Research

Physics of Graphene

Electronic properties in graphene are being intensively studied since the discovery of the anomalous quantum Hall effect in this purely two-dimensional system. Owing to its unique band structure, graphene conduction occurs via massless Dirac fermions. Graphene is a gapless semiconductor: the conduction and the valence band are touching in two inequivalent points (K and K', usually called Dirac points) where the density of state is vanished. However, the conductivity at the Dirac point remains finite. Indeed, at the Dirac point, the conduction occurs only via evanescent waves, i.e. via tunneling between the leads. A first evidence of such mechanism has been recently given by studying the minimum conductivity in short and wide strips. 200px-Bandgraph.jpg

Read more about Graphene research: http://graphene.aalto.fi/

Physics and applications of mesoscopic Josephson junctions

Mesoscopic Josephson junctions provide an unique opportunity to construct ultra sensitive quantum detectors and amplifiers. These devices are important when performing single shot read-out of quantum bits (qubits) or making quantum measurements a la quantum optics style. The ultimate goal is to develop phase sensitive quantum amplifiers, parametric amplifiers that would allow for quantum non-demolition measurements.

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Noise and high frequency measurement techniques

The dominating noise mechanism in mesoscopic samples at low temperatures is shot noise. In some cases, it is the limiting factor for the measurement sensitivity, but shot noise itself may be the actual quantity of interest as it, contrary to the thermal noise, contains information about the sample, complement to that of the average current. Many of the interesting predictions for noise have been obtained for nonlinear elements (with voltage-dependent response) whose resistance is typically in the range of kΩ or more. However, measurement of shot noise in such samples is not always straightforward as the excess noise added by the amplifiers depends on the sample impedance, and thus on the applied voltage.

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Electronic transport in carbon nanotubes

Carbon nanotubes, found in 1991 by Sumio Iijima, represent extraordinary building blocks for nanotechnology and nanoelectronics. They may be considered as graphite sheets wrapped into seamless cylinders. The two types of nanotubes are multiwalled carbon nanotube (MWNT), where many tubes are arranged in a coaxial fashion, and a single walled nanotube (SWNT), consisting of only a single layer. The tubes are either metallic, semimetallic or semiconducting depending on how the graphite sheets are wrapped around.

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Page content by: communications-phys [at] aalto [dot] fi (Department of Physics) | Last updated: 16.12.2015.