implemented as
Contract number: RITA-CT-2003-505313
Project coordinator: Teknillinen korkeakoulu
Project website: http://boojum.hut.fi
Reporting period: from 01/04/2004 to 31/03/2005
Project funded by the European Community under the “Structuring the European Research Area” specific programme
Research Infrastructures Action
1.1. Summary of the activities and major achievements
1.2. Management overview
1.3. Description of the publicity concerning the new opportunities for access
1.4. Description of the selection procedure
1.5. Transnational Access activity
1.6. Scientific output of the users at the facility
1.7. User meetings
1.8. Update of the non-confidential Project information
Annex 1 - Composition of the Users Selection Panel
Annex 2 - List of User-Projects
Annex 3 - List of Users
Annex 4 - List of publications
Annex 5 - Updated non-confidential Project information
The ULTI visitors program is funded by European Commission for the 4-year period from 1.4.2004 to 31.3.2008. It continues the services of similar ULTI III program, which was in operation during the previous 4 years. During its first year the ULTI program has supported 18 visitors in 16 different projects. The visitors have spent altogether 15,10 person months in the ULTI facility.
The supported projects cover a variety of topics from vortex physics and turbulence in superfluids, to cosmology in condensed matter physics, and to quantum electronics in mesoscopic normal metal and superconducting structures. Two of the projects have been already completed. The research activities funded by ULTI produced 2 publications. At the same time 13 publications, which were based on the work done during the ULTI III program, were written and published during this reporting period.
One of the remaining problems in classical physics is turbulence. Turbulence occurs in normal as well as in superfluids, and its closer investigation in superfluids may shed light onto the classical problem. The majority of the ULTI projects (# 1, 3, 6, 10, 11, 13, and 16) were dealing with the investigation of turbulence in superfluid 3He. In superfluid 3He, the viscosity is a strong function of temperature and for the first time the effects of viscosity can be studied in detail. The onset of the turbulence is found to be covered by two Reynold’s numbers, one related to the vorticity and the other one to the mutual friction between the vortices and the quasiparticles. The Kolmogorov cascade, describing the energy flow from long to short length scales, is also found to be altered by the mutual friction.
Due to our long experience in operating visitors programs we have not faced any insurmountable problems in running the ULTI program. The program continues to offer to the visitors professional scientific, technical and logistic support. The LTL has a strong in-house theory group which gives valuable assistance for many of the ULTI projects. The LTL, with its intensive exchange program with Russian low temperature community, provides a meeting place for the Russian and European scientists.
As technical support the LTL continued to offer to the visitors the services of its helium liquefaction center, manned by 2 technicians, and its instrument shop with 2 skilled machinists. In addition, every visitor was assigned a supporting host group. In the electron beam writing, the visitors were assisted by local graduate students.
In the logistic support, i.e., in travel, housing and reimbursement matters the visitors were assisted by one of the LTL’s secretaries. She also serves as the secretary of the Selection Panel.
We are continuously upgrading the WEB-page of the ULTI program (http://boojum.hut.fi/eu.html). It provides information about the status of the accepted projects and effective communication channel between the Selection Panel, visitors and the ULTI facility.
The European low temperature physics community has about 400 active members. The ULTI program is easily accessible to them through its WEB pages (http://boojum.hut.fi/eu.html). In addition, the new program was presented to the community in the ULTI III user meeting organized in Lammi, Finland in January 6.- 11, 2004. The Lammi meeting was widely advertised within the community and old and potential new users were invited to participate. Altogether 51 scientists from 16 countries, among them 6 members of the Selection Panel, participated and many of them paid a site visit to the Low Temperature Laboratory.
The users were selected by a Panel of Profs. Reyer Jochemsen (Univ. of Leiden, NL), Matti Krusius (LTL, FIN), Paul Leiderer (Univ. of Konstanz, D), Mikko Paalanen (LTL, FIN), George Pickett (Univ. of Lancaster, UK), Bernard Placais (ENS, F), Luciano Reatto (INFN, IT) and Peter Skyba (Slovakian Academy of Sciences, Kosice, SK). These members represent European countries with largest low temperature physics communities. Compared to the previous ULTI III program, Professor Peter Skyba from Slovakia is a new member, representing the newly elected states of the EU.
In the selection of users/projects the following criteria are followed:
- The projects should represent excellent science with unique goals.
- They should be technically feasible for the available instruments in our facility.
- Scientific and technical progress is expected.
- Preference is on first time users from countries without their own ultra low temperature facility.
- Special attention is paid to new EU-countries as well as to nanofabricated cryosensors as a new area.
- A small number of feasibility studies on suggested experiments, anticipated to be difficult, are accepted.
- Due to the small number of applications, we also accept short projects giving direct theory support for existing experimental ULTI projects.
The selection of users was conducted by email vote in 16.4.2004, 26.8.2004, 9.1.2005 and 23.2.2005. A list of candidates, based on the received proposals, was prepared for the vote by the ULTI manager. The results of the vote were posted on the ULTI WEB-site. The open WEB-site, including all the existing ULTI projects, guarantees the transparency and fairness of the selection procedure.
No research proposals were rejected.
Research in ultra low temperature physics is time consuming and requires, in most cases, months of dedicated work in both planning the experiment and especially during the measurements in the ULTI facility. The three-month time limit for ULTI projects is an unrealistic goal, which can be met only in theory collaborations.
Altogether 18 projects, 12 experimental and 6 theoretical ones were accepted by the Selection Panel. During the reporting period 16 projects were started and two of them have been already completed. The ULTI facility was visited by 18 scientists from 9 different European countries, three of the scientists were new users.
Three major scientific topics were covered by the 16 ULTI projects. Over half of the projects (9) were about superfluid hydrodynamics and its instabilities, i.e., vortex formation and turbulence. In six projects the properties of mesoscopic electron systems were investigated and one project was dealing with nuclear magnetism at sub-μK temperatures.
The complete list of User-Projects and Users can be found in Annexes 2 and 3, respectively (MS Access, Annex 2 and 3).
In addition to the major achievements in the studies of turbulence, reported in 1.1., the following interesting results have been obtained during the first year of ULTI program:
Nonequilibrium physics in hybrid superconductor-normal metal structures
(project #5):
Thermoelectric effects in small normal metal-superconductor hybrid structures contain fascinating phenomena and potential for device application. Especially non equilibrium effects in the electron distribution, obtained by passing a suitable electrical current through the structure, give rise to such interesting effects as cooling of the electrons, population inversion or Josephson tunable weak links.
In this experimental work the SINIS (superconductor-insulator-normal metal-insulator-superconductor) structure has been under investigation. The first working tunable Josephson weak link in the Al/Cu system has been realized. In this structure, supercurrent enhancement by more than a factor of two under quasiparticle extraction was demonstrated, as well as a current gain up to 20.
Measurement of noise statistics using a tunnel junction (project #12)
Electrical noise, especially its statistics and higher moments, is at the moment one of the leading topics in nanoelectronics. The higher moments of the noise are hard to measure and new probes are in demand. In this work the potential of the Josephson junction as a noise detector was studied both experimentally and theoretically.
The effect of shot noise on the IV-curve of the Coulomb blockaded normal junction has been investigated. As in the case of the superconducting Josephson junction, the IV-curve of the normal junction was found to be very sensitive to noise. The effect of monochromatic microwave with phase noise (phase decoherence) on the IV curve of the Coulomb blockade Josephson junction was also studied theoretically. This type of noise is widely known and investigated for laser radiation. It is shown that the response of the junction to the microwave input is essentially different for noiseless and noisy input.
It was also shown that at high noise current its effect on the IV curve of the Coulomb blockaded junction is strongly different for Poissonian statistics and for a periodic sequence of current pulses. This demonstates the sensitivity of the Josephson junction to the full counting statistics of the electron transport.
Other highlights of the important results among the user-projects/see Annex 4
No user meetings were organized during the reporting period. Next user meeting is planned to take place in June 2006.
1. Barceló, C. and Volovik, G.E., A stable static Universe?, Pis´ma v ZhETF, 80, 4, pp. 239-243 (2004)
2. Barceló, C. and Volovik, G.E., A stable static Universe?, JETP Letters, 80, 4, pp. 209-213 (2004)
3. Delahaye, J., Hassel, J., Lindell, R., Sillanpää, M,. Paalanen, M., Seppä. M,. and Hakonen, P., Bloch Oscillating Transistor and Coulomb blockade of Cooper pairs, Proceedings of the XXXIXth Recontres de Moriond, Quantum Information and Decoherence in Nanosystems, pp. 183-186 (2004)
4. Giazotto, F., Heikkilä, T.T., Taddei, F., Fazio, R., Pekola, J.P., and Beltram, F., Mesoscopic supercurrent transistor controlled by nonequilibrium cooling, Journal of Low Temperature Physics, 136, 5/6, pp. 435-452 (2004)
5. Hassel. J., Seppä, H., Delahaye, J., and Hakonen, P., Control of Coulomb blockade in a mesoscopic Josephson junction using single electron tunneling, Journal of Applied Physics, 95, 12, pp. 8059-8062 (2004)
6. Heikkilä, T.T., Virtanen, P., Johansson, G., and Wilhelm, F.K., Measuring non-Gaussian fluctuations through incoherent Cooper-pair current, Physical Review Letters, 93, pp. 247005/1-4 (2004)
7. Kivotides, D., Topological noise scalings in superfluid and classical turbulence, Pis´ma v ZhETF, 80, 3, pp. 174-178 (2004)
8. Kivotides, D., Quantum turbulence decay, Physics Letters A, 326, pp. 423-428 (2004)
9. Lindell. R., Delahaye, J., Sillanpää, M., Paalanen, M., Sonin, E., and Hakonen, P., Mesoscopic Josephson junction as a noise detector, Proceedings of SPIE - The International Society for Optical Engineering, Noise and Information in Nanoelectronics, Sensors, and Standards II, 5472, pp. 19-27 (2004)
10. Lindell, R.K., Delahaye, J., Sillanpää, M.A., Heikkilä, T.T., Sonin, E.B., and Hakonen, P., Observation of shot-noise-induced asymmetry in the Coulomb blockaded Josephson junction, Physical Review Letters, 93, 19, pp. 197002/1-4 (2004)
11. Savin, A., Pekola, J., Flyktman, J., and Giazotto, F., Strong enhancement of Josephson coupling under hot quasiparticle extraction, Proceedings of the XXXIXth Recontres de Moriond, Quantum Information and Decoherence in Nanosystems, pp. 209-212 (2004)
12. Savin, A.M., Pekola, J.P., Flyktman, J.T., Anthore, A., and Giazotto, F., Cold electron Josephson transistor, Applied Physics Letters, 84, 21, pp. 4179-4181 (2004)
13. Sonin, E.B., Effect of the shot-noise on a Coulomb blockaded single Josephson junction, Physical Review B, 70, pp. 140506 (2004)
1. Project # 10: L'vov, V.S., Nazarenko, S.V., and Volovik, G.E., Energy spectra of developed superfluid turbulence, Pis´ma v ZhETF, 80, 7, pp. 546-550 (2004)
2. Project # 10: L'vov, V.S., Nazarenko, S.V., and Volovik, G.E., Energy spectra of developed superfluid turbulence, JETP Letters, 80, 7, pp. 479-483 (2004)
The ULTI Large-Scale Facility offers expertise and equipment for outside users to undertake measurements at temperatures from 4 Kelvin down to the lowest attainable. The installation is located in the Low Temperature Laboratory (LTL) of the Helsinki University of Technology (TKK). ULTI, a continuation of ULTI III, will contribute to scientific progress and technical development of ultra low temperature physics in Europe, to serve as a first-rate educational center for young physicists, and to act as a node for scientific collaboration between Russia and the EU countries. The in-house research includes experimental programs on refrigeration and cryogenics in the liquid-helium range and below and experimental and theoretical studies of quantum fluids and solids, nuclear magnetism, and electrical transport in normal and superconducting structures of nanometer size. Equipment for high-precision optical interferometry at low temperatures and electron beam lithography for making nanosize samples are available as well.
The low temperature and nanophysics section of the LTL consists of about 35 persons, of whom 10 are senior scientists. The ULTI refrigeration equipment includes three sub-millikelvin cryostats, each with a 3He/4He dilution refrigerator for precooling a copper nuclear demagnetization stage. One apparatus can be rotated around its vertical axis up to 40 rev/min, Another is a cascade refrigerator, with two nuclear cooling stages in series, which holds the current low temperature world record of 100 picokelvin. Three smaller cryostats are available for mesoscopic studies down to 50 millikelvin temperatures.
Researcher and students interested in experiments at ultra low temperatures, please contact:
Prof. Mikko Paalanen
Low Temperature Laboratory
Helsinki University of Technology
P.O. Box 2200
FIN-02015 HUT
Phone: +358-9-451 2957
Fax: +358-9-451 2969
E-mail: paalanen@neuro.hut.fi