17 research outputs found
Controlled dephasing in single-dot Aharonov-Bohm interferometers
We study the Fano effect and the visibility of the Aharonov-Bohm oscillations
for a mesoscopic interferometer with an embedded quantum dot in the presence of
a nearby second dot. When the electron-electron interaction between the two
dots is considered the nearby dot acts as a charge detector. We compute the
currents through the interferometer and detector within the Keldysh formalism
and the self-energy of the non-equilibrium Green functions is found up to the
second order in the interaction strength. The current formula contains a
correction to the Landauer-B\"{uttiker} formula. Its contribution to transport
and dephasing is discussed. As the bias applied on the detector is increased,
the amplitude of both the Fano resonance and Aharonov-Bohm oscillations are
considerably reduced due to controlled dephasing. This result is explained by
analyzing the behavior of the imaginary part of the self-energy as a function
of energy and bias. We investigate as well the role of the ring-dot coupling.
Our theoretical results are consistent to the experimental observation of Buks
{\it et al.} [Nature {\bf 391}, 871 (1998)].Comment: 24 pages, 8 figure
Coulomb oscillations of the Fano-Kondo effect and zero bias anomalies in the double dot meso-transistor
We investigate theoretically the transport properties of the side-coupled
double quantum dots in connection with the experimental study of Sasaki {\it et
al.} Phys.Rev.Lett.{\bf 103}, 266806 (2009). The novelty of the set-up consists
in connecting the Kondo dot directly to the leads, while the side dot provides
an interference path which affects the Kondo correlations. We analyze the
oscillations of the source-drain current due to the periodical Coulomb blockade
of the many-level side-dot at the variation of the gate potential applied on
it. The Fano profile of these oscillations may be controlled by the
temperature, gate potential and interdot coupling. The non-equilibrium
conductance of the double dot system exhibits zero bias anomaly which, besides
the usual enhancement, may show also a suppression (a dip-like aspect) which
occurs around the Fano {\it zero}. In the same region, the weak temperature
dependence of the conductance indicates the suppression of the Kondo effect.
Scaling properties of the non-equilibrium conductance in the Fano-Kondo regime
are discussed. Since the SIAM Kondo temperature is no longer the proper scaling
parameter, we look for an alternative specific to the double-dot. The extended
Anderson model, Keldysh formalism and equation of motion technique are used.Comment: 19 pages, 8 figure
Mesoscopic Fano effect in an Aharonov-Bohm interferometer Coulomb-coupled to a nearby quantum dot
Motivated by the pionieering experiments of Buks et al. [Nature 391, 871 (1998)] we investigate the visibility of the Fano effect in a single-dot Aharonov-Bohm interferometer which is Coulomb-coupled to a nearby quantum dot. The latter acts as a 'Which Path Detector' and is coupled to two leads on which a finite bias is applied. Using the non-equilibrium Keldysh-Green function formalism we compute the currents through the detector and the interferometer. We take into account the first two contributions to the interaction selfenergy and emphasize the correction to the Landauer formula which appears beyond the single-particle approximation. Particular attention is given to the coherence properties of the interferometer in the presence of the electron-electron interaction between the embedded dot and the detector. We show that when the detector is subjected to a finite bias the amplitude of Aharonov-Bohm oscillations of the current through the interferometer decreases. The Fano line is in turn rather stable under interaction. Our results generalize an earlier work of Silva and Levit [Phys. Rev. B 63, 201309 (2001)] and complement the existing description of the controlled dephasing. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA
Measurement-induced decoherence in electronic interferometry at nanoscale
We introduce a theoretical formalism describing a wide class of 'Which Path' experiments in mesoscopic/nanoscopic transport. The physical system involves a mesoscopic interferometer (e.g. an Aharonov-Bohm ring with embedded dots or a side-coupled quantum dot) which is electrostatically coupled to a nearby quantum point constriction. Due to the charge sensing effect the latter acts as a charge detector. Therefore the interference pattern can be monitored indirectly by looking at the current characteristics of the detector as shown in the experimental work of Buks et al. [E. Buks, R. Schuster, M. Heiblum, D. Mahalu, V. Umansky, Nature (London) 391 (1998) 871]. We use the non-equilibrium Green-Keldysh formalism and a second order perturbative treatment of the Coulomb interaction in order to compute the relevant transport properties. It is shown that in the presence of the Coulomb interaction the current through the detector exhibits oscillations as a function of the magnetic field applied on a single-dot AB interferometer. We also discuss the dependence of the visibility of the Aharonov-Bohm oscillations on the gate potential applied to the dot. © 2008 Elsevier B.V. All rights reserved
Resonant and coherent transport through Aharonov-Bohm interferometers with coupled quantum dots
A detailed description of the tunneling processes within Aharonov-Bohm (AB)
rings containing two-dimensional quantum dots is presented. We show that the
electronic propagation through the interferometer is controlled by the spectral
properties of the embedded dots and by their coupling with the ring. The
transmittance of the interferometer is computed by the Landauer-B\"uttiker
formula. Numerical results are presented for an AB interferometer containing
two coupled dots. The charging diagrams for a double-dot interferometer and the
Aharonov Bohm oscillations are obtained, in agreement with the recent
experimental results of Holleitner {\it et al}. [Phys. Rev. Lett. {\bf 87},
256802 (2001)] We identify conditions in which the system shows Fano line
shapes. The direction of the asymetric tail depends on the capacitive coupling
and on the magnetic field. We discuss our results in connection with the
experiments of Kobayashi {\it et al} [Phys. Rev. Lett. {\bf 88}, 256806 (2002)]
in the case of a single dot.Comment: 30 pages, 12 figure
Analysis of the phase lapse problem in closed interferometers
We investigate the connection between the asymmetry of the Fano resonances in a mesoscopic interferometer with an embedded quantum dot and the π lapses in the phase of the bare dot transmittance. Consecutive Fano resonances with the same (opposite) sign of the Fano parameter imply the presence (absence) of a phase lapse with π between the corresponding resonances of the dot. Our results suggest that the famous phase lapse problem, first reported by Schuster et al. [R. Schuster, E. Buks, M. Heiblum, D. Mahalu, V. Umansky, H. Shtrikman, Nature 385 (1997) 417], can therefore be experimentally addressed in closed interferometers. It is also proposed that the Fano effect can be used to extract the phase distributions of the eigenfunctions for a mesoscopic 2D shape, via the parity of the resonances. In the presence of electron-electron interaction, one can calculate the phases of the T-matrix elements. The numerical results lead to the same conclusions as for the non-interacting case. © 2012 Elsevier B.V
Coherent and incoherent transport through T-shaped double quantum dots
We investigate the measurement induced dephasing of the Fano effect in the electronic transport through a double quantum dot mesoscopic interferometer coupled to a charge detector. The current and the differential conductance are computed within the Keldysh formalism, taking into account of the inelastic processes due to the dot-detector interaction. We show that the visibility of the Fano lineshape is reduced by applying a finite bias on the charge detector. © 2007 Elsevier B.V. All rights reserved
Spin-flip Effects in the Mesoscopic Spin-Interferometer
We investigate the properties of the electron spin-transmission through an
Aharonov-Bohm interferometer with an embedded multilevel quantum dot containing
magnetic impurities. A suitable formalism is developed. The amplitude and the
phase of the flip- and nonflip-transmittance are calculated numerically as
function of the magnetic field and the gate potential applied on the dot. The
effects induced by the exchange interaction to spin-dependent
magnetoconductance fluctuations and transmittance phase are shown.Comment: 10 pages, 9 figure
Mesoscopic fano effect in aharonov-bohm rings with an embedded double dot
We investigate theoretically in a tight-binding model the transport properties of the Aharonov-Bohm interferometer (ABI) with one dot embedded in each of its arms. For weak interdot coupling the model Hamiltonian describes the system considered in the experiments of Holleitner et al. [Phys. Rev. Lett. 87, 256802 (2001)]. The electronic transmittance of the interferometer is computed within the Landauer-Büttiker formalism while the coexistence of resonant and coherent transport is explicitly emphasized by using the Feschbach formula. The latter produces effective Hamiltonians whose spectral properties describe the tunneling processes through each dot. We reproduce numerically the stability charging diagrams reported in the experiments of Holleitner et al. When the magnetic flux is fixed and one dot is set to resonance the interferometer transmittance shows Fano lineshapes as a function of the gate voltage applied to the other dot. Our model includes the effect of the magnetic field on the dot levels and explains the change of the asymmetric tail as the magnetic flux is varied. The transmittance assigned to the Fano dips located in the almost crossing point of the charging diagrams shows Aharonov-Bohm oscillations. © 2006 American Institute of Physics