R. Taranko

Influence of microwave fields on electron transport through a quantum dot in the presence of direct tunneling between leads

We consider the time-dependent electron transport through a quantum dot coupled to two leads in the presence of the additional overdot (bridge) tunneling channel. By using the evolution operator method together with the wide-band limit approximation we derived the analytical formulas for the quantum dot charge and current flowing in the system. The influence of the external microwave field on the current and the derivatives of the current with respect to the gate and source-drain voltages has been investigated for a wide range of parameters. The most characteristic feature of including the additional overdot tunneling channel is an asymmetric behavior of the function describing the dependence of the average current vs the gate voltage or the differential conductance vs the source-drain voltage.

Spin and charge pumping in a quantum wire: the role of spin-flip scattering and Zeeman splitting

We investigate theoretically charge and spin pumps based on a linear configuration of quantum dots (quantum wire) which are disturbed by an external time-dependent perturbation. This perturbation forms an impulse which moves as a train pulse through the wire. It is found that the charge pumped through the system depends non-monotonically on the wire length, N. In the presence of the Zeeman splitting pure spin current flowing through the wire can be generated in the absence of charge current. Moreover, we observe electron pumping in a direction which does not coincide with the propagation direction of the pulse and the spin pumping direction (spin-charge separation). Additionally, on-site spin-flip processes significantly influence electron transport through the system and can also reverse the charge current direction.

Optical conductivity of substitutionally disordered alloys: Intraband transitions

The coherent potential approximation (CPA) is applied to the investigation of the off-diagonal disorder effect on the AC conductivity of the disordered binary alloys, due to intraband absorption. The frequency dependence of the conductivity σ(ω) is numerically calculated for various parameters describing the alloy and various positions of the Fermi level in the band. The anomalous behaviour in the frequency dependence of the conductivity is found. The parameter τ(ω) — optical relaxation time, used by many researchers, in this case is invalid.