project title: Quantum Coherent Effects in Josephson Junction Circuits and Quasiparticle
project leader: Dr. Frank Hekking
access given (in days): 123
access used (in days): 109
local host: Prof. Jukka Pekola
home institution: CRTBT/CNRS
country of institution: France
starting date (yyyy-mm-dd): 2004-09-01
Professor Hekking is from the Joseph Fourier University and CNRS, Grenoble. The goal of his project was to understand theoretically some observations, made in experiments at the Low Temperature Laboratory on Josephson junctions (JJ), in particular those concerning a sudden change of the behaviour at the switching threshold of small junctions, which are, however, still in the regime where Coulomb effects are unimportant. Another goal was to investigate how Josephson junctions could function as threshold detectors of noise and current statistics. The third objective was to understand adiabatic pumping in JJ circuits and its relation to Berry phase. Finally we wanted to understand better the quasiparticle non-equilibrium in electronic microrefrigerators.
In this project quasiparticle non-equilibrium was studied, and in particular the problem of electronic refrigeration. The concept of Brownian refrigeration was developed and published [J.P. Pekola and F.W.J. Hekking, Normal metal - superconductor tunnel junction as a Brownian refrigerator, Phys. Rev. Lett. 98, 210604 (2007)]. The experiments on the Brownian refrigerator are under way and a favourable configuration is already found to observe this exciting effect. Another topic of this project was electron-phonon coupling and electronic cooling in narrow metallic suspended beams. The theoretical studies have lead to first experimental results, and to a theoretical predictions (F. W. Hekking, A. O. Niskanen, and J. P. Pekola, Electron-phonon coupling and longitudinal mechanical-mode cooling in a metallic nanowire, Phys. Rev. B 77, 033401 (2008)).