Electron transport through a two-terminal Aharonov-Bohm interferometer coupled with linear di-quantum dot molecules

Abstract

A two-terminal Aharonov-Bohm (A-B) interferometer coupled with linear di-quantum dot molecules is presented. By employing Keldysh non-equilibrium Green's function technique, the conductance without introducing time-dependent external field and the average current with applying time-dependent external field are theoretically studied. In the absence of time-dependent external field, two identical linear diquantum dot molecules embedded respectively in the two arms of A-B interferometer lead to degeneracy energy levels. The central resonance peak at εd = 0 in the conductance spectrum splits into two resonance peaks as the inter-coupling strength of di-quamtum dot increases over a threshold. In the case that the two linear di-quantum dot molecules are different, three or four resonance peaks appear in the conductance spectrum. When tuning magnetic flux ψ= π, the destructive quantum interference of electron waves in the A-B interferometer takes place. The conversion between 0 and 1 for conductance is performed by switching on/off the magnetic flux, which suggests a new physical scheme of quantum switches. The effect of Rashba spin-orbit interaction on the conductance is discussed. The functionality of spin filter is suggested through adjusting the Rashba spin-orbit coupling strength and the external magnetic flux. When time-dependent external field is applied, the notable side-band effect appears in the average current curve. A series of resonance peaks is produced, with the peak-peak separation of ħω. Two main peaks become reduced as the amplitude of time-dependent external field increases, however, the sideband peaks grow gradually. This indicates that both the magnitude and the position of average current resonance peak are controllable by adjusting the amplitude of time-dependent external field. The sideband effect remains always in the average current curve no matter how much the frequency of time-dependent external field changes. But the increase in the frequency of external field leads to the growth of two main peaks at the bonding and anti-bonding energy respectively, and the decay of the corresponding sideband peaks as well. The conversion between the current peak and valley can be realized by tuning the frequency of time-dependent field. Moreover, the dependence of A-B effect of the average current on the magnetic flux is found. As the magnetic flux is ψ≠nπ, each peak in average current curves splits into two peaks. But under the condition of ψ=2nπ, the splitting phenomenon disappears. The spin-dependent average current shows effective controllability by tuning the magnetic flux and Rashba spin-orbit coupling. The results would be useful for gaining a physical insight into electron transport in the multi-quantum-dot molecules coupled A-B interferometer and for designing the quantum devices.