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@PHDTHESIS{Riwar:229331,
author = {Riwar, Roman-Pascal},
othercontributors = {Splettstößer, Janine},
title = {{C}urrent and noise in interacting quantum pumps},
address = {Aachen},
publisher = {Publikationsserver der RWTH Aachen University},
reportid = {RWTH-CONV-144301},
pages = {180 S. : graph. Darst.},
year = {2013},
note = {Zsfassung in dt. und engl. Sprache. - Prüfungsjahr: 2013.
- Publikationsjahr: 2014; Aachen, Techn. Hochsch., Diss.,
2013},
abstract = {This thesis is a theoretical study of the current and
zero-frequency noise through interacting quantum systems
coupled to reservoirs. We investigate the electron transport
between system and reservoirs, when both the system and
(possibly) the reservoirs are subject to an external
time-dependent driving. We focus on systems so small that
the confinement gives rise to quantised energy levels, and
quantum coherences become important in order to describe the
transport. If only very few levels participate in the
transport, we refer to the system as a quantum dot, which is
the main building block for our theoretical investigation.
In this thesis we consider transport that arises due to a
time-dependent driving of the system. The transport
behaviour depends strongly on how fast the driving is with
respect to the time scales that govern the system dynamics.
A major focus in this thesis is on adiabatic driving, i.e.,
a driving so slow that the system can almost immediately
follow the time-dependent modulation. Adiabatic
time-dependent driving can be used in metrology, to realise
very precise current sources in order to establish a quantum
standard for the ampere. In fact, an adiabatic single
electron pump driven in a periodic fashion, can transport
one electron per pumping cycle. The reliability of quantised
pumping depends on the driving speed, as too fast driving
may result in the system failing to follow the
time-dependent driving. We study this aspect in
collaboration with an experimental group, who realised an
electron pump based on two atomic dopants in a silicon
nanowire. The experimentalists aim at measuring an adiabatic
quantised electron transport, and moreover investigate a
cross-over to a nonadiabatic regime where charging errors
occur due to fast driving. We derive a formalism that can
provide a complete picture of the pumping mechanism, and
accurately describes the experiment, including different
nonadiabatic effects. There occurs a purely nonadiabatic
current signal where no adiabatic transport is possible. We
show that this additional signal is of high value for
spectroscopy, as it gives information about the system
parameters governing the nonadiabatic processes.
Furthermore, the electron spin can encode logical
information. In the field of spintronics, the aim is to not
only use the electron spin as the logical entity, but to
coherently manipulate and transport it. Spin-dependent
transport may emerge in the presence of ferromagnets: when
two ferromagnets are connected via a thin metallic layer,
there arises the giant magnetoresistance, where the
conductance decreases significantly for antiparallel
alignment of the magnetisations. This effect is of
importance for instance in the readout of magnetic hard
drives. Based on this, there has been a lot of interest to
study spin valves in the context of quantum transport, i.e.,
where the metallic layer is replaced by a quantum dot. In
this thesis we study in particular the charge and spin
transport in a double quantum dot contacted to normal metal
as well as ferromagnetic contacts, due to a time-dependent
modulation of the energy levels of the quantum dots. In the
adiabatic driving regime, we examine the possibility of pure
spin pumping in the absence of a pumped charge. Also we
study how the relative orientation of the ferromagnets' spin
polarisation affects the charge transport. In general, the
current through a quantum system is accompanied by
fluctuations. These fluctuations can be quantified by the
zero-frequency current noise, given as the variance of the
number of electrons that arrive at a contact averaged over a
large measuring time. In quantum transport there are two
intrinsic sources of noise: thermal fluctuations and shot
noise due to the electronic charge being quantised. While in
an equilibrium situation the thermal contribution is
dominant, for strong nonequilibrium the shot noise starts to
abound. The noise signal contains crucial information about
the system and its statistics. In particular the Coulomb
interaction may give rise to correlations in the electron
transport, visible in the noise. When considering adiabatic
quantum pumps, an additional pumping noise contribution
arises due to the driving. This pumping noise has been
studied extensively for the case of weakly interacting
systems. So far, there has been no theoretical treatment of
the pumping noise in strongly interacting quantum dot pumps.
Here, we study the pumping noise for the specific model of a
single-level quantum dot pump, and focus on the interplay of
quantum and interaction effects in the pumping noise. As a
substantial part of this thesis we derive a formalism based
on real-time diagrammatics. By means of this formalism, we
shed light onto the characteristics and statistics of the
quantum pump. Moreover, we will be able to show that the
zero-frequency noise gives information about the
time-resolved pumping current.},
keywords = {Quantenmechanik (SWD) / Elektronischer Transport (SWD) /
Funkelrauschen (SWD) / Periodische Störung (SWD) /
Coulomb-Wechselwirkung (SWD) / Vielteilchensystem (SWD)},
cin = {130000 / 135110},
ddc = {530},
cid = {$I:(DE-82)130000_20140620$ / $I:(DE-82)135110_20140620$},
shelfmark = {72.25.-b * 73.23.Hk},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-opus-49228},
url = {https://publications.rwth-aachen.de/record/229331},
}
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