetries, chiral crystals possess a well-defined handedness which, when combined with time-reversal symmetry breaking from the application of magnetic fields, can give rise to directional dichroism of the electrical transport phenomena via the magnetochiral anisotropy. In this study, we investigate the nonreciprocal magneto-transport in microdevices of NbGe$_{2}$, a superconductor with structural chirality. A giant nonreciprocal signal from vortex motions is observed during the superconducting transition, with the ratio of nonreciprocal resistance to the normal resistance ${\gamma}$ reaching 6$\times10^{5}$~T$^{-1}$$\cdot$A$^{-1}$. Interestingly, the intensity can be adjusted and even sign-reversed by varying the current, the temperature, and the crystalline orientation. Our findings illustrate intricate vortex dynamics and offer ways of manipulation on the rectification effect in superconductors with structural chirality.

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Estimation of cancer cell migration in biomimetic random/oriented collagen fiber microenvironments Jingru Yao(姚静如), Guoqiang Li(李国强), Xiyao Yao(姚喜耀), Lianjie Zhou(周连杰), Zhikai Ye(叶志凯), Yanping Liu(刘艳平), Dongtian Zheng(郑栋天), Ting Tang(唐婷), Kena Song(宋克纳), Guo Chen(陈果), and Liyu Liu(刘雳宇) Chin. Phys. B, 2024, 33 (5): 058706.   DOI: 10.1088/1674-1056/ad334c Abstract （104）   HTML （4）    PDF （3033KB）（144）       Knowledge map    Increasing data indicate that cancer cell migration is regulated by extracellular matrixes and their surrounding biochemical microenvironment, playing a crucial role in pathological processes such as tumor invasion and metastasis. However, conventional two-dimensional cell culture and animal models have limitations in studying the influence of tumor microenvironment on cancer cell migration. Fortunately, the further development of microfluidic technology has provided solutions for the study of such questions. We utilize microfluidic chip to build a random collagen fiber microenvironment (RFM) model and an oriented collagen fiber microenvironment (OFM) model that resemble early stage and late stage breast cancer microenvironments, respectively. By combining cell culture, biochemical concentration gradient construction, and microscopic imaging techniques, we investigate the impact of different collagen fiber biochemical microenvironments on the migration of breast cancer MDA-MB-231-RFP cells. The results show that MDA-MB-231-RFP cells migrate further in the OFM model compared to the RFM model, with significant differences observed. Furthermore, we establish concentration gradients of the anticancer drug paclitaxel in both the RFM and OFM models and find that paclitaxel significantly inhibits the migration of MDA-MB-231-RFP cells in the RFM model, with stronger inhibition on the high concentration side compared to the low concentration side. However, the inhibitory effect of paclitaxel on the migration of MDA-MB-231-RFP cells in the OFM model is weak. These findings suggest that the oriented collagen fiber microenvironment resembling the late-stage tumor microenvironment is more favorable for cancer cell migration and that the effectiveness of anticancer drugs is diminished. The RFM and OFM models constructed in this study not only provide a platform for studying the mechanism of cancer development, but also serve as a tool for the initial measurement of drug screening.

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Dynamical localization in a non-Hermitian Floquet synthetic system Han Ke(可汗), Jiaming Zhang(张嘉明), Liang Huo(霍良), and Wen-Lei Zhao(赵文垒) Chin. Phys. B, 2024, 33 (5): 050507.   DOI: 10.1088/1674-1056/ad36bb Abstract （107）   HTML （5）    PDF （761KB）（142）       Knowledge map    We investigate the non-Hermitian effects on quantum diffusion in a kicked rotor model where the complex kicking potential is quasi-periodically modulated in the time domain. The synthetic space with arbitrary dimension can be created by incorporating incommensurate frequencies in the quasi-periodical modulation. In the Hermitian case, strong kicking induces the chaotic diffusion in the four-dimension momentum space characterized by linear growth of mean energy. We find that the quantum coherence in deep non-Hermitian regime can effectively suppress the chaotic diffusion and hence result in the emergence of dynamical localization. Moreover, the extent of dynamical localization is dramatically enhanced by increasing the non-Hermitian parameter. Interestingly, the quasi-energies become complex when the non-Hermitian parameter exceeds a certain threshold value. The quantum state will finally evolve to a quasi-eigenstate for which the imaginary part of its quasi-energy is large most. The exponential localization length decreases with the increase of the non-Hermitian parameter, unveiling the underlying mechanism of the enhancement of the dynamical localization by non-Hermiticity.

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Electronic structure and effective mass of pristine and Cl-doped CsPbBr3 Zhiyuan Wei(魏志远), Yu-Hao Wei(魏愉昊), Shendong Xu(徐申东), Shuting Peng(彭舒婷), Makoto Hashimoto, Donghui Lu(路东辉), Xu Pan(潘旭), Min-Quan Kuang(匡泯泉), Zhengguo Xiao(肖正国), and Junfeng He(何俊峰) Chin. Phys. B, 2024, 33 (5): 057403.   DOI: 10.1088/1674-1056/ad3c31 Abstract （103）   HTML （3）    PDF （5143KB）（87）       Knowledge map    Organic-inorganic lead halide perovskites (LHPs) have attracted great interest owing to their outstanding optoelectronic properties. Typically, the underlying electronic structure would determinate the physical properties of materials. But as for now, limited studies have been done to reveal the underlying electronic structure of this material system, comparing to the huge amount of investigations on the material synthesis. The effective mass of the valance band is one of the most important physical parameters which plays a dominant role in charge transport and photovoltaic phenomena. In pristine CsPbBr$_{3}$, the Fröhlich polarons associated with the Pb-Br stretching modes are proposed to be responsible for the effective mass renormalization. In this regard, it would be very interesting to explore the electronic structure in doped LHPs. Here, we report high-resolution angle-resolved photoemission spectroscopy (ARPES) studies on both pristine and Cl-doped CsPbBr$_{3}$. The experimental band dispersions are extracted from ARPES spectra along both $\bar{\varGamma}$-$\bar{M}$-$\bar{\varGamma }$ and $\bar{X}$-$\bar{M}$-$\bar{X}$ high symmetry directions. DFT calculations are performed and directly compared with the ARPES data. Our results have revealed the band structure of Cl-doped CsPbBr$_{3}$ for the first time, which have also unveiled the effective mass renormalization in the Cl-doped CsPbBr$_{3}$ compound. Doping dependent measurements indicate that the chlorine doping could moderately tune the renormalization strength. These results will help understand the physical properties of LHPs as a function of doping.

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Symmetry transformation of nonlinear optical current of tilted Weyl nodes and application to ferromagnetic MnBi2Te4 Zhuo-Cheng Lu(卢倬成) and Ji Feng(冯济) Chin. Phys. B, 2024, 33 (4): 047303.   DOI: 10.1088/1674-1056/ad2bfb Abstract （309）   HTML （1）    PDF （2239KB）（402）       Knowledge map    A Weyl node is characterized by its chirality and tilt. We develop a theory of how nth-order nonlinear optical conductivity behaves under transformations of anisotropic tensor and tilt, which clarifies how chirality-dependent and -independent parts of optical conductivity transform under the reversal of tilt and chirality. Built on this theory, we propose ferromagnetic m MnBi2Te4 as a magnetoelectrically regulated, terahertz optical device, by magnetoelectrically switching the chirality-dependent and -independent DC photocurrents. These results are useful for creating nonlinear optical devices based on the topological Weyl semimetals.

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Coexistence of Dirac and Weyl points in non-centrosymmetric semimetal NbIrTe4 Qingxin Liu(刘清馨), Yang Fu(付阳), Pengfei Ding(丁鹏飞), Huan Ma(马欢), Pengjie Guo(郭朋杰), Hechang Lei(雷和畅), and Shancai Wang(王善才) Chin. Phys. B, 2024, 33 (4): 047104.   DOI: 10.1088/1674-1056/ad2a79 Abstract （248）   HTML （4）    PDF （2350KB）（269）       Knowledge map    Using angle-resolved photoemission spectroscopy and density functional theory calculations methods, we investigate the electronic structures and topological properties of ternary tellurides NbIrTe4, a candidate for type-II Weyl semimetal. We demonstrate the presence of several Fermi arcs connecting their corresponding Weyl points on both termination surfaces of the topological material. Our analysis reveals the existence of Dirac points, in addition to Weyl points, giving both theoretical and experimental evidences of the coexistence of Dirac and Weyl points in a single material. These findings not only confirm NbIrTe4 as a unique topological semimetal but also open avenues for exploring novel electronic devices based on its coexisting Dirac and Weyl fermions.

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Improving the electrical performances of InSe transistors by interface engineering Tianjun Cao(曹天俊), Song Hao(郝松), Chenchen Wu(吴晨晨), Chen Pan(潘晨), Yudi Dai(戴玉頔), Bin Cheng(程斌), Shi-Jun Liang(梁世军), and Feng Miao(缪峰) Chin. Phys. B, 2024, 33 (4): 047302.   DOI: 10.1088/1674-1056/ad24d7 Abstract （140）   HTML （0）    PDF （1195KB）（193）       Knowledge map    InSe has emerged as a promising candidate for next-generation electronics due to its predicted ultrahigh electrical performance. However, the efficacy of the InSe transistor in meeting application requirements is hindered due to its sensitivity to interfaces. In this study, we have achieved notable enhancement in the electrical performance of InSe transistors through interface engineering. We engineered an InSe/h-BN heterostructure, effectively suppressing dielectric layer-induced scattering. Additionally, we successfully established excellent metal—semiconductor contacts using graphene ribbons as a buffer layer. Through a methodical approach to interface engineering, our graphene/InSe/h-BN transistor demonstrates impressive on-state current, field-effect mobility, and on/off ratio at room temperature, reaching values as high as 1.1 mA/μm, 904 cm2·V-1·s-1, and >106, respectively. Theoretical computations corroborate that the graphene/InSe heterostructure shows significant interlayer charge transfer and weak interlayer interaction, contributing to the enhanced performance of InSe transistors. This research offers a comprehensive strategy to elevate the electrical performance of InSe transistors, paving the way for their utilization in future electronic applications.

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