44 research outputs found
Comparison of quantization of charge transport in periodic and open pumps
We compare the charges transported in two systems, a spatially periodic and
an open quantum pump, both depending periodically and adiabatically on time.
The charge transported in a cycle was computed by Thouless, respectively by
Buttiker et al. in the two cases. We show that the results agree in the limit
where the two physical situations become the same, i.e., that of a large open
pump.Comment: 7 page
Adiabatic pumping in the mixed-valence and Kondo regimes
We investigate adiabatic pumping through a quantum dot with a single level in
the mixed-valence and Kondo regimes using the slave-boson mean field
approximation. The pumped current is driven by a gauge potential due to
time-dependent tunneling barriers as well as by the modulation of the Friedel
phase. The sign of the former contribution depends on the strength of the
Coulomb interaction. Under finite magnetic fields, the separation of the spin
and charge currents peculiar to the Kondo effect occurs.Comment: RevTeX, 4+pages, 4 figures, textual improvemen
Universal decay cascade model for dynamic quantum dot initialization
Dynamic quantum dots can be formed by time-dependent electrostatic potentials
in nanoelectronic devices, such as gate- or surface-acoustic-wave-driven
electron pumps. Ability to control the number of captured electrons with high
precision is required for applications in fundamental metrology and quantum
information processing. In this work we propose and quantify a scheme to
initialize quantum dots with a controllable number of electrons. It is based on
the stochastic decrease in the electron number of a shrinking dynamic quantum
dot and is described by a nuclear decay cascade model with "isotopes" being
different charge states of the dot. Unlike the natural nuclei, the artificial
confinement is time-dependent and tunable, so the probability distribution for
the final "stable isotopes" depends on the external gate voltage. We derive an
explicit fitting formula to extract the sequence of decay rate ratios from the
measurements of averaged current in a periodically driven device. This provides
a device-specific fingerprint which allows to compare different devices and
architectures, and predict the upper limits of initialization accuracy from low
precision measurements.Comment: 4 pages; more general derivation, new figure on
Robust single-parameter quantized charge pumping
This paper investigates a scheme for quantized charge pumping based on
single-parameter modulation. The device was realized in an AlGaAs-GaAs gated
nanowire. We find a remarkable robustness of the quantized regime against
variations in the driving signal, which increases with applied rf power. This
feature together with its simple configuration makes this device a potential
module for a scalable source of quantized current.Comment: Submitted to Appl. Phys. Let
Constructive role of non-adiabaticity for quantized charge pumping
We investigate a recently developed scheme for quantized charge pumping based
on single-parameter modulation. The device was realized in an AlGaAl-GaAs gated
nanowire. It has been shown theoretically that non-adiabaticity is
fundamentally required to realize single-parameter pumping, while in previous
multi-parameter pumping schemes it caused unwanted and less controllable
currents. In this paper we demonstrate experimentally the constructive and
destructive role of non-adiabaticity by analysing the pumping current over a
broad frequency range.Comment: Presented at ICPS 2010, July 25 - 30, Seoul, Kore
Reply to Comment on "Exact analytic solution for the generalized Lyapunov exponent of the 2-dimensional Anderson localization"
We reply to comments by P.Marko, L.Schweitzer and M.Weyrauch
[preceding paper] on our recent paper [J. Phys.: Condens. Matter 63, 13777
(2002)]. We demonstrate that our quite different viewpoints stem for the
different physical assumptions made prior to the choice of the mathematical
formalism. The authors of the Comment expect \emph{a priori} to see a single
thermodynamic phase while our approach is capable of detecting co-existence of
distinct pure phases. The limitations of the transfer matrix techniques for the
multi-dimensional Anderson localization problem are discussed.Comment: 4 pages, accepted for publication in J.Phys.: Condens. Mat
A quantum criticality perspective on the charging of narrow quantum-dot levels
Understanding the charging of exceptionally narrow levels in quantum dots in
the presence of interactions remains a challenge within mesoscopic physics. We
address this fundamental question in the generic model of a narrow level
capacitively coupled to a broad one. Using bosonization we show that for
arbitrary capacitive coupling charging can be described by an analogy to the
magnetization in the anisotropic Kondo model, featuring a low-energy crossover
scale that depends in a power-law fashion on the tunneling amplitude to the
level. Explicit analytical expressions for the exponent are derived and
confirmed by detailed numerical and functional renormalization-group
calculations.Comment: 4+ pages, 3 figures, PRL versio
Quantized charge pumping by surface acoustic waves in ballistic quasi-1D channels
Adiabatic pumping of electrons induced by surface acoustic waves (SAWs) in a
ballistic quasi-1D quantum channel is considered using an exactly solvable
tight-binding model for non-interacting electrons. The single-electron degrees
of freedom, responsible for acoustoelectric current quantization, are related
to the transmission resonances. We study the influence of experimentally
controllable parameters (SAW power, gate voltage, source-drain bias, amplitude
and phase of a secondary SAW beam) on the plateau-like structure of the
acoustoelectric current. The results are consistent with existing experimental
observations.Comment: 11 pages, 8 figure
Single-parameter non-adiabatic quantized charge pumping
Controlled charge pumping in an AlGaAs/GaAs gated nanowire by
single-parameter modulation is studied experimentally and theoretically.
Transfer of integral multiples of the elementary charge per modulation cycle is
clearly demonstrated. A simple theoretical model shows that such a quantized
current can be generated via loading and unloading of a dynamic quasi-bound
state. It demonstrates that non-adiabatic blockade of unwanted tunnel events
can obliterate the requirement of having at least two phase-shifted periodic
signals to realize quantized pumping. The simple configuration without multiple
pumping signals might find wide application in metrological experiments and
quantum electronics.Comment: 4 pages, 4 figure