摘要：
One-dimensional nanotubes have become an indispensable ideal candidate material for nano-device applications due to their excellent and unique electronic, mechanical, and thermal properties. By the first-principles method of density functional theory, we have theoretically investigated the structural stability, electronic properties, carrier mobility, and Poisson's ratio of C3N single-walled nanotubes (C3NSWNT). We find that C3NSWNT is stable and the ground state of the system is non-magnetic. The electronic properties and carrier mobilities of C3NSWNT can be adjusted by diameter and edge engineering. The electron mobility of (n,n) armchair C3NSWNT (A-C3NSWNT) is lower than that of (n,0) zigzag C3NSWNT (Z-C3NSWNT), but the hole mobility of (n,n) A-C3NSWNT is higher than that of (n,0) Z-C3NSWNT. Moreover, both A-C3NSWNT and Z-C3NSWNT can transfer from semiconductor to metal by tuning the electric field, and Z-C3NSWNT is more sensitive to the applied electric field than A-C3NSWNT due to smaller energy gap. But only A-C3NSWNT can transfer from semiconductor to metal by tuning strain, and be more suitable to the application in nano electromechanical switching devices. These research results may provide some theoretical support for the potential application and development of nanoelectronic devices based on C3NSWNT.
摘要：
Based on the first-principles calculations and the non-equilibrium Green's function method, we theoretically investigate the transport property of zigzag phosphorene nanoribbons (ZPNRs) passivated with different atoms, such as N, C, N, O, H. We found that the O-passivated ZPNR is the most stable structure. ZPNRs can be semiconductor and metallic phases, depending sensitively on the passivated atoms at the edges of the ZPNRs. We find that the system can be a metal/semiconductor junction, displaying a pronounced negative differential resistance with a large peak-to-valley under a bias. This feature provides us a new way to amplify and convert DC signal to AC output, construct phosphorene-based oscillator and amplifier.
摘要：
We demonstrate theoretically the anisotropic quantum transport of electrons through an electric field on monolayer and multilayer phosphorene. Using the long-wavelength Hamiltonian with continuum approximation, we find that the transmission probability for transport through an electric field is an oscillating function of incident angle, electric field intensity, as well as the incident energy of electrons. By tuning the electric field intensity and incident angle, the channels can be transited from opaque to transparent. The conductance through the quantum waveguides depends sensitively on the transport direction because of the anisotropic effective mass, and the anisotropy of the conductance can be tuned by the electric field intensity and the number of layers. These behaviors provide us an efficient way to control the transport of phosphorene-based microstructures.
摘要：
We theoretically investigate the transport through a planar magnetic and electric barrier on the surface of monolayer black phosphorus (BP). In monolayer BP superlattice system, there are two different kinds of mechanics that block the transmission: One comes from the shift of gap in the energy spectrum induced by the magnetic field, the other comes from the enhanced superlattice minigap effect by the resonant coupling. There is strong anisotropic conductances along different directions, which caused by unique band structure. We find that the conductance ratio can be equal to 1 or -1, which can be controlled by tuning the incident energy, the magnetic field and the number of parallel magnetic modulation. This behavior offers us an efficient way to control the anisotropy transport and pave a way to construct monolayer black phosphorus-based electronic devices.
摘要：
We investigate theoretically the effect of periodic magnetic barriers on the transport for a Weyl semimetal. We find that there are momentum and spin filtering tunneling behaviors, which is controlled by the numbers of the magnetic barriers. For the tunneling through periodic square-shaped magnetic barriers, the transmission is angular φ asymmetry, and the asymmetrical transmission probability becomes more pronounced with increasing the superlattice number n. However, the transmission is symmetric with respect to angle γ, and the window of the transmission become more and more narrower with increasing the number of barriers, i.e., the collimator behavior. This feature comes from the electron Fabry-Pérot modes among the barriers. We find that the constructive interference of the backscattering amplitudes suppress transmissions, and consequently form the minigaps of the transmission. The transmission can be switched on/off by tuning the incident energies and angles, the heights and numbers of the magnetic barriers, and result in the interesting collimator behavior.
作者机构：
[Huang, Yongwei; Lou, Wenkai; Chang, Kai] Chinese Acad Sci, Inst Semicond, SKLSM, POB 912, Beijing 100083, Peoples R China.;[Huang, Yongwei; Lou, Wenkai; Chang, Kai] Univ Chinese Acad Sci, CAS Ctr Excellence Topol Quantum Computat, Beijing 100190, Peoples R China.;[Cheng, Fang] Changsha Univ Sci & Technol, Dept Phys & Elect Sci, Changsha 410004, Hunan, Peoples R China.;[Yang, Wen] Beijing Computat Sci Res Ctr, Beijing 100193, Peoples R China.
通讯机构：
[Yang, Wen] B;Beijing Computat Sci Res Ctr, Beijing 100193, Peoples R China.
摘要：
Terahertz (THz) radiation sources ranging from 0.3 to 10 THz are the last frontier of the light spectrum because of the relative lack of physical systems that can operate in this regime, the well-known "THz gap." We propose a mechanism for frequency down-conversion to produce THz radiation covering most of the THz gap by utilizing the approximately equidistant helical edge states in topological insulator quantum dots. If the edge-state level separation inside the phonon gap is chosen to suppress phonon-induced nonradiative decay, a topological insulator quantum dot array in a resonant cavity can form a continuous-wave THz laser operating at room temperature, with an output power reaching 28 mW at similar to 3 THz and an energy conversion efficiency of similar to 14%. Our work may pave the way to applications of topological insulator quantum dots for THz emission.
摘要：
Cutting two-dimensional (2D) CN2 sheet along specific crystallographic orientations to construct CN2 nanoribbon, its electronic structure is investigated systemically. We show by first-principles calculations that the electronic properties of CN2 nanoribbon exhibit response to applied electric field and strain. The lowest conduction band and highest valence bands of the spin-up and spin-down states approach to the Fermi level respectively with increasing the strength of the electric field and tensile strain. More interestingly, an applied electric field can transform the nature of the CN2 nanoribbon from semiconductor to metal. These results provides us an efficient way to design spintronic devices based on the CN2 nanoribbons.
摘要：
Exploring half-metallic nanostructures is a crucial solution for developing high-performance spintronic devices. Black phosphorene is an emerging two-dimensional material possessing strong anisotropic band structure and high mobility. Based on the first principles calculations, we investigated the electronic and magnetic properties of zigzag phosphorene nanoribbons (ZPNRs) with three different functionalization groups (OH/CN, OH/NO2, NH2/NO2) at the edges. We find that the interplay between edge functionalization and edge oxidation can induce the half metal phase in the ZPNRs, and the half metal phase can be controlled by the external transverse in-plane electric field and the proportion of the functional groups and edge oxidation. The results may pave a new way to construst nanoscale spintronic devices based on black phosphorene nanoribbons.
摘要：
We investigate quantum transport of carriers through a strained region on monolayer phosphorene theoretically. The electron tunneling is forbidden when the incident angle exceeds a critical value. The critical angles for electrons tunneling through a strain region for different strengths and directions of the strains are different. Owing to the anisotropic effective masses, the conductance shows a strong anisotropic behavior. By tuning the Fermi energy and strain, the channels can be transited from opaque to transparent, which provides us with an efficient way to control the transport of monolayer phosphorene-based microstructures.
摘要：
We theoretically investigate the transport in a magnetic/normal/magetic hybrid structure on the surface of a Weyl semimetal. We find a directional-dependent tunneling which is sensitive to the magnetic field configuration and the electric gate voltage. The momentum filtering behavior becomes more significant for two-delta-function-shaped magnetic barriers. There are many Fabry-Pérot resonances in the transmission determined by the distance between the two magnetic barriers. The combined effects of the magnetic field and the electrostatic potential can enhance the difference in the transmission between the parallel and antiparallel magnetization configurations, and consequently lead to a giant magnetoresistance.
摘要：
We investigate theoretically quantum transport through a single barrier on monolayer MoS2. It is found that the transmission properties of spin-up (down) electrons in the K valley are the same as spin-down (up) electrons in the K′ valley due to the time-reversal symmetry. Generally, the transmission probability for transport through an nnn (or ppp) junction is an oscillating function of incident angle, barrier height, as well as the incident energy of electrons. The present transmission shows a directional-dependent tunneling depending sensitively on the spin orientation for transport through a ppp junction. While for transport through an npn junction, monolayers of MoS2 become opaque for almost all angles of incident θ0 except for θ0 ∼ θ0m (the resonant angles). The positions and numbers of resonant peaks in the transmission are determined by the distance between the two barriers and the spin orientation. The conductance in such systems can be tuned significantly by changing the height of the electric potential.
