title: Quasiparticle relaxation in optically excited high-Q superconducting resonators.
abstract: The quasiparticle relaxation time in superconducting films has been measured as a function of temperature using the response of the complex conductivity to photon flux. For tantalum and aluminum, chosen for their difference in electron-phonon coupling strength, we find that at high temperatures the relaxation time increases with decreasing temperature, as expected for electron-phonon interaction. At low temperatures we find in both superconducting materials a saturation of the relaxation time, suggesting the presence of a second relaxation channel not due to electron-phonon interaction.
authors.affiliation: Kavli Institute of NanoScience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Barends
authors.forename: J J A
authors.initials: JJ
authors.lastname: Baselmans
authors.forename: S J C
authors.initials: SJ
authors.lastname: Yates
authors.forename: J R
authors.initials: JR
authors.lastname: Gao
authors.forename: J N
authors.initials: JN
authors.lastname: Hovenier
authors.forename: T M
authors.initials: TM
authors.lastname: Klapwijk