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QEDwiki



Researchers within the QED group are investigating the electrical and optical properties of nanometer scale semiconductor devices. At these small length scales the device properties are no longer governed by semi-classical physics, but are instead determined by quantum mechanical effects. The group makes its own quantum semiconductor devices here at UNSW, and uses a variety of electronic and optical probes, at milliKelvin temperatures and in strong magnetic fields, to further the understanding of quantum electronics.

Single electron/hole transistors and quantum dots

In a single electron transitor it is possible to observe effects associated with the motion of individual electrons. We have developed a novel technique for making highly stable nanoscale single electron and single hole transistors, and are investigating the coherent properties of electrons and holes in quantum dots and chaotic billiards.
For further details see O. Klochan et al, Applied Physics Letters 96, 092103 (2010) and A.M. See et al, Applied Physics Letters 96, 112104 (2010).

 

Hole quantum wires

In a ballistic quantum wire there is no scattering, yet the resistance is quantised in units of h/e^2. Although electron quantum wires have been studied for over a decade, hole quantum wires remain almost completely unexplored. We have developed unique techniques for fabricating ultra-high quality quantum wires that use holes, instead of electrons, to carry current. These offer new ways to probe the fundamental electronic properties of nanoscale devices: Unlike electrons, the electric and magnetic properties of holes are coupled, so that electric voltages can affect the hole's magnetic properties. This is relevant to the emerging new field of spintronics

Electron-electron interactions and the forbidden metal-insulator transition in two dimensional systems

Most transistors, such as the building block of modern computers, the MOSFET, use a thin (two-dimensional) sheet of highly mobile electrons to carry the electric current. These 2D systems are not only of immense technological significance, but have led to profound new fundamental phenomena, with discoveries such as the Quantum Hall Effect, the Fractional Quantum Hall Effect, and the High Electron Mobility Transistor (HEMT) have each leading to separate Nobel prizes for physics in recent years (1985, 1998, and 2000 respectively). However, despite being created over 40 years ago, there is still no universally accepted theoretical understanding of the fundamental electronic properties of high quality two-dimensional systems. Even the nature of the electronic state is not completely known over the complete range of carrier density and disorder (pictured left).

Quantum and scattering lifetimes in two dimensional systems

We are examining the low-temperature properties of high-quality heterostructures, in which scattering is dominated by two types of disorder: remote ionised impurities (RII) and homogeneous background (BG) impurities. However it turns out calculations involving the homogeneous background impurities, which affect all quantum devices, is non-trivial and hinders direct comparison between theory and experiment. We are working to make comparison between theory and experiment easier, and to related these scattering lifetimes to observed transport phenomena.

Inter-device interactions in strongly coupled quantum devices

As the dimensions of individual components in a "chip" shrink, and we pack these components ever closer together, it will no longer be possible to ignore interactions between devices. So as well as understanding how electron-electron interactions within a device affect its electrical properties, it is also important to understand the interactions between devices in order to design the next generation of nano-electronic devices.

   
   

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Updated: 3-Oct-2002