Transport phenomena in quantum wells and wires in presence of disorder and interactions
(2012) Abstract (Swedish)
 Popular Abstract in Undetermined
All of our present information technology culture with computers, internet, smartphones, Bluetooth links, 3DTv, iPad tablets, programmable washing/cooking machines, car engines, navigation computers, etc. (the list goes on and on) is based on small electrical circuits. The smaller these circuits can be made, the faster and the better microelectronics can perform.
There is much more round the corner: nanochip technology could soon dim the
boundary between living and nonliving entities, and perhaps even between us and
what is just outside our body: the external world. Some of our capabilities could
be improved or fully regained from deﬁcit situations... (More)  Popular Abstract in Undetermined
All of our present information technology culture with computers, internet, smartphones, Bluetooth links, 3DTv, iPad tablets, programmable washing/cooking machines, car engines, navigation computers, etc. (the list goes on and on) is based on small electrical circuits. The smaller these circuits can be made, the faster and the better microelectronics can perform.
There is much more round the corner: nanochip technology could soon dim the
boundary between living and nonliving entities, and perhaps even between us and
what is just outside our body: the external world. Some of our capabilities could
be improved or fully regained from deﬁcit situations (think of people recovering
neural abilities, improving their eyesight, using cyberprostethics, having realtime monitoring of nonperfect vital functions, etc.)
It is fair to say that some of these developments could impel us to deal with
novel bioethical conﬂicts (voices of concern exist already), but science has forced us before to face dilemmas of this sort. Past experience over the last few millennia shows that each time humanity has made a great discovery (e.g. the ﬁre, the wheel, the printing press, the steam engine, the electricity, penicillin, the transistor, internet) the subsequent technological evolution has always proceeded in one
direction: forward.
Regaining a more downtoearth perspective, presentday electrical circuits
have reached such small dimensions that the laws of physics which govern the
microscopic world, called quantum mechanics, are becoming centerstage. Even
within the statusquo of technological development (we refer to it as "nanoelec
tronics"), it is becoming increasingly important to have a basic understanding
of how small systems with a ﬁnite number of atoms and electrons behave when
subjected to perturbing agents, for example by electric current passing through
them.
The knowledge we have of such systems relies, ﬁrst and foremost, on elaborate
and careful experiments. However, experimental data can be diﬃcult to interpret,
because even such small systems are infact manyparticle systems. The analysis
can be (and usually is) further complicated by the fact that samples are "disor
dered", i.e. we have incomplete knowledge and control of the kind of atoms and
their positions in the sample.
In principle, theoretical research can contribute signiﬁcantly to this endeavor,
by answering a number of important questions. In practice, often a major obstacle
is the lack of accurate theoretical information on how interactions among particles
and disorder aﬀect the results.
This thesis is about research work in this direction, namely theoretical investi
gations of the electric current in diﬀerent nanostructures. We have analyzed quan
tum wells (layered slices of semiconductors), and quantum wires (onedimensional
conducting aggregates of atoms). Both are manmade artiﬁcial structures where,
as their name suggests, quantum eﬀect play an important role in the current transmission. These systems have great potential for technological breakthroughs. We
have employed rather diﬀerent theoretical techniques, aimed to look directly into
the behavior of the current in the steadystate (where the current does not change
in time), or to follow how the current changes in time to reach such steady state.
We have used the Boltzmann’s equation, a method with a long and eminent ser
vice record in physics, but also a rather new approach (called "density functional
theory"), which uses the total electron density as a basic but only variable and
therefore requires signiﬁcantly less computing power than traditional methods.
In the end, the actual common denominator to the diﬀerent parts of our thesis
work is the presence of disorder in our systems. Disorder is ubiquitous in nature:
in fact, in many instances, the notion of order corresponds more to our need for
simple conceptualizations of reality, than to reality itself (that is, in most cases,
in nature, order exists only in an approximate way). Nanoscale systems are no
exception and, in fact, the eﬀects of disorder are expected to be strong in these
small systems.
From the outside, and especially to the eye of the professional physicist, these
considerations can seem a rather tenuous link to thread together somewhat diﬀer
ent subjects, systems and methodologies in the same thesis. For us, who worked
on these topics for several years, this thesis is a conﬁrmation that, as life itself,
scientiﬁc research is often made of pieces whose mutual connection is not imme
diately apparent, and that, in the end, there is beauty in all diﬀerent parts of
Physics. (Less)  Abstract
 Presentday electronics employ circuits of smaller and smaller dimensions, and today the length scales are so small that the laws of physics which rule microcosmos, quantum mechanics, become directly important. This thesis reports on theoretical work on electron
transport in different nanostructures. We have studied semiconductor quantum wells, layered materials where each layer can be only a few atomic layers thick, and transport in thin atomic wires. The layered materials have been studied semiclassically by means the socalled
Bolzmann equation and MonteCarlo techniques. The works on layered
materials focused on effects of resonant scattering mechanisms on the
electron transport and the feasibility... (More)  Presentday electronics employ circuits of smaller and smaller dimensions, and today the length scales are so small that the laws of physics which rule microcosmos, quantum mechanics, become directly important. This thesis reports on theoretical work on electron
transport in different nanostructures. We have studied semiconductor quantum wells, layered materials where each layer can be only a few atomic layers thick, and transport in thin atomic wires. The layered materials have been studied semiclassically by means the socalled
Bolzmann equation and MonteCarlo techniques. The works on layered
materials focused on effects of resonant scattering mechanisms on the
electron transport and the feasibility to use semiconductor super
lattices for generating terahertz (THz)radiation. The quantum wires
were modeled by 1D Hubbard chains connected to semiinfinite leads and
were treated fully quantummechanically via the timedependent density
functional theory (TDDFT). Our TDDFT treatment appears to be able to
capture complex features due to competition between correlation and
disorder. The merits of the coherentpotential approximation are also
analyzed for contacted chains.
In total, four papers are included in the thesis.
In paper I, Monte Carlo simulations of transport in various two
dimensional semiconductor heterostructures, in particular in cases
where accurately calculated scattering probabilities are needed.
In paper II, we present result for electron transport in įdoped
Si/SiGe quantum wells at different temperatures and field strengths.
In paper III, we develop a MonteCarlo technique to handle electron
transport between quantumwell layers when an electric field is applied
along the growth direction. We use this method to study scattering
assisted transport under strong fields in the WannierStark regime.
In paper IV, finally, the static and dynamical behavior of 1D Hubbard
chains are investigated. The focus is on how the interplay of
interactions and disorder affects the localization of fermions in
Hubbard chains contacted to semiinfinite leads. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/record/2520291
 author
 Vettchinkina, Valeria ^{LU}
 supervisor
 opponent

 Professor Sanvito, Stefano, Department of Physics Trinity College, Dublin
 organization
 publishing date
 2012
 type
 Thesis
 publication status
 published
 subject
 keywords
 timedependent densityfunctional theory, disorder, electron correlation, Lowdimensional semiconducting systems, transport phenomena, Fysicumarkivet F:2012:Vettchinkina
 pages
 144 pages
 publisher
 Department of Physics, Lund University
 defense location
 Lecture hall F, Sölvegatan 14A
 defense date
 20120529 13:30
 ISBN
 9789174733280
 language
 English
 LU publication?
 yes
 id
 5797b65cb2154773a4eb89b6c4919468 (old id 2520291)
 date added to LUP
 20120503 21:24:02
 date last changed
 20160919 08:45:08
@misc{5797b65cb2154773a4eb89b6c4919468, abstract = {Presentday electronics employ circuits of smaller and smaller dimensions, and today the length scales are so small that the laws of physics which rule microcosmos, quantum mechanics, become directly important. This thesis reports on theoretical work on electron<br/><br> transport in different nanostructures. We have studied semiconductor quantum wells, layered materials where each layer can be only a few atomic layers thick, and transport in thin atomic wires. The layered materials have been studied semiclassically by means the socalled<br/><br> Bolzmann equation and MonteCarlo techniques. The works on layered<br/><br> materials focused on effects of resonant scattering mechanisms on the<br/><br> electron transport and the feasibility to use semiconductor super<br/><br> lattices for generating terahertz (THz)radiation. The quantum wires<br/><br> were modeled by 1D Hubbard chains connected to semiinfinite leads and<br/><br> were treated fully quantummechanically via the timedependent density<br/><br> functional theory (TDDFT). Our TDDFT treatment appears to be able to<br/><br> capture complex features due to competition between correlation and<br/><br> disorder. The merits of the coherentpotential approximation are also<br/><br> analyzed for contacted chains.<br/><br> In total, four papers are included in the thesis.<br/><br> In paper I, Monte Carlo simulations of transport in various two<br/><br> dimensional semiconductor heterostructures, in particular in cases<br/><br> where accurately calculated scattering probabilities are needed.<br/><br> In paper II, we present result for electron transport in įdoped<br/><br> Si/SiGe quantum wells at different temperatures and field strengths.<br/><br> In paper III, we develop a MonteCarlo technique to handle electron<br/><br> transport between quantumwell layers when an electric field is applied<br/><br> along the growth direction. We use this method to study scattering<br/><br> assisted transport under strong fields in the WannierStark regime.<br/><br> In paper IV, finally, the static and dynamical behavior of 1D Hubbard<br/><br> chains are investigated. The focus is on how the interplay of<br/><br> interactions and disorder affects the localization of fermions in<br/><br> Hubbard chains contacted to semiinfinite leads.}, author = {Vettchinkina, Valeria}, isbn = {9789174733280}, keyword = {timedependent densityfunctional theory,disorder,electron correlation,Lowdimensional semiconducting systems,transport phenomena,Fysicumarkivet F:2012:Vettchinkina}, language = {eng}, pages = {144}, publisher = {ARRAY(0x823d748)}, title = {Transport phenomena in quantum wells and wires in presence of disorder and interactions}, year = {2012}, }