308 research outputs found
Turnstile pumping through an open quantum wire
We use a non-Markovian generalized master equation (GME) to describe the
time-dependent charge transfer through a parabolically confined quantum wire of
a finite length coupled to semi-infinite quasi two-dimensional leads. The
quantum wire and the leads are in a perpendicular external magnetic field. The
contacts to the left and right leads depend on time and are kept out of phase
to model a quantum turnstile of finite size. The effects of the driving period
of the turnstile, the external magnetic field, the character of the contacts,
and the chemical potential bias on the effectiveness of the charge transfer of
the turnstile are examined, both in the absence and in the presence of the
magnetic field. The interplay between the strength of the coupling and the
strength of the magnetic field is also discussed. We observe how the edge
states created in the presence of the magnetic field contribute to the pumped
charge.Comment: RevTeX (pdf-LaTeX), 9 pages with 12 included jpg figure
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
Quantum turnstile operation of single-molecule magnets
The time-dependent transport through single-molecule magnets coupled to
magnetic or non-magnetic electrodes is studied in the framework of the
generalized master equation method. We investigate the transient regime induced
by the periodic switching of the source and drain contacts. If the electrodes
have opposite magnetizations the quantum turnstile operation allows the
stepwise writing of intermediate excited states. In turn, the transient
currents provide a way to read these states. Within our approach we take into
account both the uniaxial and transverse anisotropy. The latter may induce
additional quantum tunneling processes which affect the efficiency of the
proposed read-and-write scheme. An equally weighted mixture of molecular spin
states can be prepared if one of the electrodes is ferromagnetic.Comment: 19 pages, 6 figure
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
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