Spin-Polarized Transport Through The T-Shaped Double Quantum Dots

As the typical representation of exhibiting quantum effect in low dimensional mesoscopic system, the quantum dot system becomes the hot topic recently. Recent advances in nanofabrication technology have made it possible to investigate various aspects of Fano versus Kondo resonance, which has aroused new interest in the two phenomena. Meanwhile, T-shaped double-quantum-dot systems have attracted much attention in the condensed matter physics. Contrasting with the usual series and parallel DQD systems, the T-shaped DQD systems show some different properties. On the one hand, the T-shaped DQD systems provide an idea model system for studying the two impurity effects and the related experiment can be performed under controlled circumstance. On the other hand, the T-shaped DQD systems are another prototype of correlated systems, for which the special arrangement of the DQD provides two paths for the electrons to go through, one is through the central QD and the other is through the side QD. Besides, the Kondo effect arises from the interactions between a single magnetic impurity and the electrons of the bulk mental under low temperature, so the observation of the Kondo effect in QD systems opened a new path for the investigation of quantum correlation between localized spin in QD and the free lead. The Fano effect appears as a result of quantum interference between a discrete single energy level and a direct channel characterized by its continuous spectrum. It is thus interesting to study how the Kondo versus Fano effect affect the characteristic transport properties in the T-shaped DQD system. Through our study, we find the following results: (1) when the central dot is in the Kondo regime and the Coulomb interaction of the side coupled dot is not considered, it is shown that the interdot coupling and the relative position of side coupled dot levels play an essential role in the DOS and the liner conductance of central dot. There are different Kondo and Fano line shapes under the control of spin-polarized strength both in the equilibrium and nonequilibrium cases.(2) when the Coulomb interaction of the two dots is considered, the DOS of the two dots depends sensitively on the spin-polarized strength in both the equilibrium and nonequilibrium case. We also pay attention to the influence of the spin-polarized strength on the differential conductance and the current of the system. The behaviors of them provide more information about the transport properties in the T-shaped DQD system, as well as that the rich physical behavior can be attributed to the coexistence of both the Fano effect and Kondo effect. The T-shape DQD system is also a very promising quantum dot configuration. Such system involving single or multiple quantum dots may provide many opportunities for strong interaction effects, which stimulate further experimental and theoretical studies in the spintronics.