Nano group of the Low Temperature Laboratory investigates fundamental quantum phenomena in nanostructures using low temperature and electronic transport measurements. In both normal and superconducting nanosamples quantum mechanical wave character of the electrons and their Coulomb repulsion lead to new phenomena, which we try to utilize in new sensor/amplifier applications.
We have developed, among others, record-sensitive single electron transistor (SET) components made out of carbon nanotubes and nearly back-action-free, reactively read superconducting electrometers. In addition, we have developed a novel, low-noise current amplifier, Bloch oscillating transistor, which lies between the superconducting quantum interferometer (SQUID) and the SET according to its characteristics. We also recently started to work on graphene field effect devices.
The Nano group is involved in several European projects such as "Suspended Graphene Nanostructures" (RODIN)  sponsored by the European Commission and "Entangled Spin Pairs in Graphene"  within the EUROgraphene program coordinated by European Science Foundation. We also benefit from several national and international bilateral collaborations.
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. (more)
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. (more)
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. (more)
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. (more)
Group photo (Summer 2012)
- See also: Current members
- Leiden Cryogenics MNK126-500 dilution refrigerator
- Dry dilution refrigerator BF-SD250 
- Nanoway PDR50 dilution refrigerator
- Microwave set-up for shot noise measurements at 4.2 K
- e-beam lithograpgy facilities
Recent publications and preprints
- See also: Publications of the Nano group
- Lahteenmaki, P.; Vesterinen, V.; Hassel, J.; Seppa, H. ; and Hakonen, P., "Josephson junction microwave amplifier in self-organized noise compression mode ", Scientific Reports, 2 (2012). [DOI]
Graczykowski, B., Mielcarek, S., Trzaskowska, A., Sarkar, J., Hakonen, P., and Mroz, B., "Tuning of a hypersonic surface phononic band gap using a nanoscale two-dimensional lattice of pillars", Physical Review B, 86, 085426/1-6 (2012). [DOI]
Lähteenmäki, P., Vesterinen, V., Hassel, J., Seppä, H., and Hakonen, P., "Josephson junction microwave amplifier in self-organized noise compression mode", Scientific Reports, 2 (2012).
Pasanen, P., Voutilainen, M., Helle, M., Song, X., and Hakonen, P.J., "Graphene for future electronics", Physica Scripta, T146 (2012). [DOI]
Song, X., Oksanen, M., Sillanpää, M.A., Craighead, H.G., Parpia, J.M., and Hakonen, P.J., "Stamp Transferred Suspended Graphene Mechanical Resonators for Radio Frequency Electrical Readout", Nano Letters, 12, 198–202 (2012). [DOI]
Fay, A., Danneau, R., Viljas, J.K., Wu, F., Tomi, M.Y., Wengler, J., Wiesner, M., and Hakonen, P.J., "Shot noise and conductivity at high bias in bilayer graphene: Signatures of electron-optical phonon coupling", Physical Review B, 84, 1-7 (2011).