Biomedical Engineering Reference
In-Depth Information
Chapter 7
Interference Single Electron Transistors Based
on Quantum Dot Molecules
Andrea Donarini and Milena Grifoni
Abstract
We consider nanojunctions in the single electron tunnelling regime
which, due to a high degree of spatial symmetry, have a degenerate many-body
spectrum. They comprise single molecule quantum dots as well as artificial quantum
dot molecules. As a consequence, interference phenomena which cause a current
blocking can occur at specific values of the bias and gate voltage. We present here
a general formalism providing necessary and sufficient conditions for interference
blockade also in the presence of spin-polarized leads. As examples we analyze a
triple quantum dot as well as a benzene molecule single electron transistor.
7.1
Introduction
Single particle interference is one of the most genuine quantum mechanical effects.
Since the original double-slit experiment [
1
], it has been observed with electrons
in vacuum [
2
,
3
] and even with the more massive
C
60
molecules [
4
]. Mesoscopic
rings threaded by a magnetic flux provided the solid-state analogous [
5
,
6
]. Intra-
molecular interference has been recently discussed in molecular junctions for the
case of strong [
7
-
18
] and weak [
19
-
21
] molecule-lead coupling. What unifies
these realizations of quantum interference is that the travelling particle has two (or
more)
spatially equivalent
paths at disposal to go from one point to another of the
interferometer.
Interference, though is hindered by decoherence. Generally, for junctions in the
strong coupling regime decoherence can be neglected due to the short time of flight
of the particle within the interferometer. In the weak coupling case, instead, the
dwelling time is long. It is the regime of the single electron tunnelling devices
A. Donarini M. Grifoni
Theoretische Physik, Universitat Regensburg, 93040 Regensburg, Germany
