The magnetic behavior of a two-electron quantum dot/ring system is analytically studied with electron-electron(e-e)interaction taking into account the Rashba spin-orbit interaction(SOI)and magnetic field.The Jacobi tr...The magnetic behavior of a two-electron quantum dot/ring system is analytically studied with electron-electron(e-e)interaction taking into account the Rashba spin-orbit interaction(SOI)and magnetic field.The Jacobi transformation has been employed to separate the Hamiltonian of the system to the center of mass and relative terms.The Schrödinger equation is analytically solved,and energy spectra are obtained.Then,the magnetization and susceptibility are calculated.The magnetization decreases by raising the magnetic field without and with SOI,and also without e-e interaction.Also,the SOI slightly modifies the magnetization of the system without e-e interaction.The susceptibility displays a peak structure as the magnetic field changes from low values to high values.The susceptibility by considering e-e interaction and without the SOI is always negative and its value decreases by rising the magnetic field.The susceptibility displays a transition from diamagnetic to paramagnetic with e-e interaction and SOI.展开更多
The spin-polarized linear conductance spectrum and current–voltage characteristics in a four-quantum-dot ring embodied into Aharonov–Bohm （AB） interferometer are investigated theoretically by considering a local R...The spin-polarized linear conductance spectrum and current–voltage characteristics in a four-quantum-dot ring embodied into Aharonov–Bohm （AB） interferometer are investigated theoretically by considering a local Rashba spin–orbit interaction. It shows that the spin-polarized linear conductance and the corresponding spin polarization are each a function of magnetic flux phase at zero bias voltage with a period of 2π, and that Hubbard U cannot influence the electron transport properties in this case. When adjusting appropriately the structural parameter of inter-dot coupling and dot-lead coupling strength, the electronic spin polarization can reach a maximum value. Furthermore, by adjusting the bias voltages applied to the leads, the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situations. Based on the numerical results, such a model can be applied to the design of a spin filter device.展开更多
Calculations of electronic structures about the semiconductor quantum dot and the semiconductor quantum ring are presented in this paper. To reduce the calculation costs, for the quantum dot and the quantum ring, thei...Calculations of electronic structures about the semiconductor quantum dot and the semiconductor quantum ring are presented in this paper. To reduce the calculation costs, for the quantum dot and the quantum ring, their simplified axially symmetric shapes are utilized in our analysis. The energy dependent effective mass is taken into account in solving the Schrodinger equations in the single band effective mass approximation. The calculated results show that the energy dependent effective mass should be considered only for relatively small volume quantum dots or small quantum rings. For large size quantum materials, both the energy dependent effective mass and the parabolic effective mass can give the same results. The energy states and the effective masses of the quantum dot and the quantum ring as a function of geometric parameters are also discussed in detail.展开更多
Using the Keldysh nonequilibrium Green function and equation-of-motion technique, this paper studies the mag- netotransport through an Aharonov-Bohm （AB） ring with parallel double quantum dots coupled to ferromagnet...Using the Keldysh nonequilibrium Green function and equation-of-motion technique, this paper studies the mag- netotransport through an Aharonov-Bohm （AB） ring with parallel double quantum dots coupled to ferromagnetic leads. It calculates the transmission probability in both the equilibrium and the nonequilibrium case, analyses the conduc- tance and the tunnel magnetoresistance for various parameters, and obtains some new results. These results show that this system is provided with an excellent spin filtering property, and that a large tunnelling magnetoresistance and a negative tunnelling magnetoresistance can arise by adjusting relative parameters; these facts indicate that this system is a possible candidate for spin valve transistors, and has important applications in spintronics.展开更多
By using semiclassical theory combined with multiple-scale method, we analytically study the linear absorption and the nonlinear dynamical properties in a lifetime broadened Λ-type three-level self-assembled quantum ...By using semiclassical theory combined with multiple-scale method, we analytically study the linear absorption and the nonlinear dynamical properties in a lifetime broadened Λ-type three-level self-assembled quantum dots. It is found that this system can exhibit the transparency, and the width of the transparency window becomes wider with the increase of control light field. Interestingly, a weak probe light beam can form spatial weak-light dark solitons. When it propagates along the axial direction, the soliton will transform into a steady spatial weak-light ring dark soltion. In addition, the stability of two-dimensional spatial optical solitons is testified numerically.展开更多
We have studied the transport properties of a ring-coupled quantum dot array driven by an AC magnetic field, which is connected to two leads, and we give the response of the transport current to the dynamical localiza...We have studied the transport properties of a ring-coupled quantum dot array driven by an AC magnetic field, which is connected to two leads, and we give the response of the transport current to the dynamical localization. We found that when the ratio of the magnetic flux to the total quantum dots number is a root of the zeroth order Bessel function, dynamical localization and collapse of quasi-energy occurs and importantly~ the transport current displays a dip which is the signal of dynamical localization. The dynamical localization effect is strengthened as a result of the increase of the quantum dot number, and it is weakened on account of the increase of the dots-lead hopping rate.展开更多
This article puts forward a new method in calculating the band structures of low-dimensional semiconductor structures. In this study, the valence band structures of InAs/GaAs quantum ring and lens-shaped quantum dot a...This article puts forward a new method in calculating the band structures of low-dimensional semiconductor structures. In this study, the valence band structures of InAs/GaAs quantum ring and lens-shaped quantum dot are calculated with four-band model, in the framework of effective-mass envelope function theory. To determine the Hamiltonian matrix elements, this article develops the numerical Fourier transform method instead of the widely used analytical integral method. The valence band mixing is considered. The hole energy levels change dramatically with the geometrical parameters of the quantum ring and quantum dot. It is demonstrated that numerical Fourier transform method can be adopted in low-dimensional structures with any shape. The results of Fourier transform method are consistent with the ones of analytical integral in literature; and they are helpful for studying and fabricating optoelectronic devices.展开更多
Using the Keldysh nonequilibrium Green function and equation-of-motion technique, we investigate Fano versus Kondo resonances in a closed Aharonov-Bohm interferometer coupled to ferromagnetic leads and study their eff...Using the Keldysh nonequilibrium Green function and equation-of-motion technique, we investigate Fano versus Kondo resonances in a closed Aharonov-Bohm interferometer coupled to ferromagnetic leads and study their effects on the conductance of this system. The conductance with both parallel and antiparallel lead-polarization alignments is analysed for various values of the magnetic flux. Our results show that this system can provide an excellent spin filtering property, and a large tunnelling magnetoresistance can arise by adjusting the system parameters, which indicates that this system is a possible candidate for spin valve transistors and has important applications in spintronics.展开更多
文摘The magnetic behavior of a two-electron quantum dot/ring system is analytically studied with electron-electron(e-e)interaction taking into account the Rashba spin-orbit interaction(SOI)and magnetic field.The Jacobi transformation has been employed to separate the Hamiltonian of the system to the center of mass and relative terms.The Schrödinger equation is analytically solved,and energy spectra are obtained.Then,the magnetization and susceptibility are calculated.The magnetization decreases by raising the magnetic field without and with SOI,and also without e-e interaction.Also,the SOI slightly modifies the magnetization of the system without e-e interaction.The susceptibility displays a peak structure as the magnetic field changes from low values to high values.The susceptibility by considering e-e interaction and without the SOI is always negative and its value decreases by rising the magnetic field.The susceptibility displays a transition from diamagnetic to paramagnetic with e-e interaction and SOI.
基金Project supported by the Natural Science Foundation of Liaoning Province, China (Grant No. 201202085)the National Natural Science Foundation of China(Grant No. 11004138)+1 种基金the Excellent Young Scientists Fund of Liaoning Provence, China (Grant No. LJQ2011020)the Young Scientists Fund of Shenyang Ligong University (Grant No. 2011QN-04-11)
文摘The spin-polarized linear conductance spectrum and current–voltage characteristics in a four-quantum-dot ring embodied into Aharonov–Bohm （AB） interferometer are investigated theoretically by considering a local Rashba spin–orbit interaction. It shows that the spin-polarized linear conductance and the corresponding spin polarization are each a function of magnetic flux phase at zero bias voltage with a period of 2π, and that Hubbard U cannot influence the electron transport properties in this case. When adjusting appropriately the structural parameter of inter-dot coupling and dot-lead coupling strength, the electronic spin polarization can reach a maximum value. Furthermore, by adjusting the bias voltages applied to the leads, the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situations. Based on the numerical results, such a model can be applied to the design of a spin filter device.
基金Project supported by the National Basic Research Program of China (Grant No 2003CB314901)the National Natural Science Foundation of China (Grant No 60644004)the High School Innovation and Introducing Talent Project of China (B07005)
文摘Calculations of electronic structures about the semiconductor quantum dot and the semiconductor quantum ring are presented in this paper. To reduce the calculation costs, for the quantum dot and the quantum ring, their simplified axially symmetric shapes are utilized in our analysis. The energy dependent effective mass is taken into account in solving the Schrodinger equations in the single band effective mass approximation. The calculated results show that the energy dependent effective mass should be considered only for relatively small volume quantum dots or small quantum rings. For large size quantum materials, both the energy dependent effective mass and the parabolic effective mass can give the same results. The energy states and the effective masses of the quantum dot and the quantum ring as a function of geometric parameters are also discussed in detail.
基金Project supported by the Scientific Research Fund of the Education Department of Sichuan Province of China (Grant No. 2006A069)Funds for Major Basic Research Project of Sichuan Province of China (Grant No. 2006J13-155)
文摘Using the Keldysh nonequilibrium Green function and equation-of-motion technique, this paper studies the mag- netotransport through an Aharonov-Bohm （AB） ring with parallel double quantum dots coupled to ferromagnetic leads. It calculates the transmission probability in both the equilibrium and the nonequilibrium case, analyses the conduc- tance and the tunnel magnetoresistance for various parameters, and obtains some new results. These results show that this system is provided with an excellent spin filtering property, and that a large tunnelling magnetoresistance and a negative tunnelling magnetoresistance can arise by adjusting relative parameters; these facts indicate that this system is a possible candidate for spin valve transistors, and has important applications in spintronics.
基金Project supported by the Special Funds of the National Natural Science Foundation of China(Grant No.11247313)
文摘By using semiclassical theory combined with multiple-scale method, we analytically study the linear absorption and the nonlinear dynamical properties in a lifetime broadened Λ-type three-level self-assembled quantum dots. It is found that this system can exhibit the transparency, and the width of the transparency window becomes wider with the increase of control light field. Interestingly, a weak probe light beam can form spatial weak-light dark solitons. When it propagates along the axial direction, the soliton will transform into a steady spatial weak-light ring dark soltion. In addition, the stability of two-dimensional spatial optical solitons is testified numerically.
文摘We have studied the transport properties of a ring-coupled quantum dot array driven by an AC magnetic field, which is connected to two leads, and we give the response of the transport current to the dynamical localization. We found that when the ratio of the magnetic flux to the total quantum dots number is a root of the zeroth order Bessel function, dynamical localization and collapse of quasi-energy occurs and importantly~ the transport current displays a dip which is the signal of dynamical localization. The dynamical localization effect is strengthened as a result of the increase of the quantum dot number, and it is weakened on account of the increase of the dots-lead hopping rate.
基金supported by the Hi-Tech Research and Development Program of China (2009AA03Z405)the National Natural Science Foundation of China (60908028)+1 种基金the National Natural Science Foundation of China (60971068)the High School Innovation and Introducing Talent Project of China (B07005)
文摘This article puts forward a new method in calculating the band structures of low-dimensional semiconductor structures. In this study, the valence band structures of InAs/GaAs quantum ring and lens-shaped quantum dot are calculated with four-band model, in the framework of effective-mass envelope function theory. To determine the Hamiltonian matrix elements, this article develops the numerical Fourier transform method instead of the widely used analytical integral method. The valence band mixing is considered. The hole energy levels change dramatically with the geometrical parameters of the quantum ring and quantum dot. It is demonstrated that numerical Fourier transform method can be adopted in low-dimensional structures with any shape. The results of Fourier transform method are consistent with the ones of analytical integral in literature; and they are helpful for studying and fabricating optoelectronic devices.
基金Supported by NSFC(11147147)Distinguished Young Talents in Higer Education of Guangdong China(LYM11021)+1 种基金Research Training and Innovation Fund of Jinan University(21612439)Young Teacher Fund of Huaiyin Institute of Technology(2717577)
文摘Using the Keldysh nonequilibrium Green function and equation-of-motion technique, we investigate Fano versus Kondo resonances in a closed Aharonov-Bohm interferometer coupled to ferromagnetic leads and study their effects on the conductance of this system. The conductance with both parallel and antiparallel lead-polarization alignments is analysed for various values of the magnetic flux. Our results show that this system can provide an excellent spin filtering property, and a large tunnelling magnetoresistance can arise by adjusting the system parameters, which indicates that this system is a possible candidate for spin valve transistors and has important applications in spintronics.
