|
Direct Strong Measurement of a High-Dimensional Quantum State
Chen-Rui Zhang, Meng-Jun Hu, Guo-Yong Xiang, Yong-Sheng Zhang, Chuan-Feng Li, and Guang-Can Guo
Chin. Phys. Lett. 2020, 37 (8):
080301
.
DOI: 10.1088/0256-307X/37/8/080301
It is of great importance to determine an unknown quantum state for fundamental studies of quantum mechanics, yet it is still difficult to characterize systems of large dimensions in practice. Although the scan-free direct measurement approach based on a weak measurement scheme was proposed to measure a high-dimensional photonic state, how weak the interaction should be to give a correct estimation remains unclear. Here we propose and experimentally demonstrate a technique that measures a high-dimensional quantum state with the combination of scan-free measurement and direct strong measurement. The procedure involves sequential strong measurement, in which case no approximation is made similarly to the conventional direct weak measurement. We use this method to measure a transverse state of a photon with effective dimensionality of $65000$ without the time-consumed scanning process. Furthermore, the high fidelity of the result and the simplicity of the experimental apparatus show that our approach can be readily used to measure the complex field of a beam in diverse applications such as wavefront sensing and quantitative phase imaging.
|
|
Pressure Generation above 35 GPa in a Walker-Type Large-Volume Press
Yu-Chen Shang, Fang-Ren Shen, Xu-Yuan Hou, Lu-Yao Chen, Kuo Hu, Xin Li, Ran Liu, Qiang Tao, Pin-Wen Zhu, Zhao-Dong Liu, Ming-Guang Yao, Qiang Zhou, Tian Cui, and Bing-Bing Liu
Chin. Phys. Lett. 2020, 37 (8):
080701
.
DOI: 10.1088/0256-307X/37/8/080701
Pressure generation to a higher pressure range in a large-volume press (LVP) denotes our ability to explore more functional materials and deeper Earth's interior. Pressure generated by normal tungsten carbide (WC) anvils in a commercial way is mostly limited to 25 GPa in LVPs due to the limitation of their hardness and design of cell assemblies. We adopt three newly developed WC anvils for ultrahigh pressure generation in a Walker-type LVP with a maximum press load of 1000 ton. The hardest ZK01F WC anvils exhibit the highest efficiency of pressure generation than ZK10F and ZK20F WC anvils, which is related to their performances of plastic deformations. Pressure up to 35 GPa at room temperature is achieved at a relatively low press load of 4.5 MN by adopting the hardest ZK01F WC anvils with three tapering surfaces in conjunction with an optimized cell assembly, while pressure above 35 GPa at 1700 K is achieved at a higher press load of 7.5 MN. Temperature above 2000 K can be generated by our cell assemblies at pressure below 30 GPa. We adopt such high-pressure and high-temperature techniques to fabricate several high-quality and well-sintered polycrystalline minerals for practical use. The present development of high-pressure techniques expands the pressure and temperature ranges in Walker-type LVPs and has wide applications in physics, materials, chemistry, and Earth science.
|
|
Characterization of Scanning SQUID Probes Based on 3D Nano-Bridge Junctions in Magnetic Field
Yin-Ping Pan, Yue Wang, Ruo-Ting Yang, Yan Tang, Xiao-Yu Liu, Hua Jin, Lin-Xian Ma, Yi-Shi Lin, Zhen Wang, Jie Ren, Yi-Hua Wang, and Lei Chen
Chin. Phys. Lett. 2020, 37 (8):
080702
.
DOI: 10.1088/0256-307X/37/8/080702
We develop superconducting quantum interference device (SQUID) probes based on 3D nano-bridge junctions for the scanning SQUID microscopy. The use of these nano-bridge junctions enables imaging in the presence of a high magnetic field. Conventionally, a superconducting ground layer has been employed for better magnetic shielding. In our study, we prepare a number of scanning SQUID probes with and without a ground layer to evaluate their performance in external magnetic fields. The devices show the improved magnetic modulation up to 1.4 T. It is found that the ground layer reduces the inductance, and increases the modulation depth and symmetricity of the gradiometer design in the absence of the field. However, the layer is not compatible with the use of the scanning SQUID probe in the field because it decreases its working field range. Moreover, by adding the layer, the mutual inductance between the feedback coil and the SQUID also decreases linearly as a function of the field.
|
|
$\mathcal{PT}$ Symmetry of a Square-Wave Modulated Two-Level System
Liwei Duan, Yan-Zhi Wang, and Qing-Hu Chen
Chin. Phys. Lett. 2020, 37 (8):
081101
.
DOI: 10.1088/0256-307X/37/8/081101
We study a non-Hermitian two-level system with square-wave modulated dissipation and coupling. Based on the Floquet theory, we achieve an effective Hamiltonian from which the boundaries of the $\mathcal{PT}$ phase diagram are captured exactly. Two kinds of $\mathcal{PT}$ symmetry broken phases are found, whose effective Hamiltonians differ by a constant $\omega / 2$. For the time-periodic dissipation, a vanishingly small dissipation strength can lead to the $\mathcal{PT}$ symmetry breaking in the $(2k-1)$-photon resonance ($\varDelta = (2k-1) \omega$), with $k=1,2,3\dots$ It is worth noting that such a phenomenon can also happen in $2k$-photon resonance ($\varDelta = 2k \omega$), as long as the dissipation strengths or the driving times are imbalanced, namely $\gamma_0 \ne - \gamma_1$ or $T_0 \ne T_1$. For the time-periodic coupling, the weak dissipation induced $\mathcal{PT}$ symmetry breaking occurs at $\varDelta_{\rm eff}=k\omega$, where $\varDelta_{\rm eff}=(\varDelta_0 T_0 + \varDelta_1 T_1)/T$. In the high frequency limit, the phase boundary is given by a simple relation $\gamma_{\rm eff}=\pm\varDelta_{\rm eff}$.
|
|
Electro-Optically Switchable Optical True Delay Lines of Meter-Scale Lengths Fabricated on Lithium Niobate on Insulator Using Photolithography Assisted Chemo-Mechanical Etching
Jun-xia Zhou, Ren-hong Gao, Jintian Lin, Min Wang, Wei Chu, Wen-bo Li, Di-feng Yin, Li Deng, Zhi-wei Fang, Jian-hao Zhang, Rong-bo Wuand Ya Cheng
Chin. Phys. Lett. 2020, 37 (8):
084201
.
DOI: 10.1088/0256-307X/37/8/084201
Optical true delay lines (OTDLs) of low propagation losses, small footprints and high tuning speeds and efficiencies are of critical importance for various photonic applications. Here, we report fabrication of electro-optically switchable OTDLs on lithium niobate on insulator using photolithography assisted chemo-mechanical etching. Our device consists of several low-loss optical waveguides of different lengths which are consecutively connected by electro-optical switches to generate different amounts of time delay. The fabricated OTLDs show an ultra-low propagation loss of $\sim 0.03$ dB/cm for waveguide lengths well above 100 cm.
|
|
Temperature Gradient, Toroidal and Ion FLR Effects on Drift-Tearing Modes
Hao Shi, Wenlu Zhang, Chao Dong, Jian Bao, Zhihong Lin, Jintao Cao, and Ding Li
Chin. Phys. Lett. 2020, 37 (8):
085201
.
DOI: 10.1088/0256-307X/37/8/085201
The influences of the temperature gradient and toroidal effects on drift-tearing modes have been studied using the Gyrokinetic Toroidal code. After the thermal force term is introduced into the parallel electron force balance equation, the equilibrium temperature gradient can cause a significant increase in the growth rate of the drift-tearing mode and a broadening of the mode structure. The simulation results show that the toroidal effects increase the growth rate of the drift-tearing mode, and the contours of the perturbation field “squeeze” toward the stronger field side in the poloidal section. Finally, the hybrid model for fluid electrons and kinetic ions has been studied briefly, and the dispersion relation of the drift-tearing mode under the influence of ion finite Larmor radius effects is obtained. Compared with the dispersion relation under the fluid model, a stabilizing effect of the ion finite Larmor radius is observed.
|
|
Coupling between Particle Shape and Long-Range Interaction in the High-Density Regime
Can-can Zhou, Hongchuan Shen, Hua Tong, Ning Xu, and Peng Tan
Chin. Phys. Lett. 2020, 37 (8):
086301
.
DOI: 10.1088/0256-307X/37/8/086301
We experimentally probe the coupling between particle shape and long-range interaction, using long-range interacting polygons. For two typical space-filling polygons, square and triangle, we find two types of coupling modes that predominantly control the structure formation. Specifically, the rotational ordering of squares brings a lattice deformation that produces a hexagonal-to-rhombic transition in the high density regime, whereas the alignment of triangles introduces a large geometric frustration that causes an order-to-disorder transition. Moreover, the two coupling modes lead to small and large “internal roughness” of the two systems, and thus predominantly control their structure relaxations. Our study thus provides a physical picture to the coupling between long-range interaction effect and short-range shape effect in the high-density regime unexplored before.
|
|
de Haas–van Alphen Quantum Oscillations in BaSn$_{3}$ Superconductor with Multiple Dirac Fermions
Gaoning Zhang, Xianbiao Shi, Xiaolei Liu, Wei Xia, Hao Su, Leiming Chen, Xia Wang, Na Yu, Zhiqiang Zou, Weiwei Zhao, and Yanfeng Guo
Chin. Phys. Lett. 2020, 37 (8):
087101
.
DOI: 10.1088/0256-307X/37/8/087101
Characterization of Fermi surface of the BaSn$_{3}$ superconductor ($T_{\rm c} \sim 4.4$ K) by de Haas–van Alphen (dHvA) effect measurement reveals its non-trivial topological properties. Analysis of non-zero Berry phase is supported by the ab initio calculations, which reveals a type-II Dirac point setting and tilting along the high symmetric $K$–$H$ line of the Brillouin zone, about 0.13 eV above the Fermi level, and other two type-I Dirac points on the high symmetric $\varGamma$–$A$ direction, but slightly far below the Fermi level. The results demonstrate BaSn$_{3}$ as an excellent example hosting multiple Dirac fermions and an outstanding platform for studying the interplay between nontrivial topological states and superconductivity.
|
|
Experimental Observation of Electronic Structures of Kagome Metal YCr$_{6}$Ge$_{6}$
Pengdong Wang, Yihao Wang, Bo Zhang, Yuliang Li, Sheng Wang, Yunbo Wu, Hongen Zhu, Yi Liu, Guobin Zhang, Dayong Liu, Yimin Xiong, and Zhe Sun
Chin. Phys. Lett. 2020, 37 (8):
087102
.
DOI: 10.1088/0256-307X/37/8/087102
Using angle-resolved photoemission spectroscopy, we study electronic structures of a Kagome metal YCr$_{6}$Ge$_{6}$. Band dispersions along $k_{z}$ direction are significant, suggesting a remarkable interlayer coupling between neighboring Kagome planes. Comparing ARPES data with first-principles calculations, we find a moderate electron correlation in this material, since band calculations must be compressed in the energy scale to reach an excellent agreement between experimental data and theoretical calculations. Moreover, as indicated by band calculations, there is a flat band in the vicinity of the Fermi level at the $\varGamma$–$M$–$K$ plane in the momentum space, which could be responsible for the unusual transport behavior in YCr$_{6}$Ge$_{6}$.
|
|
Type-II Dirac Semimetal State in a Superconductor Tantalum Carbide
Zhihai Cui, Yuting Qian, Wei Zhang, Hongming Weng, and Zhong Fang
Chin. Phys. Lett. 2020, 37 (8):
087103
.
DOI: 10.1088/0256-307X/37/8/087103
The exploration of topological Dirac semimetals with intrinsic superconductivity can be a most plausible way to discover topological superconductors. We propose that type-II Dirac semimetal states exist in the band structure of TaC, a well-known s-wave superconductor, by using the first-principles calculations and the ${\boldsymbol{k} \cdot {\boldsymbol p}}$ effective model. The tilted gapless Dirac cones, which are composed of Ta $d$ and C $p$ orbitals and are protected by $C_{4v}$ symmetry, are found to be below the Fermi level. The bands from Ta $d$ orbitals are greatly coupled with the acoustic modes around the zone boundary, indicating their significant contribution to the superconductivity. The relatively high transition temperature $\sim$10.5 K is estimated to be consistent with the experimental data. To bring the type-II Dirac points close to chemical potential, hole doping is needed. This seems to decrease the transition temperature a lot, making the realization of topological superconductivity impossible.
|
|
Predicting the Potential Performance in P-Type SnS Crystals via Utilizing the Weighted Mobility and Quality Factor
Wenke He , Bingchao Qin , and Li-Dong Zhao
Chin. Phys. Lett. 2020, 37 (8):
087104
.
DOI: 10.1088/0256-307X/37/8/087104
The figure of merit $ZT$ is the direct embodiment of thermoelectric performance for a given material. However, as an indicator of performance improvement, the only $ZT$ value is not good enough to identify its outstanding inherent properties, which are highly sought in thermoelectric community. Here, we utilize one powerful parameter to reveal the outstanding properties of a given material. The weighted mobility is used to estimate the carrier transports of p-type SnS crystals, including the differences in doping level, carrier scattering and electronic band structure. We analyze the difference in carrier scattering mechanism for different crystal forms with the same doping level, then evaluate and confirm the temperature-dependent evolution of electronic band structures in SnS. Finally, we calculate the quality factor $B$ based on the weighted mobility, and establish the relationship between $ZT$ and $B$ to further predict the potential performance in p-type SnS crystals with low cost and earth abundance, which can be realized through taking advantage of the inherent material property, thus improving $B$ factor to achieve optimal thermoelectric level.
|
|
Symmetry-Assisted Protection and Compensation of Hidden Spin Polarization in Centrosymmetric Systems
Yingjie Zhang, Pengfei Liu, Hongyi Sun, Shixuan Zhao, Hu Xu, and Qihang Liu
Chin. Phys. Lett. 2020, 37 (8):
087105
.
DOI: 10.1088/0256-307X/37/8/087105
It was recently noted that in certain nonmagnetic centrosymmetric compounds, spin–orbit interactions couple each local sector that lacks inversion symmetry, leading to visible spin polarization effects in the real space, dubbed “hidden spin polarization (HSP)”. However, observable spin polarization of a given local sector suffers interference from its inversion partner, impeding material realization and potential applications of HSP. Starting from a single-orbital tight-binding model, we propose a nontrivial way to obtain strong sector-projected spin texture through the vanishing hybridization between inversion partners protected by nonsymmorphic symmetry. The HSP effect is generally compensated by inversion partners near the ${\varGamma}$ point but immune from the hopping effect around the boundary of the Brillouin zone. We further summarize 17 layer groups that support such symmetry-assisted HSP and identify hundreds of quasi-2D materials from the existing databases by first-principle calculations, among which a group of rare-earth compounds LnIO (Ln = Pr, Nd, Ho, Tm, and Lu) serves as great candidates showing strong Rashba- and Dresselhaus-type HSP. Our findings expand the material pool for potential spintronic applications and shed light on controlling HSP properties for emergent quantum phenomena.
|
|
Structure-Spin-Transport Anomaly in Quasi-One-Dimensional Ba$_{9}$Fe$_{3}$Te$_{15}$ under High Pressure
Jun Zhang, Mei-Ling Jin, Xiang Li, Xian-Cheng Wang, Jian-Fa Zhao, Ying Liu, Lei Duan, Wen-Min Li, Li-Peng Cao, Bi-Juan Chen, Li-Juan Wang, Fei Sun, Yong-Gang Wang, Liu-Xiang Yang, Yu-Ming Xiao, Zheng Deng, Shao-Min Feng, Chang-Qing Jin, and Jin-Long Zhu
Chin. Phys. Lett. 2020, 37 (8):
087106
.
DOI: 10.1088/0256-307X/37/8/087106
Recently, a series of novel compounds Ba$_{3}$MX$_{5}$ (M = Fe, Ti, V; X = Se, Te) with hexagonal crystal structures composed of quasi-1-dimensional (1D) magnetic chains has been synthesized by our research team using high-pressure and high-temperature methods. The initial hexagonal phases persist to the maximum achievable pressure, while spin configurations and magnetic interactions may change dramatically as a result of considerable reductions in interchain separations upon pressurization. These compounds therefore offer unique possibilities for studying the evolution of intrinsic electronic structures in quasi-1D magnetic systems. Here we present a systematic investigation of Ba$_{9}$Fe$_{3}$Te$_{15}$, in which the interchain separations between trimerized 1D chains ($\sim $10.2 Å) can be effectively modulated by external high pressure. The crystal structure especially along the 1D chains exhibits an abnormal expansion at $\sim $5 GPa, which accompanies trimerization entangled anomalous mixed-high-low spin transition. An insulator-metal transition has been observed under high pressure as a result of charge-transfer gap closing. Pressure-induced superconductivity emerges at 26 GPa, where the charge-transfer gap fully closes, 3D electronic configuration forms and local spin fully collapses.
|
|
Zirconium Aided Epitaxial Growth of In$_{x}$Se$_{y}$ on InP(111) Substrates
Cheng Zheng, Dapeng Zhao, Xinqiang Cai, Wantong Huang, Fanqi Meng, Qinghua Zhang, Lin Tang, Xiaopeng Hu, Lin Gu, Shuai-Hua Ji, Xi Chen
Chin. Phys. Lett. 2020, 37 (8):
087401
.
DOI: 10.1088/0256-307X/37/8/087401
Layered material indium selenide (In$_{x}$Se$_{y}$) is a promising candidate for building next-generation electronic and photonic devices. We report a zirconium aided MBE growth of this van der Waals material. When co-depositing zirconium and selenium onto an indium phosphide substrate with a substrate temperature of 400℃ at a constant zirconium flux rate of 0.01 ML/min, the polymorphic In$_{x}$Se$_{y}$ layer emerges on top of the insulating ZrSe$_{2}$ layer. Different archetypes, such as InSe, $\alpha$-In$_{2}$Se$_{3}$ and $\beta$-In$_{2}$Se$_{3}$, are found in the In$_{x}$Se$_{y}$ layers. A negative magnetoresistance of 40% at 2 K under 9 T magnetic field is observed. Such an In$_{x}$Se$_{y}$/ZrSe$_{2}$ heterostructure with good lattice-matching may serve as a candidate for device applications.
|
|
Electronic Evolution from the Parent Mott Insulator to a Superconductor in Lightly Hole-Doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$
Qiang Gao, Lin Zhao, Cheng Hu, Hongtao Yan, Hao Chen, Yongqing Cai, Cong Li, Ping Ai, Jing Liu, Jianwei Huang, Hongtao Rong, Chunyao Song, Chaohui Yin, Qingyan Wang, Yuan Huang, Guo-Dong Liu, Zu-Yan Xu, and Xing-Jiang Zhou
Chin. Phys. Lett. 2020, 37 (8):
087402
.
DOI: 10.1088/0256-307X/37/8/087402
High temperature superconductivity in cuprates is realized by doping the Mott insulator with charge carriers. A central issue is how such an insulating state can evolve into a conducting or superconducting state when charge carriers are introduced. Here, by in situ vacuum annealing and Rb deposition on the Bi$_2$Sr$_2$Ca$_{0.6}$Dy$_{0.4}$Cu$_2$O$_{8+\delta}$ (Bi2212) sample surface to push its doping level continuously from deeply underdoped ($T_{\rm c}=25$ K, doping level $p\sim0.066$) to the near-zero doping parent Mott insulator, angle-resolved photoemission spectroscopy measurements are carried out to observe the detailed electronic structure evolution in the lightly hole-doped region for the first time. Our results indicate that the chemical potential lies at about l eV above the charge transfer band for the parent state at zero doping, which is quite close to the upper Hubbard band. With increasing hole doping, the chemical potential moves continuously towards the charge transfer band and the band structure evolution exhibits a rigid band shift-like behavior. When the chemical potential approaches the charge transfer band at a doping level of $\sim$0.05, the nodal spectral weight near the Fermi level increases, followed by the emergence of the coherent quasiparticle peak and the insulator–superconductor transition. Our observations provide key insights in understanding the insulator–superconductor transition in doping the parent cuprate compound and for establishing related theories.
|
|
Mode Structures and Damping of Quantized Spin Waves in Ferromagnetic Nanowires
Qingwei Fu, Yong Li, Lina Chen, Fusheng Ma, Haotian Li, Yongbing Xu, Bo Liu, Ronghua Liu, and Youwei Du
Chin. Phys. Lett. 2020, 37 (8):
087503
.
DOI: 10.1088/0256-307X/37/8/087503
Magnonic devices based on spin waves are considered as a new generation of energy-efficient and high-speed devices for storage and processing of information. Here we experimentally demonstrate that three distinct dominated magneto-dynamic modes are excited simultaneously and coexist in a transversely magnetized ferromagnetic wire by the ferromagnetic resonance (FMR) technique. Besides the uniform FMR mode, the spin-wave well mode, the backward volume magnetostatic spin-wave mode, and the perpendicular standing spin-wave mode are experimentally observed and further confirmed with more detailed spatial profiles by micromagnetic simulation. Furthermore, our experimental approach can also access and reveal damping coefficients of these spin-wave modes, which provides essential information for development of magnonic devices in the future.
|
|
Enhancement of Curie Temperature under Built-in Electric Field in Multi-Functional Janus Vanadium Dichalcogenides
Shilei Ji , Hong Wu , Shuang Zhou , Wei Niu , Lujun Wei , Xing-Ao Li , Feng Li, and Yong Pu
Chin. Phys. Lett. 2020, 37 (8):
087505
.
DOI: 10.1088/0256-307X/37/8/087505
Functionalized two-dimensional materials with multiferroicity are highly desired to be next-generation electronic devices. Here we theoretically predict a family of Janus vanadium dichalcogenides VXX' (X/X' = S, Se, Te) monolayers with multiferroic properties, combing ferromagnetism, ferroelasticity and piezoelectricity. Due to the unpaired electrons on the V atom, the Janus VXX' monolayers have intrinsic long-range ferromagnetic orders. Particularly, the Curie temperature of 1T-VSeTe monolayer is up to 100 K, which is greatly higher than 2D 1T-VSe$_{2}$ and 1T-VTe$_{2}$. Furthermore, the six Janus VXX' monolayers have similar crater-like ferroelastic switching curves. Compared to black phosphorus, 2H-VSSe monolayer has the similar ferroelastic switching signal and 4 times lower energy barrier. In addition, the out-of-plane piezoelectricity induced by the structure asymmetry in the vertical direction gives the 2H-VXX' monolayers the potential to be piezoelectric materials. It is found that a built-in electric field in the vertical direction due to the different electronegativity values of chalcogen atoms induces the changes of electronic structures, which leads to the appearance of three different types of band gaps in the three H-phase structures. Recently, the experimental growth of the Janus MoSSe monolayers and the electrochemical exfoliation of ferromagnetic monolayered VSe$_{2}$ make the Janus VXX' monolayers possibly fabricated in experiments.
|
|
Large Photoluminescence Enhancement by an Out-of-Plane Magnetic Field in Exfoliated WS$_2$ Flakes
Sibai Sun, Jianchen Dang, Xin Xie, Yang Yu, Longlong Yang, Shan Xiao, Shiyao Wu, Kai Peng, Feilong Song, Yunuan Wang, Jingnan Yang, Chenjiang Qian, Zhanchun Zuo, and Xiulai Xu
Chin. Phys. Lett. 2020, 37 (8):
087801
.
DOI: 10.1088/0256-307X/37/8/087801
We report an out-of-plane magnetic field induced large photoluminescence enhancement in WS$_2$ flakes at $4$ K, in contrast to the photoluminescence enhancement provided by an in-plane field in general. Two mechanisms for the enhancement are proposed. One is a larger overlap of the electron and hole caused by the magnetic field induced confinement. The other is that the energy difference between $\varLambda$ and $K$ valleys is reduced by magnetic field, and thus enhancing the corresponding indirect-transition trions. Meanwhile, the Landé $g$ factor of the trion is measured to be $-0.8$, whose absolute value is much smaller than normal exciton, which is around $|-4|$. A model for the trion $g$ factor is presented, confirming that the smaller absolute value of the Landé $g$ factor is a behavior of this $\varLambda$–$K$ trion. By extending the valley space, we believe this work provides a further understanding of the valleytronics in monolayer transition metal dichalcogenides.
|
|
Effect of Dopant Concentration in a Base Layer on Photocurrent–Voltage Characteristics of Photovoltaic Power Converters
Wen-Xue Huo, Ming-Long Zhao, Xian-Sheng Tang, Li-Li Han, Zhen Deng, Yang Jiang, Wen-Xin Wang, Hong Chen, Chun-Hua Du, and Hai-Qiang Jia
Chin. Phys. Lett. 2020, 37 (8):
087802
.
DOI: 10.1088/0256-307X/37/8/087802
It is known that the p–n junction of an absorption region is a crucial part for power conversion efficiency of photovoltaic power converters. We fabricate four samples with different dopant concentrations in base layers. The dependences of power conversion efficiency and fill factor on input power are displayed by photocurrent–voltage measurement. Photoluminescence characteristics under open circuit and connected circuit conditions are also studied. It is found that the status of p–n junction matching is the critical factor in affecting the power conversion efficiency. In addition, series resistance of photovoltaic power converters impairs the efficiency especially at high input powers. Both the key factors need to be considered to obtain high efficiency, and this work provides promising guidance on designing photovoltaic power converters.
|
|
Polymer-Decorated 2D MoS$_{2}$ Synaptic Transistors for Biological Bipolar Metaplasticities Emulation
Yuhang Zhao , Biao Liu , Junliang Yang , Jun He, and Jie Jiang
Chin. Phys. Lett. 2020, 37 (8):
088501
.
DOI: 10.1088/0256-307X/37/8/088501
Biological bipolar metaplasticities were successfully mimicked in two-dimensional (2D) MoS$_{2}$ transistors via the implementation of two different MoS$_{2}$ surface decorations, poly (vinyl alcohol) (PVA) and chitosan bio-polymers. Interestingly, the depressing metaplasticity was successfully mimicked when the PVA bio-polymer was used as the surface decoration layer, whereas the metaplasticity of long-term potentiation was realized when the chitosan bio-polymer was taken as the surface decoration layer. Furthermore, the electronic band structures of the 2D MoS$_{2}$ devices with different surface decorations were further investigated using first-principles calculations for understanding the underlying mechanisms of such bipolar metaplasticities. These results will deepen our understanding of metaplasticity, and have great potential in neuromorphic computing applications.
|
|
Normal Strain-Induced Tunneling Behavior Promotion in van der Waals Heterostructures
Yi-Fan He , Lei-Xi Wang , Zhi-Xing Xiao , Ya-Wei Lv, Lei Liao , and Chang-Zhong Jiang
Chin. Phys. Lett. 2020, 37 (8):
088502
.
DOI: 10.1088/0256-307X/37/8/088502
Van der Waals heterostructures (vdWHs) realized by vertically stacking of different two-dimensional (2D) materials are a promising candidate for tunneling devices because of their atomically clean and lattice mismatch-free interfaces in which different layers are separated by the vdW gaps. The gaps can provide an ideal electric modulation environment on the vdWH band structures and, on the other hand, can also impede the electron tunneling behavior because of large tunneling widths. Here, through first-principles calculations, we find that the electrically modulated tunneling behavior is immune to the interlayer interaction, keeping a direct band-to-band tunneling manner even the vdWHs have been varied to the indirect semiconductor, which means that the tunneling probability can be promoted through the vdW gap shrinking. Using transition metal dichalcogenide heterostructures as examples and normal strains as the gap reducing strategy, a maximum shrinking of 33% is achieved without changing the direct tunneling manner, resulting in a tunneling probability promotion of more than 45 times. Furthermore, the enhanced interlayer interaction by the strains will boost the stability of the vdWHs at the lateral direction, preventing the interlayer displacement effectively. It is expected that our findings provide perspectives in improving the electric behaviors of the vdWH devices.
|
38 articles
|