Zhou Guang-Hui

Optoelectronic Properties for Armchair-Edge Graphene Nanoribbons

We study theoretically the electronic and transport property for an armchair-edge graphene nanoribbon (CNR) with 12 and 11 transversal atomic lines, respectively. The GNR is irradiated under an external longitudinal polarized high-frequency electromagnetic field at low temperatures. Within the framework of linear response theory in the perturbative regime, we examine the joint density of states and the real conductance of the system. It is demonstrated that, by numerical examples, some new photon-assisted intersubband transitions over a certain range of Geld frequency exist with different selection rules from those of both zigzag-edge GNR and single-walled carbon nanotube. This opto-electron property dependence of armchair-edge GNR on field frequency may be used to detect the high-frequency electromagnetic irradiation.

Persistent Spin Current in a Quantum Wire with Weak Rashba Spin–Orbit Coupling

We theoretically investigate the spin current for a parabolically confined semiconductor heterojunction quantum wire with weak Rashba spin-orbit coupling by means of the perturbation method. By analytical calculation, it is found that only two components of spin current density is non-zero in the equilibrium case. Numerical examples have demonstrated that the spin current of electron transverse motion is 10(-3) times that of electron longitudinal motion. However, the former one is much more sensitive to the strength of Rashba spin-orbit coupling. These results may suggest an approach to the spin storage device and to the measurement of spin current through its induced electric field.

Moving nonlinear localized modes for one-dimensional Klein-Gordon diatomic lattice

We study analytically the moving nonlinear localized vibrational modes (discrete breathers) for a one-dimensional Klein-Gordon diatomic lattice in the whole omega (q) plane of the system by means of a semi-discrete approximation, in which the carrier wave of the modes is treated explicitly while the envelope is described in the continuum approximation. We find that both pulse and kink envelope moving modes for this lattice system can occur with certain carrier wave vectors and vibrational frequencies in separate regions of the omega (q) plane. However, the kink envelope moving modes have not been reported previously for this lattice system.

Photon-assisted conductance structure for a quantum dot

We investigate theoretically the electron transport of a two-level quantum dot irradiated under a weak laser held at low temperatures in the rotating wave approximation. Using the method of the Keldysh equation of motion for nonequilibrium Green function, we examine the conductance for the system with photon polarization perpendicular to the tunnelling current direction. It is demonstrated that by analytic analysing and numerical examples, a feature of conductance peak splitting appears, and the dependence of conductance on the incident laser frequency and self-energy are discussed.

Conductance of a Quantum Dot in the Presence of a Phonon Field

We theoretically investigate the electrical transport property of a quantum dot with longitudinal optical phonons. The conductance through the dot connected to two leads is calculated by the nonequilibrium Green function within the Landauer-Buttiker framework. The numerical examples of the conductance with different electron-phonon coupling strengths show that the presence of a phonon field typically results in the suppression of the main peak accompanied by some phonon side peaks. Both the main peak and the side peaks are sensitive to the electron-phonon coupling strength, which is related to temperature. Our results for this system are consistent with some related previous works but the calculation is comparatively simple.

Alternating-Current Conductivity for a Two-Channel Interacting Quantum Wire

We investigate theoretically the ac conductivity of a clean two-channel spinless quantum wire in the presence of both short-ranged intra- and inter-channel electron-electron interactions. In the Luttinger-liquid regime, we formulize the action functional of the system with an external time-varying electric field. The obtained expression of ac conductivity for the system within linear response theory is generally an oscillation function of the interaction strength, the driving frequency as well as the measured position in the wire. The numerical examples demonstrate that the amplitude of ac conductivity is renormalized by the both interactions, and the do conductivity of the system with inter-channel interaction is smaller than that without inter-channel interaction.

Photon-assisted electronic structure and transport for a quantum dot

This paper investigates theoretically the electronic structure and transport of a two-level quantum dot irradiated under a strong laser field at low temperatures. Using the method of Keldysh equation of motion for nonequilibrium Green functions, it examines the time-averaged density of states and conductance for the system with photon polarization parallel with and perpendicular to the tunnelling current direction respectively. It is demonstrated that, by analysing some numerical examples, more photon sidebands resonance states and multi- and single-photon transitions are found when diagonal matrix elements dominate the interaction, while the electronic transitions due to multiphoton absorption are more or less suppressed when off-diagonal interaction dominates.

Persistent spin current in a quantum wire with weak Dresselhaus spin-orbit coupling

The spin current in a parabolically confined semiconductor heterojunction quantum wire with Dresselhaus spin–orbit coupling is theoretically studied by using the perturbation method. The formulae of the elements for linear and angular spin current densities are derived by using the recent definition for spin current based on spin continuity equation. It is found that the spin current in this Dresselhaus spin–orbit coupling quantum wire is antisymmetrical, which is different from that in Rashba model due to the difference in symmetry between these two models. Some numerical examples for the result are also demonstrated and discussed.

Resonant Photon-Assisted Structure of Conductance through a Quantum Wire

We investigate theoretically the electron transport properties of a two-sublevel quantum wire irradiated by a strong laser held resonant with the quasiparticle transition at low temperatures. Using the method of the Keldysh equation of motion for nonequilibrium Green function, we examine the time-averaged conductance for the system with photon polarization parallel and perpendicular to the tunnelling current direction, respectively. We demonstrate that, by analysing some numerical examples, a feature of absolute negative conductance appears in the parallel case, while the conductance shows a symmetry distributed peaks in the perpendicular case.

Dynamical transport property through an interacting quantum wire

Using the equation of motion, we investigate theoretically the dynamical ac conductance of a clean Luttinger-liquid quantum wire adiabatically coupled to Fermi liquid electron reservoirs in the presence of short-ranged electron-electron interactions. For a perfect single mode quantum wire, in the limit of zero-ranged interaction we conclude that the static dc conductance of omega -> 0 is e(2)/h, which is independent of the electron interactions. While in the dynamical case of omega not equal 0, the ac conductance oscillates with the amplitude e(2)/h and the period which depends on the interaction strength and the driving frequency as well as the position in the wire.