A Tunable Fano System Realized in a Quantum Dot in an Aharonov-Bohm Ring (original) (raw)
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Mesoscopic Fano Effect throughaQuantumDotinanAharonov-BohmRing
The Fano effect illustrates how the interference and resonance cooperatively occur between a discrete state and a continuum energy state. We have realized a tunable Fano system by fabricating a quantum dot embedded in an Aharonov-Bohm ring on a 2DEG. In the Coulomb oscillation, clear asymmetric lineshapes were observed, which manifest the formation of the Fano state, namely, a mixture of the discrete state and the continuum state. The non-equilibrium transport and the temperature dependence reveal the essential role of the coherence for this effect. Through the phase controlling by the magnetic flux piercing the ring, Fano's asymmetric parameter q is obtained as a complex number for the first time.
Fano interference in mesoscopic rings with quantum dots
Physica Status Solidi (c), 2006
We propose a general formalism for describing the coexistence of coherent and resonant transport in hybrid mesoscopic structures. The approach is based on Landauer-Büttiker formula for the electronic transmittance and on an old formula of Feshbach. The latter gives the complete Green function of coupled subsystems in terms of effective Green functions of the disconnected parts and provides informations about the individual contributions of each subsystem to transport. Motivated by the experiments of Kobayashi et al.(Phys. Rev. Lett. 88, 256806 (2002)) and Holleitner et al. (Phys. Rev. Lett. 87, 256802 (2001)) we apply the formalism to study transport in Aharonov-Bohm interferometers (ABI) containing one or two coupled two-dimensional quantum dots (QD). In the single dot case, we reproduce and explain the magnetic field control of the Fano interference and investigate the interaction effects in a self-consistent approach. In the double dot case, we obtain the charging diagrams and establish precise criteria for the observation of mesoscopic Fano effect and AB oscillations. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Resonance and phase shift in an open Aharonov–Bohm ring with an embedded quantum dot
Journal of Physics: Condensed Matter, 2009
The transmission and phase properties of electron transport through a quantum dot (QD) with variable coupling to a third-terminal probe are investigated analytically for the case of the QD connected directly to source and drain reservoirs and when the QD is embedded in one arm of an Aharonov-Bohm (AB) ring. Using the tight-binding model, explicit analytical expressions of the transmission through the QD for each case are given. Expressions for the conductance with coupling to the third terminal, which breaks unitarity and phase-locking, are also given. It is shown that in a three-terminal interferometer the zero of the Fano resonance in the transmission moves off the real energy axis for finite values of the coupling parameter. The zero orbits around the pole in the complex energy plane as a function of magnetic flux through the ring, and can be returned to the real energy axis unless the coupling parameter exceeds a critical value. With the QD embedded in one arm of the AB ring, the electron transmission and the transmission phase, and the phase of the AB oscillations, are described in relation to the degree of coupling to the third-terminal probe which opens the interferometer. By tuning the degree of coupling to the probe, it is shown that the phase of the AB oscillations can be made to match the intrinsic phase of the QD, facilitating experimental characterization of the phase response of the QD.
Coulomb-Modified Fano Resonance in a One-Lead Quantum Dot
Physical Review Letters, 2004
We investigate a tunable Fano interferometer consisting of a quantum dot coupled via tunneling to a onedimensional channel. In addition to Fano resonance, the channel shows strong Coulomb response to the dot, with a single electron modulating channel conductance by factors of up to 100. Where these effects coexist, lineshapes with up to four extrema are found. A model of Coulomb-modified Fano resonance is developed and gives excellent agreement with experiment.
Tunable Fano Resonance in Double Quantum Dot Systems
2017
We investigate the electronic transport through a double quantum dot device embedded in the tunnel junction between two metallic leads. We find that transitioning from the serial to the parallel configurations is associated with the progressive reduction of tunneling through one quantum dot. As a result the asymmetric Fano lineshape appears, which we interpret as the formation of an anti-bonding and a bonding state in the junction. The bonding state facilitates the majority of the tunneling as the geometry approaches symmetric coupling to the leads. At the limit of the transition towards the parallel configuration, the anti-bonding state is completely localized from the continuum of the leads and only the bonding state is left to participate in the transmission.
Physical Review B, 2006
Although the conductance of a closed Aharonov-Bohm interferometer, with a quantum dot on one branch, obeys the Onsager symmetry under magnetic field reversal, it needs not be a periodic function of this field: The conductance maxima move with both the field and the gate voltage on the dot, in an apparent breakdown of "phase rigidity." These experimental findings are explained theoretically as resulting from multiple electronic paths around the interferometer ring. Data containing several Coulomb blockade peaks, whose shapes change with the magnetic flux, are fitted to a simple model, in which each resonant level on the dot couples to a different path around the ring.
Journal of Computational Electronics, 2007
We study a four-terminal AB-ring with three embedded quantum dots in one arm. A tight-binding model is employed to analytically obtain the transmission through the system. Results show that the magnitude and sharpness of the resonance phase-jumps diminish as a function of the degree of coupling to the extra terminals. The Fano resonance zeros become complex with a non-zero coupling matrix element to the extra terminals. The zeros can be returned to the real energy axis by increasing the flux for values of the coupling less than a critical value. A simple analytical model of the Fano resonances shows naturally how the phase transition across the resonance peak will soften and diminish in the case where the transmission zero energy is no longer real, but complex.