project title: Thermometric Effects in Hybrid Superconductor-Normal Metal Structures
project leader: Prof. F.Beltram, Dr. F. Giazotto and Mr. S. Tirelli
access given (in days): 92
access used (in days): 76
local host: Prof. Jukka Pekola
home institution: SNS, Pisa
country of institution: Italy
starting date (yyyy-mm-dd): 2004-04-15
The goal of his project was to develop quasiparticle non-equilibrium in mesoscopic hybrid structures, and to make use of them in devices, such as cold electron Josephson transistors. Another objective was to finish a review article in Reviews of Modern Physics on electronic microrefrigeration and thermometry. The goal for the last ULTI year was to manufacture hybrid structures in Pisa and characterize them in the ULTI facility.
Based on prior promising results on creating non-equilibrium quasiparticle distributions in hybrid cooler devices, and the use of non-equilibrium in cold electron transistors, Dr. Giazotto has developed these concepts further in year 2005, in collaboration with Professor Pekola from the LTL, to make use of sharp features in IVs of SIS junctions (S=superconductor, I=insulator). It turns out that a device based on SIS junctions is superior over the one studied in, as the recent experiments imply. Dr. Giazotto has also completed a common review article with Professor Pekola during the second reporting period. During the fourth reporting period samples with SIS'IS junctions were fabricated in Pisa and measured at the ULTI site. The manipulation of the supercurrent in out-of-equilibrium Al-AlO_x-Ti Josephson tunnel nanojunctions was demonstrated experimentally. This was obtained by injecting quasiparticles in a Ti island from two additional tunnel-coupled Al superconducting reservoirs. Both supercurrent enhancement and quenching with respect to equilibrium are achieved, as well as complete generation at temperatures well above Ti critical temperature. A theoretical model based on heat transport, and self-adjustment of the S' island potential, satisfactorily accounts for the features of the findings. A manuscript has been submitted for publication (arXiv:0804.2649).