Using the tight-binding approximation and the transfer matrix method,this paper studies the electronic transport properties through a periodic array of quantum-dot(QD) rings threaded by a magnetic flux.It demonstrates that the even-odd parity of the QD number in a single ring and the number of the QD rings in the array play a crucial role in the electron transmission.For a single QD ring,the resonance and antiresonance transmission depend not only on the applied magnetic flux but also on the difference between the number of QDs on the two arms of the ring.For an array of QD rings,the transmission properties are related not only to the even-odd parity of the number N0 of QDs in the single ring but also to the even-odd parity of the ring number N in the array.When the incident electron energy is aligned with the site energy,for the array of N rings with N0 = odd the antiresonance transmission cannot occur but the resonance transmission may occur and the transmission spectrum has N resonance peaks(N1 resonance peaks) in a period for N = odd(for N = even).For the array of N rings with N0 = even the transmission properties depend on the flux threading the ring and the QD number on one arm of the ring.These results may be helpful in designing QD devices.
We have studied the spin-dependent electron transmission through a quantum well driven by both dipole-type and homogeneous oscillating fields. The numerical evaluations show that Dresselhaus spin-orbit coupling induces the splitting of asymmetric Fano-type resonance peaks in the conductivity,in which the dipole modulation and the homogeneous modulation are equivalent. Therefore,we predict that the dipole-type oscillation,which is more practical in the experimental setup,can be used to realize the tunable spin filters by adjusting the field oscillation-frequency and the amplitude as well.
We have investigated theoretically the field-driven electron-transport through a double-quantum-well semiconductor-heterostructure with spin-orbit coupling. The numerical results demonstrate that the transmission spectra are divided into two sets due to the bound-state level-splitting and each set contains two asymmetric resonance peaks which may be selectively suppressed by changing the difference in phase between two driving fields. When the phase difference changes from 0 to π,the dip of asymmetric resonance shifts from one side of resonance peak to the other side and the asymmetric Fano resonance degenerates into the symmetric Breit-Wigner resonance at a critical value of phase difference. Within a given range of incident electron energy,the spin polarization of transmission current is completely governed by the phase difference which may be used to realize the tunable spin filtering.
We propose a four-terminal device consisting of two parallel quantum dots with Rashba spin-orbit interaction (RSOI),coupled to two side superconductor leads and two common ferromagnetic leads,respectively.The two ferro-magnetic leads and two quantum dots form a ring threaded by Aharonov-Bohm (AB) flux.This device possesses normal quasiparticle transmission between the two ferromagnetic leads,and normal and crossed Andreev reflections providing conductive holes.For the appropriate spin polarization of the ferromagnetic leads,RSOI and AB flux,the pure spin-up (or spin-down) current without net charge current in the right lead,which is due to the equal numbers of electrons and holes with the same spin-polarization moving along the same direction,can be obtained by adjusting the gate voltage,which may be used in practice as a pure spin-current injector.
Using the method developed by Gurvitz [1996 Phys.Rev.B 53 15932],we obtained the Bloch-type rate equations describing the entire system of a periodically driving qubit monitored by a quantum point contact detector.The results demonstrate that the isolated qubit can be kept in its initial state with a large driving frequency due to more difficult electron tunneling in qubit,and this initial state can always be measured at a small measurement-induced decoherence rate during a short time.
By means of the modal expansion method with an R-matrix propagation algorithm, effects of the coupling between resonance photonic states on the resonance tunneling through a double quantum well structure are investigated. We examine the effects on the transmission spectra due to variation of the second well width and middle barrier thickness. Drastic change of the tunneling spectra is found and analyzed when the wells are filled with left-hand media.
