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Electron transport in mesoscopic systems

We are studying properties of electron transport in nano-scale systems such as metallic islands, carbon nanotubes and quantum dots with the aim of developing the understanding that is applied in the design process of devices used in metrological applications.

One such device is the R-pump, which is a single-electron pump device that has been fabricated by the team of Alexander Zorin at PTB in Germany. This device is currently used at LNE in France in relation to the Quantum Metrological Triangle experiment which aims to test the basic assumptions of the proposed new International System of Units (SI), which should be based on a set of exactly defined values of fundamental constants. The figure below shows the schematic drawing of the device, with arcs above the junctions representing forward single electron tunnelling (solid arc) and cotunnelling of two electrons in the backward direction (dashed lines) as the gate voltages are changed. Such cotunnelling processes limit the accuracy of single electron tunnelling devices

R-Pump Schematic

As the tunnelling electron encounters the surface of the metallic island (symbolically depicted in the figure below), it changes the charge distribution on the surface in a way that depends on the island shape and details of the electronic circuit, which in turn affects the tunnelling current.

 Symbolic depection of tunneling electron

Photo by M. Shpuntov

In order to calculate the current we use the Feynman diagram technique. An example of such a diagram is below, where the solid (grey) arcs indicate electron-hole exitations and the wiggly (red) lines represent electromagnetic excitations.

 figure

Properties of electron transport at nano-scale are essential for the design of future computing devices, such as transistors and logic circuits. The ultimate goal of chip miniaturisation, a process that has been following Moore’s law for several decades, is manipulation and detection of individual electrons. Below is shown the atomic force microscope image of the single-electron memory device, fabricated by the group of Prof. Matsumoto, our collaborator from the Osaka University in Japan.

Electron transport image

We are currently collaborating with Prof. Iwabuchi from Nara Women University in Japan on transport properties of carbon nanotubes, and with Dr. Oh from the group of Prof. Ahn of the University of Seoul in Korea on transport in quantum dots.

More information: Vladimir Bubanja