project title: The electron-phonon coupling in BCS superconductors
project leader: Dr. Francesco Giazotto and Mt. Cesar Pacual Carcia
access given (in days): 40
access used (in days): 28
local host: Prof. Jukka Pekola
home institution: SNS, Pisa
country of institution: Italy
starting date (yyyy-mm-dd): 2008-03-02
The aim is to investigate the following topics: (1) Heat flux related to electron phonon coupling in a usual BCS superconductor. This is an important problem in microcooling. (2) Material issues in hybrid tunnel junction microrefrigerators. New types of junctions with alloy normal metal have been fabricated in Pisa,in order to achieve better cooling performance, and will be measured.
(1) The Pisa team has measured the electron-phonon heat flux in an ordinary superconductor (in form of a deposited aluminium thin film). Several samples were fabricated in Pisa, and the experiments were performed and the relevant theory was developed at LTL. The experiments show unambiguously that the electron-phonon coupling gets increasingly weak at temperatures far below Tc. This coupling is two orders of magnitude lower than in the normal state at the same temparature already at T/Tc = 0.3. A manuscript on this work has recently been written and submitted for publication (arXiv:0804.4413). (2) During the project it was realized that the new deposition system on TKK campus in Micronova is more suitable for fabrication of the alloy junctions than that in Pisa. Therefore also part to the sample making took place at the ULTI site.