Whereas condensed matter physics has always dealt with a macroscopically large
number of elementary constituents (electrons or sand-grains), the progress of
nanotechnology has opened up a new field of research by allowing the isolation
of few constituents from its macroscopically large condensed matter reservoir.
The canonical example is that of a quantum dot. A two dimensional gas
of electron is fabricated first by layering different types of semi-conductors
(hetero-junctions). One then applies very small gates on top of
the hetero-junctions. The gates act as potential barriers for
the two-dimensional gas. In this way it is possible
to form an island (the quantum dot) of few electrons
surrounded from the reservoir of electron (the two-dimensional gas)
by a (tunable) potential barrier. The number of electrons residing
on the quantum dot, their life-time
(i.e., the coupling strength to the reservoir),
the strength of disorder, etc, are all tunable parameters.
In mesoscopic devices, fundamental questions ranging from
the quantum nature of the electron to the role played by interactions
can be studied with ever greater experimental flexibility
(in the sense of tunability of parameters).
Because of the tunability of parameters such as the gate voltage, the number
of electrons on the quantum dot, and the strength of the disorder it is now
possible to access physical regimes that once were considered of
purely academic interest and pose new theoretical challenges.
Dr. Christopher Mudry
Paul Scherrer Institut
WHGA/125
CH-5232 Villigen PSI
Switzerland