Tunneling through Nanostructures - Interactions, Interference and
Broadening
Jonas Nyvold Pedersen
Wednesday, 17 December 2008, 10:15
Hörsal B, Fysikum
Abstract:
In this thesis, quantum transport through nanostructures is addressed
theoretically by considering simplified model systems representing the
most important features of quantum dots or molecules. The generic model
consists of a central region coupled to noninteracting leads. The key
ingredients are a discrete level spectrum of the central region and
complicated many-body interactions present therein, the coupling between
the leads and the dot, and the finite temperatures of the leads.
After a general introduction to quantum transport through nanostructures,
different theoretical methods are briefly reviewed with a particular focus
on density-matrix based approaches. Then a new method denoted the second
order von Neumann (2vN) approach is presented, which forms the core of
this thesis. By working in a basis of many-particle states for the central
region, Coulomb interactions are taken fully into account and correlated
transitions by up to two different contact states are included. The latter
extends standard rate equation approaches by including level-broadening
effects and interference due to different transport paths through the
nanostructure. The method is applied to various model systems in three of
the four papers, Paper II-IV, contained in the thesis, and supplementary
material is presented in the main part of the thesis. The models discussed
are the spinless single and double quantum dot models, the Anderson model,
and, finally, a spintronics model with a single spin-degenerate level
coupled to ferromagnetic contacts and subjected to a magnetic field.
Furthermore, cotunneling through single quantum dots is treated using the
2vN method. In Paper I, experimental data obtained from measurements on an
InAs-InP nanowire containing a double quantum is analyzed on a microscopic
basis using a capacitance model.