Berlin 2015 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 17: Superconductivity: Properties and Electronic Structure
TT 17.5: Talk
Monday, March 16, 2015, 16:00–16:15, H 2053
Signatures of Unconventional Superconductivity in Granular Aluminum — •Uwe S. Pracht1, Nimrod Bachar2,3, Eli Farber2, Guy Deutscher3, Martin Dressel1, and Marc Scheffler1 — 11. Physikalisches Institut, Universität Stuttgart, Germany — 2Laboratory for Superconductivity and Optical Spectroscopy, Ariel University, Israel — 3Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Israel
Thin films composed of nanoscale Al grains coupled through dielectric barriers exhibit peculiar superconducting properties: As the grain coupling is decreased, the normal-state resistivity ρ increases and the critical temperature Tc is elevated from 1.1 K to 3.2 K before it is suppressed to zero at a critical ρc. This dome-like appearence of superconductivity together with Kondo-like normal-state transport and presence of localized spins suggest the superconducting mechanism to be of unconventional type in contrast to the BCS nature of bulk Al.
We measured the dynamical conductivity σ(ν)=σ1(ν)+iσ2(ν) in the range 90 - 700 GHz of various films with different ρ by means of quasi-optical Mach-Zehnder interferometry above and below Tc. With increasing ρ we find an enhanced sub-gap absorption compared to the BCS theory for σ1(ν) which we discuss in various contexts such as collective modes or magnetic impurity scattering, [1,2].
[1] N. Bachar, U. S. Pracht et al., J. Low Temp. Phys (in print)
[2] D. Sherman, U. S. Pracht et al., Nat. Phys (accepted)