

PhD student Warrick Clarke in the SNF cleanroom
fabricating samples for the closely spaced quantum devices
project. 
Honours student Tom Sobey performing lowtemperature
measurements of quantum contributions in highmobility FET
devices. 
The field effect transistor plays an important role in modern electronic
appliances such as computers and mobile phones. These transistors
use a thin, almost twodimensional sheet of highly mobile electrons
or holes to carry electric current. Despite their technological
importance many of the fundamental electronic properties of these
2D systems are not yet fully understood.
Our studies of electronic interactions focus on high quality
devices fabricated at UNSW featuring two 2D conducting channels
separated by an insulating barrier only 2.5nm thick. In these
bilayer devices, competition between intralayer and interlayer
Coulomb interactions leads to new manybody quantum states similar
to those in the fractional quantum Hall effect. In our samples
we have the unique ability to tune both the relative strength
of these interactions and the balance between the number of electrons
in each of the two layers simply by adjusting gate voltages. Our
focus in 2003 was the analysis of data obtained from an experiment
where we mapped the stability of the bilayer coherent n
= 1 quantum Hall state as electrons were gradually shifted from
one layer into the other. PhD student Warrick Clarke spent early
2003 correlating our results with detailed theoretical calculations
by Prof Charles Hanna from Boise State University in the US to
reach a better understanding of the physics in this system. In
late 2003 our focus in this project has shifted to investigating
interactions between closely spaced 1D quantum wires, and we are
currently fabricating devices for these studies.
The search for a metallic ground state in 2D systems naturally
leads to the question of what the precise role of electronelectron
interactions is in determining the conductivity. In particular,
recent theoretical work suggests that the metallic behaviour observed
in these systems may be entirely the result of these interactions,
and that a signature of this is consistent behaviour in the quantum
mechanical contributions to both the longitudinal and Hall conductivity
of 2D systems. To test this hypothesis, Tom Sobey (Session II
Honours student) and Carlin Yasin (PhD student) performed a careful
experiment to compare these quantum contributions to the longitudinal
and Hall conductivity of highmobility FET devices. They found
that these corrections are consistent, thereby confirming an important
theory and taking us a step closer to understanding the origin
of metallic behaviour in 2D systems.
Warrick Clarke, Tom Sobey, Carlin Yasin, Sean McPhail, Romain
Danneau, Adam Micolich,
Alex Hamilton and Michelle Simmons