Warrick Clarke with the dilution fridge

In 2001 the Quantum Electronic Devices group at UNSW started a new research project to develop a fundamental understanding of semiconductor structures in which the device separation is deliberately engineered to be less than 0.1µm, and investigate how these interactions influence device performance. The device is made from GaAs, in which there are two parallel conducting channels separated by only 20nm, such that the current flow is strongly affected by interactions between electrons in one channel and electrons in the other channel. Very recently PhD student Warrick Clarke has developed a process to independently contact the lower 2D layer for the first time and is gearing up for low temperature (<below 0.1K) measurements on the dilution fridge (see photo). Future work will investigate the unusual quantum phase transitions that occur in these devices and develop a detailed understanding of coupling between quantum devices.

In addition an exciting development came during the year when PhD student Carlin Yasin analysed her recent data on studies in conduction in high quality 2D electron systems. For years it has been well-known that there is a theoretical global phase diagram in 2D systems proposed by Kivelson, Lee and Zhang which predicts that Landau levels float up to infinite energy at low magnetic fields (1/n). Using very high quality 2D GaAs electron systems Carlin was able to experimentally verify this phase diagram. More importantly by comparing experimental data from many different material systems she has shown experimentally that the global phase diagram is universal (see figure 2). This is the first time anyone has tied all the experimental data in the literature to the phase diagram and provides a unique insight as to why some people have observed floating and others not – it all depends on how low in 1/n you go.

Experimental verification of the universal global phase diagram

Alex Hamilton, Michelle Simmons,
Warrick Clarke and Carlin Yasin