73 research outputs found
Adiabatic charge and spin pumping through quantum dots with ferromagnetic leads
We study adiabatic pumping of electrons through quantum dots attached to
ferromagnetic leads. Hereby we make use of a real-time diagrammatic technique
in the adiabatic limit that takes into account strong Coulomb interaction in
the dot. We analyze the degree of spin polarization of electrons pumped from a
ferromagnet through the dot to a nonmagnetic lead (N-dot-F) as well as the
dependence of the pumped charge on the relative leads' magnetization
orientations for a spin-valve (F-dot-F) structure. For the former case, we find
that, depending on the relative coupling strength to the leads, spin and charge
can, on average, be pumped in opposite directions. For the latter case, we find
an angular dependence of the pumped charge, that becomes more and more
anharmonic for large spin polarization in the leads.Comment: 9 pages, 7 figures, published in Phys. Rev.
Energy and power fluctuations in ac-driven coherent conductors
Using a scattering matrix approach we study transport in coherent conductors
driven by a time-periodic bias voltage. We investigate the role of
electron-like and hole-like excitations created by the driving in the energy
current noise and we reconcile previous studies on charge current noise in this
kind of systems. The energy noise reveals additional features due to
electron-hole correlations. These features should be observable in power
fluctuations. In particular, we show results for the case of a harmonic and
bi-harmonic driving and of Lorentzian pulses applied to a two-terminal
conductor, addressing the recent experiments of Refs. 1 and 2.Comment: 12 pages, 5 figure
Correlations between charge and energy current in ac-driven coherent conductors
We study transport in coherent conductors driven by a time-periodic bias
voltage. We present results of the charge and energy noise and complement them
by a study of the mixed noise, namely the zero-frequency correlator between
charge and energy current. The mixed noise presents interference contributions
and transport contributions, showing features different from those of charge
and energy noise. The mixed noise can be accessed by measuring the correlator
between the fluctuations of the power provided to the system and the charge
current.Comment: 8 pages, 1 figur
Two-particle non-local Aharonov-Bohm effect from two single-particle emitters
We propose a mesoscopic circuit in the quantum Hall effect regime comprising
two uncorrelated single-particle sources and two distant Mach-Zehnder
interferometers with magnetic fluxes, which allows in a controllable way to
produce orbitally entangled electrons. Two-particle correlations appear as a
consequence of erasing of which path information due to collisions taking place
at distant interferometers and in general at different times. The two-particle
correlations manifest themselves as an Aharonov-Bohm effect in noise while the
current is insensitive to magnetic fluxes. In an appropriate time-interval the
concurrence reaches a maximum and a Bell inequality is violated.Comment: 4 pages, 2 figures, published in Phys. Rev. Let
Shaping charge excitations in chiral edge states with a time-dependent gate voltage
We study a coherent conductor supporting a single edge channel in which
alternating current pulses are created by local time-dependent gating and sent
on a beam-splitter realized by a quantum point contact. The current response to
the gate voltage in this setup is intrinsically linear. Based on a fully
self-consistent treatment employing a Floquet scattering theory, we analyze the
effect of different voltage shapes and frequencies, as well as the role of the
gate geometry on the injected signal. In particular, we highlight the impact of
frequency-dependent screening on the process of shaping the current signal. The
feasibility of creating true single-particle excitations with this method is
confirmed by investigating the suppression of excess noise, which is otherwise
created by additional electron-hole pair excitations in the current signal
Interaction-induced adiabatic non-linear transport
We calculate the time-dependent non-linear transport current through an
interacting quantum dot in the single-electron tunneling regime (SET). We show
that an additional dc current is generated by the electron-electron interaction
by adiabatic out-of-phase modulation of the gate and bias voltage. This current
can arise only when two SET resonance conditions are simultaneously satisfied.
We propose an adiabatic transport spectroscopy where lock-in measurement of a
"time-averaged stability diagram" probes interactions, tunnel asymmetries and
changes in the ground state spin-degeneracy.Comment: 4 pages, 2 figure
Coherence of Single Electron Sources from Mach-Zehnder Interferometry
A new type of electron sources has emerged which permits to inject particles
in a controllable manner, one at a time, into an electronic circuit. Such
single electron sources make it possible to fully exploit the particles'
quantum nature. We determine the single-particle coherence length from the
decay of the Aharonov-Bohm oscillations as a function of the imbalance of a
Mach-Zehnder interferometer connected to a single electron source. The
single-particle coherence length is of particular importance as it is an
intrinsic property of the source in contrast to the dephasing length.Comment: 4 pages, 4 figure
Finite-frequency noise of interacting single-electron emitters: spectroscopy with higher noise harmonics
We derive the symmetrized current-noise spectrum of a quantum dot, which is
weakly tunnel-coupled to an electron reservoir and driven by a slow
time-dependent gate voltage. This setup can be operated as an on-demand emitter
of single electrons into a mesoscopic conductor. By extending a real-time
diagrammatic technique which is perturbative in the tunnel coupling, we obtain
the time-resolved finite-frequency noise as well as its decomposition into
noise harmonics in the presence of both strong Coulomb interaction and slow
time-dependent driving. We investigate the noise over a large range of
frequencies and point out where the interplay of Coulomb interaction and
driving leads to unique signatures in finite-frequency noise spectra, in
particular in the first harmonic. Besides that, we employ the first noise
harmonic as a spectroscopic tool to access individual fluctuation processes. We
discuss how the inverse noise frequency sets a time scale for fluctuations,
which competes with time scales of the quantum-dot relaxation dynamics as well
as the driving.Comment: 25 pages, 9 figure
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