Phase effects on the conductance through parallel double dots

Abstract

Phase effects on the conductance of a double-dot system in a ring structure threaded by a magnetic flux are studied. The Aharonov-Bohm effect combined with the dot many-body charging effects determine the phases of the currents going through each arm of the ring. The cases for zero magnetic flux or half a quantum of flux are discussed in detail. It is shown that, depending upon the magnetic flux and the state of charge of the dots, controlled by gate potentials, the dephasing of the upper and lower arm current gives rise to a S = 1/2 or S = 1 Kondo regime.We also show that even in the absence of a magnetic flux there can be a circulating current in the ring, depending on the system parameters. 73.63.Kv In the last years attention has been focused on the properties of double-quantum-dot systems 1 since they are expected to be basic building blocks for quantum computing 2 . In this context mesoscopic coherent transport is a key phenomenon that can probe entanglement 3 and phases accumulated by electrons traversing the system. The phase-coherent transport effects can be analyzed by embedding the dots into an Aharonov-Bohm ring threaded by a magnetic flux and connected to leads. Theoretical 4 and experimental 5 works have discussed the transmission phase shifts of single and double quantum dot systems in the Coulomb blockade regime. More recently the effect of Kondo correlation on the transmission phase of a quantum dot has been measured 6 and theoretically discussed 7,8,9,10,11,12 .The two-quantum-dot system is particularly interesting since, when each dot is inserted into one arm of a ring connected to leads, as represented in Fig. 1, it presents two paths for the electrons to go through, producing interferences that depend upon the phase in each arm.The effect of the interferences on the spectral densities of such a system has been studied 14 , taking the intra and inter-dot Coulomb repulsion to be infinite. This limit restricts the study

Currents along ring arms with quantum dots: Kondo and Aharonov–Bohm effects

“…The sum of the two ring arm currents constitute the total current in the leads that is also represented in the figure (dashed line). The total current is positive for the whole range of gate potentials, as expected, and is in agreement with previous results [5].…”

“…1, is particularly interesting since it presents two paths for the electrons to go through, producing interferences. The conductance of this system in the Kondo regime has been already studied [5].…”

Kondo Effect of an Adsorbed Cobalt Phthalocyanine (CoPc) Molecule: The Role of Quantum Interference

“…The most appealing result is that when the molecule lobes do not interact no Kondo effect shows up [21]. The origin of this remarkable result is likely related to quantum interference [2,12,15,22,23,24,25]. To illustrate this assessment we have calculated the phase difference between the direct path from the gold surface to the STM tip going through the Co atom, and the path that passes through the molecule lobes.…”

“…This method is exact only as far as the calculation of the Green function of the isolated cluster is concerned, and does not account for correlation effects that extend beyond its bounds. The method has already been applied to a variety of transport problems [10,11,12,13,14] including transport through hydrogenated Pt nanocontacts [15].…”

Spin polarization in parallel double dots with spin–orbit interaction

“…The electron transport through an AB interferometer with a QD in each of its arms has been investigated widely [25][26][27][28]. However, there are few reports on the spin polarization in the QDs of the system.…”