We investigate theoretically the electron transport for a two-level quantum channel （wire） with Rashba spinorbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures....We investigate theoretically the electron transport for a two-level quantum channel （wire） with Rashba spinorbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures. Using the method of equation of motion for Keldysh nonequilibrium Green function, we examine the time-averaged spin polarized conductance for the system with photon polarization parallel to the wire direction. By analytical analysis and a few numerical examples, the interplay effects of the external laser field and the Rashba spin-orbit coupling on the spinpolarized conductance for the system are demonstrated and discussed. It is found that the longitudinally-polarized laser field can adjust the spin polarization rate and produce some photon sideband resonances of the conductance for the system.展开更多
The spin-dependent electronic transport properties of a zigzag zinc oxide(ZnO) nanoribbon are studied by using density functional theory with non-equilibrium Green's functions. We calculate the spin-polarized band...The spin-dependent electronic transport properties of a zigzag zinc oxide(ZnO) nanoribbon are studied by using density functional theory with non-equilibrium Green's functions. We calculate the spin-polarized band structure, projected density of states, Bloch states, and transmission spectrum of the ZnO nanoribbon. It is determined that all Bloch states are located at the edge of the ZnO nanoribbon. The spin-up transmission eigenchannels are contributed from Zn 4s orbital,whereas the spin-down transmission eigenchannels are contributed from Zn 4s and O 2p orbitals. By analyzing the current-voltage curves for the opposite spins of the ZnO nanoribbon device, negative differential resistance(NDR) and spin filter effect are observed. Moreover, by constructing the ZnO nanoribbon modified by the Zn-edge defect, the spin-up current is severely suppressed because of the destruction of the spin-up transmission eigenchannels. However, the spin-down current is preserved, thus resulting in the perfect spin filter effect. Our results indicate that the ZnO nanoribbon modulated by the edge defect is a practical design for a spin filter.展开更多
Using the nonequilibrium Green＇s function method combined with the tight-binding Hamiltonian, we theoretically investigate the spin-dependent transmission probability and spin Seebeck coefficient of a crossed armchai...Using the nonequilibrium Green＇s function method combined with the tight-binding Hamiltonian, we theoretically investigate the spin-dependent transmission probability and spin Seebeck coefficient of a crossed armchair-edge graphene nanoribbon （AGNR） superl＇attice p-n junction under a perpendicular magnetic field with a ferromagnetic insulator, where junction widths Wi of 40 and 41 are considered to exemplify the effect of semiconducting and metallic AGNRs, respectively. A pristine AGNR system is metallic when the transverse layer m = 3j ＋ 2 with a positive integer j and an insulator otherwise. When stubs are present, a semiconducting AGNR junction with width W1= 40 always shows metallic behavior regardless of the potential drop magnitude, magnetization strength, stub length, and per- pendicular magnetic field strength. However, metallic or semiconducting behavior can be obtained from a metallic AGNR junction with Wi = 41 by adjusting these physical parameters. Furthermore, a metal-to-semiconductor transition can be obtained for both superlattice p-n junctions by adjust- ing the number of periods of the superlattice. In addition, the spin-dependent Seebeck coefficient and spin Seebeck coefficient of the two systems are of the same order of magnitude owing to the appearance of a transmission gap, and the maximum absolute value of the spin Seebeck coefficient reaches 370 μV/K when the optimized parameters are used. The calculated results offer new possi- bilities for designing electronic or heat-spintronic nanodevices based on the graphene superlattice p-n junction.展开更多
基金Project supported by the National Natural Science Foundation of China （Grant No 10574042）, and the Hunan Provincial Natural Science Foundation of China （Grant No 06JJ2097）.
文摘We investigate theoretically the electron transport for a two-level quantum channel （wire） with Rashba spinorbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures. Using the method of equation of motion for Keldysh nonequilibrium Green function, we examine the time-averaged spin polarized conductance for the system with photon polarization parallel to the wire direction. By analytical analysis and a few numerical examples, the interplay effects of the external laser field and the Rashba spin-orbit coupling on the spinpolarized conductance for the system are demonstrated and discussed. It is found that the longitudinally-polarized laser field can adjust the spin polarization rate and produce some photon sideband resonances of the conductance for the system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61664008 and 11604286)the Scientific Technological Innovation Team of Yan’an City,China(Grant No.2017CXTD-01)
文摘The spin-dependent electronic transport properties of a zigzag zinc oxide(ZnO) nanoribbon are studied by using density functional theory with non-equilibrium Green's functions. We calculate the spin-polarized band structure, projected density of states, Bloch states, and transmission spectrum of the ZnO nanoribbon. It is determined that all Bloch states are located at the edge of the ZnO nanoribbon. The spin-up transmission eigenchannels are contributed from Zn 4s orbital,whereas the spin-down transmission eigenchannels are contributed from Zn 4s and O 2p orbitals. By analyzing the current-voltage curves for the opposite spins of the ZnO nanoribbon device, negative differential resistance(NDR) and spin filter effect are observed. Moreover, by constructing the ZnO nanoribbon modified by the Zn-edge defect, the spin-up current is severely suppressed because of the destruction of the spin-up transmission eigenchannels. However, the spin-down current is preserved, thus resulting in the perfect spin filter effect. Our results indicate that the ZnO nanoribbon modulated by the edge defect is a practical design for a spin filter.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 11704118, 11774085, and 11404230）, the Scientific Research Fund of Hu- nan Provincial Education Department （Grant Nos. 17A193 and17C0946）, the Hunan Provincial Natural Science Foundation of China （Grant No. 2017JJ3210）, and the Foundation of Science and Technology Bureau of Sichuan Province （No. 2013JY0085）.
文摘Using the nonequilibrium Green＇s function method combined with the tight-binding Hamiltonian, we theoretically investigate the spin-dependent transmission probability and spin Seebeck coefficient of a crossed armchair-edge graphene nanoribbon （AGNR） superl＇attice p-n junction under a perpendicular magnetic field with a ferromagnetic insulator, where junction widths Wi of 40 and 41 are considered to exemplify the effect of semiconducting and metallic AGNRs, respectively. A pristine AGNR system is metallic when the transverse layer m = 3j ＋ 2 with a positive integer j and an insulator otherwise. When stubs are present, a semiconducting AGNR junction with width W1= 40 always shows metallic behavior regardless of the potential drop magnitude, magnetization strength, stub length, and per- pendicular magnetic field strength. However, metallic or semiconducting behavior can be obtained from a metallic AGNR junction with Wi = 41 by adjusting these physical parameters. Furthermore, a metal-to-semiconductor transition can be obtained for both superlattice p-n junctions by adjust- ing the number of periods of the superlattice. In addition, the spin-dependent Seebeck coefficient and spin Seebeck coefficient of the two systems are of the same order of magnitude owing to the appearance of a transmission gap, and the maximum absolute value of the spin Seebeck coefficient reaches 370 μV/K when the optimized parameters are used. The calculated results offer new possi- bilities for designing electronic or heat-spintronic nanodevices based on the graphene superlattice p-n junction.
