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Periodic synchronization in a system of coupled phase oscillators with attractive and repulsive interactions
Di Yuan, Jun-Long Tian, Fang Lin, Dong-Wei Ma, Jing Zhang, Hai-Tao Cui, Yi Xiao
Frontiers of Physics. 2018, 13 (3 ): 130504-.
https://doi.org/10.1007/s11467-018-0748-4
In this study we investigate the collective behavior of the generalized Kuramoto model with an external pinning force in which oscillators with positive and negative coupling strengths are conformists and contrarians, respectively. We focus on a situation in which the natural frequencies of the oscillators follow a uniform probability density. By numerically simulating the model, it is shown that the model supports multistable synchronized states such as a traveling wave state, π state and periodic synchronous state: an oscillating π state. The oscillating π state may be characterized by the phase distribution oscillating in a confined region and the phase difference between conformists and contrarians oscillating around π periodically. In addition, we present the parameter space of the oscillating π state and traveling wave state of the model.
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Discrete ellipsoidal statistical BGK model and Burnett equations
Yu-Dong Zhang, Ai-Guo Xu, Guang-Cai Zhang, Zhi-Hua Chen, Pei Wang
Frontiers of Physics. 2018, 13 (3 ): 135101-.
https://doi.org/10.1007/s11467-018-0749-3
A new discrete Boltzmann model, the discrete ellipsoidal statistical Bhatnagar–Gross–Krook (ESBGK) model, is proposed to simulate nonequilibrium compressible flows. Compared with the original discrete BGK model, the discrete ES-BGK has a flexible Prandtl number. For the discrete ES-BGK model in the Burnett level, two kinds of discrete velocity model are introduced and the relations between nonequilibrium quantities and the viscous stress and heat flux in the Burnett level are established. The model is verified via four benchmark tests. In addition, a new idea is introduced to recover the actual distribution function through the macroscopic quantities and their space derivatives. The recovery scheme works not only for discrete Boltzmann simulation but also for hydrodynamic ones, for example, those based on the Navier–Stokes or the Burnett equations.
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First-principles calculations of nitrogen-doped antimony triselenide: A prospective material for solar cells and infrared optoelectronic devices
Sajid-ur- Rehman, Faheem K. Butt, Chuanbo Li, Bakhtiar Ul Haq, Zeeshan Tariq, F. Aleem
Frontiers of Physics. 2018, 13 (3 ): 137805-.
https://doi.org/10.1007/s11467-018-0790-2
This study is focused on calculation of the electronic structure and optical properties of non-metal doped Sb2Se3 using the first-principles method. One and two N atoms are introduced to Sb and Se sites in a Sb2 Se3 crystal. When one and two N atoms are introduced into the Sb2 Se3 lattice at Sb sites, the electronic structure shows that the doping significantly modifies the bandgap of Sb2 Se3 from 1.11 eV to 0.787 and 0.685 eV, respectively. When N atoms are introduced to Se sites, the material shows a metallic behavior. The static dielectric constants ε 1(0) for Sb16 Se24 , Sb15 N1 Se24 , Sb14 N2 Se24 , Sb16 Se23 N1 , and Sb16 Se22 N2 are 14.84, 15.54, 15.02, 18.9, and 39.29, respectively. The calculated values of the refractive index n (0) for Sb16 Se24 , Sb15 N1 Se24 , Sb14 N2 Se24 , Sb16 Se23 N1 , and Sb16 Se22 N2 are 3.83, 3.92, 3.86, 4.33, and 6.21, respectively. The optical absorbance and optical conductivity curves of the crystal for N-doping at Sb sites show a significant redshift towards the short-wave infrared spectral region as compared to N-doping at Se sites. The modulation of the static refractive index and static dielectric constant is mainly dependent on the doping level. The optical properties and bandgap narrowing effect suggest that the N-doped Sb2 Se3 is a promising new semiconductor and can be a replacement for GaSb due to its very similar bandgap and low cost.
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Penta-P2 X (X=C, Si) monolayers as wide-bandgap semiconductors: A first principles prediction
Mosayeb Naseri, Shiru Lin, Jaafar Jalilian, Jinxing Gu, Zhongfang Chen
Frontiers of Physics. 2018, 13 (3 ): 138102-.
https://doi.org/10.1007/s11467-018-0758-2
By means of density functional theory computations, we predicted two novel two-dimensional (2D) nanomaterials, namely P2 X (X=C, Si) monolayers with pentagonal configurations. Their structures, stabilities, intrinsic electronic, and optical properties as well as the effect of external strain to the electronic properties have been systematically examined. Our computations showed that these P2 C and P2 Si monolayers have rather high thermodynamic, kinetic, and thermal stabilities, and are indirect semiconductors with wide bandgaps (2.76 eV and 2.69 eV, respectively) which can be tuned by an external strain. These monolayers exhibit high absorptions in the UV region, but behave as almost transparent layers for visible light in the electromagnetic spectrum. Their high stabilities and exceptional electronic and optical properties suggest them as promising candidates for future applications in UV-light shielding and antireflection layers in solar cells.
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Interfacial properties of black phosphorus/transition metal carbide van der Waals heterostructures
Hao Yuan, Zhenyu Li
Frontiers of Physics. 2018, 13 (3 ): 138103-.
https://doi.org/10.1007/s11467-018-0759-1
Owing to its outstanding electronic properties, black phosphorus (BP) is considered as a promising material for next-generation optoelectronic devices. In this work, devices based on BP/MXene (Zrn +1 Cn T2 , T= O, F, OH, n = 1, 2) van der Waals (vdW) heterostructures are designed via first-principles calculations. Zrn +1 Cn T2 compositions with appropriate work functions lead to the formation of Ohmic contact with BP in the vertical direction. Low Schottky barriers are found along the lateral direction in BP/Zr2 CF2 , BP/Zr2 CO2 H2 , BP/Zr3 C2 F2 , and BP/Zr3 C2 O2 H2 bilayers, and BP/Zr3 C2 O2 even exhibits Ohmic contact behavior. BP/Zr2 CO2 is a semiconducting heterostructure with type-II band alignment, which facilitates the separation of electron-hole pairs. The band structure of BP/Zr2 CO2 can be effectively tuned via a perpendicular electric field, and BP is predicted to undergo a transition from donor to acceptor at a 0.4 V/Å electric field. The versatile electronic properties of the BP/MXene heterostructures examined in this work highlight their promising potential for applications in electronics.
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Recent progress on borophene: Growth and structures
Longjuan Kong, Kehui Wu, Lan Chen
Frontiers of Physics. 2018, 13 (3 ): 138105-.
https://doi.org/10.1007/s11467-018-0752-8
Boron is the neighbor of carbon on the periodic table and exhibits unusual physical characteristics derived from electron-deficient, highly delocalized covalent bonds. As the nearest neighbor of carbon, boron is in many ways similar to carbon, such as having a short covalent radius and the flexibility to adopt sp 2 hybridization. Hence, boron could be capable of forming monolayer structural analogues of graphene. Although many theoretical papers have reported finding two-dimensional allotropes of boron, there had been no experimental evidence for such atom-thin boron nanostructures until 2016. Recently, the successful synthesis of single-layer boron (referred to as borophene) on the Ag(111) substrate opens the era of boron nanostructures. In this brief review, we will discuss the progress that has been made on borophene in terms of synthetic techniques, characterizations and the atomic models. However, borophene is just in infancy; more efforts are expected to be made in future on the controlled synthesis of quality samples and tailoring its physical properties.
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Epitaxial growth of highly strained antimonene on Ag(111)
Ya-Hui Mao, Li-Fu Zhang, Hui-Li Wang, Huan Shan, Xiao-Fang Zhai, Zhen-Peng Hu, Ai-Di Zhao, Bing Wang
Frontiers of Physics. 2018, 13 (3 ): 138106-.
https://doi.org/10.1007/s11467-018-0757-3
The synthesis of antimonene, which is a promising group-V 2D material for both fundamental studies and technological applications, remains highly challenging. Thus far, it has been synthesized only by exfoliation or growth on a few substrates. In this study, we show that thin layers of antimonene can be grown on Ag(111) by molecular beam epitaxy. High-resolution scanning tunneling microscopy combined with theoretical calculations revealed that the submonolayer Sb deposited on a Ag(111) surface forms a layer of AgSb2 surface alloy upon annealing. Further deposition of Sb on the AgSb2 surface alloy causes an epitaxial layer of Sb to form, which is identified as antimonene with a buckled honeycomb structure. More interestingly, the lattice constant of the epitaxial antimonene (5 Å) is much larger than that of freestanding antimonene, indicating a high tensile strain of more than 20%. This kind of large strain is expected to make the antimonene a highly promising candidate for roomtemperature quantum spin Hall material.
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Computational study on the half-metallicity in transition metal–oxide-incorporated 2D g-C3 N4 nanosheets
Qian Gao (高乾), Hui-Li Wang (王会丽), Li-Fu Zhang (张丽芙), Shuang-Lin Hu (胡双林), Zhen-Peng Hu (胡振芃)
Frontiers of Physics. 2018, 13 (3 ): 138108-.
https://doi.org/10.1007/s11467-018-0754-6
In this study, based on the first-principles calculations, we systematically investigated the electronic and magnetic properties of the transition metal–oxide-incorporated 2D g-C3 N4 nanosheet (labeled C3 N4 – TM–O, TM= Sc–Mn). The results suggest that the TM–O binds to g-C3 N4 nanosheets strongly for all systems. We found that the 2D C3 N4 –TM–O framework is ferromagnetic for TM= Sc, Ti, V, Cr, while it is antiferromagnetic for TM= Mn. All the ferromagnetic systems exhibit the half-metallic property. Furthermore, Monte Carlo simulations based on the Heisenberg model suggest that the Curie temperatures (T c ) of the C3 N4 –TM–O (TM= Sc, Ti, V, Cr) framework are 169 K, 68 K, 203 K, and 190 K, respectively. Based on Bader charge analysis, we found that the origin of the half-metallicity at Fermi energy can be partially attributed to the transfer of electrons from TM atoms to the g-C3 N4 nanosheet. In addition, we found that not only electrons but also holes can induce half-metallicity for 2D g-C3 N4 nanosheets, which may help to understand the origin of half-metallicity for graphitic carbon nitride.
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Two-dimensional aluminum monoxide nanosheets: A computational study
Shiru Lin, Yanchao Wang, Zhongfang Chen
Frontiers of Physics. 2018, 13 (3 ): 138109-.
https://doi.org/10.1007/s11467-018-0782-2
By means of density functional theory (DFT) computations and particle-swarm optimization (PSO) structure searches, we herein predict five low-lying energy structures of two-dimensional (2D) aluminum monoxide (AlO) nanosheets. Their high cohesive energy, absence of imaginary phonon dispersion, and good thermal stability make them feasible targets for experimental realization. These monolayers exhibit diverse structural topologies, for instance, PmA- and Pmm-AlO possess buckled four- and sixmembered AlO rings, whereas P62-, PmB-, and P6m-AlO have pores of varied sizes. Interestingly, the most energetically preferred monolayers, PmA- and Pmm-AlO, feature wide band gaps (2.45 and 5.13 eV, respectively), which are promising for green and blue light-emitting devices (LEDs) and photodetectors.
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Ultrathin nanosheets of Mn3 O4 : A new two-dimensional ferromagnetic material with strong magnetocrystalline anisotropy
Jun-Chi Wu, Xu Peng, Yu-Qiao Guo, Hao-Dong Zhou, Ji-Yin Zhao, Ke-Qin Ruan, Wang-Sheng Chu, Changzheng Wu
Frontiers of Physics. 2018, 13 (3 ): 138110-.
https://doi.org/10.1007/s11467-018-0753-7
Two-dimensional (2D) materials with robust ferromagnetism have played a key role in realizing nextgeneration spin-electronic devices, but many challenges remain, especially the lack of intrinsic ferromagnetic behavior in almost all 2D materials. Here, we highlight ultrathin Mn3 O4 nanosheets as a new 2D ferromagnetic material with strong magnetocrystalline anisotropy. Magnetic measurements along the in-plane and out-of-plane directions confirm that the out-of-plane direction is the easy axis. The 2D-confined environment and Rashba-type spin-orbit coupling are thought to be responsible for the magnetocrystalline anisotropy. The robust ferromagnetism in 2D Mn3 O4 nanosheets with magnetocrystalline anisotropy not only paves a new way for realizing the intrinsic ferromagnetic behavior in 2D materials but also provides a novel candidate for building next-generation spin-electronic devices.
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Self-folding mechanics of graphene tearing and peeling from a substrate
Ze-Zhou He, Yin-Bo Zhu, Heng-An Wu
Frontiers of Physics. 2018, 13 (3 ): 138111-.
https://doi.org/10.1007/s11467-018-0755-5
Understanding the underlying mechanism in the tearing and peeling processes of graphene is crucial for the further hierarchical design of origami-like folding and kirigami-like cutting of graphene. However, the complex effects among bending moduli, adhesion, interlayer interaction, and local crystal structure during origami-like folding and kirigami-like cutting remain unclear, resulting in challenges to the practical applications of existing theoretical and experimental findings as well as to potential manipulations of graphene in metamaterials and nanodevices. Toward this end, classical molecular dynamics (MD) simulations are performed with synergetic theoretical analysis to explore the tearing and peeling of self-folded graphene from a substrate driven by external force and by thermal activation. It is found that the elastic energy localized at the small folding ridge plays a significant role in the crack trajectory. Due to the extremely small bending modulus of monolayer graphene, its taper angle when pulled by an external force follows a scaling law distinct from that in case of bilayer graphene. With the increase in the initial width of the folding ridge, the self-folded graphene, motivated by thermal fluctuations, can be self-assembled by spontaneous self-tearing and peeling from a substrate. Simultaneously, the scaling law between the taper angle and adhesive energy is independent of the motivations for thermal activation-induced self-assembly and external force tearing, providing effective insights into the underlying physics for graphene-based origami-like folding and kirigami-like cutting.
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First-principles investigation of quantum transport in GeP3 nanoribbon-based tunneling junctions
Qiang Wang, Jian-Wei Li, Bin Wang, Yi-Hang Nie
Frontiers of Physics. 2018, 13 (3 ): 138501-.
https://doi.org/10.1007/s11467-018-0750-x
Two-dimensional (2D) GeP3 has recently been theoretically proposed as a new low-dimensional material [Nano Lett. 17(3), 1833 (2017)]. In this manuscript, we propose a first-principles calculation to investigate the quantum transport properties of several GeP3 nanoribbon-based atomic tunneling junctions. Numerical results indicate that monolayer GeP3 nanoribbons show semiconducting behavior, whereas trilayer GeP3 nanoribbons express metallic behavior owing to the strong interaction between each of the layers. This behavior is in accordance with that proposed in two-dimensional GeP3 layers. The transmission coefficient T (E ) of tunneling junctions is sensitive to the connecting formation between the central monolayer GeP3 nanoribbon and the trilayer GeP3 nanoribbon at both ends. The T (E ) value of the bottom-connecting tunneling junction is considerably larger than those of the middle-connecting and top-connecting ones. With increases in gate voltage, the conductances increase for the bottom-connecting and middle-connecting tunneling junctions, but decrease for the top-connecting tunneling junctions. In addition, the conductance decreases exponentially with respect to the length of the central monolayer GeP3 nanoribbon for all the tunneling junctions. I –V curves show approximately linear behavior for the bottom-connecting and middle-connecting structures, but exhibit negative differential resistance for the top-connecting structures. The physics of each phenomenon is analyzed in detail.
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