Tianquan Lü

Tunable pure spin currents in a triple-quantum-dot ring

Electronic transport through a triple-quantum-dot ring with three terminals is theoretically studied. By introducing local Rashba spin-orbit interaction on an individual quantum dot, we calculate the charge and spin currents in one lead. We find that a pure spin current without an accompanying charge current appears even at zero magnetic field case. The polarization direction of the spin current can be inverted by altering the bias voltage. In addition, by tuning the magnetic field strength, the charge and spin currents reach their respective peaks alternately.

Calculation of the effective dielectric function of composites with periodic geometry

A method for calculating the effective dielectric function of a two-component periodic composite is described. Using a simple Fourier expansion technique, we obtain an explicit power series expression of H(t), which is one of the characteristic geometric functions of the two-component composite proposed by Bergman. The relation between the series of H(t) and that of another characteristic geometric function of composite F(s) is studied. The dielectric function of composite F, Of two kinds of model systems is calculated by using both H(t) and F(s) for finite-size reciprocal lattice. The deviations of the numerical results of epsilon (e) from the exact ones, which are caused by the limited size of the reciprocal lattice used, are investigated. It is found that the: accuracies of the numerical results of F(s) differ from those of H(t). For simple cubic arrays of nonoverlapping spheres, the results of epsilon (e), obtained from H(t) are closer to the exact ones, especially when the volume fraction of the inclusions is larger and the dielectric contrast of the composite is higher. For 2-D prisms, the averages of the results of epsilon (e) obtained from using F(s) and those from H(t) are closer to the exact ones

The effect of electron effective mass mismatch on the electron - optical-phonon scattering rate in a quantum well structure

The effective mass mismatch of a conduction-band electron in a semiconductor quantum well structure brings about a novel confinement of the electron movement along the well-growth direction in addition to the conduction-band offset. Using the electron-optical-phonon interaction Hamiltonian of the dielectric continuum model, we calculate the scattering rates due to the interaction of the electron with the well, barrier and interface phonons respectively. By comparison with the corresponding results for the case without the electron effective mass mismatch it is shown that the electron effective mass mismatch has a remarkable influence on the scattering rate, especially for relatively high electron energy, and much attention should be paid to it.

Influence of interface roughness scattering on electronic magnetotransport in a quantum well

By assuming several different analytical forms of correlation function for the interface roughness in a quantum well, the influence of interface roughness scattering on the electronic transport in the presence of a magnetic field is investigated. It is found that the roughness-limited conductivities are mainly determined by the behaviour of the correlation functions in Fourier space within the range of inverse magnetic length. Thus the electronic magnetotransport property sensitively depends on the detail of the roughness correlation function in the case of a large magnetic field. On the other hand, when the magnetic length is much larger than the roughness correlation length, which usually corresponds to the case of a relatively weak magnetic field, the conductivities calculated by different forms of roughness correlation function do not show a notable difference from each other.

Calculation of the electrical field in the periodic composite and evaluation of the nonlinear susceptibility of the periodic composite

A simple Fourier approach to the calculation of the space dependent electrical field in periodic composite was present. A series expression of the field was obtained. By using this expression, the frequency-dependent cubic nonlinear susceptibility of metal-insulator composite with periodic structure was studied